SummaryFloristic lists of the industrial city of Plzeň, W Bohemia, Czech Republic, were compiled for the periods 1880–1910, 1960s and 1990s. Data were obtained for the city and its surroundings and abundance of each species was estimated from primary literature and recent field research. Changes in species richness on the time scale of 120 years were described, and dynamics of representation of alien species was analysed. Total number of species recorded decreased from 1173 in 1880–1910 to 988 in 1960s to 1043 in 1990s. These dynamics differed between city and surroundings. In the city, species number was gradually increasing while the trend was opposite in the surroundings. When expressed per log area, initial pattern of higher species richness in the surroundings was reversed in the course of the study period. The floristic similarity between 1880–1910 and 1990s was 0.57 for the surroundings and 0.41 for the city. In the 120 years covered, 805 species remained permanently present, 368 disappeared and 238 immigrated as new. Proportional representation of common species decreased and that of rare species increased. The representation of neophytes in the total flora of the study area increased from 6.2% in 1880–1910 to 13.2% in 1960s to 17.0% in 1990s. The proportion of native species decreased accordingly, and that of archaeophytes was stable over the study period. The representation of woody plants increased in the city, namely among neophytes. Over the study period, there was an increase in the representation of C and CR-strategists, mainly on behalf of CSR and SR strategists. CSR and CS strategies are most typical of native flora elements, C and CR of neophytes, while R and CR are most represented among archaeophytes. No consistent temporal trends in indicator values were recorded but the flora of the city differed from that of the surroundings in higher demands for light, temperature, nitrogen and soil reaction and lower demands for moisture. The present paper demonstrates that historical data on urban floras provide a powerful tool to evaluate the effect of humans on the development of urban landscapes and their plant life.
Information from four archival literature sources from the late 19th century was matched to present-day plant species distribution data for the region of Turnhout (Belgium) and for 15 smaller sub-regions within this region. In the entire study area 25% of the species recorded in the late 19th century went extinct during the 20th century and the extinction rate doubled at the more detailed sub-region level. Binary survival-extinction data and continuous residuals from a linear regression between historical and present-day abundance categories were used to investigate underlying ecological factors of change including habitat preference, ecological amplitude and life strategy. Species increasing relative to the overall trend were generally correlated with nutrient-rich habitats while declining species were more associated with nutrient-poor situations. Generalist species have become relatively more common whilst habitat specialists have strongly declined, resulting in a flora with many ‘losers’ and a few tolerant ‘winners’. The winners are often competitive species while the losers are mainly stress-tolerating species and species with combined life strategies (e.g. SC, SR). Correlations between the decline of historically present habitats and extinction rates of related habitat specialist species show clear trends. We suggest the most important factors involved in changes in flora diversity and vegetation composition are habitat loss due to urbanization and habitat deterioration, mainly due to agricultural intensification.
SummaryRegeneration of fourteen tree species was investigated at Harenna forest, on the southern slopes of the Bale Mountains, Ethiopia. Tree seedling densities and their spatial distribution along gradients of altitude and light were investigated using quadrats of 10 m × 5 m along line transects. Seedling mortality and herbivore damage were examined in eight permanent plots of 10 m × 5 m laid systematically at different places. Population structures of the species were investigated using quadrats of 20 m × 20 m along line transects. Species showed variation in densities of their seedlings ranging from 1065 to only 58 seedlings per hectare.Frequency of distribution of species along altitudinal gradients varied between 15 and 69 percent, indicating differences in habitat preferences among the species. In their spatial distribution to the canopy light gradient, eight tree species were found growing under canopy shade (1–5% light level) while six grew exclusively in the open (100%). More than 42% of the populations of seedlings investigated during the dry season of the year were damaged by herbivores and 27% were lost as uprooted, died and standing or were missing. Examination of the population structure of the species showed that only few species had good representation of individuals at all size classes implying healthy or normal regeneration. Many of the species showed strong peak at lower size classes followed by missing of individuals at one or more of the medium and upper height classes, which indicated that regeneration was hampered. Tree species with healthy regeneration or reverse “J” distribution included Teclea nobilis, Ocotea kenyensis and Syzygium guineense subsp guineense, whereas Podocarpus falcatus, Aningeria adolfi-friederici, Olea capensis, Croton macrostachyus and Prunus africana showed hampered regeneration. Management alternatives to enhance regeneration status of the species are discussed.
SummaryHeterostyly is clearly confirmed in the Korean endemic, monotypic taxon Abeliophyllum distichum Nakai (Oleaceae) by studies of plants from two geographically isolated populations. Variation in the hitherto unreported floral morphological aspects including an extended study of pollen grains of A. distichum in association with distyly were studied and described in details by using stereo-microscopy, LM and SEM. In this plant styles are always significantly longer in pin flowers than in thrum flowers, and the same is also true for the size of stigma including stigmatic papillae between two morphs (P < 0.0001). Thrum flowers have significantly larger petals and longer stamens then pin flowers (P < 0.0001). Dimorphism of pollen size in relation to distyly is generally well correlated and significantly different; the thrum flowers are significantly larger than those of the pin flowers (Yul-ji-ri population: P < 0.001, Hongryung population: P < 0.0001, respectively). The thrum pollen grains have slightly larger lumina than those of the pin pollen grains, but the difference between two morphs was only marginally or not significant. The exine thickness between two morphs was not significantly differentin both studied populations. In Song-duk-ri population the two morphs do not occur in a 1:1 ratio (i.e., anisoplethy). Bees of Apis sp. and Lasioglossum sp. (both in Apidae) were found as flower visitors in A. distichum. Floral dimorphism of A. distichum with respect to heterostyly is also briefly discussed.
Silver-fir (Abies alba Mill.) populations located at the south side of the main Pyrenean axis and Pre-Pyrenees constitute the south-western distribution limit of the species and, therefore, may be responding more noticeably to climate change than those in the centre of the range. The increasing aridity detected in the Pyrenees during the 20th century should affect more negatively the physiological performance of the southernmost silver-fir stand growing under more xeric conditions in comparison with stands growing within the main distribution area under mesic conditions. To evaluate the climatic influence on the performance of silver fir near its distribution limit, we studied several physiological and growth variables in shoots and needles from two silver fir populations located in nearby but climatically contrasting sites: Paco Ezpela (site E) and Gamueta (site G). Site E showed a stronger Mediterranean influence than site G, i.e. the former site was characterized by higher temperatures and leaf-to-air water vapour pressure difference and lower precipitation in summer than the latter site. Silver firs from site E showed lower values of primary and secondary growth, needle length, stomatal conductance, net photosynthesis and photosystem II (PSII) efficiency than individuals from site G. The reduction in net photosynthesis could be ascribed to a low CO2 availability and to a lower PSII efficiency. We conclude that the physiological differences found between both sites were caused by the more xeric conditions of site E as compared with the more mesic environment in site G. The predicted increase of severe droughts in the southern Pyrenees might cause a decrease in photosynthesis and growth in those silver-fir stands located near the ecological limit of the species.
Norway spruce (Picea abies [L.] Karst.) has a pronounced ability to create different crown types embracing strongly hypotonic, epi-hypotonic, strongly amphitonic types as well as respective intermediate ones. Data of Holzer and Schultze (1987) were reanalyzed in order to identify major environmental components that may shape ecotypes and contribute to Gruber's (1989) hypothesis that phenotypic plasticity is different among different crown types. Environmental variables and crown types were assessed by Principal Components Analysis. The first principal component explained 74% of the variation that was mainly loaded by different temperature variables and altitude while the second principal component explained additional 23% mainly loaded by precipitation variables. Orientation had a statistically significant but small effect. Covariance analysis demonstrated that age had modified crown type in a way that more hypotonic types were phenotypically more variable. Overlaps between crown-type distributions were evaluated by Schoener's Index, which may range from ‘zero’ (no ecotypic overlap) to ‘one’ (complete ecotypic overlap). In the present paper this index resulted in pairwise values varying from 0.21 to 0.86. The ecotypic overlap matrix was symmetric, i.e. ecotypic pairs increased gradually with stepwise crown-type graduation. We discussed the adaptation strategy of Norway spruce based on our results and propose that adaptation in this species regarding crown architecture is mainly caused by adaptive differentiation in higher altitudes while in lower elevations phenotypic plasticity is the dominating factor.
Theoretical models predict that the relative importance of facilitation and competition may vary inversely across gradients of abiotic stress. However, these predictions have not been thoroughly tested in the field, especially in arid and semi-arid environments. In this study, we evaluated how the net effect of Acacia tortilis subsp. raddiana (syn. A. raddiana) trees on the herbaceous species varies across a gradient of water stress in arid Tunisian ecosystems. Our results show that the influence of trees on the herbaceous stratum is beneficial. An Acacia tree improves the richness of herbaceous species around it by two to three times. The positive effect of Acacia raddiana on species composition is characterised in particular by a better development of some species of high pastoral value such as Cenchrusciliaris, Cynodon dactylon, Eragrostis papposa, Sisymbrium irio and Chenopodium album. We fitted the relationship between seasonal rainfall and the relative neighbour effect index, which varied across this gradient, to a linear model. Our results show that herbaceous plant cover, plant biomass, plant density and diversity are higher under a tree canopy and this positive interaction still increase with higher abiotic stress conditions.
SummaryWe studied the species composition of vegetation and seed bank in an experiment with grassland and oldfield plots in an eutrophic alluvial wetland (called “Marais de Redon”) of Western France. In this wetland, artificial disturbances (mowing) and natural disturbances (cattle, roebucks, boars, voles…) are very frequent. In order to mime these natural disturbances, experimental disturbances were generated in March 1996 after the end of the winter flooding and the seedlings counted three months later. The seed bank, the undisturbed vegetation and seedlings emerging in disturbed quadrats were sampled. Detrended Correspondence Analysis (DCA) of the undisturbed quadrats, disturbed quadrats and seed bank samples showed significant differences of species composition. Similarity between seed bank and undisturbed aboveground vegetation was low and not very different between grassland and oldfield. Very few seedlings emerged in undisturbed vegetation both in grassland and oldfield, which indicates the importance of gaps for seed bank expression. The great majority of seedlings emerging after experimental disturbances were mainly recruited from the soil seed bank. This result contrasts with other studies where the seed bank contributed very little to the seedling flora and vegetative regrowth clearly predominated recolonisation after disturbances. In the seed bank, few species lost after succession from grassland to oldfield vegetation were still present as seeds in the soil, but in most cases, species lost were not recorded in the seed bank. The two hypotheses about changes in the seed bank during secondary succession, predicting decrease in species richness or species diversity and seed density were only confirmed for seed density parameter.
Nectar composition and concentration were analyzed for 75 samples of 70 species of Acanthaceae representing all major intrafamiliar groups. Analyses of variance were conducted to test for significant differences between pollination syndromes and between taxonomical or phylogenetic groups (similar to genera). The available data indicate that the characteristics of nectar in Acanthaceae are predominantly determined by adaptation to needs of the pollinators rather than by phylogenetic constraints. (c) 2006 Elsevier GmbH. All rights reserved.
In Brazil, studies focusing on reproductive biology and aspects of pollination in the genus Ruellia have demonstrated common characteristics such as pollination by hummingbird, the predominance of self-fertility and spontaneous self-pollination. The objectives of this study were to describe the floral biology, nectar production, the reproductive system, the effect of pollination intensity and flowering phenology of Ruellia angustiflora, as well as keeping a record of the hummingbirds that visit the flowers of this species. Data collection was performed in a stretch of the Salobrinha stream in the Serra da Bodoquena, Mato Grosso do Sul, from August 2005 to July 2006. R. angustiflora flowered throughout most of the study period; it has diurnal anthesis and has increased nectar production in the morning hours with decreasing production rates during the day. The results of the reproduction experiments indicate self-fertility and pollen limitation in R. angustiflora. Among experiments with different pollination intensity there was no significant difference in fruit formation. Four hummingbird species were observed visiting the flowers of R. angustiflora, and Phaethornis pretrei was the most frequent followed by females of Thalurania furcata. According to its behavior and frequency of visits, P. pretrei can be considered the main pollinator of R. angustiflora in the study area. The experiments on flowers treated with different pollen loads indicate that most successful fruit formation in this species is obtained in flowers that received greater pollen loads on their stigmas. Besides, data suggest that major success in fruit set could be reached with more than three visits of P. pretrei.
The fruits of 10 species of Solanum sect. Acanthophora were studied. Cross and/or longitudinal and/or tangential microtome sections, stained mostly with astra blue/basic fuchsin, were made for microscopic examination. Three different kinds of cells were found in the epidermis, immediately below which a hypodermis, consisting in any of four types of structures, was always found. The mesocarp exhibits two histologically differentiated zones, an external one (formed by normal or spongy parenchyma, according to the species), and an internal one, commonly juicy, and with proliferations among the seeds. The diagnostic value of all these structures is assessed. Morpho-anatomical information is used to define fruit types beyond the berry, traditionally described for Solanum, and the probable dispersal syndrome related to them is discussed. Fruit similarities are slightly noticeable in several cases, while differences may be the result of their sexual system – which affects specially the size – and their histology, which is related to the dispersal syndrome. The comparison of our data with previous molecular phylogeny of the section suggests that a significant morphological variation is not associated with significant DNA sequence changes.
Water points provide excellent sites for studying overgrazing effects on plant communities in dry areas. Distance from water can be considered like a surrogate of grazing pressure being high near the water and low away from it. The main aim of this study is to investigate overgrazing effects on acceptability of fodder plants along a grazing gradient around three natural watering points. To achieve this goal, we classified spontaneous plants according to their acceptability degree and we followed their cover, richness and density as well as the grazing value along a grazing gradient around these wells, using phyto-ecological studies during the spring 2004 and 2006. Main results show that very palatable plants (mainly constituted by annuals) are more dominant in both the closed and the more disturbed transect areas around wells. The unpalatable plants dominate sites with moderate disturbance around wells. Ligneous palatable species obviously have a lower degree of disturbance. During the studied seasons the grazing gradient around wells 1 and 2, the oldest ones, seemed to exert a feedback upon the grazing intensity.
The ability of simple plant traits used as surrogate of species to reflect environmental variability of grasses and herbs in a West African savanna subject to fallow land rotation is assessed by referring to plants’ functional attributes. The aim is to determine the nature and the importance of the loss of information associated with the trait-vs.-species simplification. The traits selected are easily observable and widely documented. They are related to plant responses to resource availability, environmental constraints/disturbances and to plant palatability and capacity to disperse. The co-inertia analyses of both species–environment and traits–environment are compared. Although selected traits account for only a part of the variability recorded by species, they are relevant and most of them have an ecological significance. Syndromes of attributes that reflect the functional plant–environment relationships of the grass layer along a twofold gradient of soil fertility and woody cover could then be established. Periodic clearing and soil fertility decline produced by the fallow system determine vegetation types dominated by herbaceous species ranging from competitive and ruderal-competitive on fertile and wooded sites to stress-tolerant ruderal on unfertile and non-wooded sites. Thus, selected traits do not reveal all functional aspects of the relationships of savanna plants to their environment, such as soil hydromorphy and depth of the clayey horizon. That is possibly due to the scarcity of traits that characterize the root system involved in the analysis.
Aim of the present study was to investigate the effects of two key environmental factors of estuarine ecosystems, salinity and hypoxia, on the physiological attributes in reed plants (Phragmites australis (Cav.) Trin. ex Steudel). Growth, leaf gas exchange, water (and ion) relations, and osmotic adjustment were determined in hydroponically grown plants exposed to hypoxia at varying NaCl-salinity concentrations (0, 50, 100, and 200 mM). Plants grew well under hypoxia treatment with standard nutrient solution without added salt and at NaCl concentrations up to 100 mM. Reed plants were able to produce and allocate phytomass to all their organs even at the highest salt level (200 mM NaCl). In plants subjected to hypoxia at various water potentials no clear relationships were found between growth and photosynthetic parameters except for gs, whereas growth displayed a highly significant correlation with plant–water relations. A and gs of reed plants treated with hypoxia at varying water potential of nutrient solutions were positively correlated and the former variable also had a strong positive relationship with E. Leaf Ψw and Ψπ followed a similar trend and declined significantly as water potential of watering solutions was lowered. Highly significant positive correlations were identified between leaf Ψw and photosynthetic parameters. At all NaCl concentrations, the increase in total inorganic ions resulted from increased Na+ and Cl− while K+, Ca2+, and Mg2+ concentrations decreased with increasing osmolality of nutrient solutions. Common reed has an efficient mechanism of Na+ exclusion from the leaves and exhibited a high leaf K+/Na+ selectivity ratio over a wide range of salinities under hypoxia treatment. In Phragmites australis grown in 200 mM NaCl, K+ contributed 17% toΨπ, whereas Na+ and Cl− accounted for only 11% and 6%, respectively. At the same NaCl concentration, the estimated contribution of proline to Ψπ was less than 0.2%. Changes in leaf turgor occurred with a combined effect of salinity and hypoxia, suggesting that reed plants could adjust their water status sufficiently.
Atriplex halimus subsp. schweinfurthii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. A. halimus was grown in hydroponic conditions to investigate the effect of cadmium chloride (CdCl2) on growth, water status, leaf chlorophyll concentration, proline and Cd accumulation. Treatments were prepared by adding 0, 50, 100, 200 and 400 μM CdCl2 to the nutrient medium. Plant growth was significantly affected at high-Cd treatments. Increased CdCl2 decreased chlorophyll concentration, transpiration and root hydraulic conductivity (L0). Hence water flux had only a little effect on the uptake of Cd in A. halimus seedlings. In contrast, proline content increased with increasing CdCl2 concentration. Plants accumulated substantial amount of Cd in different plant parts (shoot and root). Most of the Cd taken up was retained in roots (606.51 μg g−1DW after 15 d at 400 μM CdCl2). The addition of Cd in the culture medium affected calcium (Ca) and potassium (K) nutrition in both shoot and root. A. halimus provides a new plant resource for exploring the mechanism of Cd hyperaccumulation and has potential for use in the phytostabilization of Cd-contaminated salt soils.
We have examined slime cell distribution on the surface of the achenes of some Artemisia and Neopallasia taxa, as well as slime composition, envelope formation during the hydration, and slime relation to different morphological features and environmental factors. The results of the studies show a characteristic pattern of slime cells distribution, which could differ between taxa. The slime in the taxa studied belongs to the cellulose type and consists of two components i.e., pectins and cellulose. Although all fruits contain slime cells, not all of them show the slime envelope formation. Plants occurring in dry habitats (such as A. barrelieri) or annual species (such as A. annua) are characterised by a large amount of slime and a fast process of slime envelope formation. Slime production has not been observed in some polyploid populations (A. campestris and A. campestris ssp. sericea) and in two species occurring in relatively fertile habitats (A. verlotiorum, A. vulgaris). A reason for this may be either the immaturity of polyploid fruits leading to the production of a scarce, not detectable slime amount or, alternatively, the occurrence of not functional slime cells. Slime facilitates and stimulates the germination, as well as the adherence of the fruits to the ground or to animals (for dispersal). The slime could play important role in the distribution and colonisation of new habitats in many Artemisia taxa.
Sowing experiments were used to study seedling recruitment, growth and biomass allocation patterns in the perennial forest herbs Aconitum septentrionale and Actaea spicata in relation to the microbial soil community. Glucose and nutrients were added every second week over a 3-year period to manipulate soil microbial activity and nutrient availability. The glucose was added (400 g glucose m−2 yr−1) to reduce the nutrient availability to the plants by increasing soil microbial demands. A full nutrient solution was used to increase the nutrient availability. The experiments were performed in a deciduous forest and in an open field in South East Norway, and our study is based on a consecutive sampling of whole plants with intact root systems to be able to estimate growth and allocation patterns. Both species recruited best in the forest while their growth in the open field was ca. 100 times larger than in the forest. Shoot:root ratios were surprisingly similar in the forest and the open field sites and were only marginally affected by the glucose and nutrient treatments. However, the shoot:root ratios were characterised by highly significant seasonal variations. This was the case for both species and indicates that the shoot:root ratios were under strong ontogenetic control. Recruitment was negatively affected by glucose additions, in particular in the open field. Growth was significantly and negatively affected by glucose additions in the forest. Nutrient additions gave, as expected, a significant increase in growth. The failure of seedling recruitment and inferior growth following glucose additions support the assumption that the soil microbial community is an important determinant of plant recruitment and growth.
This research was performed to resolve temperature requirement for embryo growth, dormancy break and seed germination of Aconitum lycoctonum, an Eurasian perennial herb growing in deciduous forests. The dormancy strategy of A. lycoctonum was compared with that of other Ranunculaceae species growing in the temperate deciduous forest habitat. Seeds of A. lycoctonum germinate immediately after embryo growth is completed during winter and seedlings subsequently emerge in early spring. Experiments in controlled conditions revealed that (1) embryo growth and germination only occurred at low temperatures (<10 °C), (2) a high-temperature pre-treatment was not required for germination, and (3) application of gibberellic acid did not overcome the chilling requirement. Based on these results, seeds of A. lycoctonum can be classified as having deep complex morphophysiological dormancy. Dormancy breaking requirements of A. lycoctonum are very similar to related species studied before, suggesting stasis in seed dormancy traits has occurred in the Aconitum–Delphinium clade.
SummaryIn addition to the green leaves, commonly considered as the primary sources of photosynthate production, higher plants can potentially use almost all vegetative and reproductive structures to perform photosynthetic CO2 assimilation. Green leaves, stems and green sterile flower organs, optimized for light harvesting and photosynthetic performance, are characterized by net photosynthetic assimilation utilizing mainly the atmospheric carbon dioxide. In contrast, chlorophyll-containing bark and wood tissue, most fruit, root and fertile flower organs are principally sub-ordinated to non-photosynthetic functions, but typically perform an effective internal CO2 recycling using the respiratory released CO2. Non-foliar photosynthesis, either manifested as net photosynthesis or internal CO2 refixation is regarded as an important strategy of additional carbon-acquisition. While chlorophyllous stems or aerial roots even can serve as primary photosynthetic organs, reproductive structures could derive up to 60%; of their total carbon requirement from own CO2 fixation. In the review, the main strategies of additional carbon acquisition by non-foliar photosynthetic organs are illustrated, presenting an extensive compilation of published data completed with relevant own studies.
A sizeable number of scientists and funding organisations are of the opinion that the relevance of plant physiological ecology as an important discipline has declined to the point that it is no longer considered as one of the important topics of ecological research. Plant physiological ecology is typically associated with the autecological plant research conducted during the latter portion of the 20th century or, even worse, simply with gas exchange measurements. However, taking a closer look, it becomes obvious that, by focusing on the intermediate integration levels (individuals, populations), this discipline represents an essential link between the high integration levels (communities, ecosystems, biosphere) and the disciplines at the bottom of the complexity hierarchy (physiology, molecular biology). In this paper we show that the principal question of all ongoing community and ecosystem level research – What is the mechanistic background of vegetation composition, biodiversity structure and dynamics and how is this linked to fluxes of matter at the community and higher levels of organisation? – can only be answered if the mechanism of interactions between the relevant organisms are understood. In consequence, the classical discipline of plant physiological ecology will continuously develop into a truly interdisciplinary experimental ecology of interactions and its importance will rather increase than diminish. Promising activities of this kind are already underway. Scientists needed for this new direction should have a rather broad scientific perspective, including knowledge and experience in fields outside of typical ecological research, instead of being specialists for single ecophysiological aspects.
Actinocephalus exhibits perhaps more diversity in habit than any other genus of Eriocaulaceae. This variation is largely a result of differences in the arrangement of the paraclades. Based on the analysis of stem architecture of all 25 species of Actinocephalus, the following patterns were established: (1) leaf rosette, with no elongated axis, instead the axillary paraclades originating directly from the short aerial stem, (2) rosette axis continuing into an elongated axis with spirally arranged paraclades, (3) an elongated axis originating from a rhizome, with ramified paraclades, and (4) an elongated axis originating from a short aerial stem, with paraclades arranged in a subwhorl. The elongated axis exhibits indeterminate growth only in pattern 4. Patterns 3 and 4 are found exclusively in Actinocephalus; pattern 1 occurs in many other genera of Eriocaulaceae, while pattern 2 is also found in Syngonanthus and Paepalanthus. Anatomically, each stem structure (i.e., paraclade, elongated axis, short aerial stem, rhizome) is thickened in a distinctive way and this can be used to distinguish them. Specifically, elongated axes and paraclades lack thickening, thickening of short aerial stems results from the primary thickening meristem and/or the secondary thickening meristem. Thickening of rhizomes results from the activity of the primary thickening meristem.
The present review describes the ombrohydrochoric dispersal syndrome in plants, i.e. seed expulsion by raindrops. There are two different ombrohydrochoric dispersal modes – dispersal by rain wash and by ballistic forces. Both have been reported from the understory of tropical and temperate forests, from wetlands and from deserts, and from numerous families and genera. A special form of ombrohydrochoric dispersal is the jet-action rain-operated seed dispersal mechanism which is restricted to the semi-desert ice plants, Aizoaceae, one of the major families of the angiosperms. Within this family, 98% of the species possess hygrochastic capsules with an ombrohydrochoric seed dispersal mechanism which in part are also responsible for the remarkable speciation burst and radiation. The highly complex capsules open when wet, and the seeds are expelled by a ‘jet action’ with the kinetic energy of raindrops. The halves of the covering membranes of a locule form a nozzle near the centre of the capsule which serves as a jet. Drops of water falling on the distal opening (after the locule has been filled with water) result in an explosive expulsion of water droplets and seeds through that jet. More seeds are dispersed further away from the capsule than in those capsule types without such a jet mechanism.
We investigated the anatomical and chemical characteristics of the foliar vascular bundles in four ecotypes of common reed (Phragmites communis Trin.) inhabiting the desert region of northwest China: swamp reed (SR), low-salt meadow reed (LSMR), high-salt meadow reed (HSMR), and dune reed (DR). The cell walls of the vascular systems of all four ecotypes exhibited bright autofluorescence. Compared to SR, the three terrestrial ecotypes, LSMR, HSMR and DR, had higher percentages of bundle sheath cell areas, lower percentages of xylem and phloem areas, lower xylem/phloem ratios, and higher frequencies of leaf veins. In addition to differences in the autofluorescence intensity and the morphology of the detached cell walls of the vascular bundle sheath, the three terrestrial ecotypes also exhibited anatomical differences in the outerface tangential walls of the bundle sheath and higher frequencies of pit fields in the walls in comparison to SR. The Fourier transform infrared (FTIR) microspectroscopy spectra of the vascular bundle cell walls differed greatly among the tissues of the different ecotypes as well as within different tissues within each ecotype. Histochemical methods revealed that although pectins were present in all bundle tissue cell walls, large amounts of unesterified pectin were present in the phloem cell walls, especially in the salt reed ecotypes LSMR and HSMR, and large quantities of highly methyl-esterified pectin were present in the xylem and sclerenchyma cell walls of the SR and DR ecotypes. Differences were observed in the lignification and suberization of the xylem and sclerenchyma cell walls of the four ecotypes, but the phloem and bundle sheath cell walls were generally similar. These results suggest that the adaptation of common reed, a hydrophytic species, to saline or drought-prone dunes triggers changes in the anatomical and chemical characteristics of the foliar vascular bundle tissues. These alterations, including higher percentages of bundle sheath areas and lower percentages of xylem and phloem areas and their ratios, changes in the chemical compositions and modifications of the cell walls of different vascular bundle tissues, and differences in the deposition of major cell wall components in the walls of different vascular bundle tissues, could contribute to the high resistance of reeds to extreme habitats such as saline and drought-prone dunes.
SummaryEucalyptus camaldulensis Dehnh., considered as a drought tolerant species, was examined in relation to some mechanisms linked to drought tolerance (cell-wall elastic adjustment and osmotic adjustment) and to the intraspecific variation related to those features. Rooted cuttings of five clones obtained from three different provenances from Australia (Gilgandra: 106, 109; Lake Albacutya: 119, 125; Condamine: 105) were gradually submitted to a water limitation regime. Water stress curtailed relative leaf area growth rate, pre-dawn relative water content (RWC) and noon stomatal conductance (gs) in all clones. Shoot water parameters were estimated at the end of the drought period by pressure-volume (P–V) analysis through a repeat pressurization method. The curves obtained were analyzed by Schulte’s P–V Curve Analysis Program. Drought decreased very significantly the osmotic potential at full turgor (χπFT) and at the turgor loss point (χπTLP), with a significant clone effect: 105 had the lowest values (–2.12±0.04 MPa and –2.39±0.05 MPa). Osmotic adjustment (OA) on average was 0.34±0.02 MPa. Drought increased maximum bulk modulus of elasticity (ɛMAX) by 6.60.7 MPa. There were no clonal differences in either OA or elastic adjustment.Water stress increased significantly turgor potential at full turgor (χFT), and differences between control and stress plants show that the OA recorded did not fully account for the positive changes in turgor of stressed plants. Drought decreased shoot turgid mass/dry mass ratio (TM/DM), again with a significant clone effect: 105 had the lowest value (2.66±0.11). Reduced shoot TM/DM combined with increases in ɛMAXduring stress were indicative of cell wall adjustment, reduced turgor-loss volumes and tightening of the cell walls around the protoplasts, suggesting a cell size reduction. No effects were observed on RWC at the turgor loss point. A regression model that considered ɛMAX and χπFT explained best the response patterns of stressed plants. The mechanisms observed in Eucalyptus camaldulensis that delay growth while maintaining turgor and water uptake allow us to consider it as a dehydration postponement species.
The ecological and economic importance of oleoresin produced by Copaifera langsdorffii is well established. This study aims to investigate the ontogeny, anatomy and ultrastructure of the internal glands of C. langsdorffii during plant development. Samples were processed for light and electron microscopy and a specific technique was applied to impregnate endomembranes. Internal secretory glands were observed in the hypocotyl, epicotyl and eophylls of seedlings, and in the primary stem, pulvinus, petiole, rachis and leaf blade of adult plants. Canals and cavities show differential distribution. They arise from ground meristem cells, and the lumen is first formed by schizogenesis followed by later schizolysigenous development. The dense cytoplasm of epithelial cells shows mitochondria, plastids without thylakoids, polyribosomes and endoplasmic reticulum. A periplastidial reticulum was also observed. Secretion is released by eccrine, granulocrine and holocrine processes. Lipophilic and hydrophilic compounds were histochemically detected in both canals and cavities, whereas resin was detected only in canals. The presence of these substances has been associated with plants’ defences against dehydration, as well as against attacks from herbivores and pathogens, from seedling stage onwards.
Marked morphological changes occur during development from young seedlings to adults in Geissois pruinosa. At successive stages, leaves change from simple to trifoliolate and finally to 5-foliolate, palmately compound leaves, the margin of the blades changes from dentate to entire, the venation from craspedodromous to brochidodromous, and the stipules switch at about the 7th level from four free lateral ones per node to two fused intrapetiolar ones. Stems and leaves in young seedlings have sparse, erect hairs, but are glabrous in adults. Scattered and often incomplete information on other Cunoniaceae suggest that differences between seedlings and adults in other genera are generally less pronounced. Some seedling characters of G. pruinosa (including toothed leaflet margins and free lateral stipules) occur in the adult foliage of some of its close relatives (the genera Lamanonia and Pseudoweinmannia and Geissois in Australia) and are plesiomorphic within this clade.
To assess whether foliar application of K+S as potassium sulfate (K2SO4) could alleviate the adverse effects of salt on sunflower (Helianthus annuus L. cv. SF-187) plants, a greenhouse experiment was conducted. There were two NaCl levels (0 and 150 mM) applied to the growth medium and six levels of K+S as K2SO4 (NS (no spray), WS (spray of water+0.1% Tween 20 solution), 0.5% K+0.21% S, 1.0% K+0.41% S, 1.5% K+0.62% S, and 2.0% K+0.82% S in 0.1% Tween-20 solution) applied two times foliarly to non-stressed and salt-stressed sunflower plants. Salt stress markedly repressed the growth, yield, photosynthetic pigments, water relations and photosynthetic attributes, quantum yield (Fv/Fm), leaf and root K+, Mg2+, P, Ca2+, N as well as K+/Na+ ratios, while it enhanced the cell membrane permeability, and leaf and root Na+ and Cl− concentrations. Foliar application of potassium sulfate significantly improved growth, achene yield, photosynthetic and transpiration rates, stomatal conductance, water use efficiency, leaf turgor and enhanced shoot and leaf K+ of the salt-stressed sunflower plants, but it did not improve leaf and root Na+, Cl−, Mg2+, P, Ca2+, N as well as K+/Na+ ratios. The most effective dose of K+S for improving growth and achene yield was found to be 1.5% K+0.62% S and 1% K+0.41% S, respectively. Improvement in growth of sunflower plants due to exogenously applied K2SO4 was found to be linked to enhanced photosynthetic capacity, water use efficiency, leaf turgor and relative water content.
The root tubers of Asphodelus aestivus consist mostly of enlarged fleshy storage tissue. They are bounded by a multiple-layered velamen, responsible for rapid water uptake, water loss reduction, osmotic and mechanical protection. In the cortex area, thin-walled idioblasts contain numerous raphides of calcium oxalate in their large vacuole with a distinctive tonoplast. Wide morphological variations are observed among the raphide cross sections. Electron-dense compounds penetrate the raphide surface and raphide groove. Raphides seem to be vital for the protection of the root tuber parenchyma from herbivores. The cells of uniseriate endodermis are heavily thickened possessing a few plasmodesmata. The vascular cylinder is 20–28-arch and the root xylem consists of vessels in short radial rows, alternating with clusters of phloem cells. The presence of cells, which contain soluble polysaccharides in their large vacuole, is conspicuous after employing the Schiff's reagent. Exodermis cells and all cell walls, especially the thick ones of the endodermis, are also stained. Numerous parenchyma cells, especially those around vascular bundles are stained intensely, when exposed to Sudan Black B. These cells occurring as solitary idioblasts abundantly accumulate oil. Electron-dense remnants are evident within the vacuoles of the storage cells especially near the vascular tissue. The morphological features of A. aestivus root tubers and the major part of the total plant biomass are responsible for the species’ occurrence and frequent dominance in a wide array of arid environments. A. aestivus possessing root tubers is proved to be very efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations of the Mediterranean environment.
SummaryThe heterostyle Primula vulgaris is a rare and declining species in Northern Belgium; its presence is restricted to a limited number of small landscape elements in a matrix of intensively managed agricultural land. In 1986 and 1999 we recorded numbers of pin-thrum flower morphs in respectively 34 and 89 populations.No structural imbalance in flower morph numbers was found, but imbalances were significantly larger in small populations. Moreover, relative imbalance also increased between 1986 and 1999. Population persistence however, was not correlated with morph imbalance: changes in population size between the two survey periods did not depend on initial flower morph imbalance.Results are compared with other heterostyly-related population research in Primula species and the relative importance of deterministic and stochastic processes for population persistence are discussed. To conclude, the introduction of missing morphs into relic populations with only pin or thrum plants is suggested to reduce pollinator-limited seed set.
Previously unexploited legume species may offer utilization potential where environmental stresses constrain the use of more conventional forage crops. Melilotus indicus (L.) All., Yellow sweet clover, occurs as a weed in different habitats in Egypt. It grows in moderately saline areas, where traditional forage legumes cannot be cultivated. Our extensive field studies have recorded the species in many different habitats ranging from healthy agricultural lands to abandoned saline areas. The studied plants maintained high nodulation capacity (68 – 95%) and nitrogenase activities (about 1.81 μmol C2H4 plant−1 h−1) in different habitats. Greenhouse experiments demonstrated that seed germination was maintained at 80% when growing on substrats containing 200 mM NaCl and that 25% of the germination capability was preserved when 300 mM NaCl was added to the growth medium. The growth rate of seedlings was not significantly affected by 200 mM NaCl but was reduced by 30% under 300 mM NaCl. It is supposed that M. indicus uses a salt inclusion mechanism for maintaining growth under saline conditions, as it accumulated high amounts of Na+ and Cl− ions. Leaf succulence and indices of leaf water status did not differ among the salt treatments, whereas relative water content was reduced by only 3% and water content at saturation increased by about 14% at high salt concentrations in the growing medium. Our results suggest recommending the cultivation of M. indicus in salt-affected soils, which are widespread and pose a problem for the farmers of Egypt and other countries in the world's arid belt.
This study, aimed at elucidating changes in the foliar and cambial behavior in Azadirachta indica (Neem tree) due to coal-smoke pollution, has revealed inhibitory effects of pollution stress on leaf pigments concentrations, nitrate reductase activity and the contents of reducing sugars and total N content, whereas stimulatory effects were given on stomatal index and nitrate and sulphur contents. Under smoke effects, stomatal conductance was low, leading to a drop in the net photosynthetic rate and a rise in the internal CO2 concentration of leaf. Cambial reactivation in the stem was delayed at the polluted site. Although the total span of the cambial activity was reduced, greater amount of wood was observed to accumulate in the stem axis under heavy pollution stress. Vessel proportion in the wood increased, whereas size of vessel elements and xylem fibers decreased. “Vulnerability factor” (ratio between mean vessel diameter and mean vessel abundance) and “mesomorphic ratio” (multiplication product of vulnerability factor and mean length of vessel element) of the stem–wood, both declined with increase in the pollution stress, thus indicating a tendency of the species for shifting towards xeromorphy when grown under stress. Given the opposite trends of photosynthetic rate and wood increment, the carbon-partitioning pattern rather than the photosynthetic rate seems to have influenced the accumulation of new wood. The Neem tree proves to be suitable for growing in the polluted areas.
The morphology and distribution of leaf trichomes of Tetradenia riparia were studied using light and scanning microscopy. Three morphologically distinct types of trichomes were observed on T. riparia leaf surfaces: glandular capitate (short and long stalked), peltate and non-glandular. The glandular and non-glandular trichomes were present in abundance on both the adaxial and abaxial surfaces. Young leaves were densely covered with trichomes; however, the density of trichomes decreases progressively with leaf maturity. This suggests that the trichomes are established early in leaf differentiation and their density decreases with leaf development and age.
In West Africa, policies for prescribed early fire, grazing and selective tree cutting in the savanna-woodlands are rarely based on long-term experimental studies. The purpose of this study was to provide scientific evidence based on field data from two case studies for an informed discussion on the long-term response of herbaceous abundance both at the community and individual species levels to fire, grazing, selective cutting and their interactions. A long-term factorial experiment was established in two State forest reserves in Burkina Faso that mainly differ in their soil attributes. Community abundance data recorded from line intercept sampling over 13 years were analyzed using a multivariate ordination technique known as principal response curves (PRC).The results indicate that disturbance regimes, independently or interactively, influenced species abundance over time with inter-site specificity. The dynamics of these disturbance regimes exhibited temporal variation which could be related, to some extent, to inter-annual variation in annual rainfall. The PRC ordination accounted for 38% and 34% of the variation within the data set for sites with deep and shallow soils, respectively. At the site with deep soils, more than one PRC axis was needed to summarize the community response sufficiently, suggesting that the species reacted in different ways to disturbances. The PRC method approach to the analysis of disturbance dynamics allowed us to distil the complexity of the community responses to those of individual species and to identify species that can serve as indicators of certain disturbance regimes.
Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropical America and has now naturalized worldwide, particularly in Southeast Asia. The present study investigated the nature and potential of root-mediated allelopathic interference of A. conyzoides against rice (Oryza sativa). Root and shoot length and biomass accumulation of rice were significantly reduced (by 18–30%) when grown in the rhizosphere soil of the weed indicating the release of putative allelochemicals from the weed into the soil. The growth of rice was also progressively reduced in the soil amended with increasing amounts of root residues (5, 10 and 20 g kg−1 soil) of A. conyzoides. The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorated the negative effects of root residues amended in the soil. Further, there was no negative effect on the availability of soil nutrients in the root-amended soils. These were rather nutrient rich with greater electrical conductivity, and higher amount of organic matter, thus indicating no role in observed growth reduction. The reduction in allelopathic effects of root residue upon charcoal addition further indicated that putative phytotoxins released from the weed roots are water-soluble phenolic compounds. A significant amount of water-soluble phenolics were present in rhizosphere (∼6-times higher) and root-amended soils (∼5–10-fold higher) and their content was reduced (to ∼3.6–7.0-fold higher) when charcoal was added. The observed growth reduction in Ageratum rhizospheric or root-amended soils was concomitant with the amount of phenolic compounds. Upon HPLC analyses, these were identified as p-coumaric acid, gallic acid, ferulic acid, p-hydroxybenzoic acid and anisic acid. Under laboratory conditions, these phenolic acids reduced the root length and seedling weight of rice individually as well as in equimolar mixture, though no synergistic effect was noticed. The study concludes that root exudates and residues of A. conyzoides suppress the growth of rice by releasing phenolic allelochemicals into the soil rhizosphere and not through alteration of soil nutrients, and allelopathy plays a significant role in root-mediated negative interference of A. conyzoides.
Plant species in fragmented populations are affected by landscape structure because persistence within and migration among inhabited patches may be influenced by the identity and configuration of surrounding habitat elements. This may also be true for species of the semi-natural vegetation in agricultural landscapes. To determine the effect of landscape elements we analyzed Wood Avens (Geum urbanum L.) populations within three 4×4 km2 agricultural landscapes in Germany, Switzerland and Estonia, which differ in levels of land use intensity and habitat fragmentation. Genetic variation was determined in 15 randomly selected populations in each landscape using 10 microsatellite loci. The landscape structure was assessed at two circles around each population, with radii defined by the range limits of spatial genetic autocorrelation. Multiple regression analysis was used to determine the influence of landscape structure variables for inter- and intrapopulation genetic diversity. Gene diversity was equally high in Germany (He=0.27) and Switzerland (He=0.26) but lower in Estonia (He=0.16). A high overall inbreeding coefficient (FIS=0.89) was found, as expected for a selfing breeding system in G. urbanum. Genetic differentiation among populations was high (overall FST=0.43, 0.48, and 0.45 in Estonia, Switzerland and Germany, respectively), and did not differ among the three landscapes. Only a moderate influence of individual land use types on genetic diversity within and among populations was found with some idiosyncratic relationships. Genetic variation within populations was correlated to the amount of hedgerows positively in Estonia but negatively in Switzerland. The study demonstrates that the distribution of individual land use types affects the genetic pattern of a common plant species. However, different variables were identified to influence the genetic structure in three different landscapes. This indicates a major influence of landscape-specific land use history and stochastic processes determining gene flow and plant population structure.
In the present study we relate the variability in life-history traits (such as flowering time and lifespan) of the herbaceous biennial–perennial Erucastrum nasturtiifolium (Brassicaceae) to habitat type. We studied plant populations from arable fields and from eroded mountain habitats, such as badlands and rocky slopes. Collection sites ranged from low basin to sub-alpine regions in the NE Iberian Peninsula. Plants were grown under common garden conditions to evaluate genetic variation among and within populations. Plants were also subjected to a resource gradient to detect genetic variation in phenotypic plasticity. The populations exhibited differentiation across a number of life-history traits (mainly flowering time and lifespan) and morphological traits related to growth (basal stem diameter, plant height and number of branches). This suggests that life-history differences among populations are genetically based. Moreover, our results show that variation in flowering time and lifespan are affected by habitat type independent of other abiotic factors such as altitude or continentality. Thus, populations from arable fields started flowering in their first year and displayed annual cycles, whereas those from wild habitats generally flowered in their second year and showed biennial or even perennial cycles. Intra-population differences in flowering time were observed in only one population, and were related to nutrient availability. We suggest that early-flowering and shorter lifespan populations of E. nasturtiifolium may have been selected from late-flowering and longer lifespan populations as part of a selective process ensuring survival and future offspring amidst unpredictable and frequently disturbed environments such as exist in many agricultural habitats.
Emergent trees may have an influence on the volume and the spatial distribution of water input into agroforestry stands and may thus affect water availability for the main crops. Our goal was to analyze the influence of such trees on rainfall distribution in a cacao agroforest area in the rainforest margin zone of Central Sulawesi, Indonesia. The emergent trees studied belong to the species Bischofia javanica (Phyllanthaceae) and were 15 m high remnants from the natural forest. A set of 96 throughfall gauges was systematically distributed underneath canopies of cacao only, and underneath canopies of cacao plus emergent trees (cacao plus trees). From an earlier study we knew that stemflow can safely be estimated with less than 1% of gross precipitation (Pg).
SummaryEcologists have widely neglected the long term impact of vpd (the water vapor saturation deficit of the air) on plant growth and development. This paper tests the hypothesis that the prevailing vpd level during growth has a significant influence on the ecology of temperate woodland herbs, independently of soil moisture status. Eight herbaceous species (Scrophularia nodosa, Digitalis purpurea, Campanula trachelium, Rumex sanguineus, Geum urbanum, Hieracium sylvaticum, Hordelymus europaeus, Brachypodium sylvaticum) were grown in climate chambers at four different saturation deficits (vpd = 120, 580, 930 or 1210 Pa) with unlimited water supply in solution cultures in order to experimentally analyse long-term effects of vpd on shoot water relations, plant morphology and plant growth rate. In their natural forest floor environment these species are exposed to vpd levels of 200 to 600 Pa on summer days. After 50 to 90 days of cultivation I compared the four vpd treatments with respect to dry matter production, leaf anatomy, leaf conductance, transpiration rate, bulk leaf water potential (χl), leaf water content (θl), and shoot nutrient concentrations.Productivity was significantly higher at 120 than at 580, 930 or 1210 Pa in seven of eight species. Plants grown at low vpd had larger leaves and leaf epidermal cells, and a lower stomatal frequency than plants of high-vpd treatments which indicates a stimulation of leaf expansion by high air humidities. Low saturation deficits also affected leaf anatomy (less compact leaf mesophyll with larger fractional air space) but did not alter mesophyll cell dimensions. Leaf water potential and leaf water content were more favorable at 120 Pa than at higher vpd levels in all eight species although a clear dependence of leaf water status (χl and θl) on transpiration rate did not exist.Shoot nutrient concentrations generally were lower at low than high vpd which reflects a nutrient dilution effect caused by an increased carbon assimilation of the low vpd plants. In contrast, no correlation was found between transpiration rate and shoot concentrations of Ca or other mineral nutrients. I conclude that vpd acts as a soil water-independent growth-controlling factor for hygromorphic woodland herbs. Environments with a vpd of 100 to 500 Pa improve leaf water status and stimulate leaf expansion of these species which leads to enhanced growth. Other growth-relevant parameters (leaf conductance, transpiration rate and nutrient uptake), which were also affected by vpd, had only a minor or no influence on productivity.
Seed germination percentage and rate of Rubia fruticosa, an endemic Macaronesian shrub was assessed with seed lots collected at three levels of an altitudinal gradient (200–800 m asl) located in El Hierro Island (Canarian Archipelago). Both seeds collected from control plants and those found in lizard droppings were studied. A significant decrease in the germination percentage was observed with control seeds and those seeds which are previously eaten by lizards if collected at 800 m asl. This indicates that R. fruticosa is a plant whose optimal germination environment is located between 200 and 500 m asl, occurring in higher altitudes only under sub-optimal conditions. The effect of lizard gut on R. fruticosa seeds was variable in the two study years: while germination percentage of seeds having passed through the lizards was not significantly different to that of control seeds in the first year, an increased germination was found for the animal-treated seeds in all three altitudinal zones in the second year. In general, germination rate of control seeds was rather variable between years. However, improvement of R. fruticosa seed germination caused by lizards may be important for its fitness; and a co-evolution may have occurred, since lizards and seeds of this endemic plant have been intensively interacting for millions of years in the lower zones of the Canary Islands.
Solidago gigantea is a rhizomatous perennial herb native to northern America and introduced in Europe. It is a serious invader of disturbed mesic sites, often forming dense monospecific stands. We review the literature on taxonomy, morphology, population biology, cytology, physiology, chemistry, and ecology of this species.
SummaryIn a greenhouse experiment, single ramets of Ajuga reptans, a stoloniferous herb, were planted on the divider of two halves of trays. The two halves of a tray had the same or different nutrient supply. The aim was to study root and shoot plasticity and the placement of ramets and roots in response to the heterogeneous nutrient environment.Number of primary stolons, number of secondary stolons, stolon internode length, number of leaf ramets, total root length (including fine and coarse roots) and root dry weight were greater, but biomass allocation to fine and coarse roots and specific coarse root length were lower under the homogeneous nutrient-rich (the HH-treatment) than under the homogeneous nutrient-poor (the LL-treatment) conditions. No significant response was observed in specific stolon length and specific fine root length.In the heterogeneous nutrient environment (the HL-treatment), total root length, root dry weight, root biomass allocation and specific root length did not differ between the nutrient-rich and the nutrient-poor halves of the trays for both fine and coarse roots. The same response pattern was found for the number of primary and secondary stolons, the number of leaf ramets, spacer lengths between leaf-ramets (internode length) and specific stolon length. Only the number of shoot ramets was larger in the nutrient-rich than in the nutrient-poor patch.Ajuga reptans responded strongly to the different homogeneous nutrient supplies (the HH-treatment vs. the LL-treatment) in terms of morphology and growth of roots and shoots. In the heterogeneous environment (the HL-treatment), the differences in response to local nutrient conditions seemed to be reduced due to intraclonal physiological integration. Predictions of an increase in root mass in the nutrient-rich patch as compared to root mass in the homogeneous HH-treatment or even in the nutrient-poor patch of the HL-treatment were not confirmed by the results. Apparently, behaviour of clonal plants in a heterogeneous environment cannot be simply predicted from their behaviour in different homogeneous environments.
The carnivorous bladderworts (Utricularia) possess complicated suction traps. Remarkably, information on the prey trapped is relatively sparse. We have conducted a detailed survey on the prey spectra found in traps of selected aquatic bladderworts (U. australis, U. vulgaris) occurring in ponds in northeastern Germany. A close examination of more than 200 traps revealed cladocerans, copepods, rotiferas, ciliates and insect larvae as being common prey.Of particular interest was the considerable amount of phytoplankton (i.e. algae, cyanobacteria) found in the traps. In total, more than 160 algae species (among others, Kirchneriella lunaris, Scenedesmus quadricauda and S. acuminatus) belonging to more than 50 genera were present, with Chlorophyceae being dominant. The role of the vegetarian diet for nutrient supply of bladderworts is discussed.
Lygeum spartum L. is a native species in Algerian salt steppes. The plant is of interest because of its tolerance to environmental stresses and its use as a fodder grass for livestock in low-rainfall Mediterranean areas. Nevertheless, plant responses of this plant to salt stress are still not investigated in detail. Therefore, L. spartum L. was grown in hydroponic conditions to investigate the effect of salinity (0, 30, 60 and 90 mM NaCl) on growth, water relations, gas exchange, leaf chlorophyll concentration, glycine betaine and mineral uptake. Plant growth was reduced at 60 and 90 mM NaCl, but was not significantly lower than in the controls at 30 mM NaCl. Sodium (Na+), chloride (Cl−) and glycine betaine contents in plants increased, whereas calcium (Ca2+), potassium (K+), relative water content (RWC), root hydraulic conductivity (L0) and chlorophyll content decreased with an increase in salinity. Water potential (Ψω) and osmotic potential (Ψπ) of plants decreased with an increase in salinity. No change was observed in the turgor potential (Ψτ). Photosynthesis parameters (CO2 assimilation rate, stomatal conductance and transpiration rate) did not change significantly at 30 mM NaCl, as compared to the control. Higher salt levels impaired photosynthetic capacity of L. spartum mainly via a stomatal limitation leading to a low CO2 assimilation rate. This might be a consequence of the reduced whole-plant hydraulic conductivity under salt stress. The results demonstrated that L. spartum L. can be characterised as a moderately salt-tolerant species. Salt tolerance in this species is achieved by appropriate osmotic adjustment involving accumulation of ions and glycine betaine. At high salinities, growth reduction probably occurs as a result of high concentrations of Na+ and Cl− and their interference with other ions such as Ca2+ and K+. This plant can be used locally as a fodder for livestock and to stabilise sand dunes and rehabilitate salt soils.
Mapping the distribution of invasive alien plant species is significant for testing ecological hypotheses and for guiding effective management. Little is known about the distribution of invasive plants at landscape scale, and the factors controlling their dispersal and establishment are still poorly understood. This is the case for Rosa rugosa, an invasive shrub with negative effects on biodiversity in dune ecosystems of NW Europe. The aim of the study was to identify the factors which determine the distribution of R. rugosa in coastal dunes. In a large semi-natural dune area of NW Denmark (2364 ha) all patches of the species (1321, 1.3–59.1 m2) were GPS mapped. Patch distribution was GIS analysed, based on aerial photographs and vegetation maps. The distance of R. rugosa from the most conspicuous landscape elements was compared with randomly placed reference points. The species had invaded 0.35% of the dune landscape, and it was present in all vegetation types and all parts of the study area. Rosa rugosa patches were slightly smaller in grey dunes than in white dunes and brown dunes, and some of the largest patches were found close to villages. The occurrence of the shrub was positively correlated with distance to the coastline, to roads, tracks and houses. We conclude that the distribution of R. rugosa is determined by both natural and anthropogenic factors. It is further discussed how these factors may control dispersal and establishment of the species, and how the results can be used for improved management of coastal dunes.
Drought is common in Mediterranean-type climates. Water stress can have serious physiological consequences for plant fitness. Here we analysed the response of two alien invasive species, Senecio inaequidens DC. and S. pterophorus DC., and one native non-invasive, Senecio malacitanus Huter, in terms of photosynthesis, water relations and growth. The proportional reduction in growth as a result of water stress was smaller in S. malacitanus, followed by S. inaequidens and finally S. pterophorus. Variations in relative growth rate were related to differences in unit leaf rates, which are strongly correlated with photosynthesis. At a similar level of leaf relative water content (RWC), photosynthesis in S. inaequidens and S. malacitanus did not differ, whereas it was lower in S. pterophorus. S. malacitanus started to show a reduction in RWC later than the other species. The hypothesis that alien invaders have greater physiological tolerance to drought than native non-invaders is not supported by our results since S. malacitanus showed a more adaptive response to drought than the aliens and was also the most resistant of the three species to water shortage. Differences in invasiveness would therefore be explained by a combination of traits, including establishment capacity, competitive capacity and drought resistance, among others.
Petiole anatomy of the north-eastern Brazilian species Echinodorus glandulosus, E. palaefolius, E. pubescens, E. subalatus, E. lanceolatus and E. paniculatus were examined. All species had petioles with an epidermis composed of tabular cells with thin walls. The chlorenchyma just below the epidermis alternates with collateral vascular bundles. The interior of the petiole is filled by aerenchyma with ample open spaces or lacunas. The lacunas are bridged at intervals by plates, or by diaphragm-like linkages. There are lactiferous ducts and groups of fibres throughout the entire length of the petiole, but more frequently in the chlorenchyma. Important taxonomic characteristics for the genus Echinodorus include the shape and outline of the petiole in transversal section, the presence of winged extensions, and the number of vascular bundle arcs. Exceptions occur in E. lanceolatus and E. paniculatus, whose petioles have similar anatomic patterns. A comparative chart of the petiole anatomic characteristics analyzed is presented.
Among the plant traits that affect performance, vitality and herbivore resistance in rangeland vegetation, biomass partitioning ranks top, commonly outweighing processes at single leaves (e.g., photosynthesis, respiration). We explored the allometry of a broad sample of herbaceous species from two high elevation sites in the Andes in order to explain biomass partitioning under harsh climatic conditions and risk of biomass losses under strong camelid grazing pressure. We combined data from NW-Argentina and W-Bolivia from elevations between 4200 and 4250 m in a landscape dominated by tall Festuca orthophylla tussocks and a drought driven seasonality (rainfall only between November and March). Across 10–20 taxa per region we found less investment in leaves with a mean leaf mass fraction of only 11% and instead a massive storage in below-ground compartments (rhizomes, tap roots), particularly at the colder Argentinean site. Though grazing pressure was much greater in Bolivia, the foliage mass fraction was there larger than in Argentina. The inter-tussock space in these open, dry plains (‘pajonal’) was dominated by rosette forming species with a below-ground shoot apex and massive tap roots (70% of all species), rendering these species less sensitive to grazing and trampling. The storage organs of these species represented more than 50% of total biomass. Llamas, which represented the main vertebrate herbivore in these open plains at the Bolivian site, preferred non tap-root herbs and species with low leaf nitrogen concentration. Palatable forbs for llamas (22% of all species at the Bolivian site) only survived when nested (facilitated) in the rigid, tall Festuca orthophylla tussocks or thorny shrubs. In conclusion, these extremely high elevation rangeland herbs invest preferentially in structures for persistence (K-strategy) rather than maximizing carbon gain.
We investigated the effects of ramet defoliation frequency on clonal propagation and the patterns of biomass production and allocation on five rhizomatous species (Carex divisa Hude., Eleocharis palustris L., Juncus articulatus L., Juncus gerardii Lois. and Elytrigia repens L.). Plants were grown during an 18-week experiment in greenhouse conditions. The above ground parts of ramets were clipped following three treatments: frequent (every 2 weeks), moderate (every 4 weeks) and unclipped (control). The growth of C. divisa, J. articulatus and E. repens was strongly affected by defoliation whereas E. palustris and J. gerardii maintained a similar performance when defoliated. The latter were able to compensate for the biomass loss even after six consecutive clippings. Defoliation frequency had a significant effect on total biomass production for C. divisa, J. articulatus and E. repens while J. gerardii and E. palustris maintained total biomass production. Most of the studied species showed a decrease in clonal traits when defoliated. Clipped plants displayed fewer and shorter rhizomes. Defoliation had a strong influence in biomass production with a decrease in rhizome mass in all clipped species. A greater allocation to aerial parts and a lower to rhizomes were also detected. Moderate defoliation entailed intermediate response in 1/3 of detected significant effects of defoliation on plant traits. Finally, in the experimental conditions, E. palustris and J. gerardii were the most tolerant species to defoliation, while J. articulatus was intermediate and C. divisa and E. repens had the lowest tolerance.
The green algal lichen Placopsis pycnotheca was identified at Pia and Marinelli glaciers (Isla Grande of Tierra de Fuego, Chile) as a primary colonizer of bare soil in areas close to the front of the glacier or around small ponds created after glacier retreatment. Electron microscopy study showed that P. pycnotheca formed a thick hypothallus within which hyphae and their extracellular polymeric substances bind numerous soil particles. This structure augments water holding and soil stabilization capacities and constitutes an early stage in soil crust development. In addition, numerous cephalodia are formed within the hypothallus and subsequently develop upwards towards the thallus surface, sometimes before the formation of squamules with green algae. These anatomical and morphological strategies together with physiological properties such as the long photosynthetic activity period (measured in the laboratory) help explain its pioneering role as a colonizer and its apparently high growth rate.
Many alpine plants display a generalist pollination system where almost any available flower visitor could act as a legitimate pollinator. Co-flowering related plant species displaying a generalized pollination system can decrease their fitness due to interspecific mating. In this study, we determine the difference in diversity and composition of the pollination systems of two co-occurring species endemic to the alpine region of the Sierra Nevada (SE Spain), Erysimum nevadense Reut. and Erysimum baeticum baeticum (Heywood) Polatschek (Brassicaceae), and check for the potential role of floral and plant traits in explaining the observed differences. For this, we labeled 30 plants in two populations of each plant species located in the same area. We determined flower visitor assemblage by sampling all insects approaching the flowers and contacting the sexual organs during 60-min surveys. We found that the diversity of the pollinator assemblage was similar between the two studied wallflower species, both species showing a much generalized pollination system. However, the composition of the pollinator assemblage was different, since the flowers of E. nevadense were visited mostly by beetles and in a lesser extent by hover-flies, whereas the flowers of E. baeticum baeticum were visited mostly by ants and bees. Interestingly, flower traits varied between species, with E. nevadense displaying yellow, smaller and shallower flowers and E. baeticum baeticum displaying purple, large and deeper flowers. These findings suggest that differences in floral traits can explain the observed differences in the composition of the pollinator assemblage between both wallflower species.