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Differential photosynthetic and morphological adaptations to low light affect depth distribution of two submersed macrophytes in lakes
Abstract and Figures
To evaluate the relative importance of photosynthetic versus morphological adaptations of submersed macrophytes to low light intensity in lakes, rapid light curves (RLCs), morphological parameters, relative growth rate (RGR), clonal reproduction and abundance of two submersed macrophytes (Potamogeton maackianus and Vallisneria natans) were examined under 2.8%, 7.1%, 17.1% and 39.5% ambient light in a field and outdoor experimental study. The plants increased their initial slope of RLCs (α) and decreased their minimum saturating irradiance (Ek) and maximum relative electron transport rate (ETRm) of RLCs under low light stress, but V. natans was more sensitive in RLCs than P. maackianus. Accordingly, the RGR, plant height and abundance of P. maackianus were higher in the high light regimes (shallow water) but lower in the low light regimes than those of V. natans. At the 2.8% ambient light, V. natans produced ramets and thus fulfilled its population expansion, in contrast to P. maackianus. The results revealed that P. maackianus as a canopy-former mainly elongated its shoot length towards the water surface to compensate for the low light conditions, however, it became limited in severe low light stress conditions. V. natans as a rosette adapted to low light stress mainly through photosynthetic adjustments and superior to severely low light than shoot elongation.
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... However, we do not think that the lower values of chlorophyll (a:b) and chlorophyll (a + b) of M. spicatum under high light were caused by photo-damage (Fig. 2). This scenario possibly occurred because a plant should not invest more energy to chlorophyll to improve the effectiveness of its photosynthesis when the ambient light is sufficient, but it must increase its concentration of chlorophyll to enhance its photosynthesis efficiency when the ambient light is limited (Lu et al. 2013;Chen et al. 2016;He et al. 2019), as observed in our experiment (Fig. 2). Nevertheless, the contents of chlorophyll (a:b) and chlorophyll (a + b) of V. natans were not significantly affected by the light gradient, which was likely possible because the light compensation point of V. natans is much lower than that of M. spicatum (Lu et al. 2013;Chen et al. 2016;He et al. 2019). ...
... This scenario possibly occurred because a plant should not invest more energy to chlorophyll to improve the effectiveness of its photosynthesis when the ambient light is sufficient, but it must increase its concentration of chlorophyll to enhance its photosynthesis efficiency when the ambient light is limited (Lu et al. 2013;Chen et al. 2016;He et al. 2019), as observed in our experiment (Fig. 2). Nevertheless, the contents of chlorophyll (a:b) and chlorophyll (a + b) of V. natans were not significantly affected by the light gradient, which was likely possible because the light compensation point of V. natans is much lower than that of M. spicatum (Lu et al. 2013;Chen et al. 2016;He et al. 2019). Furthermore, the maximum values of plant mass, RGR, stem mass and root mass of M. spicatum at the percentage of light treatment (50%) were higher than those of plant mass, RGR, shoot height and leaf mass of V. natans at the percentage of light treatment (30%), which also suggests that the light compensation point of V. natans is much lower than that of M. spicatum (Lu et al. 2013;Chen et al. 2016;He et al. 2019). ...
... Nevertheless, the contents of chlorophyll (a:b) and chlorophyll (a + b) of V. natans were not significantly affected by the light gradient, which was likely possible because the light compensation point of V. natans is much lower than that of M. spicatum (Lu et al. 2013;Chen et al. 2016;He et al. 2019). Furthermore, the maximum values of plant mass, RGR, stem mass and root mass of M. spicatum at the percentage of light treatment (50%) were higher than those of plant mass, RGR, shoot height and leaf mass of V. natans at the percentage of light treatment (30%), which also suggests that the light compensation point of V. natans is much lower than that of M. spicatum (Lu et al. 2013;Chen et al. 2016;He et al. 2019). ...
The negative effects, caused by high light, on algae, terrestrial and marine aquatic plants are well documented, those negative effects on freshwater submerged plants are, however, not well known. We determined the negative effects of two common submerged species, Myriophyllum spicatum and Vallisneria natans, on their growth and reproduction in a shallow water experiment along an irradiance gradient. Our results highlighted that the plant mass, relative growth rate (RGR) and shoot height of V. natans and M. spicatum, and root mass and root length : root mass of M. spicatum and leaf mass and shoot height : shoot mass of V. natans were significantly negatively affected in shallow water with high light regime (> 50% of full light). While the ramet number of the two species was stimulated by from 20.0% to 36.4%, and root length, root : shoot, chlorophyll (a : b), chlorophyll (a + b), leaf carbon, nitrogen and phosphorus contents of the two studied macrophytes were not significantly impacted by light. Our results indicated that the high light inhibition of plant growth were greater on the shoots than on the roots of the plants, although these effects were significantly different between the two studied submerged species and among the measured traits. Accordingly, we should avoid negative effects caused by high light to improve the performance of submerged species when we conduct submerged aquatic vegetation restoration programs in eutrophic lakes.
... However, many submersed macrophytes in lakes have declined or even disappeared in recent years in China and worldwide, and there were still many difficult in recovering the whole lake submersed macrophytes due to unclear recession mechanism (Qin et al., 2014;Zhang et al., 2017). One of the most important factors is the ubiquitous decrease in underwater light availability, limiting the growth of submersed macrophytes (Chen et al., 2016). Underwater light availability is critical for determining the growth, distribution, morphology and carbon (C) and nitrogen (N) metabolism of submersed macrophytes (Cao et al., 2011;Fu et al., 2012;Chen et al., 2016;Yuan et al., 2016;Chen et al., 2020a;. ...
... One of the most important factors is the ubiquitous decrease in underwater light availability, limiting the growth of submersed macrophytes (Chen et al., 2016). Underwater light availability is critical for determining the growth, distribution, morphology and carbon (C) and nitrogen (N) metabolism of submersed macrophytes (Cao et al., 2011;Fu et al., 2012;Chen et al., 2016;Yuan et al., 2016;Chen et al., 2020a;. Although many studies have studied the response of macrophytes to low light conditions, most of them focused on response strategies to shading conditions on a relatively short time scale. ...
... However, the adaptation mechanisms of submersed macrophytes to low-light environments are still undefined. Because the adaptation strategies of submersed macrophytes are usually species-specific and varied in different life history period, the performance of plant traits along light gradients is usually nonlinear and markedly different in different growth periods (Cao et al., 2011;Fu et al., 2012;Chen et al., 2016;Yuan et al., 2016;Chen et al., 2020a). Hence, additional data concerning submersed macrophyte adaptation to low-light environments, particularly during a relatively long-term growth period with continuous monitoring of key plant traits, is needed. ...
Decreased underwater light availability is one of the most important environmental factors leading to the decline in submersed macrophytes in lakes. However, previous studies mostly focused on a relatively short time scale and lack data on the continuous monitoring of plant life history traits under different light conditions. The present experiment studied the growth, morphology and C/N metabolism of a representative submersed macrophyte, Vallisneria natans, in response to various light regimes (2.8%, 7.1%, 17.1%, and 39.5% ambient light intensity) over a period of 12 months. The results showed that the total biomass and ramet number increased with increased light intensity; in contrast, individual biomass, leaf number and maximum leaf length decreased with increased light intensity. The C/N metabolism indices of V. natans indicated that leaves were the most sensitive to light availability, stems were moderately sensitive, and roots were the least sensitive. V. natans grown in an extremely low-light environment exhibited decreased soluble carbohydrate (SC) and starch and increased free amino acid (FAA) and total nitrogen (TN) levels. The increasing function of the ramet number under different light regimes was fitted. The obtained maximum environmental capacity of the ramet number (K) and the days that the ramet number reached K/2 in each treatment are useful for lake V. natans restoration and seedling cultivation in similar limited-resource environments. Harvesting partial ramets properly and maintaining the ramet number near K/2 could ensure the maximum increase rate of the population to satisfy the demand of V. natans seedlings for lake restoration. The results obtained in this study can be used for lake water level management to achieve specific purposes during submerged macrophyte recovery, such as plant height elon-gation or plant population quantity expansion.
... Recently, the species has also been widely used in the ecological restoration of freshwater ecosystems (Ke and Li, 2006;Li et al., 2018;Liu et al., 2020). However, studies investigating the adaptation characteristics of this species to water depth are rare except for a few controlled experiments and field investigations (Fu et al., 2012;Chen et al., 2016;He et al., 2019;. Water depth is an integrated environmental factor that affects many variables, including light intensity, dissolved oxygen, pH and nutrient concentrations, making it difficult to separate the effect of light on plant growth from that of other variables. ...
... Underwater photosynthetically active radiation (PAR) was measured at noon during the day of sample collection by a handheld Li-COR sensor coupled with a data logger (Li-1400; Li-Cor Company, Lincoln, NE, U.S.A.) to estimate the vertical light profile in the lake. The light extinction coefficient (K) was calculated based on the equation: K = (lnI 1 -lnI 2 )/(d 2 -d 1 ), where d 1 and d 2 stand for water depth, and I 1 and I 2 are light intensity at water depth d 1 and d 2 , respectively (Chen et al., 2016). The K value was used to calculate the corresponding water depth in the light control experiment. ...
... When the water in the aquarium evaporated more than 5 cm, we refilled the tank to the initial water level. As Lake Donghu is eutrophic, the water used in the experiment was a mixture of lake water and tap water (with a volume ratio of 3:7) to avoid algae blooming (Chen et al., 2016). The experiment involved four different light shading treatments, obtained by one-layer black nylon mesh (L1), two-layer black nylon mesh (L2), three-layer black nylon mesh (L3) and four-layer black nylon mesh (L4), which did not alter the spectrum of the incident light. ...
Adaptations to low light and water depth stresses are crucial for the survival of submerged macrophytes. To determine the phenotypic responses of Vallisneria natans to such stresses, we combined a field investigation, a light control experiment and an in situ response experiment to evaluate adaptive variations in fresh weight and
morphological and physiological characteristics. In the field
investigation and the light control experiment, water depth and light intensity were the main environmental factors affecting the fresh weight and morphological characteristics of V. natans.Fresh weight and leaf length were the most significant responding variables, and they were positively correlated with water depth and negatively correlated with underwater light intensity, although the root length and leaf number exhibited no variation. The leaf length elongated more rapidly at sites with intermediate water depth and low light intensity, and the allometric slopes were steeper. Furthermore, the in situ response experiment results showed a unimodal distribution of the chlorophyll-a concentrations of V. natans along with increasing water depths (from 0.5 m to 8.5 m). The turning point of the chlorophyll-a concentration occurred at 5.5 m, which is almost the maximum water depth at which V. natans occurs in Lake Erhai. Overall, our results
evidenced that light availability is an important driving factor that controls the status
... The ratio of the dark respiration rate to net photosynthesis is high in submerged macrophytes, ranging between 6 and 50 %, while for terrestrial plants, the ratio is only 5 -0 % (Pokorný and Květ 2004;Binzer et al. 2006;Tóth et al. 2011) found that Potamogeton perfoliatus responded to poor light conditions not by altering its photosynthetic features but by changing its morphology, including increases in height and SLA. Chen et al. (2016Chen et al. ( , 2020 found that Vallisneria natans better supports experimental severe light stress by using photosynthetic adjustments than does Potamogeton maackianus, which uses only shoot elongation. ...
... These few studies notwithstanding, the photosynthetic traits of aquatic species have been studied very little (Maberly and Gontero 2018) and their distribution in ecosystems according to light stress even less. In eutrophic shallow lakes, tall competitive species that avoid areas with low light availability appear to be dominant (Chen et al. 2016); however, the frequent occurrence of small submerged species in eutrophic lakes suggests that they have the capacity to tolerate very low light availability (Arthaud et al. 2012). ...
... The 8 light intensities selected were 0, 2, 10, 35, 90, 450, 1080 and 1800 µmol photons•m − 2 •s − 1 (representing the maximum amount of light that an aquatic plant can receive during summer in the surface water of the Dombes lakes, personal measurements). Similar experimental gradients were observed in the literature: Chen et al. (2016) (35 to 1282 µmol photons m − 2 s − 1 ), Binzer et al. (2006) (37 to 1800 photons m − 2 s − 1 ), and Pedersen et al. (2013) (> 1000 photons m − 2 s − 1 ). The measurements were performed at narrower light intensity intervals for low light intensities to obtain a better estimate of the light compensation point. ...
The eutrophication of aquatic systems resulting from human activities frequently leads to phytoplankton blooms, which decrease water transparency and therefore limit light availability for aquatic plants. However, several submerged macrophytes are able to grow despite the light competition pressure exerted by phytoplankton. Photosynthetic performance and plant morphology may be key traits allowing plant species to tolerate phytoplankton-induced light limitation in eutrophic systems. The aim of this study was to explore how morphological and photosynthetic traits allow submerged macrophytes to withstand the stress induced by decreased light in eutrophic systems. Morphological and photosynthetic traits were measured in 7 species of submerged macrophytes collected from mesotrophic to hypertrophic shallow lakes (Dombes, Ain, France). Then, we determined whether these traits were related to species occurrence in lakes according to depth and water turbidity. This study highlighted 2 strategies potentially resulting in a trade-off between morphological and photosynthetic traits. The first strategy was tolerance to reduced light and was characterized by a higher investment in leaf area and photosynthetic efficiency (initial slope of photosynthetic activity measured at low light intensities), allowing plants to use low amounts of light energy. The second strategy was to avoid the regions of reduced light and was characterized by a greater investment in vertical growth and maximum photosynthesis at high light intensities. The morphological and physiological traits favoured in turbid lakes corresponded to the avoidance strategy with a low compensation point, allowing plants to grow to the photic zone to reach the water areas where light is at a maximum. Small species exhibiting a light stress tolerance strategy may be maintained in turbid lakes subjected to disturbances, offering a window of opportunity for successful recruitment and reproduction.
... Zervas et al. (2019) found that with increased nutrients and light preference, macrophyte species leaf morphology changes from tubular/capillary leaf types with low leaf area to entire leaf types with greater leaf area. Chen et al. (2016) also showed that rosette macrophytes (e.g. Vallisneria natans) adjust leaf photosynthesis while canopy macrophytes (e.g. ...
... Different growth forms of submerged macrophytes can adjust functional traits and trade-offs to avoid niche overlap of species and competition of resource acquisition (Westoby et al., 2002;Wright et al., 2004;Lukacs et al., 2017). For example, compared with rosette-forming, canopy-forming submerged macrophytes can better adapt to the underwater low-light environment of eutrophic lakes by growing rapidly, increasing leaf area and specific leaf area, prolonging petiole length, and increasing node spacing and stem height (Chen et al., 2016;Zhu et al., 2018;Su et al., 2019;Zervas et al., 2019;Hao et al., 2020). Similarly, leaf shapes, as an important phenotypic trait, can also reflect the adaptation strategy of submerged macrophytes to their ambient stress environments (Pierce et al., 2012). ...
... V. natans and P. wrightii) had greater morphological traits (LA, LDW, SLA, FD) than the needle-leaf types (e.g. C. demersum and N. minor) (Figs. 2a, b, c, d and 4a), indicating they can acquire more light and other resources by adjusting leaf morphological traits (Chambers, 1987;Chen et al., 2016). Variations in leaf morphological traits can reflect species responses to stressed environments, for example, plants growing in poor light environments tend to have higher specific leaf area (SLA). ...
Trait-based approaches have been widely used to explore the relationships between submerged macrophytes and their surrounding environments. However, the effects of functional traits on ecological functions of submerged macrophytes in eutrophic lakes are still not well understood. Here, 1745 individuals of eight dominant submerged macrophyte species in 19 Yangtze floodplain lakes were collected and classified as needle-leaf (Myriophyllum spicatum, Ceratophyllum demersum, Stuckenia pectinatus, Najas minor) or flat-leaf (Vallisneria natans, Hydrilla verticillata, Potamogeton wrightii, Potamogeton maackianus) types according to photosynthetic trait-based cluster analysis. The flat-leaf type submerged macrophytes possessed greater photosynthetic (e.g. higher Fv/Fm) and morphological traits (e.g. higher SLA), while the needle-leaf types held greater stoichiometric traits (e.g. higher plant N/P). Moreover, the RDA analysis indicated that water depth (distribution depth of submerged macrophytes) was the key factor influencing functional traits of flat-leaf types, while it was water quality (e.g. WTP and WChl a) for the needle-leaf types. Furthermore, the flat-leaf types showed better performance in improving underwater light conditions (e.g. SD, Kd, Zeu/WD and Red/Blue) and water quality (e.g. WChl a and TSM). Additionally, distribution depth (WD) of the flat-leaf types was shallower than the needle-leaf types in eutrophic shallow lakes along the middle-lower reaches of the Yangtze River. Our study highlights that functional traits of submerged macrophytes in eutrophic shallow lakes affect their ecological functions.
... Submersed macrophytes, which are large aquatic plants that grow underwater, are crucial for stable water clarity in shallow, mesotrophic and eutrophic lakes (Jeppesen et al., 1997;Scheffer, 1998;Su et al., 2019). The growth of submersed macrophytes is affected by many environmental factors, among which light availability is critical for determining the growth, distribution and species composition of submersed macrophytes in lakes (Barko et al., 1986;Chambers, 1987;Goldsborough and Kemp, 1988;Ni, 2001;Hautier et al., 2009;Yuan et al., 2016;Verhofstad et al., 2017;Chen et al., 2016Chen et al., , 2019Chen et al., , 2020. Indeed, light availability is often considered the most important factor that determines the maximum depth distribution of submersed macrophytes in lakes (Caffrey et al., 2007;Yuan et al., 2016). ...
... Received 26 October 2019; Received in revised form 12 February 2020; Accepted 19 February 2020 along an environmental gradient and their trade-offs are crucial approaches for exploring the relationships between plants and their environments, and trait-based approaches can serve as tools for highlighting the mechanisms underlying plant responses to stress (such as low-light stress) (Fu et al., 2014;Liu and Ma, 2015). Changes in specific environmental factors might impact specific plant characteristics, such as height, leaf area, biomass allocation, specific leaf area (SLA), soluble carbohydrate (SC) and starch contents (Cornwell and Ackerly, 2009;Fu et al., 2012;Weiner, 2004;Chen et al., 2016Chen et al., , 2019Chen et al., , 2020Yuan et al., 2016). In a low-light stress environment, macrophytes with different growth forms exhibit varying adaption strategies. ...
... In a low-light stress environment, macrophytes with different growth forms exhibit varying adaption strategies. For example, rosette macrophytes generally undergo physiological adjustment to better adapt to light conditions (Chen et al., 2016;Yuan et al., 2016), whereas canopy-forming macrophytes mainly utilize morphological adjustment strategies to capture more light (Titus and Adams, 1979;Ni, 2001;Fu et al., 2012;Chen et al., 2016). Using the latter strategy, canopyforming macrophytes allocate more biomass towards stems to increase both the plant height (Ni, 1997;Yang et al., 2004;Fu et al., 2012) and leaf area to enhance the light-use efficiency by expanding the lightreceiving area (Owens et al., 2008). ...
... Submersed macrophytes with different growth forms usually have different adaptive strategies for responding to stress, which are often species-specific. Changes in morphological and physiological traits, for example, ensure better adaptation to various light regimes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). In the present study, the substantially increased plant height and lowest branch height ensured that the shoots of H. verticillata easily reached the water surface and formed a canopy to maintain a competitive advantage under light competition, as indicated by the large number of branches. ...
... Submersed macrophytes with different growth forms usually have different adaptive strategies for responding to stress, which are often species-specific. Changes in morphological and physiological traits, for example, ensure better adaptation to various light regimes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). In the present study, the substantially increased plant height and lowest branch height ensured that the shoots of H. verticillata easily reached the water surface and formed a canopy to maintain a competitive advantage under light competition, as indicated by the large number of branches. ...
... Recently, the species has also been widely used in the ecological restoration of freshwater ecosystems (Ke and Li, 2006;Li et al., 2018;Liu et al., 2020). However, studies investigating the adaptation characteristics of this species to water depth are rare except for a few controlled experiments and field investigations (Fu et al., 2012;Chen et al., 2016;He et al., 2019;. Water depth is an integrated environmental factor that affects many variables, including light intensity, dissolved oxygen, pH and nutrient concentrations, making it difficult to separate the effect of light on plant growth from that of other variables. ...
... Underwater photosynthetically active radiation (PAR) was measured at noon during the day of sample collection by a handheld Li-COR sensor coupled with a data logger (Li-1400; Li-Cor Company, Lincoln, NE, U.S.A.) to estimate the vertical light profile in the lake. The light extinction coefficient (K) was calculated based on the equation: K = (lnI 1 -lnI 2 )/(d 2 -d 1 ), where d 1 and d 2 stand for water depth, and I 1 and I 2 are light intensity at water depth d 1 and d 2 , respectively (Chen et al., 2016). The K value was used to calculate the corresponding water depth in the light control experiment. ...
... When the water in the aquarium evaporated more than 5 cm, we refilled the tank to the initial water level. As Lake Donghu is eutrophic, the water used in the experiment was a mixture of lake water and tap water (with a volume ratio of 3:7) to avoid algae blooming (Chen et al., 2016). The experiment involved four different light shading treatments, obtained by one-layer black nylon mesh (L1), two-layer black nylon mesh (L2), three-layer black nylon mesh (L3) and four-layer black nylon mesh (L4), which did not alter the spectrum of the incident light. ...
Phenotypic plasticity is an important adaptation to spatial and temporal environmental variations. For submerged macrophytes, adaptation to water depth and light variation is particularly important. To determine the morphological and physiological adaptive strategies of Vallisneria natans at different water depths and light conditions, we combined field investigation, light control experiment and in situ physiological response experiment. In the field investigation and the light control experiment, both water depth and light intensity had prominent effects on the morphological of V. natans , especially in fresh weight and leaf length. The leaf length elongated more rapidly at intermediate water depth sites with lower light intensity. In the in situ experiment, the survival boundary of V. natans is 5.5 m in Lake Erhai. Below this depth, the chlorophyll-a content increased gradually with increasing water depth. Our results demonstrated that V. natans can adapt to water depth and light availability by changing morphological, physiological and resource allocation. At low light condition, V. natans invested more resource for light acquisition, simultaneously, changing the photosynthetic pigment content to compensate for light attenuation; conversely, more resource was directed towards reproduction. These results will provide new insight for species selection when conducting aquatic plants restoration in freshwater ecosystem.
HIGHLIGHTS
Water depth and light availability affect the morphology, physiology, and resource allocation of V. natans .
An alternative resource allocation pattern of V. natans could shift between light acquisition and reproduction.
... Submersed macrophytes, which are large aquatic plants that grow underwater, are crucial for stable water clarity in shallow, mesotrophic and eutrophic lakes (Jeppesen et al., 1997;Scheffer, 1998;Su et al., 2019). The growth of submersed macrophytes is affected by many environmental factors, among which light availability is critical for determining the growth, distribution and species composition of submersed macrophytes in lakes (Barko et al., 1986;Chambers, 1987;Goldsborough and Kemp, 1988;Ni, 2001;Hautier et al., 2009;Yuan et al., 2016;Verhofstad et al., 2017;Chen et al., 2016Chen et al., , 2019Chen et al., , 2020. Indeed, light availability is often considered the most important factor that determines the maximum depth distribution of submersed macrophytes in lakes (Caffrey et al., 2007;Yuan et al., 2016). ...
... Received 26 October 2019; Received in revised form 12 February 2020; Accepted 19 February 2020 along an environmental gradient and their trade-offs are crucial approaches for exploring the relationships between plants and their environments, and trait-based approaches can serve as tools for highlighting the mechanisms underlying plant responses to stress (such as low-light stress) (Fu et al., 2014;Liu and Ma, 2015). Changes in specific environmental factors might impact specific plant characteristics, such as height, leaf area, biomass allocation, specific leaf area (SLA), soluble carbohydrate (SC) and starch contents (Cornwell and Ackerly, 2009;Fu et al., 2012;Weiner, 2004;Chen et al., 2016Chen et al., , 2019Chen et al., , 2020Yuan et al., 2016). In a low-light stress environment, macrophytes with different growth forms exhibit varying adaption strategies. ...
... In a low-light stress environment, macrophytes with different growth forms exhibit varying adaption strategies. For example, rosette macrophytes generally undergo physiological adjustment to better adapt to light conditions (Chen et al., 2016;Yuan et al., 2016), whereas canopy-forming macrophytes mainly utilize morphological adjustment strategies to capture more light (Titus and Adams, 1979;Ni, 2001;Fu et al., 2012;Chen et al., 2016). Using the latter strategy, canopyforming macrophytes allocate more biomass towards stems to increase both the plant height (Ni, 1997;Yang et al., 2004;Fu et al., 2012) and leaf area to enhance the light-use efficiency by expanding the lightreceiving area (Owens et al., 2008). ...
The decline in submersed macrophytes induced by low-light stress is ubiquitous in mid-lower Yangtze lakes in China. However, the trade-offs among the adaptation mechanisms used by submersed macrophytes to low-light stress remain unclear. Moreover, the experimental period used in most previous studies was relatively short, and plant traits were not monitored multiple throughout the experimental period. In the present study, we examined the growth of a representative submersed macrophyte, Potamogeton maackianus, under four light regimes (2.8%, 7.1%, 17.1% and 39.5% of ambient light) over a course of 12 months and assessed various plant traits at monthly and quarterly intervals. The results showed that P. maackianus exhibited a lower leaf moisture content and a higher stem moisture content under decreased light conditions. Under the lowest light regime, P. maackianus had low soluble carbohydrate (SC) contents in the leaves and low starch contents in the stems at all the seasons. P. maackianus showed different allometric relationships among different treatments reflected different adaption strategies resulting from different light environment. P. maackianus exhibited a relatively stable biomass allocation pattern characterized by a continual increase in the stem mass fraction of total biomass under relatively high light transmittance (17.1% and 39.5%), which is a response of P. maackianus that can ensure a high initial biomass in the next spring season. However, under low light transmittance, the biomass allocation pattern fluctuated early in the experiment, and the amplitude increased with decreases in the light transmittance (2.8% and 7.1%). P. maackianus exhibited trade-offs between the stem (plant height) and leaf mass (leaf area) fractions of the total biomass, which help improve the adaptation of the macrophyte to a low-light environment. Our results can be useful for estimating light-use conditions of P. maackianus according to regression relationships between the leaf/stem mass fractions of the total biomass and time.
... Submersed macrophytes with different growth forms usually have different adaptive strategies for responding to stress, which are often species-specific. Changes in morphological and physiological traits, for example, ensure better adaptation to various light regimes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). ...
... Previous studies have reported different adaptation strategies to low-light environments by different growth forms of submersed macrophytes (Cao et al., 2011;Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Yuan et al., 2016). Consistent with previous studies, canopyforming macrophytes usually elongate their shoots towards the water surface to compensate for low-light conditions (Chen et al., 2016;Chen et al., 2019;Fu et al., 2012;Goldsborough and Kemp, 1988). In the present study, the substantially increased plant height and lowest branch height ensured that the shoots of H. verticillata easily reached the water surface and formed a canopy to maintain a competitive advantage under light competition, as indicated by the large number of branches. ...
Benthivorous fish disturbance and snail herbivory are two important factors that determine the community structure of submersed macrophytes. We conducted an outdoor mesocosm experiment to examine the separate and combined effects of these two factors on water quality and the growth of two mixed-cultivation submersed macrophytes, Vallisneria natans and Hydrilla verticillata, with different growth forms. The experiment involved two levels of fish (Misgurnus anguillicaudatus) disturbance crossed with two levels of snail (Radix swinhoei) intensity. The results revealed that fish activity rather than snail activity significantly increased the overlying water concentrations of total suspended solids (TSS), total nitrogen (TN), ammonia nitrogen (N-NH4), total phosphorus (TP) and phosphate phosphorus (P-PO4). However, no differences among treatments were observed for chlorophyll a (chl a) concentrations. Fish disturbance or snail herbivory alone did not affect the relative growth rate (RGR) of H. verticillata, but their combined effects significantly decreased the RGR of H. verticillata. Although snail herbivory alone did not affect the RGR of V. natans, fish disturbance alone and the combined effects of these factors drastically reduced its RGR. Both species exhibited increased free amino acid (FAA) contents and decreased ramet numbers, soluble carbohydrate (SC) contents and starch contents in the presence of the fish. Moreover, compared to H. verticillata, V. natans showed exceedingly low ramet numbers and starch contents in the presence of the fish. H. verticillata had a higher RGR and summed dominance ratio (SDR2) than V. natans in all treatments; H. verticillata also displayed a larger competitive advantage in the presence of fish disturbance. The present study suggests that (1) fish disturbance rather than snail activity increases water nutrient concentrations, (2) low snail density may be harmful to submersed macrophyte growth when the plants are under other abiotic stress conditions and (3) the competitive advantage of H. verticillata over V. natans is more preponderant in a turbid environment.
... Many studies have been conducted to explore the adaption mechanisms of submersed macrophytes to low-light stress. Submersed macrophytes have various strategies to address low-light stress and adapt to low-light environments, including morphological plasticity (Goldsborough and Kemp, 1988;Ni, 2001;Fu et al., 2012;Chen et al., 2016) and physiological plasticity (Cao et al., 2011;Chen et al., 2016;Yuan et al., 2016). In addition, the adaption strategies are often correlated with specific plant growth forms (Chen et al., 2016;Yuan et al., 2016). ...
... Many studies have been conducted to explore the adaption mechanisms of submersed macrophytes to low-light stress. Submersed macrophytes have various strategies to address low-light stress and adapt to low-light environments, including morphological plasticity (Goldsborough and Kemp, 1988;Ni, 2001;Fu et al., 2012;Chen et al., 2016) and physiological plasticity (Cao et al., 2011;Chen et al., 2016;Yuan et al., 2016). In addition, the adaption strategies are often correlated with specific plant growth forms (Chen et al., 2016;Yuan et al., 2016). ...
... Submersed macrophytes have various strategies to address low-light stress and adapt to low-light environments, including morphological plasticity (Goldsborough and Kemp, 1988;Ni, 2001;Fu et al., 2012;Chen et al., 2016) and physiological plasticity (Cao et al., 2011;Chen et al., 2016;Yuan et al., 2016). In addition, the adaption strategies are often correlated with specific plant growth forms (Chen et al., 2016;Yuan et al., 2016). However, the adaption strategies of submersed macrophytes to low-light stress remain unclear, especially in the presence of other influential aquatic animals. ...
Low underwater light availability and benthivorous fish-mediated disturbance are two important factors that influence the growth of submersed macrophytes. However, the combined effects of these factors remain unclear. To determine the combined effects of low light and fish-mediated disturbance on the growth of two submersed macrophytes with contrasting growth forms, i.e., Vallisneria natans and Hydrilla verticillata, we conducted an outdoor mesocosm experiment with a two-by-two factorial design. The experiment involved two fish-mediated disturbance levels (0 and 1 Misgurnus anguillicaudatus) crossed with two levels of light intensity (ambient light and a low-light environment created by culturing the macrophytes under a shelter). The results showed that the chlorophyll a (chl a) concentration in the overlying water showed no difference among treatments for each macrophyte species. The fish-mediated disturbance significantly decreased the relative growth rate (RGR) of both species in the low-light environment but showed no effects in the ambient light environment. Low light availability and/or fish-mediated disturbance led to increased plant heights of both species compared with the heights under the ambient light regime. Low light availability combined with fish-mediated disturbance significantly reduced the ramet number and soluble carbohydrate (SC) content of both species; however, the free amino acid (FAA) content was not affected. Compared to V. natans, H. verticillata exhibited a high RGR and high ramet numbers in a low-light environment combined with fish-mediated disturbance. Our results indicated that the adaptability of H. verticillata is better than that of V. natans in turbid, shallow and hydrostatic water. Fish-mediated disturbance can negatively influence submersed macrophyte recovery in lakes when light is not abundant.
... Canopy-forming species, such as Myriophyllum spicatum and Potamogeton wrightii, tend to allocate more biomass to stems, grow taller and form dense canopies to counter light attenuation in the water column (Strand and Weisner, 2001;Fu et al., 2012). In contrast, rosette-type macrophytes such as Vallisneria species can increase their plant height in deeper sites as well (Fu et al., 2012), but mainly tolerate shading through a lower light compensation point and a higher leaf mass ratio of total plant mass compared to canopy-forming macrophytes (Su et al., 2004;Chen et al., 2016). ...
... Stem elongation was found as a major response strategy to low light conditions by the canopy-forming species P. maackianus, while the rosette-type species V. natans produced more chl a per shoot biomass at deeper sites to tolerate light attenuation. These findings are consistent with a similar study by Chen et al. (2016) assessing the response of P. maackianus and V. natans to low light conditions in Lake Donghu, China. In our study, V. natans increased leaf chl a content and allocated more biomass to leaves at deep sampling points, resulting in a strong increase of chl a content per shoot biomass. ...
... In our study, V. natans increased leaf chl a content and allocated more biomass to leaves at deep sampling points, resulting in a strong increase of chl a content per shoot biomass. Such strategy combined with a low light compensation point for photosynthesis (Chen et al., 2016), allows V. natans to successfully survive at sites with low light conditions in Lake Erhai and colonize deep areas with high slopes. Other rosette-type species such as V. americana have shown a similar morphological and physiological response to low light conditions (French and Moore, 2003). ...
Light is a major limiting resource in aquatic ecosystems and numerous studies have investigated the response of submerged macrophytes to low light conditions. However, few studies have tested whether different light response strategies can also have consequences for macrophyte distribution along different littoral slopes in lakes, which are known to affect macrophyte biomass due to differences in drag forces and sediment characteristic. In this study, we tested (1) whether two macrophyte species of different growth forms (canopy-forming: Potamogeton maackianus, rosette-type: Vallisneria natans) differ in their response strategies to low light conditions and (2) how these responses influence their distribution along different basin slopes in the mesotrophic Lake Erhai, China. We hypothesized that the canopy-forming species responds to low light conditions at deeper sites by stem elongation while the rosette-type species increases its shoot chlorophyll content. As a consequence, P. maackianus should have a higher susceptibility to drag forces and thus prevail at sites with lower slopes. Sites with higher slopes should offer a niche for rosette-type species like V. natans that can better withstand drag forces. We surveyed the distribution and abundance of the two macrophyte species at 527 sampling points along 97 transects in Lake Erhai and measured their height, leaf and stem/rhizome biomass, and leaf chlorophyll a content at different water depths. Our results confirmed stem elongation as a strategy to low light conditions by the canopy-forming species P. maackianus, while V. natans produced more chlorophyll a per shoot biomass at deeper sites to tolerate shading. As hypothesized, these alternative response strategies to low light conditions resulted in a trade-off regarding the plants ability to grow at different basin slopes. P. maackianus was dominant at sites with low-moderate slope (0–4%) and low-moderate water depth (2–4 m), while sites with high basin slope (4–7%) combined with moderate-high water depth (3–5 m) were dominantly colonized by V. natans. The latter habitat thus represents a potential refuge for rosette-type macrophyte species that are often outcompeted when shading increases during eutrophication.
... Some macrophytes can grow very well, which leads to overgrowth that might disturb the ecosystem. Several environmental parameters reveal the dynamics in terms of diurnal such as light and temperature, which affect the growth and photosynthetic activities of macrophytes [12,13]. ...
... Shading decreased the net photosynthesis in C. aspera and C. canescens within 24 h; however, their photosynthetic performance was recovered within a short period [17]. Chen et al. [12] revealed that Potamogeton maackianus and Vallisneria natans decreased their minimum saturating irradiance (E k ) and maximum relative electron transport rate (rETR max ) and increased their initial slope (α) of RLCs under low light stress. ...
Macrophytes play an important role in the freshwater ecosystem. However, human activities and climate change are currently affecting aquatic lakes and species in various ways. The heterogeneity of macrophyte ecophysiology might lead to different responses to changing environments. To understand the photosynthetic responses of freshwater macrophytes to changes in light, six freshwater macrophyte species from Songkhla Lagoon were investigated. The results showed that there was a diurnal response of photosynthetic activities in all species. The Fv/Fm and ∆F/Fm′ of all species decreased at midday (9 a.m.–3 p.m.) then recovered at 6 p.m. close to the 6 a.m. level. As well as alpha, the positive relation between alpha and light showed the adaptation of plants. The saturating irradiance (Ik) revealed that plants from different light regimes showed different responses to light and temperature changes. To maintain a positive carbon balance and cope with light and temperature conditions, macrophytes had strategies such as modifying light harvesting capacity and light use. This study provides a better understanding of the vulnerability of each species to environmental changes and photosynthetic responses that enable species from different light regime to adapt to changing light environments.
... The functional composition of submerged macrophyte community from oligo-mesotrophic to eutrophic and hypereutrophic states would select species with low relative growth rate, small specific leaf area, longer shoot height, a wider range of flowering duration and small ramet size. These traits reflect the adaptation characteristics of vegetation to harsh environments under increasing eutrophication (Wright et al., 2004;Fu et al., 2012b;Chen et al., 2016). ...
... For example, the low relative growth rate and small specific leaf area made species composition become more competitive (i.e., transition from r-strategist to K-strategist) (MacArthur et al., 1967) and tolerant (Reich et al., 1999) under deteriorating eutrophic conditions. Low transparency in eutrophic water bodies forces macrophytes to lengthen their shoots to obtain more light (Chen et al., 2016), leading to lower resource allocation for ramet size (Fu et al., 2012b). Fu et al. (2019) also found that anthropogenic pressure (high nutrient levels in lakes) results in environmental homogeneity and low β diversity, especially turnover among macrophyte assemblages. ...
Increasing eutrophication poses a considerable threat to freshwater ecosystems, which are closely associated with human well-being. As important functional entities for freshwater ecosystems, submerged macrophytes have suffered rapidly decline with eutrophication. However, it is unclear whether and how submerged macrophytes maintain their ecological functions under increasing eutrophication stress and the underlying patterns in the process. In the current study, we conducted an extensive survey of submerged macrophytes in 49 lakes and reservoirs (67% of them are eutrophic) on the Yunnan-Guizhou Plateau of southwestern China to reveal the relationship between submerged macrophyte biodiversity and ecosystem functioning (BEF) under eutrophication stress. Results showed that submerged macrophytes species richness, functional diversity (FD), and β diversity had positive effects on ecosystem functioning, even under eutrophication. Functional diversity was a stronger predictor of community biomass than species richness and β diversity, while species richness explained higher coverage variability than FD and β diversity. This suggests that species richness was a reliable indicator when valid functional traits cannot be collected in considering specific ecological process. With increasing eutrophication in water bodies, the mechanisms underlying biodiversity-ecosystem functioning evolved from “niche complementarity” to “selection effects”, as evidenced by decreased species turnover and increased nestedness. Furthermore, the relative growth rate, specific leaf area, and ramet size in trade-off of community functional composition became smaller along eutrophication while flowering duration and shoot height became longer.
This study contributes to a better understanding of positive BEF in freshwater ecosystems, despite increasing anthropogenic impacts. Protecting the environment remained the effective way to protect biodiversity and corresponding ecological functions and services. We hope focus on specific eco-functioning in future studies so as to effective formulation of management plans.
... Recent research has also shown that species with different growth forms may exhibit distinct mechanisms to cope with low-light conditions. For example, to compensate for low-light stress, canopy-forming species (e.g., Potamogeton maackianus) converge on the water surface through stem elongation (He et al., 2019), species without roots or rhizoids (e.g., Ceratophyllum demersum) adapt by elongating shoot length or floating, and rosette-forming species (e.g., Vallisneria natans) increase their photosynthetic efficiency (Chen et al., 2016). Therefore, in the current study, we examined how the depth distribution of different submerged macrophytes responds to seasonal fluctuations in background water levels and environmental factors to provide insights into the ecological management of aquatic vegetation in lakes. ...
... Specifically, this specie allocate more biomass to the stems to ensure that leaves are better distributed in the upper water column to increase light utilization efficiency (Abernethy et al., 1996;Yang et al., 2004;Fu et al., 2012). However, P. maackianus balances the distribution of biomass between stems and leaves in the early stages of growth, first allocating biomass to stems to increase plant height to a certain level, then distributing more biomass to the leaves to increase leaf area and enhance light capture ability (Chen et al., 2016;He et al., 2019). In terms of reproductive strategies, the asexual cloning ability of P. maackianus is more inhibited under low-light stress than that of V. natans, which is likely because plants with longer and thinner stems are more vulnerable to hydrodynamic forces and hydraulic pressure damage (Dale, 1984;Puijalon et al., 2011). ...
Submerged plants are crucial for maintaining a clear water state in lakes, and their distribution area is usually determined by the lowest distribution boundary (LDB). However, LDBs of submerged macrophytes often exhibit species differences and vary with seasonal water level fluctuations. In this study, we carried out a three-year field investigation to compare differences in the LDBs of three submerged macrophyte species (i.e., Vallisneria natans, Ceratophyllum demersum, and Potamogeton maackianus) and explore their distinct determinants. We assumed that LDB differences would exist among the three species and that water level (WL) would be a key environmental driver of LDB dynamics, with an association between the LDBs of submerged macrophytes and water level fluctuations. Indeed, our results showed significant seasonal differences between C. demersum and V. natans in the period of September - May, with mean annual values in the order (low to high) V. natans, C. demersum, and P. maackianus. Furthermore, water level was a major driving force of the LDB dynamics of the three species. Changes in the LDBs of the three species in response to water level fluctuations could be divided into three periods: i.e., recovery growth period (April to June), stress tolerance period (July to September), and recession period (October to following March). This study not only clarifies the impact of water level on submerged macrophyte growth and distribution, but also has larger practical implications for the ecological restoration and management of large deep lakes.
... Macrophytes are potentially used as powerful natural tools for water quality improvement in lakes and reservoirs due to their capacity in nutrient uptake and in preventing phytoplankton blooms (Liu et al., 2000;Lone et al., 2014). The growth and photosynthesis of submerged macrophytes can be affected by temperature (Chalanika De Silva and Asaeda, 2017), light (Chen et al., 2016), and high organic loads in sediments ( Barko and Smart, 1983) due to several coupled biological, physical and chemical modifications of the benthic system (Sand-Jensen et al., 2005; Raun et al., 2010). Diurnal light changes affect photosynthetic activities, and Jiang et al. (2018) found that the Maximum Quantum Yield of photosystem II (MQY) of six common submerged macrophytes decreased at midday under ambient light, but there was no significant change under shade, and MQY was negatively correlated with photon radiance, except for Ceratophyllum demersum, which probably could support high light levels. ...
... A high load of suspended particles can reduce light transmission to photosynthetically active leaf surfaces (Reitsema et al., 2018) and alter gas and nutrient exchanges in submerged macrophytes (Korschgen et al., 1997). Chen et al. (2016) found that Potamogeton maackianus and Vallisneria natans increased their initial slope of RLC (α) and decreased their minimum saturating irradiance (Ek) and maximum relative electron transport rate (ETRm) under low light stress, while higher Relative Growth Rate of P. maackianus than V. natans was seen with a stronger light intensity but it was decreased in a low light intensity. Shading caused a decrease in net photosynthesis in Chara aspera and Chara canescens within 24 hours, but their photosynthetic performances recovered within a short period, suggesting that these charophytes are able to adapt to low light conditions (Kovtun-Kante et al., 2014). ...
Macrophytes play an important role in maintaining high physical and biological diversity in freshwater ecosystems. However, during the past several centuries since the industrial revolution, human activities and climate change have caused significant changes in the structure and function of aquatic environments, for example via increased temperature or high sedimentation that reduces light penetration. This study investigated the combined effects of elevated temperature and low light on growth and photosynthetic performance of submerged macrophytes Ceratophyllum demersum and Elodea canadensis and identified temperature and light thresholds for these species. Photosynthetic performance, chlorophyll a and b concentrations, organic and carbon contents, and growth rates were estimated in these two dominant macrophytes sampled from the middle of Songkhla lagoon, subjected to 9 treatments (3 light intensities and 3 temperatures) for 9 weeks. The results show that photosynthetic performance according to the indicators EQY, α and rETRmax was inhibited by low light in both species. C. demersum was more tolerant to temperature and light stresses. This study provides an understanding of physiological tolerance and response to light and temperature stresses, and improves the understanding of how aquatic macrophytes respond to future climatic and anthropogenic changes, supporting the development of sustainable lagoon management plans.
... Hydrologic regime is a major determinant of macrophyte community structure and productivity in lake ecosystems (Reddy et al. 2004;Ren et al. 2020). By altering a series of environmental factors, especially light intensity, water depth has great influences on growth and metabolism of submerged macrophytes (Chen et al. 2016;. Shallow waters not only compress the living space of submerged macrophytes but generally causes photoinhibition (Winters et al. 2003;Li et al. 2020), while photosynthetic efficiency often declines greatly under low-light conditions in deep waters Min et al. 2019). ...
... Previous studies have shown similar results. For instance, the plant height of Myriophyllum spicatum (a canopy-type submerged macrophyte) and Vallisneria natans (a rosette-type submerged macrophyte) were lower at 50 cm than at deeper water (Li et al. 2019a, b), V. natans had the least leaf length and area when exposed in strong light or planted at water depth less than 60 cm (Chen et al. 2016;Gu et al. 2017), and the specific leaf area of Potamogeton maackianus and Potamogeton malaianus were lower at 1.0 m water depth than at 2.5 m water depth (Fu et al. 2012). Together, these findings indicate that submerged plants will adapt to strong light stress by adjusting a series of morphological traits in shallow-water environments. ...
Submerged macrophytes, important primary producers in shallow lakes, play a crucial role in maintaining ecosystem structure and function. By altering a series of environmental factors, especially light intensity, water depth has great influences on growth of submerged macrophytes. Here, by hanging pots statically at water depths of 40, 60, 80, 100, 120, 140, 160, 180, 200, and 220 cm, respectively, we investigated effects of water depths on morphological plasticity and physiological traits of Potamogeton crispus. At 40 and 60 cm water depths versus other water depths, P. crispus showed lower plant height, larger stem diameter, thicker leaves, and smaller leaf area, leaf length, and specific leaf area. With water depth increasing, the plant height, leaf area, and leaf length gradually increased until 160 cm water depth, while the stem diameter and leaf thickness gradually decreased until 200 cm water depth. In comparison, the plant height, leaf length, and leaf number significantly decreased when the water depth further increased to 180-220 cm. The leaves contained lower concentrations of superoxide dismutase and peroxidase at 100-160 cm water depth, and lower catalase concentrations at 40-140 cm water depth, especially at 80-100 cm. In shallow waters, the concentration of chlorophyll a and b in leaves were both lower, while the ratio of chlorophyll a to b was relatively higher. As the water depth of 40-220 cm, the chlorophyll a and b concentrations increased significantly with increasing water depth, while their ratio gradually decreased. The present study provides new insights into the adaptation strategies of submerged macrophytes to the variation in water levels, and our findings are beneficial for ecosystem construction and management.
... A reduction of water column depth increases the light availability at the sediment and the mean available light (MAL) over the water column nonlinearly. These two aspects of light availability are particularly critical at the beginning of the growing season for short-growing plants but also for tall-growing ones because MAL is likely decisive for whether the entire water volume can be used for efficient photosynthesis and the formation of dense macrophyte stands (Chen et al., 2016;Lauridsen, Mønster, Raundrup, Nymand, & Olesen, 2020). Empirical evidence from various climate regions including subtropical (Havens, East, & Beaver, | 3 ERSOY Et al. Bucak et al., 2012;Coppens, Özen, et al., 2016;Özkan, Jeppesen, Johansson, & Beklioğlu, 2010) confirms a positive effect of a water level decline on submerged macrophyte growth due to improved light conditions in the water column and expansion of the littoral zone (Beklioğlu et al., 2006;Beklioğlu & Tan, 2008;Coppens, Hejzlar, et al., 2016;Kosten et al., 2009;Stefanidis & Papastergiadou, 2013). ...
... In line with our Hypotheses (1-3), results from regression and correlation-based analyses identified MAL in the water column to be the most proximate and important driver for PVI (Tables 1 and 3). This is supported by several studies showing the correspondence between better light conditions and macrophyte growth (Chen et al., 2016;Li, Lan, Chen & Song, 2018). However, semi-partial correlation indicates that temperature, despite its high correlation with MAL ( Figure 4a,b), also had a direct positive effect on PVI. ...
Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardised pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1 m (shallow) and 2 m (deep) depth along a latitudinal
temperature gradient with average water temperatures ranging from 14.9 to 23.9 °C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined Percent Plant Volume Inhabited (PVI) of submerged macrophytes on a monthly basis for five months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms.
We identified three pathways along which water temperature likely affected PVI, exhibiting: (1) a direct positive effect if light was not limiting, (2) an indirect positive effect due to an evaporation driven water level reduction, causing a non-linear increase in mean available light, (3) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a
carbon store and food source.
... During the experiment, pH, water temperature (T) and light intensity in the overlying water were measured according to methods described earlier (Chen et al., 2016) every 10 days. The means and ranges (in the parentheses) of pH, T and light intensity were 9.55 (8.56-10.97), ...
... Sandjensen and Sondergaard (1981) showed that over 80% light intensity reduced through a dense epiphyton before reaching the chloroplasts (Sandjensen and Sondergaard, 1981). Furthermore, it has been reported that P. maackianus is more sensitive to low light stress than V. natans (Chen et al., 2016). Therefore, FGA proliferation either in high density treatment of P. maackianus or in low density treatment of V. natans may have negative effects on the photosynthesis of macrophytes by the shading effect. ...
Excessive proliferation of filamentous green algae (FGA) is a problem that commonly occurs following the re-mediation of submerged macrophytes during lake restoration. Cultivation of submerged macrophytes changes the physical and chemical environment and micro-habitats for survival and growth of FGA. However, effects of submerged macrophytes on FGA and the mechanisms are largely unknown. In this study, artificial grass (con-trols) and two submerged macrophytes (Potamogeton maackianus and Vallisneria natans) with different leaf complexity were cultivated at densities of 3, 6, and 9 in aquaria for a month. The proliferation of FGA, pho-tosynthetic performance of macrophytes, and possible roles of bacteria in the interaction of macrophytes and FGA were studied. Compared with controls, planting of P. maackianus promoted the proliferation of epiphytic FGA, and the effects were density-dependent. Also, density-dependent decrease of photosynthetic performance of P. maackianus were observed. However, in the groups of V. natans, proliferation of epiphytic FGA showed density-dependent inhibition, but photosynthesis of V. natans showed density-dependent promotion. Furthermore, photosynthesis of macrophytes was negatively correlated with growth of epiphytic FGA (Chl a contents). Abundances of epiphytic bacteria taxa such as members of orders Rhodobacterales, Nitrosomonadales and Gemmatimonadales on P. maackianus were greater than those on V. natans. The abundances of these bacteria were positively related to Chl a contents of epiphytic algae (FGA). Thus, proliferation of FGA might be partly attributed to accumulation of certain bacteria taxa on the submerged macrophytes planted during lake restoration. To avoid excess proliferation of FGA, careful selection of submerged aquatic macrophytes is needed.
... Many studies have examined the physiological and morphological response in vegetative structures (phenotypic plasticity) of submerged macrophytes to varying water depths (Maberly, 1993;Strand and Weisner, 2001;Zhou et al., 2017). Submerged macrophytes normally adapt to low light availability in water column by one of two distinct strategieselongating shoot toward water surface to alleviate low light stress or enhancing low light tolerance through photosynthetic adjustments (Riis et al., 2012;Chen et al., 2016). Yet relatively fewer studies exist dealing with the variation in plant reproductive traits (Li et al., 2017(Li et al., , 2018, and even fewer studies have been conducted to further understand patterns of sexual dimorphism in dioecious macrophytes compared to their terrestrial relatives (Dorken and Barrett, 2004;Li et al., 2019b). ...
... For submerged macrophytes, the efficiency of carbon assimilation is strongly affected by reduced or variable light availability in the water column (Bornette and Puijalon, 2011). It is, therefore, critical for submerged macrophytes to evolve adaptive strategies (e.g., phenotypic plasticity) to reduced light availability (Strand and Weisner, 2001;Fu et al., 2012;Chen et al., 2016). In the present study, sexual morphs of V. natans had striking differences in their life history traits, and reproductive males and females differed in how they adjusted their expression of important traits in response to altered water ...
Sexual dimorphism in vegetative and reproductive traits is associated with contrasting strategies of males and females for response to varied environmental conditions, causing sex-specific reproduction success and consequently long-distance dispersal and colonization. Aquatic plants usually exhibit rich phenotypic plasticity and great diversity in reproductive systems, but the influence of aquatic conditions on the plasticity of sexual dimorphism has received less attention. Using a common garden experiment with dioecious submerged plant Vallisneria natans grown at various water depths simulating different light availability, we measured variations in 20 traits for females and 19 traits for males (total = 540 plants from 30 seed families) including morphology, reproductive traits and photosynthesis. We investigated sex-specific plastic responses and variation of sexual dimorphism in response to water depth change. Females displayed much greater leaf length, vegetative biomass and resource allocation to reproduction than males at all depths, whereas spathe number and gamete production per spathe displayed reverse pattern. Besides most traits in each sex (16 in female and 12 in male) showing striking phenotypic plasticity, the degree of sexual dimorphism increased significantly for total biomass and reproductive investment, but decreased for leaf length, spathe number and flowering ramet percentage in low light and deep water. Females varied more than males in leaf length, total biomass, reproductive investment, length and biomass of reproductive organs and rate of photosynthesis in response to decreased underwater light availability, suggesting that female has greater plasticity than male. These findings illustrated considerable plasticity in the degree of sexual dimorphism in a variety of vegetative and reproductive traits across different environments driven by the contrasting reproductive functions of the sexes in relation to pollen and seed dispersal. Females of V. natans responded more plastically than males to low light conditions resulted from water depth variation in either aboveground vegetative growth or reproduction. This study provides novel insight into adaptive strategies of submerged dioecious macrophytes to survive and increase fitness in freshwater habitats.
... Substantial phenotypic plasticity for resource capture is important for submerged macrophytes (Barrett et al., 1993;Going et al., 2008;Hyldgaard and Brix, 2012), enabling them to be more competitive (Chambers and Kalff, 1987). For instance, submerged species are highly responsive to light shortage and can have morphological and structural adaptations over the period of growth to optimize light utilization by increasing shoot length, decreasing branches, producing longer, wider and thinner leaves and changing resource allocation to various plant structures (Riis et al., 2012;Schneider et al., 2015;Chen et al., 2016). Numerous studies have been conducted to address the responses of submerged macrophytes to decreased light, albeit mostly from the perspective of growth conditions. ...
... In our experiment, resource allocation in V. spinulosa was highly responsive to a change in light availability. Although various macrophyte species may respond differently to light deficiency (Chambers, 1987), decreased light in water often reduces coverage and decreases growth of macrophytes in the littoral zone and vice versa (Vallisneria americana, French and Moore, 2003; Vallisneria natans, Chen et al., 2016). In our experiment, both vegetative and reproductive traits tended to decrease as light decreased from 100% to 20% incident light. ...
Environmental changes, e.g., eutrophication, in aquatic ecosystems can greatly alter light available to submerged macrophytes. In dioecious plants, given potential for sex-specific differences in resource requirements (i.e., high-carbon for seeds vs. high-nitrogen for pollen), females and males are expected to divergently adjust allocations toward resource acquisition structures when resources are limited during growth. Here, Vallisneria spinulosa was used as a representative dioecious submerged macrophyte to detect sex-specific responses to light limitation and assess whether sexual dimorphism varied with resource availability. Plants were grown under varying levels of light availability in nine outdoor mesocosms for 14 weeks. Late in the reproductive season, allocations to vegetative and reproductive traits for both sexes were determined and relative allocation to reproduction vs. vegetative growth was analyzed. Female and male reproductive plants differed in adjustments of resource allocation in response to light availability. Under low light, females showed a smaller reduction in allocation of resources to vegetative tissues and greater leaf area than males, suggesting female plasticity to increase carbon capture. Under low light, males showed a smaller reduction in reproductive allocation than females (flowers and inflorescences in males vs. fruits in females), suggesting that carbon limitation has greater impacts on sexual reproduction by females than males. Our study provides evidence of differences in reproductive costs and currencies for female vs. male reproduction in aquatic macrophytes, as V. spinulosa responded plastically to reduced light, with sexually dimorphic allocation strategies. Sex-related resource currencies are potentially important drivers for sex-specific variations in allocation patterns, with females safeguarding their vegetative carbon-rich biomass to satisfy future fruit and seed production.
... These different growth forms (Chambers 1987b) result in different adjustments and resistance to environmental stresses. For example, to compensate for low-light conditions, Potamogeton maackianus, which is a species with developed stems, was shown to mainly elongate its shoot length towards the water surface, whereas V. natans, which is a rosette species, compensates for low-light conditions mainly through photosynthetic adjustments (He 2015; Chen et al. 2016). In terms of hydrodynamic stress, Myriophyllum spicatum L., which is a species with developed stems, was found to be more susceptible to mechanical damage than plants such as Vallisneria americana Michaux, which is a rosette species, in a flume-wave experiment (Stewart et al. 1997). ...
... This finding implies that hydrodynamic forces could be the critical factor that determines the natural distribution of submerged macrophytes. Hydrodynamic forces mainly act through mechanical damage and influence the establishment and recruitment of macrophytes, whereas low-light and eutrophication conditions increase the chances of mechanical damage in highly dynamic environments via adverse effects on growth, morphology, physiology or biomechanics (La Nafie et al. 2013;Zhu et al. 2014Zhu et al. , 2018Soissons et al. 2018), particularly in eutrophic lakes (Schutten et al. 2005;Istvánovics et al. 2008;Zhu et al. 2015;Chen et al. 2016). ...
Few studies have focused on the biomechanical responses of submerged, rosette-forming macrophytes to wave action, water depth, or their co-occurrence in naturally eutrophic systems. The plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics of Vallisneria natans inhabiting a range of water depths were examined along three transects (T1, T2, and T3) in a eutrophic lake, Lake Erhai, in Yunnan Province, China. These transects were exposed to weak wave action and hyper-eutrophication (T1), moderate wave action and eutrophication (T2), or strong wave action and eutrophication (T3). The results showed that V. natans was mainly distributed at intermediate depths, with the widest colonization depth in T1. The values of plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics were generally highest in T3 and smallest in T2. Along the depth gradient, these values were generally highest at 3.5, 2.5, and 2.5 m for the plants growing in T1, T2, and T3, respectively. These findings suggest that V. natans adopts a “tolerance” strategy to cope with the effects of strong wave action in eutrophic habitats and an “avoidance” strategy when exposed to moderate wave action in eutrophic areas. Since the absence of an avoidance strategy increases the resistance to low-light stress at the expense of increased drag forces, there is a limit to the wave action that V. natans can withstand. This study indicates that biomechanics could be important when determining the distribution pattern of V. natans in Lake Erhai.
... The diffuse attenuation coefficient was expressed as light attenuation at the surface and 40 cm underwater. The photon flux densities at the surface and 40 cm underwater were measured by an Apogee MQ-510 underwater PAR meter (Apogee Instruments, Inc.; Chen et al., 2016). The diffuse attenuation coefficient reflects the transparency of the water. ...
Due to climate change and increasing anthropogenic activities, lakes are disturbed frequently, usually by press (e.g., diffused pollution, rising temperatures) or pulse (e.g., storms, rainfall, pollution events) disturbances. Both press and pulse disturbances can affect abiotic and biotic environments, changing the structure of ecosystems and affecting ecosystem services. To confront with the effects of climate change and increasing anthropogenic activities, understanding the different effects of press and pulse disturbances on lake ecosystems is essential. This study assessed the effect of press and pulse disturbances of phosphorus on a microcosmic aquatic ecosystem by measuring the total phosphorus (TP), algae density, and physiological indicators of submerged macrophytes. We found that the microcosmic aquatic ecosystem responded differently to press and pulse disturbances. Our results suggested that it had a lower resistance to pulse phosphorus disturbances than to press phosphorus disturbances. There were significantly higher nutrient concentrations and algal densities in the pulse treatment than in the press treatment. Positive feedback was found between the biomass of submerged macrophytes and the water quality. There was a higher submerged macrophytes biomass at low TP concentration and algal density. In the context of climate change, press and pulse disturbances could have severe impacts on lake ecosystems. Our findings will provide some insight for further research and lake management. The differences in aquatic ecosystem responses to press and pulse disturbances were experimentally investigated. Pulse disturbances were more stressful than press disturbances to submerged macrophytes.
... In Hongshan Bay, Potamogeton maackianus and Vallisneria natans are dominant species (He et al., 2015). Studies have shown that Potamogeton maackianus can increase shoot length (morphological trait) and Vallisneria natans can increase light utilization efficiency (photosynthetic trait) to adapt to different water depths (Chen et al., 2016;He et al., 2019). Other studies have also found niche complementarity to be a more prevalent describing the relationship between biodiversity and biomass productivity Isbell et al., 2009;Ashton et al., 2010). ...
The impact of biodiversity on ecosystem functions and services remains a hot topic in ecology, especially under increasing biodiversity loss. Studies on the relationship between biodiversity and ecosystem functioning have identified two regulatory mechanisms: i.e., “niche complementarity” and “selection effect”. However, the relative importance of these mechanisms within communities and how they change along ecological gradients remain unclear. Moreover, most studies have focused on relatively stable ecosystems (e.g., forest, grassland), with limited attention paid to ecosystems with obvious seasonal changes, e.g., freshwater ecosystems. In this study we conducted a seasonal survey of submerged macrophyte communities to clarify the mechanisms of biodiversity on biomass productivity accounting for seasons and water depth. Our results showed that (1) seasonal variations of community indicators exhibited different trends along the water depth gradient. Biomass productivity showed high seasonal variation at intermediate depth while temporal beta diversity showed the opposite pattern. (2) Water depth not only inhibited biomass productivity directly but also indirectly by reducing species richness and enhancing temporal beta diversity. (3) The positive effect of species richness on biomass productivity was lower than the negative effect of evenness (path coefficients: 0.13 vs. 0.27), indicating that “selection effect” played a more important role in the relationship. (4) In shallow areas, the mechanism underlying the effects of biodiversity on biomass productivity was more from “selection effect”, whereas, in deep areas, the effects were related to both “niche complementarity” and “selection effect”. Our findings suggest that “niche complementarity” and “selection effect” are two complementary mechanisms underpinning the relationship between biodiversity and biomass productivity, and their relative importance varies with specific ecological gradients. Our results also provide a reference for studies on other freshwater organisms with analogous distribution patterns as submerged macrophytes with water depth. Scale dependence of the above relationship should be considered in future studies.
... Submerged plants tend to elongate their stems to reduce the stress associated with low-light conditions (Chen et al., 2016). In this experiment, when nutrient enriched, the C and P contents in the stem of P. crispus increased during the elongation stage. ...
The loss of submerged macrophytes from freshwater ecosystems is accelerating owing to the combined effects of eutrophication and climate change. Submerged macrophytes depend on spring clear water; however, increased water temperatures and excessive phosphorus (P) inputs often lead to the dominance of phytoplankton. It is still not clear how the stoichiometric characteristics of carbon (C), nitrogen (N), and P in different tissues of submerged macrophytes respond to P enrichment and temperature increases. In this study, we established 36 mesocosm ecosystems to explore the effects of warming and P addition on the leaf, turion, stem, and seed stoichiometry of Potamogeton crispus. The results revealed that different functional plant organs show distinct responses to P addition and warming, which demonstrates the importance of evaluating the responses of different submerged macrophyte organs to environmental changes. In addition, interactive effects between P addition and warming were observed in the leaf, turion, and seed C:N:P stoichiometry, which highlights the importance of multifactorial studies. Our data showed that warming caused a decrease in the C content in most organs, with the exception of the stem; P addition increased the P content in most organs, with the exception of seed; N content in the turion and seed were influenced by interactive effects. Collectively, P addition could help P. crispus to resist the adverse effects of high temperatures by aiding growth and asexual reproduction, and asexual propagules were found to be more sensitive to P enrichment than sexual propagules.
... rETR max was significantly higher in aerial leaves, indicating that this type of leaf had a higher capacity to utilize the absorbed light energy (Marshall et al., 2000). The larger value of E k reflects a higher tolerance with strong light (Ralph and Gademann, 2005;Chen et al., 2016;Jiang et al., 2018), while a less Fig. 7. Adaptive mechanism of Potamogeton wrightii for differential morphology and photosynthesis in aquatic and terrestrial environments, respectively. value of β is generally indicative of weaker photoinhibition (Platt et al., 1980). ...
Wetlands are strongly affected by seasonal hydrological changes and extreme drought events that can cause low water levels. In response, some freshwater plants can produce emergent growth forms that experience a drastic change in environmental conditions. Potamogeton wrightii is a freshwater plant, which grows primarily underwater but can also produce terrestrial shoots when emerged. The objective of this study was to investigate the anatomical and physiological responses of P. wrightii to these two distinct environments, as well as the genetic responses behind them. Aerial leaves of P. wrightii were thicker, and had larger amounts of cutin and wax, developed stomata, had a greater tolerance to strong light, and a greater photochemical efficiency. In contrast, submerged leaves had a greater ability to use HCO3– and to synthesize photosynthetic pigments. The differentially expressed genes including cutin and wax biosynthesis, photosynthesis-antenna proteins and photosynthesis pathways, clarified the molecular adaptive mechanisms in P. wrightii to aquatic and terrestrial environments. The capacity of P. wrightii to survive fluctuating water level can be attributed to its genotype that resulted from its evolution from land plants and its phenotypic plasticity. Further work is needed to assess the possibility and costs of aerial leaves to survive when re-submerged.
... The growth and community dynamics of submerged macrophytes are influenced by both biotic and abiotic factors, such as light availability, water temperature, nutrient concentrations in both the water and the sediments, and water flow [7,39,40]. The life history-related parameters of aquatic plants will change with the changing circumstances to avoid or resist in order to reduce the potentially negative effects from the adverse environmental conditions [41][42][43][44]. For instance, the reduced availability of nutrients in the sediments leads to the increase in biomass allocation to the root system resulting in a higher root to shoot ratio [45,46]. ...
Eutrophication often results in the loss of submerged vegetation in shallow lakes and turns the lake to be a turbid state. Recovery of submerged macrophytes is the key in the restoration of shallow eutrophic lakes to create a clear water state. However, internal loading control was considered as the critical process for the recovery of submerged macrophytes in shallow lakes after the external nutrient reduction. Phoslock® (Lanthanum modified bentonite) is a useful passivation material in controlling the internal loadings (release of phosphorus from the sediments), which was applied to restore the eutrophic lakes. However, the effects of Phoslock® on the growth and life strategies of submerged macrophytes are less focused so far. In the present study, we studied the responses in the growth and morphological characteristics of Myriophyllum spicatum to the addition of Phoslock® to the sediments. Our results showed that the addition of Phoslock® significantly decreased the contents of bioavailable forms of phosphorus in the sediments, such as redox-sensitive phosphorus bound to Fe and Mn compounds (BD–P), phosphorus bound to aluminum (Al–P) and organic phosphorus (Org–P). However, the concentration of the non-bioavailable forms of phosphorus in the sediments, such as calcium bound phosphorus (Ca–P), increased significantly in the Phoslock® treatments compared with the controls. At the end of the experiments, the total biomass, aboveground biomass and relative growth rate (RGR) of M. spicatum decreased significantly in the Phoslock® mesocosms compared with the controls. In contrast, the wet root biomass, root–shoot biomass ratio, root numbers and root length of M. spicatum were significantly higher in the Phoslock® treatments than that in the controls. Our results indicated that the growth of M. spicatum was suppressed by the addition of Phoslock®, and thus the biomass was decreased; however, the increase of root biomass might be beneficial to the inhibition of phosphorus release and resuspension of sediments and to the restoration of the lake ecosystem.
... 等。但是, 在污染严重的 水体中, 沉水植物的自然恢复是十分困难的, 一 般而言, 湖泊低透明度和水下植物繁殖体的缺 乏是影响水生植被恢复的主要限制因素 [6,7] 。在 这种情况下应尽快进行生态工程促进水生植 被生境改善, 并积极开展水生植被重建与恢复工 作 [8] 。就污染水体的低透明度而言, 水生植物必 然会受到光照不足的影响, 一般认为环境光强持 久或短时间显著低于植物光饱和点, 可以称为弱 光逆境 [9] 。在弱光条件下, 首先通过降低光合作 用效率抑制沉水植物的生长, 此外还通过抑制抗 氧化酶活性影响沉水植物的生存 [10,11] , 而大多数 富营养化湖泊普遍表现出弱光或极度弱光的水 下环境, 成为影响这些湖泊中沉水植被恢复的一 大难题。除了水下光照环境, 底质条件对沉水植 物的恢复亦有重要的影响, 底质是沉水植物的固 定基质和营养来源, 对沉水植物生根、繁殖和生 长产生不同程度的影响 [12,13] , 研究表明富营养水 体中肥沃底质对沉水植物造成胁迫, 使其生物量 下降 [14] 。 洱海位于云南西北部的大理州境内, 是我国著 名的高原淡水湖泊之一, 在洱海水面高程为1973.7 m 时, 湖泊面积是249. 8 [15][16][17] ; 自1998年洱海发生大面积水华后, 湖心 平台区域沉水植被大幅退化 [18,19] , 在2009年该区域 未发现沉水植物生存 [20] 。如果能成功恢复湖心平 台的沉水植被, 将大幅提升洱海沉水植物群落的分 布面积和生态功能。 2015年以来, 随着洱海环境保护力度的加大, 洱海水质呈现出逐年向好的发展趋势, 透明度逐年 提高, 湖心平台水下光环境基本达到沉水植物的光 补偿点, 理论上有沉水植物恢复的可能性, 但是没 有出现自然恢复的现象, 因此我们希望通过人工强 化的修复措施实现该区域的沉水植被重建。这里 面有两个问题: (1)选用哪种沉水植物; (2)如何通过 改善局部环境来帮助沉水植物应对弱光胁迫。苦 草(Vallisneria natans)是水鳖科(Hydrocharitaceae)苦 草属(Vallisneria)沉水草本植物, 无直立茎, 叶基生, 条形 [21] , 生长区域广泛, 在淡水湖泊、沟渠、池塘和 内河航道的静水或流动水体中均能很好地生长 [22] 。 苦草对弱光环境具有很强的耐受能力, 因此成为洱 海沉水植物群落中分布下限最深的物种 [23] , 并且在 1980s中后期以来, 苦草成为洱海水生植被的优势 种之一 [24] , 所以我们选择了对弱光环境耐受能力强 [29] , 所以弱光是苦草植被恢复的主要限制因子。 在实验结束时, 实验桶内的苦草存活数量已稳 定下来, 存活数量显著小于初始种植数量。相比于 初始状态, 单株苦草的叶生物量、根生物量及根长 和叶长均显著性下降。有研究表明, 随水深梯度的 增加苦草生物量和和无性系分株数显著性下降, 而 株高呈先增加后降低的趋势 [31] , 本研究结果与其一 致。一方面苦草株高和生物量下降, 使其长期处于 弱光胁迫下；另一方面低光照会减弱沉水植物的 胁迫耐受能力 [32] , Chen H D. An approach to the restoration of aquatic vegetation in the Xihu Lake of Hangzhou, with reference to the water quality problem [J]. ...
In restoration of aquatic vegetation in the degraded area of shallow lakes, it is necessary to study the effects of low light stress and sediment types on aquatic plants. Vallisneria natans has strong tolerance to low light and sediment, and can be selected as a estoration species. The central part of the southern Erhai Lake (a mesotrophic lake in Yunnan Province, China) is flat, with an average annual water depth of about 6.3 m, which was called the “lake center platform” (LCP). Large areas of aquatic vegetation, including V. natans, was used to exist in LCP, it played important roles in the lake ecological function, but has completely disappeared since 2003. So, we chose V. natans as experimental material, and set two kinds of sediment conditions to study the morphological and physiological responses of V.natans under weak light of LCP and two kinds of sediment (clay and silt) environment, in order to explore the effect of substrate improvement on the restoration of V. natans. The results showed that: (1) Under the extremely low light environment, the survival number of V. natans decreased, and it also showed morphological and physiological responses to stress. The biomass and length of leaf and rhizome decreased in both sediments, and the contents of carbon (C), soluble
carbohydrate and starch decreased, but the contents of free amino acid (FAA) and nitrogen (N) increased. The low light intensity inhibited the growth of V. natans and caused some plant deaths. (2) The effect of weak light stress on leaves in both sediments was greater than that on rhizome, which was shown in the increasing biomass ratio of rhizome and leaf. The physiological stress response of leaves was relatively greater than that of rhizomes, which was reflected in the decrease in the ratio of N and FAA contents, and the increase in the ratio of soluble carbohydrate and starch contents. (3) There were significant differences in the responses of V. natans to weak light environment under different sediment conditions, which was shown below: the survival number, starch content and biomass of rhizome in clay group were higher than those in sludge group, while FAA and N contents of leaves were lower. This attempt indicated that under
the current water quality environment, it was possible to achieve the restoration of submerged plants in the LCP by combining with local sediment improvement.
... Saturating irradiant (Ik) revealed adaptation of E. canadensis to cope with light situation in this study. Light reduction led to decreased Ik (Ralph and Gademann, 2005) especially in 50% and 75% treatments in the final week, which was consistent with Chen et al. (2016) where Potamogeton maackianus and Vallisneria natans under low light (2.8%, 7.1%, 17.1%, and 39.5% ambient light) increased their initial slopes of RLCs (α) and decreased their minimum saturating irradiances (Ik). On the other hand, Fv/Fm increased revealing that E. canadensis was able to maintain its photosynthesis. ...
... 沉水植物是浅水湖泊中最为重要的初级生产者 (Carr et al., 2010;Søndergaard et al., 2010;Pan et al., 2011)，在维持浅水湖泊生态系统的结构和功能中起着重要作用 (Søndergaard et al., 2010;Li et al., 2017;赵凯等, 2017)。沉水植物在吸收营养盐以及抑制蓝藻爆发方面有较强的 能力 (Pakdel et al., 2013;Zhou et al., 2016;Zhou et al., 2017)， 在控制富营养化和抑制蓝藻水华 方面起着关键作用。因此，沉水植物被广泛用于富营养化湖泊的生态系统恢复和良性生态系 统的构建 (Sayer et al., 2010;Blindow et al., 2014)。 水文情势是湖泊生态系统中沉水植物群落结构和生产力的主要影响因素 (Reddy et al., 2004;Ren et al., 2020)。其中，水深能够改变一系列水体环境因素，尤其是水下光强度，从 而对沉水植物的生长产生很大影响 (吴晓东等, 2012;Chen et al., 2016Chen et al., , 2020。具体而言，在浅 水区域，较浅的水深不仅压缩了沉水植物的生存空间，还通常会引起光抑制作用 (Winters et al., 2003;Li et al., 2020)；在深水区域的弱光环境下，光合作用效率通常会大大降低 Min et al., 2019)。因此，极端深水或浅水环境均不利于沉水植物的生长 (Wang et al., 2020)。不同沉水植物的耐荫性不同，对水深的响应和适应具有特异性 (Li et al., 2020;Wang et al., 2020 (Leong et al., 1984;曹昀等, 2014)；抗氧化酶活性可以从间接反映植物体内活性氧的情况，体现出植物受 到氧化胁迫的状况 (Blokhina et al., 2003;Ji et al., 2018)。因此，探究沉水植物在不同水深和基 质条件下生长特征及生理性状的差异，可以揭示沉水植物对环境变化的适应策略，并有助于 因地制宜地指导沉水植被恢复。 苦草是一种多年生沉水植物，地理分布广泛，具有有性和无性繁殖，产生的匍匐茎可扩 散，形成-草甸‖状的克隆种群 (Xiao et al., 2007;Lin et al., 2020 (Marklund et al., 1974;Ritchie,2008 (Leong et al., 1984)，若叶绿素 a 与 b 的比值增加，捕光复合体Ⅱ的含量则会减少 (Anderson et al., 1994)。本研究中，泥土中 ...
Submerged macrophytes are important primary producers in shallow lakes. Water depth and sediment type are key factors affecting the growth of submerged macrophytes. Vallisneria natans is a common submerged macrophyte in shallow lakes in the middle and lower reaches of the Yangtze River in China. The effects of water depth and sediment type on the growth of V.natans have been partially studied, but studies on the physiological traits of V.natans leaves are relatively lacking. In this study, two sediment types (sand and mud) were used to plant V. natans at three water depths (40, 120, and 200 cm) to explore the ecological and physiological adaptation strategies of V. natans under different water depths and sediment conditions. The results showed that V. natans adapted to shallow water (40 cm) and deep water (200 cm) by changing plant height, ramet number, and leaf number, increasing antioxidant enzyme activity, and reducing chlorophyll concentration. V.natans had low antioxidant enzyme activity but a high chlorophyll concentration at the medium water depth (120 cm). Different sediment types also affected the growth of V. natans. The height, number of leaves, and ramets of V. natans were generally higher in the mud than those in the sand. The chlorophyll concentration of V. natans in the mud at a water depth of 40 cm was higher than that in the sand, while the chlorophyll concentration of V. natans in the sand was higher at water depths of 120 and 200 cm. In addition, changing the sediment type did not cause significant differences in the antioxidant enzyme activity of V. natans. This study showed that 40–120 cm water depth and mud sediment were more conducive to the growth of V. natans than the other conditions. V. natans revealed different physiological and ecological adaptation strategies under different water depths and sediment conditions, which are of great significance to the restore of submerged vegetation and the construct a freshwater ecosystem.
... Underwater light availability is one of the most important environmental factors affecting the growth and morphology of aquatic plants ( Barko et al., 1986). In the case of low light availability in the water column, submerged macrophytes might adopt one of two distinct strategies: elongation of shoot length towards the water surface to alleviate low-light stress or enhancing low-light tolerance by photosynthetic adjustments (Chen et al., 2016). ...
One of the most southern European occurrences of Potamogeton praelongus is in the Czech Republic (CR), with only one native population in the Orlice River floodplain in Eastern Bohemia, the only surviving site from 10 Czech localities known 45 years ago. This species is critically endangered in the CR and needs to be actively protected with a rescue program. The number of P. praelongus sites increases along a latitudinal gradient, from Central to North Europe (CR, Poland, Sweden, and Norway), and correlates with improving conditions (water transparency and nutrient content in water) for this species along this gradient. Although differences in site conditions between Central and North Europe were caused by changes in landscape geomorphology and vegetation during the glacial and postglacial eras, presently, anthropogenic impact is primarily observed.
The Czech sites for P. praelongus have distinctly lower water depth and transparency, and conversely, higher conductivity, temperature, and shade levels than the Nordic ones. These extreme conditions in most biotopes of this light-demanding and mesotrophic species in the CR result in lower fitness and different morphological parameters in the Czech populations. These changes lead to decreased competitive ability against filamentous algae and more competitive aquatic plant species and increase the impact of animals.
The Nordic nonintensively managed landscape provides numerous large, deep lakes, which are optimal for this aquatic species. In the CR, P. praelongus can currently only survive in rivers and their oxbows, but these are heavily influenced by intensive landscape management and fishing. Comparison of the populations and their site conditions in the CR and other European countries showed that all Czech native and artificially established sites are exposed to eutrophication and its consequences, which are the most important factors affecting the survival of P. praelongus .
... Photosynthetic organisms are highly vulnerable to light extremes; thus, their physiology and morphology are affected by the available light intensity Chen et al., 2016). Therefore, the interactions between E. densa and M. aeruginosa can also be influenced by the light intensities in ranges that exceed favorable levels. ...
Egeria densa release allelochemicals harmful to other species, including cyanobacteria. Under natural conditions, E. densa and Microcystis aeruginosa can be found in various aquatic systems with different light levels. The effect that the coexistence of E. densa has on M. aeruginosa was tested under different photosynthetically active radiation (PAR) intensities. The growth, chlorophyll-a, oxidative stress, and antioxidant activities of M. aeruginosa were quantified after 7 days of coexistence with E. densa. A control experiment without E. densa was conducted for M. aeruginosa under the same conditions to distinguish the effect of the PAR intensity from the allelopathic effect. The allelopathy of E. densa on M. aeruginosa is significantly influenced by the PAR intensity. PAR intensities lower or higher than the favorable range further suppressed M. aeruginosa under coexistence. Research has revealed that the allelopathic effect of E. densa can be utilized to biologically suppress M. aeruginosa under various light conditions. Strong second-order polynomial distributions between the optical density (OD) and cellular H2O2 content of M. aeruginosa were found for both the control and coexistence conditions. In the practical application of E. densa allelopathy, OD can be adopted as a convenient method to obtain an approximate stress status on M. aeruginosa.
... Each form has adapted to different habitats in terms of light availability and nutrient status, indicating species-specific resource utilization and allocation strategies. For instance, canopy formers (as well as erect species) tend to elongate the shoot to alleviate conditions of low light stress, while rosette species usually produce longer and wider leaves to enhance their photosynthetic ability (Strand and Weisner, 2001;Schneider et al., 2015;Chen et al., 2016). Such adjustments in morphological characteristics entail nutrient reallocation from the whole plant, such that nutrient concentrations across plant organs are tightly coordinated. ...
The allocation of limiting elements among plant organs is an important aspect of the adaptation of plants to their ambient environment. Although eutrophication can extremely alter light and nutrient availability, little is known about nutrient partitioning among organs of submerged macrophytes in response to eutrophication. Here, we analyzed the stoichiometric scaling of carbon (C), nitrogen (N), and phosphorus (P) concentrations among organs (leaf, stem, and root) of 327 individuals of seven common submerged macrophytes (three growth forms), sampled from 26 Yangtze plain lakes whose nutrient levels differed. Scaling exponents of stem nutrients to leaf (or root) nutrients varied among the growth forms. With increasing water total N (WTN) concentration, the scaling exponents of stem C to leaf (or root) C increased from <1 to >1, however, those of stem P to root P showed the opposite trend. These results indicated that, as plant nutrient content increased, plants growing in low WTN concentration accumulated leaf C (or stem P) at a faster rate, whereas those in high WTN concentration showed a faster increase in their stem C (or root P). Additionally, the scaling exponents of stem N to leaf (or root) N and stem P to leaf P were consistently large than 1, but decreased with a greater WTN concentration. This suggested that plants invested more N and P into stem than leaf tissues, with a higher investment of N in stem than root tissues, but eutrophication would decrease the allocation of N and P to stem. Such shifts in plant nutrient allocation strategies from low to high WTN concentration may be attributed to changed light and nutrient availability. In summary, eutrophication would alter nutrient allocation strategies of submerged macrophytes, which may influence their community structures by enhancing the competitive ability of some species in the process of eutrophication.
... Either lower or higher intensity than the optimal requirement could lead to reduced chlorophyll content and optical density, and increased oxidative stress in M. aeruginosa [28]. Similarly, unfavourable light intensities may reduce the macrophyte growth rate and cause oxidative stress [29,30]. It is plausible that stress resistance of E. densa and allelopathy of M. aeruginosa would change in response to changing light conditions. ...
In this study, Egeria densa plants were exposed to a low concentration of (OD730 = 0.04) Microcystis aeruginosa for seven days, under different photosynthetically active radiation (PAR) intensities (0, 50, 100, 200, and 300 µmol m⁻² s⁻¹). Experiments were conducted under controlled conditions inside incubators. The H2O2 content, antioxidant responses, pigmentation, and chlorophyll fluorescence parameters were measured. The biochemical parameters of E. densa varied with PAR intensity; under the 50 and 100 µmol m⁻² s⁻¹ PAR intensities, E. densa performed relatively better than under other intensities. When exposed to M. aeruginosa, the levels of the measured biochemical parameters reduced in E. densa. Under unfavourable light conditions, the optical density of M. aeruginosa was also reduced when E. densa was also present. Even at low concentrations, the presence of M. aeruginosa in the water can have a negative effect on E. densa pigmentation and physiological parameters, though E. densa also has negative effects on M. aeruginosa growth. Further studies are recommended to evaluate the responses of E. densa after prolonged exposure to M. aeruginosa and the effects of E. densa on M. aeruginosa.
... These irradiance and flow changes may have positive or negative consequences for macrophytes, which may be related to the type of macrophyte species. Thus, based on these resource fluctuations, adaptive strategies may be developed for survival (Chen et al. 2016). Biochemical changes that take place at the cellular level might be an effective adaptive mechanism for abiotic stress that is controlled genetically and physiologically and may be expressed as an antioxidant system. ...
This study was implemented to investigate the diurnal biochemical changes that occur in Ceratophyllum demersum in four growth habitats under in situ experiments. The results showed that compared to the other treatments, the open-flow treatments had the highest hydrogen peroxide (H2O2) concentration that occurred with the acceleration of antioxidant activity at midday, mainly due to the independent effect of irradiance and flow movement. The plant diurnal H2O2 and antioxidant activity rhythms had varying fluctuations, and peroxidase (POD) activity showed a rapid response to oxidative stress. The increase in POD activity followed a more similar pattern aligned with H2O2 synthesis, while catalase (CAT) and ascorbate peroxidase (APX) activities were dominant in the late hours of the day. The ability of this species to successfully grow in these habitats is related to the adaption of the diurnal cycles of antioxidant activity according to flow and irradiance changes.
... In the present study, the shoot height and total branch length were higher in low light than in high light for M. spicatum during the pulse phase under high and moderate NH 4 -N loading; moreover, the shoot height and leaf number were greater for V. natans under control. These results are consistent with previous findings that terrestrial and aquatic plants would allocate more resources to the above ground part by increasing their height or number of leaves to obtain more light and improve their light competitiveness and survival fitness [71][72][73][74]. The roots act as organs for absorption and assimilation of nitrogen and phosphorus from sediments particularly in oligotrophic lakes [75,76]. ...
Ammonium pulse attributed to runoff of urban surface and agriculture following heavy rain is common in inland aquatic systems and can cause profoundly effects on the growth of macrophytes, especially when combined with low light. In this study, three patterns of NH4-N pulse (differing in magnitude and frequency) were applied to examine their effects on the growth of three submersed macrophytes, namely, Myriophyllum spicatum, Potamogeton maackianus, and Vallisneria natans, in terms of biomass, height, branch/ramet number, root length, leaf number, and total branch length under high and low light. Results showed that NH4-N pulse caused negative effects on the biomass of the submerged macrphytes even on the 13th day after releasing NH4-N pulse. The negative effects on M. spicatum were significantly greater than that on V. natans and P. maackianus. The effects of NH4-N pulse on specific species depended on the ammonium loading patterns. The negative effects of NH4-N pulse on P. maackianus were the strongest at high loading with low frequency, and on V. natans at moderate loading with moderate frequency. For M. spicatum, no significant differences were found among the three NH4-N pulse patterns. Low light availability did not significantly aggregate the negative effects of NH4-N pulse on the growth of the submersed macrophytes. Our study contributes to revealing the roles of NH4-N pulse on the growth of aquatic plants and its species specific effects on the dynamics of submerged macrophytes in lakes.
... In contrast, among the slow-growing types, Vallisneria spp. can adapt to increasing water levels through photosynthetic adjustment [30], and it thus does not exhibit significant shoot elongation when exposed to high water levels and low light availability [31]. ...
More frequent extreme climate events (e.g., extreme precipitation) are to be expected in the future, and such events may potentially have significant effects on freshwater ecosystems. In the present mesocosm study, the effects of simulated extreme precipitation on submerged macrophytes were evaluated for three different macrophyte community (MC) treatments (MC1, MC2 and MC3). MC1 consisted of only Vallisneria denseserrulata, while MC2 and MC3 included three and six species of various growth forms. Two treatments of extreme precipitation (EP) were simulated-an extreme treatment (E) simulating a sudden increase of water level from 75 cm to 150 cm within one day and a gradual treatment (G) simulating an increase to the same water level within 3 months, combined with two control treatments. Total macrophyte community biomass was resilient to the EP and MC treatments, while species-specific variations in responses, in terms of biomass, maximum height, and sexual reproduction, were found. For instance, E led to earlier flowering of Potamogeton lucens and production of more flowers, while it had adverse effects on the flowering of Ottelia alismoides. We conclude that freshwater ecosystems with high coverage of submerged macrophytes may be overall resilient to extreme precipitation under nutrient-limited conditions, especially communities with diverse growth forms.
... In our study, the primary shoots of Stuckenia pectinata produced longer stems and leaves in response to the lower light condition. Similarly, enhanced shoot elongation under low light stress has been reported for S. pectinata (Pilon and Santamaria, 2002), as well as species in the Potamogeton genus: P. maackianus (Fu et al., 2012;Chen et al., 2016), P. malaianus (Fu et al., 2012), and P. perfoliatus (Asaeda et al., 2004;Sultana et al., 2010;Toth et al., 2011). S. pectinata adopts a shade-avoiding strategy (Niinemets, 2010) with longer stems and leaves to reach the upper waters, which results in an exponential gain in PAR in turbid waters. ...
Loss of a long-term stable submerged macrophyte community reverses shallow lakes from a clear into a turbid water state. Stuckenia pectinata densely colonised the marginal area of a shallow coastal lagoon Te Waihora (Lake Ellesmere)before its removal by the 1968 “Wahine” storm. This study aims to understand the current light availability for S. pectinata growth in Te Waihora with high turbidity and water level fluctuations. In a greenhouse experiment, acclimations in S. pectinata to lower light intensities involved elongation in stems and leaves, and an increase in photosynthetic efficiency per unit dry weight for both leaves and stems. However, these acclimations did not reduce the daily compensation irradiance (under which daily net photosynthesis equals zero)that was identified at 8.8 ± 0.9 μmol photons m ⁻² s ⁻¹ . Subsequently, we estimated light compensation depth (LCD), based on the derived daily compensation irradiance, incident irradiance at the water surface, and light attenuation coefficients for the lake. In areas shallower than LCD, there is no light limitation for the growth of S. pectinata. The LCD ranged from 0.23 to 0.54 m and well explained the growth range of S. pectinata in Te Waihora during the 2016–2017 ecological survey. The estimated LCD also suggests low turbidity levels in early spring are critical for the growth of S. pectinata with the current water level fluctuation regimes. LCD is a useful parameter for understanding the growth of submerged macrophytes in shallow turbid lakes from the perspective of light availability.
Numerous studies note the overwhelming influence of functional diversity on ecosystem functioning. It remains unclear how functional diversity affects the productivity of aquatic plant communities with different life-forms. We constructed free-floating plant communities dominated by Salvinia natans and submerged plant communities dominated by Vallisneria natans to explore the effects of disturbance (clonal fragmentation) on functional diversity-productivity relationships under different nutrient availability. Results showed that, in free-floating plant communities, disturbance had significant impacts on three community-weighted means traits (average leaf length, average leaf width and average root length), functional evenness (FEve) and productivity under high nutrient conditions. Three single-trait indices and FEve showed reverse correlations with productivity. In submerged plant communities, disturbance-induced considerable variations of single- and multi-trait indices and inapparent variation of productivity. Functional evenness was negatively related to community productivity under low nutrient conditions. Our results suggest that mechanisms of mass ratio and niche complementarity can simultaneously explain variations in free-floating plant community productivity under high nutrient conditions. Niche complementarity had a weak explanatory power for variations in submerged plant community productivity under low nutrient conditions. Our study provides the first evidence for the non-negligible role of nutrients and life-forms in functional diversity-productivity relationships of aquatic plant communities.
Plant trait network analysis can calculate the topology of trait correlations and clarify the complex relationships among traits, providing new insights into ecological topics, including trait dimensions and phenotypic integration. However, few studies have focused on the relationships between network topology and community structure, functioning, and adaptive strategies, especially in natural submerged macrophyte communities. In this study, we collected 15 macrophyte community-level traits from 12 shallow lakes in the Yangtze River Basin in the process of eutrophication and analyzed the changes in trait network structure (i.e., total phosphorus, TP) by using a moving window method. Our results showed that water TP significantly changed the topology of trait networks. Specifically, under low or high nutrient levels, the network structure was more dispersed, with lower connectance and higher modularity than that found at moderate nutrient levels. We also found that network connectance was positively correlated with community biomass and homeostasis, while network modularity was negatively correlated with community biomass and homeostasis. In addition, modules and hub traits also changed with the intensity of eutrophication, which can reflect the trait integration and adaptation strategies of plants in a stressful environment. At low or high nutrient levels, more modules were differentiated, and those modules with higher strength were related to community nutrition. Our results clarified the dynamics of community structure and functioning from a new perspective of plant trait networks, which is key to predicting the response of ecosystems to environmental changes.
With the increasing exogenous nutrients, the continued declining water quality, the year-to-year increasing algae biomass, and the sharply fluctuating water levels, the succession rate of the submerged macrophyte community in Lake Erhai increases over the past several decades. The survey in July 2016 showed that the submerged macrophyte community in Lake Erhai was seriously degraded, the number of species was significantly lower than recent (2011) historical level, and the distribution area fell by more than 70% from the historical high, and the dominant species were transformed from Ottelia acuminata, Stuckenia pectinata and Najas marina (1960s) to Ceratophyllum demersum, Potamogeton maackianus and Vallisneria natans. Submerged macrophytes mainly suffered from the stress caused by Trapa maximowiezii in shallow waters (0-2.5 m), and faced the simplification of the community structure caused by the overgrowth of C. demersum and P. maackianus in the area with medium water depth (2.5-4 m), and subjected to area shrinkage in deep waters (>4 m), which severely inhibited its positive ecological functions. By comparing the structures of submerged macrophyte community before and after the implementation of the submerged vegetation restoration and management project in the waters of Erbin Village, a typical bay in Lake Erhai, we found that artificial restoration and optimization measures positively improved the submerged plant communities in various areas with different water depths in Erbin Village. The abundance of restored species and the diversity indicators of the community was significantly improved. Therefore, we put forward suggestions and countermeasures for the restoration and optimal management of submerged vegetation in the typical eutrophic lake bays of Lake Erhai, with a view to provide a basis for the follow-up projects of the ecosystem restoration in Lake Erhai.
The mathematical prediction of the growth of submerged macrophytes provides direct inference in harvest management, estimation of habitat structuring, and calculation of incidence areas, in function to the main environmental constraints. The aim of this study was to enable us the equivalence between the liquid photosynthetic rates (obtained from the light and dark flasks method) and the growth rates derived from first order models applied to aquatic plants cultures. The association allows the achievement of the values of the growth rates (µ) due to short-term environmental changes, usually well evidenced by the net photosynthetic rates (net primary production; NPP), increasing the accuracy of the growth model. Growth experiments were conducted with two submerged specimens. Using the results of the: (i) carbon content of the plants tissues, (ii) NPP of incubations (light and dark bottles method) and (iii) biomass of cultures growths, it was feasible to verify the range of variation of NPP (coefficient of variation: 62%) and µ values, and establish the calculations for the equivalence of these two parameters. Thus, changes in environmental conditions, including specific and short-term events, can be readily transformed to the µ values, improving the accuracy of the growth simulation of submerged aquatic plants.
Abstract: Low light environment under water is a common problem in the revegetation of submerged macrophytes. Therefore, it is necessary to study their adaptability to low light stress. The central part of the southern Lake Erhai (a mesotrophic lake in Yunnan Province, China) is flat, with an average annual water depth of about 6.3 m, which was called the-lake center platform‖ (LCP). Large areas of aquatic vegetation were once existed in the LCP, which had important roles in the lake ecological function but completely disappeared since 2003. Therefore, we chose the LCP as our experimental site, and select four common submerged macrophytes (Vallisneria natans, Hydrilla verticillata, Myriophyllum spicatum, and Potamogeton wrightii) as the research objects for the in-situ pot
• In shallow lakes, submerged macrophytes can stabilise clear‐water conditions and prevent phytoplankton blooms. Nutrient enrichment can promote their abundance. Above critical thresholds in water nutrient concentrations, however, submerged macrophytes have collapsed in many lakes worldwide with negative consequences for important ecosystem functions. The mechanisms behind this decline are complex and subject to debate.
• We conducted mesocosm and laboratory experiments to investigate the top‐down effect of invasive herbivorous snails (Pomacea canaliculata) on native submerged macrophytes (Vallisneria natans) under low and moderate nutrient treatment. We tested whether effects of nutrient addition to the water column on snail herbivory were influenced by shading by phytoplankton and epiphyton, macrophyte elemental tissue content and snail nutrient release.
• We found that herbivorous snails had strong negative top‐down effects on macrophytes, which were amplified by nutrient enrichment in the water column leading to higher macrophyte consumption rates. In moderate nutrient treatment, macrophyte consumption was faster and snails grew better than in low nutrient treatment. Additionally, snail treatments had higher nitrogen concentrations in the water leading to a negative feedback loop.
• Our results suggest that snail herbivory may increase the chance for macrophyte collapse and shifts of shallow lakes to turbid states, and this effect occurs at lower snail densities when nutrient concentrations increase. Shallow lakes are thus severely at risk from projected increases in nutrient loading and spread of invasive herbivorous molluscs.
Biochar is a good adsorbent for water pollutants. However, the effects of biochar on aquatic organisms are not well understood. In this study, different amounts of biochar (CK, 0 mg/g; T1, 10 mg/g; T2, 30 mg/g) were added to sediment to study changes in water quality and its impact on three submerged macrophytes (Hydrilla verticillata, Vallisneria natans, and Ceratophyllum demersum) and the sediment microbial community. The results indicated that biochar treatments significantly increased the water pH and conductivity. Compared with the initial values, the total phosphorus (P) contents in the water of the CK, T1, and T2 treatments decreased by 78.5%, 95.0%, and 58.3%, respectively, while the total nitrogen contents increased by 26.26%, −5.81%, and 19.70%, respectively. Compared with those in CK, the relative growth rates of H. verticillata, V. natans, and C. demersum in T1 increased by 28.4%, 163.1%, and 61.3%, respectively, while those in T2 showed no significant difference except that the growth rates of H. verticillata decreased by 17.7%. The P contents of the three submerged macrophytes increased with the increase of biochar addition, except that there was no significant difference between T2 and CK for H. verticillata. Biochar treatments reduced the biomass of total microbial, bacterial, and fungal phospholipid fatty acids in the sediment for H. verticillata and V. natans, and they increased fungal: bacterial ratios in the low-dose biochar treatments for V. natans and C. demersum. This study demonstrates that the addition of biochar to sediment significantly increased the pH and conductivity, and decreased total P contents in the water. Low-dose biochar treatments were more beneficial for water quality improvements and the growth of submerged macrophytes than high-dose biochar.
Leaves are critical plant organs for photosynthesis. In addition, leaf length is an important indicator of leaf size. Although previous studies have revealed the maximum length of leaves from terrestrial plants, as well as their limiting factors, these issues remain relatively unexplored for leaves of submerged macrophytes. Based on meta-analysis of 48 species of aquatic plants, we found that the strap-shaped leaves of submerged macrophytes were particularly long, with a maximum length among studied species of 300 cm (e.g., Vallisneria australis). To explore the role of light in regulating maximum leaf length, we first calculated the suitable growth zone (SGZ) for submerged macrophytes according to light conditions. Results showed that the vertical range of the SGZ was approximately twice that of the maximum leaf length mentioned above. This suggests that light was not the only factor limiting maximum leaf length. In addition to hydraulic conditions and water depth, the short lifespan and slow leaf growth rate also contributed to the limitation of maximum leaf length. Correlation analysis between maximum leaf length and ramet density also revealed a potential trade-off between the two traits in submerged macrophytes. Thus, in addition to light conditions, various other factors limited leaf elongation and thus regulated the maximum length of submerged strap-like leaves.
Allelopathic inhibition activity of Spirogyra and Ceratophyllum demersum (C. demersum) on Microcystis aeruginosa were compared using a series of experiments. Culture solution of Spirogyra was found to inhibit growth of M. aeruginosa resulting in the destruction of chlorophyll-a and increased MDA content of the algae. The inhibitory effect was increased with greater concentrations of macrophyte culture solution and with continuous addition of the macrophytes. Filter size also had an effect in the inhibition of M. aeruginosa growth. Poor algal growth may have resulted from metabolic secretions from Spirogyra and associated epiphytic bacteria. Inhibition of algal growth and growth of the macrophytes and tolerance of Spirogyra to eutrophic conditions were further improved by synergistic effects of co-existing Spirogyra and C. demersum. Maximum inhibition effects and macrophyte biomass were recorded when the ratio of Spirogyra to C. demersum was 6:4.
Nutrient availability can affect both the morphology and the nutrient uptake strategies of submerged macrophytes, with different species responding differently to increases in nutrient levels. A 98-day mesocosm experiment was conducted to investigate the responses of co-cultured Hydrilla verticillata and Vallisneria natans to nutrient enrichments of 3.0 mg N/(L ∙ week) and 0.2 mg P/(L week), mimicking external loading. Water samples were collected every 2 weeks for measuring nutrient and total suspended solid (TSS) concentrations and biomass of phytoplankton (Chl a). Dry biomasses of roots and shoots of both species were measured at the end of the experiment. Results showed that under nutrient-enriched conditions, both species reduced the ratio of root to shoot growth and increased nutrient storage per unit of biomass. However, only H. verticillata exhibited enhanced growth and nutrient storage, as well as a lower root: shoot ratio and greater shoot biomass than seen in Vallisneria. Our findings demonstrate that nutrient enrichment of the water column can invoke morphological plasticity in both H. verticillata and V. natans, but when both species grow together, the growth advantage goes to the former.
The photosynthesis and growth responses of Sargassum thunbergii germlings to different light intensities (10, 60, and 300 mu mol photons m(-2) s(-1)) were investigated. Maximum photochemical efficiency (F (v)/F (m)), rapid light curves (RLCs), and photochemical and non-photochemical quenching (qP and NPQ) were estimated by a pulse amplitude-modulated fluorometer. The photosynthesis of S. thunbergii germlings exhibited different properties to optimize light capture and utilization. The excitation pressure (1 -aEuro parts per thousand qP) was rapidly increased to approximately 0.27 showing that germlings responded to high light by chronic photoinhibition with an accumulation of closed reaction centers, which ultimately resulted in a slow growth. This was accompanied by a reduced F (v)/F (m) with time and a development of high capacity for NPQ. Although F (v)/F (m) in moderate-light germlings did not fully recover overnight, germlings demonstrated a less severe chronic photoinhibition considering the reduced degree of excitation pressure accumulation of approximately 0.15. The relative stability of photosynthetic capacity (rETR(max), E (k), and alpha) could endow germlings with the highest relative growth rate (RGR) of approximately 9.3 % day(-1) in moderate light. By contrast, low-light germlings demonstrated high F (v)/F (m) and F (o), corresponding high alpha collectively suggested greater efficiency of light absorption and energy transformation. Sustained increases in electron transport capacity (rETR(max) and E (k)) occurred in low-light germlings, which resulted in a stable RGR of over 8.2 % day(-1). Consequently, S. thunbergii germlings are considered to prefer low light regimes and have a relative capacity of moderate and high light tolerance. However, the light acclimation to oversaturating conditions is at the cost of slow growth to maintain survival.
This review presents an overview of the most important succession patterns and underlying processes associated with the deterioration of soft water macrophyte communities in atlantic and boreo-atlantic regions. As acidification, eutrophication and alkalinisation are the dominant processes, this paper will focus on the successional changes caused by these processes. Observed differences in the succession between soft waters in different areas in Europe are discussed. Most attention has been given to vegetation changes related to acidification, as most research has been carried out on this topic.
Human activities have increased the availability of nutrients in terrestrial and aquatic ecosystems.
In grasslands, this eutrophication causes loss of plant species diversity, but the mechanism of this loss has been difficult to determine. Using experimental grassland plant communities, we found that addition of light to the grassland understory prevented the loss of biodiversity caused by eutrophication. There was no detectable role for competition for soil resources in diversity loss. Thus, competition for light is a major mechanism of plant diversity loss after eutrophication and explains the particular threat of eutrophication to plant diversity. Our conclusions have implications for grassland management and conservation policy and underscore the need to control nutrient enrichment if plant diversity is to be preserved.
Status quo was investigated and evolution trend analyzed of eutrophication in 25 lakes in the typical lake regions of China, and causes of the eutrophication in these lakes explored. Results show that about 52% of the investigated lakes were at eutrophication level status during the period from 2009 to 2010. Lake Hulun in Inner Mongolia, as well as the lakes in Jiangsu were severely eutrophicated and the lakes in Northeast China were at moderate eutrophication level, while those in Xinjiang at low eutrophication level. However, the lakes in Yunnan have evoluted into two extremes in europhication. In the past 30 years. 16 (80%) of the total 25 lakes investigated demonstrated a significant rising trend in eutrophication, indicating that this period is one of rapid development of lake eutrophication in China. Alpine lakes in Yunnan, in particular, are the most significant in eutrophication, while the lakes in Jiangsu show a eutrophicating trend that is not optimistic, either. The investigation suggests that human activities are the major cause of eutrophication. As the point source pollution has been gradually put under control, agricultural non-point source pollution has emerged as the primary source supplying nutrients to lakes in Jiangsu, Yunnan and Northeast China, causing eutrophication, which deserves attention from all the aspects concerned.
Increasing sediment fertility was associated with an increase in the proportion of the total plant biomass attributable to canopy-producing or erect growth forms and a decrease in the importance of rosette and bottom-dwelling forms.-from Author
Carbohydrate reserves are nonstructural carbohydrates. Sucrose and fructosan are the predominant reserve constituents of temperate-origin grasses; sucrose and starch, of tropical-origin grasses. Nitrogenous compounds are used in respiration, but probably are not alternately stored and utilized as are carbohydrate reserves. Most carbohydrate reserves are stored in the lower regions of the stems-stem bases, stolons, corms, and rhizomes. Nonstructural carbohydrates in the roots of grasses are probably not used directly in herbage regrowth following herbage removal. Plant development stage, temperature, water stress, and nitrogen fertilization can drastically change the reserve level. The seasonal variation of carbohydrate reserves is often different for the same species when grown in different environments. The level of carbohydrate reserves in the lower regions of the stems apparently affects the regrowth rate for the first 2 to 7 days following herbage removal. Following the initial period, plant regrowth rate depends on other factors, such as leaf area and nutrient uptake. This initial effect from the level of carbohydrate reserves can be maintained during subsequent exponential growth. Grazing may be more detrimental than clipping if it removes herbage from some plants and not others. The ungrazed plants may take the available nutrients and water away from the grazed plants. However, grazing may be less detrimental than clipping if grazing leaves ungrazed tillers on a plant while removing others, thus allowing for the transfer of carbohydrates.
Responses and acclimation of the submersed vascular plant Potamogeton perfoliatus to changes in total irradiance were investigated by growing replicate populations under 3 treatment levels (11, 32 and 100% of ambient). Significant morphological responses to and recovery from shade were evident within 10 d, including: elongation of stems, thinning of lower leaves, and canopy formation at the water surface. Both photosynthetic and morphological acclimations to shade conferred substantial improvements in P. perfoliatus production at experimentally reduced irradiance compared to pretreatment conditions. Significant decreases in plant stem density, biomass and reproduction, as well as increases in mortality, were observed for plants at low growth irradiance. The inability of populations treated at low irradiance to exhibit any recovery (posttreatment increases) in these variables after 16 d of full ambient light suggests that 11% of ambient irradiance was below the minimum level needed for survival of this plant. Although stem elongation is a beneficial response to shade for P. perfoliatus in turbid lakes, it may be nonadaptive in turbulent tidal waters because of increased susceptibility to fragmentation. -from Authors
Decline of submersed macrophytes in Lake Donghu of China with the progress of eutrophication is assumedly due to low light stress by algae blooming. I conducted a laboratory experiment to study the impact of low-light stress on the growth of Potamogeton maackianus A. Been, a dominant submersed macrophyte of the lake before the 1970s.Plants were grown for six weeks in aquaria with Lake Donghu sediment and enriched water. Light delivered to aquaria was adjusted to simulate the typical Lake Donghu light intensities that exist at several water depths from 0.6m to 1.7m.Biomass growth of the plant was inversely related to light intensity at the simulated depths of ≥ 1.0m (r = 0.96, p < 0.05, n=6) and was negative at the depths of ≥ 1.4m. These results indicate that photosynthetic light saturation and compensation points of the plant in Lake Donghu should be ca. 0.9m and ca. 1.5m depths, respectively. Chlorophyll content, growth of main shoot, total shoot lengths and density of the plant all peaked at 1.2–1.3m simulated depths.These results indicate that P. maackianus responds to low light stress primarily by elongation of shoots, and increase of density. Its biomass growth and nutrient uptake rate did not correlate with the accelerated shoot growth. Below the light intensities of water deeper than 1.2–1.3m, shoot growth rate decreased. The flexible tolerant strategy of P. maackianus to low-light stress suggests that the disappearance of this plant from the lake was not mainly due to eutrophication-induced low-light stress.
To assist in formulating a model of seagrass growth, the photosynthesis-irradiance (P-I) relationships of Posidonia sinuosa, Posidonia australis, Amphibolis griffithii and Amphibolis antarctica were determined by oxygen flux measurements at a range of light intensities and water temperatures. Net and gross photosynthesis and respiration rates generally increased in response to increasing temperature within the range 13–23°C and the observed trends suggest that the optimum temperature range for photosynthesis is between 18°C and 23°C for P. sinuosa and 23°C or greater for the other species. The geographic distributions of the seagrass species studied here are generally consistent with their respective metabolic responses to water temperature. In general, the genus Amphibolis has higher maximum photosynthetic rates, and these are reached at lower light intensities, than Posidonia. Comparisons of the metabolic rates and critical light requirements of P. sinuosa between summer and winter suggest that ambient environmental conditions rather than seasonal changes in physiology are primarily responsible for the seasonal differences in growth rates that occur in the field. P. sinuosa plants growing near their natural lower depth limit are morphologically different and their maximum photosynthetic rates are reached at lower light intensities than plants growing in shallower water, but genotypic rather than phenotypic adaptation is suggested as the cause.
Artificial fertilization of lakes ultimately leads to reduction in submerged macrophyte productivity. This has usually been attributed to shading by increasing populations of phytoplankton. Evidence is given that loss of macrophytes is often due to increased growth of, and shading by, epiphytes and filamentous algae associated with the weed beds, and that phytoplankton development is subsequent rather than causative. A new hypothesis is outlined in Fig. 1 and support for it is drawn from palaeolimnological studies, laboratory experiments and field observations and experiments in the Norfolk Broads, an area of shallow, peat-excavated lakes, and from the literature.
1. Increased ammonium concentrations and decreased light availability in a water column have been reported to adversely affect submersed vegetation in eutrophic waters worldwide.
2. We studied the chronic effects of moderate enrichment (NH4–N: 0.16–0.25 mg L−1) on the growth and carbon and nitrogen metabolism of three macrophytes (Ceratophyllum demersum, Myriophyllum spicatum and Vallisneria natans) under contrasting light availability in a 2-month experiment.
3. The enrichment greatly increased the contents of free amino acids and nitrogen in the shoot / leaf of the macrophytes. This indicates that was the dominant N source for the macrophytes.
4. Soluble carbohydrate contents remained relatively stable in the shoot / leaf of the macrophytes irrespective of the treatments. Under ambient light, the starch contents in the shoot / leaf of C. demersum and M. spicatum increased with enrichment, whereas V. natans did not exhibit any change. The starch contents decreased in C. demersum, increased in M. spicatum and remained unchanged in V. natans after the combined treatment of enrichment and reduced light.
5. The enrichment did not affect the growth of the three macrophytes under the ambient light. However, it did suppress the growth of C. demersum and M. spicatum under the reduced light. The results indicate that a moderate enrichment was not directly toxic to the macrophytes although it might change their viability in eutrophic lakes in terms of the carbon and nitrogen metabolism.
1. To test several hypotheses about acclimation and adaptation of photosynthesis and respiration to differing light conditions, we investigated the interspecific relationships between leaf and root metabolism, chemistry and morphology in high and low light conditions for young seedlings of nine boreal tree species that differ in relative growth rate (RGR).
2. Light-saturated net photosynthesis (Asat), whole-plant nitrogen (N) uptake rates, leaf and root respiration and morphology, and RGR all varied in parallel among the nine species when grown in both 5% and 25% of full sunlight. RGR, Asat, leaf and root respiration (Rd), and N uptake rate per unit root mass or length differed significantly among species, ranking (from high to low): Populus, Betula and Larix spp. (all deciduous) and then to five evergreen conifers (Pinus, Picea and Thuja spp.), which were generally comparable in these measures.
3.Asat, leaf and root Rd and N uptake rates were all correlated (r≈ 0·8 to 0·9) with species traits, such as seed mass, leaf life span and shade-tolerance rankings. Mass-based Asat was greater in conifer seedlings raised in low than high light. In contrast, area-based Asat was higher for plants grown in high than low light, especially in the deciduous species. Once adjusted for differences in plant mass, leaf or root respiration rates did not differ for plants grown in low vs high light.
4. Interspecific variation in RGR was positively correlated (r≈ 0·9) with rates of photosynthesis, respiration and N uptake. Leaf photosynthesis and respiration rates were correlated to specific leaf area and leaf N concentrations (r≈ 0·9). Root respiration rates, N uptake rates, specific root length (root length per root dry mass) and root N concentrations were all highly correlated with each other (r≈ 0·8 to 0·9). These data suggest a close coupling of tissue-level metabolism, chemistry and structure with whole-plant performance and species ecophysiological and life-history traits.
Photosynthetic electron transport rates (ETR), calculated from chlorophyll fluorescence parameters, were compared in long term light and dark adapted as well as photoinhibited Pisum sativum leaves using a novel chlorophyll fluorescence method and a new instrument: rapid light curves (RLC) generated with the MINI-PAM. RLCs are plots of ETRs versus actinic irradiances applied for 10 s. Large changes in maximum electron transport rates (ETRmax) were observed when leaves were shifted from dark to moderate light, or from dark to photoinhibitory light and vice versa. Maximum ETRs were very low following long term dark adaptation, but increased to maximum levels within 8 to 15 minutes of illumination. It took more than 3 hours, however, to return irradiance-exposed leaves to the fully dark adapted state. Quenching analysis of RLCs revealed large qE development in long-term dark adapted leaves accounting for the low ETRs. Leaves photoinhibited for 3 hours had similarly reduced ETRs. In these leaves, however, qI was largely responsible for this reduction. Actinic irradiance exposures and saturating flashes affected leaves with different irradiance histories differently.
The Eurasian watermilfoil (Myriophyllum spicatum L.) has partially replaced wild celery (Vallisneria americana Michx.) as a community dominant in the littoral zones of lakes of Madison, Wisconsin. The two species have very different growth forms, with that of M. spicatum corresponding more closely to the optimal growth form simulated by the macrophyte production model WEED. The objective of this research was to investigate the mechanisms by which Vallisneria could compensate for its nonoptimal growth form and coexist with Myriophyllum.
A quantification of midsummer growth form for the two species at a rooting depth of 80–90 cm showed that M. spicatum had 68% of its shoot biomass within 30 cm of the surface, whereas V. americana had 62% of its leaf biomass within 30 cm of the bottom. Vallisneria had a light extinction coefficient ranging from 0.013 to 0.019 m2·g-1, much higher than the value (ca. 0.006 m2·g-1) for M. spicatum. This indicates less effective penetration of light to lower leaves of V. americana. Half-saturation constants describing the light-dependence of carbon uptake in “shade” and “sun” tissues ranged from 60–197 microeinsteins·m-2·s-1 for V. americana, and 164–365 μeinsteins·m-2·s-1 for M. spicatum. The optimum temperature for photosynthesis was 33.6°C for M. spicatum and 32.6°C for V. americana, but Myriophyllum was nearly twice as effective at carbon uptake at 10°C. Integration of all of the above features with WEED showed that, for midsummer conditions, V. americana more than compensated for apparently disadvantageous morphological features by its greater physiological adaptability to low light regimes. Coupled with the temperature-dependence of photosynthesis, it appears that V. americana is favored by midsummer conditions, whereas M. spicatum is at an advantage at other times.
Rapid light curves provide detailed information on the saturation characteristics of electron transport, as well as the overall photosynthetic performance of a plant. Rapid light curves were collected from samples of Zostera marina grown under low and high-light conditions (50 and 300 μmol photons m−2 s−1) and the distinctive patterns of RLC parameters are discussed, in terms of differential sink capacity and PSII reaction centre closure. Derived cardinal points of a rapid light curve (α, Ek and rETRmax) describe the photosynthetic capacity of a seagrass leaf, its light adaptation state and its capacity to tolerate short-term changes in light. The shapes of the corresponding F and F′m curves also provide information on the development of the trans-thylakoid proton gradient and thermal energy dissipation. Low-light leaves showed limited photosynthetic capacity and reduced activity of non-photochemical quenching pathways, whereas photosynthesis of high light leaves were not limited and showed an elevated level of non-photochemical quenching, possibly associated with xanthophyll cycle activity. Light-dark kinetics are also discussed in relation to relaxation of non-photochemical quenching and its various components. A curve fitting model is recommended based on the double exponential decay function. In this paper, we explain the fundamental aspects of a RLC, describe how it reflects the response to light exposure of a leaf, how to interpret these curves, and how to quantitatively describe and compare RLCs.
1 To survive in forest understoreys, seedlings must depend on carbohydrate reserves when they experience negative carbon balance imposed by occasional light reduction and tissue loss to herbivores and diseases. We present the first experimental evidence in support of this hypothesis, using seven woody neotropical species.
2 We transplanted seedlings that had recently expanded their first photosynthetic cotyledon or leaf to the forest understorey (1% of full sun) and quantified initial biomass and total non-structural carbohydrate (TNC) in stems, roots and storage cotyledons. We then randomly assigned seedlings to control and two stress treatments: light reduction (0.08% of full sun for 8 weeks) and complete defoliation.
3 First-year survival of control seedlings, a comparative measure of shade tolerance, differed widely among species. The two stress treatments reduced survival and relative growth rates (RGR) of all species. Shade-tolerant species were little impacted by the stress treatments, whereas the two least shade-tolerant species experienced 100% mortality.
4 In all treatments, 8-week and first-year survival was positively correlated with initial TNC pool size in stems and roots. By contrast, survival was generally not correlated with initial TNC concentration in any organ, TNC pools in cotyledons, seed mass or seedling biomass.
5 TNC in stems and roots, but not in cotyledons, decreased in response to light reduction and defoliation over 8 weeks. Leaf area recovery of defoliated seedlings was positively correlated with initial TNC pools in stems and roots.
6 First-year survival in each treatment was negatively correlated with 0–8 week RGR of control seedlings, suggesting higher stress tolerance of species with inherently slow growth rates in shade. RGR of control seedlings from 0 to 8 weeks was negatively correlated with initial TNC pools, but not concentrations, in stems and roots. After 8 weeks, RGR was positive for all species, without clear relationships with survival or TNC.
7 We conclude that carbohydrate storage in stems and roots enhances long-term survival in shade by enabling seedlings to cope with periods of biotic and abiotic stress. Carbohydrate storage is a key functional trait that can explain species differences in growth and survival that lead to species coexistence through niche assembly processes and life-history trade-offs.
External mechanical forces resulting from the pressure exerted by wind or water movement are a major stress factor for plants and may cause regular disturbances in many ecosystems. A plant's ability to resist these forces relies either on minimizing the forces encountered by the plant (avoidance strategy), or on maximizing its resistance to breakage (tolerance strategy). We investigated plant resistance strategies using aquatic vegetation as a model, and examined whether avoidance and tolerance are negatively correlated. We tested the avoidance-tolerance correlation across 28 species using a phylogenetically corrected analysis, after construction of a molecular phylogeny for the species considered. Different species demonstrated contrasting avoidance and tolerance and we demonstrated a significant negative relationship between the two strategies, which suggests an avoidance-tolerance trade-off. Negative relationships may result from costs that each strategy incurs or from constraints imposed by physical laws on plant tissues. The existence of such a trade-off has important ecological and evolutionary consequences. It would lead to constraints on the evolution and variation of both strategies, possibly limiting their evolution and may constrain many morphological, anatomical and architectural traits that underlie avoidance and tolerance.