Article

Effect of defoliation on silica accumulation in five tropical fodder grass species in Benin

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Abstract

This study tests the hypothesis that silica accumulation in grasses is an inducible response to grazing. It also examines if silica concentration is correlated to other leaf structural and chemical parameters. To that end, five tropical grass species (Andropogon gayanus var. bisquamulatus, Elymandra androphila, Hyparrhenia subplumosa, Panicum maximum var. C1 and Panicum maximum var. local) were subjected to various clipping treatments in cultivation. Clipping was found to increase silica concentration in three of five species (blades and sheaths), but this response was rarely strong and varied with clipping frequency. Defoliation also caused other changes in leaf structure, i.e. production of leaves with juvenile characters including higher Specific Leaf Area (SLA), higher Relative Water Content (RWC), and lower carbon concentration. This suggests that enhanced silica accumulation is not a very specific response to defoliation. Silica concentration also varied among species and was correlated to leaf structure and chemical composition. Andropogon gayanus var. bisquamulatus had the lowest silica concentration and the highest carbon concentration, while Panicum maximum showed the opposite combination of traits, suggesting that species with more sclerified leaves might be less silicified. Positive correlations between silica content and RWC, soluble ash, and SLA suggest that variation in silica accumulation among species and treatments might be related to transpiration rate.

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... [13]) or species-specific (e.g. [14]) Si uptake responses to grazing. Emerging evidence suggests that Si uptake can vary with soil Si availability, root and shoot biomass, and transpiration rate [15,16], yet there is particular controversy over the extent to which induction responses can be mediated by changes in soil water availability and transpiration rate [17]. ...
... Instead, M. stipoides responded to clipping by storing Si in its roots and shoots, indicative of an induced defensive response, which was consistent across all watering regimes. Kindomihou et al. [14] also identified a Si-uptake response to simulated grazing in three of five tropical fodder grass species, whereas KM Quigley and TM Anderson [13] identified no effects of simulated grazing on Si accumulation in two Serengeti grasses, suggesting that Si uptake responses are contingent upon plant identity and/or grazing intensity. Grasses that respond to wounding by increasing Si uptake likely involve active processes that are regulated at the gene level, as demonstrated by E McLarnon, S McQueen-Mason, I Lenk and SE Hartley [16]. ...
Article
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Background Grasses are hyper-accumulators of silicon (Si) and often up-regulate Si following herbivory. Positive correlations exist between Si and plant water content, yet the extent to which Si uptake responses can be mediated by changes in soil water availability has rarely been studied and never, to our knowledge, under field conditions. We used field-based rain-exclusion shelters to investigate how simulated grazing (shoot clipping) and altered rainfall patterns (drought and elevated precipitation, representing 50% and 150% of ambient precipitation levels, respectively) affected initial patterns of root- and shoot-Si uptake in a native Australian grass (Microlaena stipoides) in Si-supplemented and untreated soils. Results Si supplementation increased soil water retention under ambient and elevated precipitation but not under drought, although this had little effect on Si uptake and growth (tiller numbers or root biomass) of M. stipoides. Changes in rainfall patterns and clipping had strong individual effects on plant growth and Si uptake and storage, whereby clipping increased Si uptake by M. stipoides under all rainfall treatments but to the greatest extent under elevated precipitation. Moreover, above-ground–below-ground Si distribution only changed following elevated precipitation by decreasing the ratio of root:shoot Si concentrations. Conclusions Results highlight the importance of soil water availability for Si uptake and suggest a role for both active and passive Si transport mechanisms. Such manipulative field studies may provide a more realistic insight into how grasses initially respond to herbivory in terms of Si-based defence under different environmental conditions. Electronic supplementary material The online version of this article (10.1186/s12898-018-0208-6) contains supplementary material, which is available to authorized users.
... aji et al. 2017). Recently, the SPAD-502 Leaf Chlorophyll Meter (Konica Minolta Inc.) was proposed for quick and in-situ quantifying chlorophyll. Nevertheless, some previous studies pointed out that variation in leaf thickness causes a variable relationship between SPAD readings and leaf structure, which is correlated with silica fertilizer levels (Kindomihou, et. al. 2006) and then an alternative method of quantifying chlorophyll is thus required. ...
Article
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Dimensionality reduction Zizania latifolia Hyperspectral Machine learning The amount of chlorophyll in a plant useful to indicate its physiological activity and then changes in chlorophyll content have been used as a good indicator of disease as well as nutritional and environmental stresses on plants. Chlorophyll content estimation is one of the most applications of hyperspectral remote sensing data. The aim of this study is to evaluate dimensionality reduction for estimating chlorophyll contents from hyperspectral reflectance. Random Forest (RF) has been applied to assess biochemical properties such as chlorophyll content from remote sensing data; however, an approach integrating with dimensionality reduction techniques has not been fully evaluated. A total of 200 Zizania latifolia leaves with 5 treatments from Shizuoka University field were measured for reflectance and chlorophyll content. then, the regression models were generated based on RF with three dimensionality reduction methods including principal component analysis, kernel principal component analysis and independent component analysis. This research clarified that PCA is the best method for dimensionality reduction for estimating chlorophyll content in Zizania Latifolia with a RMSE value of 5.65 ± 0.58 μg cm-2 .
... The above inconsistencies may simply stem from the lack of sufficient statistical power of these analyses, since the longest timeseries analyses lasted between 3 (Soininen et al., 2013) and 4 years (Wieczorek, Zub, et al., 2015) and are therefore based on a small number of degrees of freedom. Long-term studies, able to capture the time course of the putative plant-herbivore association, are particularly needed because changes in silicon levels in plant tissues are not only due to grazing but are also responsive to abiotic factors, chiefly water availability, which drives silicon absorption in the form of silicic acid (Brightly et al., 2020;Faisal et al., 2012;Kindomihou et al., 2006;Raven, 1983;Sangster et al., 2001). The effect of the water on the induction of silicon in plants has been indirectly demonstrated in sedge leaves in European ecosystems (Wieczorek, Zub, et al., 2015) and in leaves of two African grass species (Quigley & Anderson, 2014). ...
Article
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• Accumulation of silica (Si) by plants can be driven by (1) herbivory pressure (and therefore plant–herbivore interactions), (2) geohydrological cycles, or (3) a combination of (1) and (2), with (1–3) possibly affecting Si concentration with a 1-year delay. • To identify the relative significance of (1–3), we analyzed the concentration of Si in fibrous tussock sedge (Carex appropinquata), the population density of the root vole (Microtus oeconomus), and the groundwater level, over 11 years. • The largest influence of autumn Si concentration in leaves (Sileaf) was on the level of the current-year groundwater table, which was positive and accounted for 13.3% of its variance. The previous year's vole population density was weakly positively correlated with Sileaf, and it alone explained 9.5% of its variance. • The only variable found to have a positive, significant effect on autumn Si concentration in rhizomes (Sirhiz) was the current-year spring water level, explaining as much as 60.9% of its variance. • We conclude that the changes in Si concentration in fibrous tussock sedge are predominantly driven by hydrology, with vole population dynamics being secondary. • Our results provide only partial support for the existence of plant–herbivore interactions, as we did not detect the significant effects of Si tussock concentration on the vole density dynamics. This was mainly due to the low level of silicification of sedges, which was insufficient to impinge herbivores. • Future studies on plant–herbivore interactions should therefore aim at disentangling whether anti-herbivore protection is dependent on threshold values of herbivore population dynamics. Furthermore, studies on Si accumulation should focus on the effect of water-mediated Si availability.
... Perhaps for these reasons some grass species do not show Si accumulation following herbivory (Kindomihou et al., 2006), whereas others require high frequency and intensity of damage for Si induction (Massey et al., 2007b;Reynolds et al., 2012). Unsurprisingly, many other functions for Si have been identified in addition to protecting plants from herbivory, such as conferring resistance to pathogens and alleviating the impacts of several abiotic pressures, for example, water and temperature stress and nutrient deficiency (Cooke & Leishman, 2011, and references therein). ...
Article
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1. Herbivore-induced changes in both leaf silicon-based defence and nutrient levels are potential mechanisms through which grazers alter the quality of their own grass supply. In tundra-grasslands, herbivores have been shown to increase nutrient contents of grasses; yet, it is an open question whether they also increase grass silicon-based defence levels. Here, we asked if, and to what extent, herbivores affect silicon-content and silicon:nutrient ratios of grasses found in tundra-grasslands. 2. We performed an herbivore-interaction field-experiment spanning four tundra-grassland sites. At each site, we established reindeer-open and reindeer-exclusion plots in tundra-patches that had been disturbed or not by small rodents during the previous winter, for a total of 96 plots. We randomly collected over 1150 leaf samples of inherently silicon-rich and silicon-poor grass species throughout a growing season and analysed silicon, nitrogen, and phosphorus contents of each leaf. 3. Small-rodent winter disturbance did not affect grass silicon-content, but increased grass quality (i.e. lowered silicon:nutrient ratios) by enhancing nutrient levels of both silicon-rich (+20-22%) and silicon-poor (+26-34%) grasses. Reindeer summer herbivory increased the quality of silicon-rich grasses by decreasing their silicon-content (−7%). However, the two herbivores together offset both these quality increments in silicon-rich grasses, thus reducing their quality towards the level of those found in absence of herbivores and further enhancing their silicon:nutrient ratios (+13-22%) relative to silicon-poor grasses. 4. Synthesis. We provide the first community-level, field-based assessment of how herbivory-driven changes in both leaf silicon-based defence and nutrient levels alter grass-forage quality in tundra-grasslands. Herbivores did not promote a net silicon accumulation in grasses, but rather enhanced their overall quality. Yet, the magnitude of these quality increments varied depending on the herbivore(s) involved and differed between silicon-rich and silicon-poor grasses. Such differential herbivory-induced changes in grass quality between and within tundra-patches may mediate plant-herbivore interactions by altering herbivore forage patterns and food choices. In tundra-patches utilised by both herbivores, the quality of silicon-rich grasses was further decreased relative to that of silicon-poor grasses. This could provide an advantage against herbivory, potentially being one of the pathways through which tundra-grassland vegetation states dominated by silicon-rich grasses are maintained by herbivores.
... The above inconsistencies may simply stem from the lack of sufficient statistical power of these analyses, since the longest of them lasted between three (Soninen et al., 2012) to four years (Wieczorek et al., 2015a) and are therefore based on a small number of degrees of freedom. Long-term studies, able to capture the time-course of the putative plant-herbivore association, are particularly needed because changes in silicon levels in plant tissues are not only due to grazing, but are also responsive to abiotic factors, chiefly water availability, which drives silicon absorption in form of silicic acid (Raven, 1983;Sangster, Hodson, & Tubb, 2001;Kindomihou, Sinsin & Meerts, 2006;Faisal et al., 2012;Brightly et al" 2020). The effect of the water on the induction of silicon in sedge leaves has been indirectly demonstrated in European (Wieczorek et al., 2015a) and in African ecosystems (Quigley & Anderson, 2014). ...
Preprint
1. Silicon mediated plant–herbivore interactions have gained increasing recognition and have now been studied in a wide range of species. Many studies have also considered accumulation of Si by plants as a process largely driven by geo-hydrological cycles. 2. To identify factors driving the water - plant Si - herbivore nexus we analysed the concentration of Si in fibrous tussock sedge (Carex appropinquata), the population density of the root vole (Microtus oeconomus) and the ground water level, over 11 years. 3. The largest influence of autumn Si concentration in leaves (Sileaf) was the level of the current year’s ground water table, which accounted for 13.3% of its variance. The previous year’s vole population density was weakly positively correlated with Sileaf and alone explained 9.5% of its variance. 4. The only variable found to have a positive, significant effect on autumn Si concentration in rhizomes (Sirhiz) was the current year spring water level explaining as much as 60.9% of its variance. 5. We conclude that the changes in Si concentration in fibrous tussock sedge are predominantly driven by hydrology, with vole population dynamics being secondary. Our results provide only partial support for the existence of plant-herbivore interactions, as we did not detect the significant effects of Si tussock concentration on the vole density dynamics. This was mainly due to low level of silification of sedges, which was insufficient to impinge herbivores. Future studies on plant–herbivore interactions should therefore mainly focus on identification of mechanisms and conditions allowing plants to accumulate silica at the levels sufficient to act as an anti-herbivore protection.
... However, the light transmittance of a leaf is also influenced by leaf structure, water content and leaf pigment distribution (Padilla et al. 2018). Portable chlorophyll meters were shown to be unsuitable for quantifying chlorophyll content in Manchurian wild rice (Zizania latifolia) since it is silica-rich, and silica content is correlated with leaf structure (Kindomihou et al. 2006). ...
Article
Hyperspectral remote sensing is frequently used to monitor chlorophyll content, an important characteristic for assessing photosynthetic ability, health and defence against a variety of degenerative diseases. To obtain hyperspectral data, field portable spectroradiometers, such as Ocean Optics Hyperspectral Vis-NIR spectroradiometers and Analytical Spectral Devices FieldSpec series, have been widely used. The development of an affordable hyperspectral remote sensing system would be advantageous. Highly sensitive, affordable and cost-effective finger-tip size spectrometers have recently been released. In this study we investigate the potential of hyperspectral data obtained from such a compact spectrometer (C12880MA-10, Hamamatsu Photonics) for estimating chlorophyll content in Zizania latifolia. We also tested the efficacy of five pre-processing techniques (first derivative reflectance, continuum-removal transformation, de-trending, multiplicative scatter correction and standard normal variate) in conjunction with five machine learning algorithms.
... Moreover, induction of plant silica by herbivory is not consistently observed in modern studies (Quigley and Anderson 2014). Many factors play a role in whether Si uptake is induced, including damage thresholds (Reynolds et al. 2012) and plant species identity (Kindomihou et al. 2006, Garbuzov et al. 2011, Soininen et al. 2013, Hartley 2015). An alternative hypothesis for grass Si accumulation is that heavily silicified leaves are a response to resource-poor, open environments into which grasses expanded in the Miocene (e.g., Coughenour 1985, Edwards andSmith, 2010) and that the antiherbivore benefits of silica are secondary. ...
Article
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Grasses accumulate high concentrations of silicon (Si) in their tissues, with potential benefits including herbivore defense, improved water balance, and reduced leaf construction costs. Although Si is one of the most widely varying leaf constituents among individuals, species and ecosystems, the environmental forces driving this variation remain elusive and understudied. To better understand relationships between environmental factors and grass Si accumulation, we analyzed foliar chemistry of grasses from 17 globally distributed sites where nutrient inputs and grazing were manipulated. These sites span natural gradients in temperature, precipitation, and underlying soil properties, which allowed us to assess the relative importance of soil moisture and nutrients across variation in climate. Foliar Si concentration did not respond to large mammalian grazer exclusion, but significant variation in herbivore abundance among sites may have precluded the observation of defoliation effects at these sites. However, nutrient addition consistently reduced leaf Si, especially at sites with low soil nitrogen prior to nutrient addition. Additionally, a leaf‐level tradeoff between Si and carbon (C) existed that was stronger at arid sites than mesic sites. Our results suggest soil nutrient limitation favors investment in Si over C‐based leaf construction and that fixing C is especially costly relative to assimilating Si when water is limiting. Our results demonstrate the importance of soil nutrients and precipitation as key drivers of global grass silicification patterns.
... bisquamulatus, Elymandra androphila, Hyparrhenia subplumosa, Panicum maximum C 1 and Panicum maximum. Silica was correlated negatively with carbon and positively with relative water content, nitrogen, soluble ash and specific leaf area [37]. Furthermore, leaf traits differed with rainfall and species from drier sites showed lower SLA and higher N, as a response to stronger average irradiance in arid habitats [38]. ...
Article
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Silica (SiO 2) in forage grasses has been found in reducing cell-wall digestibility. This study investigates whether: (i) the seasonal variability affects the silica and minerals accumulation and forage values of leaves of R. cochinchinensis and (ii) silica concentration is correlated with minerals and fodder value. In an itchgrass population selected in the W Biosphere Reserve, leaves were collected on 90 marked plants from May to October 2003 and 2004, at 15 days intervals except May, June and October. Some 300 g of fresh blades from the 3 rd most recently expanded leaves were oven dried and analyzed for dry mass, SiO 2, ash, N, Na, Ca, P, K, and Mg. Digestible Nitrogen Matter (DNM) and Fodder Energetic Value (FEV) were calculated using the Demarquilly formula. Apart from SiO 2, ash and forage value, data were log-transformed to restore homoscedasticity before statistical analyses. SiO 2 ranges from 5.69 % to 9.95 %, i.e. varying 1.4 fold between May and October, reaching 1.75 fold at mid-September. SiO 2 is positively related to Ca but negatively to K, P, N, DNM and FEV. The negative correlations suggest that SiO 2 concentration in R. cochinchinensis could be reduced with a significant increase in energy and accumulation of important nutrients such as N, P and K. Therefore, leaf silicification and nutritive value relationship should be conclusive in the case of itchgrass.
... It is generally expected that when exposed to stronger herbivory, plants will be better defended due to induction or strengthening of existing defences (in the short run), and/or natural selection (in the long run), and this should also apply for Si if it plays an antiherbivory role [22][23][24][25][26]. Induction of increased Si uptake and accumulation following herbivory damage has been observed in several grass species, exposed to vertebrate [1,29] and invertebrate [29,30] herbivores, as well as following artificial leaf clipping [22,23,29,31]. Nonetheless, this induction was not observed in some laboratory experiments that were conducted on other grass species exposed to locusts [32] and artificial clipping [29,31,[33][34][35], possibly because exposure periods were too short to initiate a Si uptake response or to allow Si accumulation [29]. In their literature survey, Quigley and Anderson [33] show that although increased Si uptake and deposition is commonly observed in plants that are exposed to real herbivores, exceptions are not rare. ...
Article
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Purpose When studying the effects of environmental variables on plant Si contents, results of laboratory and field experiments do not always agree with each other. However, new insights into the roles silicon plays in plant life can be gained if both approaches are integrated. Methods Experimental and natural-habitat studies of the effects of water availability and herbivory on plant silicon contents are reviewed and integrated. Results Although higher water availability is expected to have a positive effect on plant silicon contents, naturally-growing plants often have high silicon contents when grown under drought conditions. Likewise, although experimentation suggests that herbivory has a positive effect on plant silicon contents, such a correlation is not often found in nature. Conclusions Stronger effects of multiple environmental variables or selection in favour of constitutive silicon uptake and deposition as protection from drought and grazing stresses are the reasonable causes of discrepancies between experimental and natural-habitat studies.
... Two studies have explored respectively the effects of defoliation and moisture stress on silica accumulation in tropical grasses, but the covariations pattern between SiO 2 concentration and leaf traits (i.e. SLA, RWC, soluble ash, carbon) was not strongly conclusive (Kindomihou et al., 2006;2010). Until now, there has been no attempt to correlate variation in SiO 2 concentration with variation in the structural, anatomical and functional traits of the leaves of grasses. ...
Article
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: Variation in silica content was examined in relation to foliar structure, chemical composition and anatomy of nine perennial tropical fodder grass species cultivated under uniform conditions. The following parameters were determined: silica (SiO2) and soluble ash (SA) in blades and sheaths; carbon, relative water content (RWC) and specific leaf area (SLA) of blades only. Proportions of different tissues were determined by image analysis of transverse sections of leaves. There was a large variation in SiO2 concentration among species (range 2.4 –13.6%). SiO2 and SA were positively correlated in blades and sheaths. All other traits also showed significant variation among species. The nine species also showed contrasting anatomy. A significant pattern of covariations existed between SLA, RWC and proportion of parenchyma. High SiO2 concentrations were generally associated with sclerophylly (i.e. a high proportion of vascular tissue and sclerenchyma, and a low SLA and RWC). Therefore, the results did not support the hypothesis that SiO2 might represent an alternative mechanism of structural support without carbon cost. Keywords: Grass, silicification, anatomy, leaf structure, specific leaf area
... Although silica has long been thought to be a potentially inducible defence mechanism in grasses (McNaughton and Tarrants 1983), the main mechanism by which silica was thought to deter herbivores was a constitutive one, namely increased abrasion and physical resistance by phytoliths (Reynolds et al. 2009). Attempts to demonstrate that silica is inducible by experimental damage have produced conflicting results (Kindomihou et al. 2006), possibly because many studies use artificial defoliation, which does not cause the same defence induction response as real herbivory (Massey et al. 2007a). This distinction between plant responses to real and artificial herbivory is long established (e.g. ...
Article
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Some grass species mount a defensive response to grazing by increasing their rate of uptake of silica from the soil and depositing it as abrasive granules in their leaves. Increased plant silica levels reduce food quality for herbivores that feed on these grasses. Here we provide empirical evidence that a principal food species of an herbivorous rodent exhibits a delayed defensive response to grazing by increasing silica concentrations, and present theoretical modelling that predicts that such a response alone could lead to the population cycles observed in some herbivore populations. Experiments performed under greenhouse conditions revealed that the rate of deposition of silica defences in the grass Deschampsia caespitosa is a time-lagged, nonlinear function of grazing intensity and that, upon cessation of grazing, these defences take around one year to decay to within 5 % of control levels. Simple coupled grass-herbivore population models incorporating this functional response, and parameterised with empirical data, consistently predict population cycles for a wide range of realistic parameter values for a (Microtus) vole-grass system. Our results support the hypothesis that induced silica defences have the potential to strongly affect the population dynamics of their herbivores. Specifically, the feedback response we observed could be a driving mechanism behind the observed population cycles in graminivorous herbivores in cases where grazing levels in the field become sufficiently large and sustained to trigger an induced silica defence response.
Article
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Variation in and distribution of cell wall constituents such as cellulose, lignin and silica in the leaf blade, leaf sheaths and stems, and roots were investigated in 47 indica and 6 japonica cultivars of rice (Oryza sativa L). Cellulose, lignin, and silica were the most abundant components. Lignin and cellulose increased from the leaves to the roots, but silica decreased exponentially, with an almost insignificant amount found in the roots. The absorbed silica was mainly accumulated in the shoots, particularly in the leaf blade. A highly significant negative correlation was found between silica and lignin, and between silica and cellulose in the leaf blade. DMRT showed highly significant variations in the cell wall constituents among the cultivars. Cell wall modifications during biotic and abiotic stresses are also discussed. There is need for further research on the localization of cell wall constituents and the mechanism of cellulose and lignin contributing to tolerance.
Article
Oat plants, Avena sterilis L., were grown on soils in which the concentration of monosilicic acid in the soil solution, that is the level of supply of silica, ranged from 7 to 67 ppm SiO 2. Analyses at intervals throughout the growing period showed that the level of supply affected the amount and concentration of silica in the plant but not the pattern of its distribution among the parts. At maturity the caryopsis contained only 0.5 to 0.8 per cent of the total silica in the tops while the other parts of the inflorescence contained 40.7 to 41.3 per cent. The leaves (blade and sheath) contained 42.5 to 45.0 per cent of the total silica and the stems contained 7.8 to 10.9 per cent; the remainder was present in small sterile tillers. The concentration of silica in the dry matter was highest in the palea, lemma glumes, awn, and leaves. Among the leaves, the flag leaf had the highest silica content, both in terms of concentration in the dry matter and amount per leaf. The distribution of silica along a leaf followed a hyperbolic curve, the concentration being highest at the apex and lowest at the base of the blade. The chemistry of silica and the pattern of its distribution in the tops suggest that monosilicic acid and water move concomitantly in the transpiration stream and that solid silica is deposited in greatest quantities in those parts and regions from which water is lost in greatest quantities.
Chapter
Publisher Summary This chapter discusses several aspects of silica in the chain from soil through plant to animal. Soil solution is the immediate source of the silica that is always absorbed by soil-grown plants. The factors affecting the silica content of plants include: soil pH and the content of iron and aluminum oxides present in plants. Plants take up different amounts of silica, according to their species. Silicon sometimes has a beneficial effect through alleviating manganese toxicity. Silicon alters the distribution of manganese in the leaf tissues, thereby preventing it from collecting into localized areas that become necrotic. The presence of silica in pasture plants ensures that grazing ruminants ingest rather large amounts of silica, most of which is in the solid form. Apart from slight dissolution, this silica is unchanged in passing along the alimentary tract and its known effects on the animal are physical or mechanical. The dissolved silica that is absorbed from the alimentary tract is carried to the kidney and excreted in the urine. Although it is normally excreted readily, the silica is sometimes deposited to form calculi or uroliths that can cause serious economic loss.
Article
In a study of the relation of silica content of grass and grasslike species to some aspects of the rangeland environment, significant differences were found between years and between species within years. It was not possible to relate silica content to location or to detect any consistent relation between silica content and annual precipitation, either current or long-term, or between silica content and April–September or May–June rainfall. Seasonal trends in percentage silica and in percentage sand plus silica are shown.
Article
(1) The contents of water, crude protein, cell contents, cell wall, lignocellulose, hemicellulose, cellulose, lignin, silica, ash and nineteen elements, and their variation with season, soil type and grazing intensity, were examined in East African savanna grasses. (2) As the growing season progressed, there was a systematic decline in nutritional value at all sites, as indicated by fibre properties. However, fibre nutritional values were at all times higher in areas of high herbivore use intensity (HUI) than of low HUI. There were few differences in fibre properties between soil types. (3) In contrast, there were marked differences in element contents between samples from different soil types, and relatively less variation in element contents with time and HUI. Much of the between-site variation was due to different plant species compositions. (4) These contrasting patterns of variation resulted in poor correlations between fibre properties and element contents. (5) The data suggest that grazing animals can regulate plant nutritional properties by increasing soil nutrient levels and by changing species composition. Their activities may contribute to the development of localized areas of nutritional sufficiency in the absence of intrinsic soil differences.
Article
Evaluates the hypothesis that silicification of grass parts is a product of herbivore-mediated natural selection and that leaf silicification represents an inducible defense against herbivores, using Agropyron smithii and Schizachyrium scoparium.-from Authors
Article
Silicon in forage reduces dry matter digestibility and may reduce grazing preference. Two studies were conducted with the following objectives: (1) to evaluate a method of determining grazing preference, and (2) to characterize the distribution and solubility of silicon in 31 accessions of C-3 grasses and relate these traits to grazing preference and estimated forage digestibility. Forage samples were clipped at the beginning of each 7 to 10-day grazing period corresponding to 6 phenological stages of the Agropyron sp. Samples were washed and analyzed for acid detergent fiber (ADF), neutral detergent fiber (NDF), and silicon in ADF and NDF residues. Leaf silicon concentrations increased from the vegetative to seed-ripe stage. Genera were aligned into 3 groups based on the increase in leaf silicon concentration with advancing phenological age. Silicon concentrations in leaves of Agropyron, Pseudoroegneria, and Thinopyrum increased at nearly twice the rate of those in Critesion, Hordeum, Leymus and Psathyrostachys. Elymus leaves contained higher concentrations of silicon at the vegetative stage than the other groups, but the accumulation rate was intermediate. About 32% of total leaf silicon remained in NDF and 76% in ADF residues at the vegetative stage. These insoluble portions of silicon increased with aging. Preference was positively related to estimated dry matter digestibility at boot and anthesis, but was not related to fiber or silicon measurements. Leaf harshness was negatively related to preference at seed-ripe stage. Further progress in characterizing the role of silicon in C-3 forage grasses should be possible by studying a representative species from each group.
Article
Samples of the principal forage species of the alpine tundra of the southeastern Canadian Cordillera were analyzed for crude protein, calcium, phosphorus, ash, silica, and cellulose. Digestibility coefficients of cellulose were determined in vitro. Seven grass and grass-like species at five stages of growth and 12 herbaceous and shrubby species at three stages of growth were studied. Percentages of crude protein and phosphorus of all species decreased with advancing maturity while calcium and cellulose contents increased. In vitro digestibility coefficients decreased with advancing maturity. High percentages of crude protein and phosphorus, a low calcium to phosphorus ratio, and a high percent digestibility of cellulose were found in alpine vegetation at all stages of growth. The vegetation provides a nutritious forage for bighorn sheep (Ovis canadensis) during the summer.
Article
To study the importance of silica as an anti-herbivore defense, two brome grasses were grown hydroponically to control silica, nitrogen, phosphorus, and potassium content and subsequently offered to the prairie vole, Microtus ochrogaster, in food choice experiments. Feeding experiments used two designs. In the first design, voles were presented a choice of a standard grass having intermediate silica content, and another grass with high or low silica and nitrogen content. In the second design, voles were presented with one of eight pairwise combinations of grasses. Voles consumed less grass of high silica content in both experiments, suggesting that silica acts as an effective deterrent to mammalian herbivores.
Article
A controlled environment experiment was performed on plants from 2 Agropyron sndthii Rydb. (western wheatgass) populations to determine how defollltion at iweek intervals and graxing bis-tory affected total silicon accumulation in shoots, and how Si was distributed within the plant. Plants were collected from a heavily grazed, IO-year-old prairie dog colony and an ungazed, 40-year-old exciosure at Wind Cave National Park, South Dakota. After 18 weeks, the total amount of Si accumuhtted in shoots was similar in plants from both populations, regardless of whether or not the plants were clipped. However, the Si concentration in shoots was greater in nondefoliated than defoliated phmts of both populations because of Si dilution resulting from greater shoot production in defoliated pIants. In both populations, roots and leaf blades had the highest Si concentrations, rhizomes had the lowest concentra-tions, and sheaths, crowns, and belowground stems had interme-diate concentrations.
Article
Breeding and selection for higher transpiration efficiency (W) has been hampered by tedious and costly methodology. Rapid and less costly methods are needed for screening W in plant improvement programmes. We report the relationship of ash, silicon (Si) concentration, and Si uptake to W in crested wheatgrass (Agropyron desertorum Fischer ex Link] Schultes), an important C3 range grass in western North America. Clones of crested wheatgrass were grown under three water levels in a field rainout shelter and as potted plants under two water levels in the field and greenhouse. Ash and Si concentrations were compared to previously determined values of shoot mass, transpiration, W, and carbon isotope discrimination (Δ). Ash and Si concentrations were not consistently related to Δ and W across all environments; however, ash concentration was positively correlated with Δ (r=0.69**, df= 22) and negatively correlated with W (r= -0.61**, df =22) in the well-watered field environment. Across all environments and studies, the ranges in the coefficients of variation (CV, %) for clonal means were: W, 4-15; Δ, 1-4; ash concentration, 6-14; Si concentration, 13-30; and Si uptake, 21-33. The generally lower CV for W, Δ, and ash concentration suggest that these traits were more repeatable than Si concentration or uptake. Although a consistent relationship was not observed between Si and W and between ash and W, the correlations of ash and W from the well-watered field environment were encouraging. In view of the low cost for ash analysis, we conclude that further research is needed to evaluate the potential of ash as a criterion in selecting for improved W, particularly during the early phases of a breeding programme when large populations are usually involved. Later selections could be based on the more precise and accurate, but costly, Δ analysis.
Article
Certain physicochemical stresses affect the susceptibility of plants to insects. The objective of this study was to determine the effects of different levels of Fe, Si, and Al on the establishment of Sogatella furcifera (Horvath) on resistant IR2035-117-3 (IR2035) and susceptible Taichung Native 1 (TN1) rice (Oryza sativa L.) cultivars under glasshouse conditions in natural daylight of 12 h, 29/21 o C (day/night), and minimum 70% relative humidity(.)
Article
The presence of silica (SiO2) has been reported as significantly affecting the nutritional value of forages. This study was conducted to determine the SiO2 concentration in forage samples collected monthly from 2-ha paddocks of ungrazed tall fescue (Festuca arundinacea Schreb.) and ‘Coastal’ bermudagrass (Cynodon dactylon (L.) Pers.) as they matured, and to determine the monthly SiO2 concentrations of vegetative tall fescue, tall fescue-‘Ladino’ clover (Trifolium repens L.), orchardgrass (Dactylis glomerata L.), orchardgrass-Ladino clover, Coastal bermudagrass, and stockpiled tall fescue which were incorporated into four grazing systems. Samples representative of forage grazed by yearling beef heifers were collected monthly from caged areas to determine the SiO2 levels. The SiO2 concentrations ranged from 0.30 to 2.65% in dry matter and exhibited variations between species and from month to month within a given species. Silica accumulated rapidly in the forage tissue early in the growing season and thereafter concentrations remained relatively constant. Actively growing forages maintained in a vegetative state by grazing did not exhibit appreciable monthly differences in SiO2 concentration. Increases in SiO2 concentration were noted during winter dormancy. These results indicate the need for further study of the hypothesis that SiO2 can be used to reveal the nutritive value of a forage, particularly the nutritive value of grazed forages. Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © . .
Article
Wear is a predominant stress affecting growth of turfgrass. Silica, which is deposited in epidermal cells of leaf blades, may potentially increase rigidity of a turfgrass stand. This research was undertaken to determine if application of silicon (Si) would enhance turfgrass wear tolerance, growth, and quality. This research was conducted during two consecutive field trials in 1998 on two greens-quality ecotypes established on a native Applying (Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Silica was applied to two ecotypes of seashore paspalum (Paspalum vaginatum Swartz.) as potassium (K) silicate at two foliar rates (1.1 and 2.2 kg Si ha) and as a soil drench rate of 22.4 kg Si ha. Potassium chloride, which added K at the amount in the drench treatment (15.6 kg K ha), was also applied as a K check. Best turf quality responses on nonwear plots resulted from highest rates of Si application as well as from the K only treatment. A positive association was found between leaf tissue K concentration and turf quality scores, while increasing Si concentration reduced quality scores. Wear tolerance was enhanced either by K alone or by the high rate of Si and K. Turf growth was not affected by fertility treatments. Enhanced wear tolerance, due to application of either K alone or Si and K, reduced wear injury from 35% to 14% (K) or 20% (Si and K) averaged across both studies. This may be attributed to increased leaf turgor pressure or reduced total cell wall (TCW).
Article
summaryPrevious experiments have shown that leaf specific mass (LSM: the ratio of leaf dry mass lo area) was lower and leaf water content (LWC) was higher in annuals than in perennials, differences that are more generally found between fast-and slow-growing species. Leaf transverse sections of seven annual-perennial pairs of grass species grown in the laboratory were analyzed to elucidate the anatomical bases of these differences.Leaf thickness was similar in annuals and perennials, but leaf density was significantly higher in perennials. The proportion of the leaf volume occupied by mesophyll was higher in annuals, at the expense of the three other tissues (i.e. epidermis, sclerenchyma and vascular tissues). The cross-sectional area of mesophyll cells was higher in annuals than in perennials, but epidermal cell size was similar for both life-forms.The ranges of LSM (23.1–49.5 g m −2) and LWC (0.70–0.86 g g−1) displayed by the 14 species were large enough to examine the general relationships between these two parameters and various anatomical characters. LSM was significantly correlated with leaf density, but not with leaf thickness. The anatomical character that best explained interspecific differences in LSM was the volume of cell walls per unit leaf area (approximated by the sum: sclerenchyma + vascular tissues (including its living component) + cell wall components of mesophyll and epidermis). LWC was found to depend on leaf density, and interspecific differences in this parameter were best explained by the proportion of mesophyll protoplast (i.e. proportion of mesophyll minus proportion of mesophyll occupied by cell walls) in the transverse sections.The physiological and ecological implications of these findings are discussed in terms of a trade-off between leaf productivity and persistence.
Article
Shear strength and grinding resistance of leaves of four species of Brachiaria collected at 4 and 6 weeks of re-growth were determined using modifications of techniques described in the literature. Physical attributes of strength were correlated with analyses of plant cell wall constituents and in vitro digestibility (IVDMD). Methodologies were compared to determine which was best able to describe the physical strength of the samples. Both the grinding resistance and the shear strength technique were able to detect differences between Brachiaria species and ages of re-growth. However, the shear strength technique was more sensitive for identifying physical strength differences at the species level. Both techniques identified the same species (Brachiaria ruziziensis) as the softest, but subsequent ranking of species by the shear strength technique depended on the leaf morphological characteristic used to express the results. Shear strength measurements were correlated to the cell wall components and IVDMD of the samples. The highest correlations were obtained for acid detergent fibre (ADF), cellulose and lignin with shear strength measurements expressed per unit of leaf width (kg/cm), per unit of linear density (kg/gcm) and for the raw shear strength data (kg). Grinding resistance was not correlated to the chemical composition and IVDMD of the samples. Preferential use of the shear strength technique is suggested since it provides a sensitive measure of the physical strength of forage leaf tissue and is a suitable indicator for identifying nutritive quality differences between Brachiaria species.
Article
The two major mechanical defences of plants are toughness and hardness. These have different material causes and ecological functions. In any non-metal, high toughness is achieved by composite construction (i.e. by an organized mixture of components). The primary source of toughening in plants is the composite cell wall (cellulosic microfibrils set in a hemicellulose and, sometimes, lignin matrix), with a toughness of 3.45kJm−2, which is ten-times the probable toughness of its individual components if they could be isolated. The toughness of most plant tissues is roughly proportional to the volume fraction of tissue occupied by cell wall (Vc) and, compared to animal tissues and non-biological composites, is very low. High toughness in plant cells is not produced by the walls themselves, but by their plastic intracellular collapse. This is a truly cellular toughening mechanism, one of the most potent ever discovered by materials scientists, depending on an elongate cell shape with microfibrils directed uniformly at a small angle to the cellular axis. Only ‘woody’ cells, tracheids and fibres, have this framework and only in the S2 layer of their secondary wall. Despite this non-optimum configuration, toughness is elevated by this mechanism ten-times above that due to cell wall resistance alone. The effectiveness of toughness in preventing herbivory is indisputable, but largely indirect due to confusion over a false equivalence between nutritional ‘fibre content’ and toughness. In contrast, generalized hardness requires high density. If hardness is due to high Vc, this conflicts with ‘woody’ toughness because there is then no lumen for cell walls to collapse into. Thus, dense seed shells may be brittle (i.e. low toughness) even if built from fibres. However, solid cell wall is not very hard. Instead, high hardness in plants is associated with amorphous silica and is always localized. The efficacy of hardness is more difficult to evaluate than toughness because some animals specialize in coping with it.
Article
1. It is common practice to express measurements of leaf composition and morphology using dry mass as a basis. Relationships established using those measurements are difficult to interpret because the leaves may have different liquid contents or fractional air space. 2. In a previous theoretical investigation, we showed that the liquid content of leaves was important and the following hypotheses were proposed: (1) the mass of nitrogen per unit mass of liquid is relatively constant within leaves and (2) the surface area to volume ratio of leaves is proportional to leaf liquid content. That investigation also proposed that fractional air spaces were important, because they confer plasticity in construction, with apparently minimal cost in terms of CO2 uptake. In this paper we use a set of comprehensive measurements to address the above hypotheses and to assess whether the fractional air space does vary in a consistent manner. 3. We found that the specific gravity of the non-gaseous fraction in the leaves we measured was within the range ≈ 0·9–3·0 and increased with the fractional air space in a regular manner. Consequently, the specific gravity varied over a much smaller range (≈ 0·9–1·4). The specific gravity at high liquid contents approached unity but at low liquid contents it was variable. 4. The mass of nitrogen (N) per unit mass of liquid was found to be relatively constant (0·01 ± 0·003, n = 76). 5. The surface area to volume ratio was positively correlated with the liquid content (R2 = 0·87, n = 27). 6. The mass of carbon (C) per unit dry mass was relatively constant (0·49 ± 0·04, n = 76). Because N was a constant fraction of the liquid mass but C was a constant fraction of the dry mass, the N:C ratio was positively correlated with the liquid content (R2 = 0·76, n = 27). 7. A comparison with leaf measurements from several external databases confirm that the relationships described above are widely applicable. 8. It is concluded that the composition and morphology of leaves are linked and that leaf function is a consequence of that linkage. Both the liquids and air spaces are integral to leaf function and need to be considered in analysis of experimental results.
Article
Chionochloa species vary in the degree to which they are grazed by introduced ruminants. This is presumed to reflect the relative nutritive value and/or palatability of the forage provided by these indigenous grasses. Data are presented here on silicon content, in vitro organic matter digestibility (OMD), metabolisable energy (ME), crude protein and total nutrient mineral (TNM) contents of mature leaves of eleven Chionochloa species in southern New Zealand. Silification in all species is low, possibly as an evolutionary consequence of the absence of native mammalian herbivores in New Zealand. OMD determinations indicate a generally low nutritive value for these tussock grasses. Species characteristic of oligotrophic peats (c. acicularis and C. crassiuscula ssp. torta) produced very low values (20-25%) but others (C. pallens ssp. cadens, C. macra and C. ovata) approached OMD levels of medium quality pasture (50-60%). Crude protein values are also in the poor to moderate range (4.13% in C. acicularis to 8.34% in C. ovata). The values for total nutrient mineral content largely parallel those for protein. The results are discussed in relation to the apparent relative palatability of each species in the field, and the vulnerability to grazing of some species with restricted distributions.
Article
Leaves of 12 accessions of Brachiaria sp. (three accessions from each of four species) were subjected to tests of shearing strength using a Warner Bratzler meat shear. Morphological measurements of these leaves were also taken in an attempt to standardize shearing strength measurements per unit of leaf tissue. The technique was evaluated for its capacity to detect differences between accessions of the same species. All samples were also analysed for dry matter (DM), organic matter (OM), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, crude protein, silica and digestibility in order to relate measures of physical strength to chemical components. Results demonstrated the presence of a clear relationship between shearing strength and structural (cell wall) components. Correlations between shearing strength and NDF, ADF and lignin were 0·74, 0·82 and 0·80 respectively. The technique identified clear differences between accessions of the same species (P < 0·05). These measurements can thus be used as a powerful tool for identifying forage plants of superior nutritional quality within selection programmes. Measurements of strength standardized for morphological characteristics illustrated that the ranking of the samples varied considerably depending on which morphological character was used.
Article
Morphologically distinct populations of a North American perennial grass, Agropyron smithii, collected from a heavily grazed prairie dog (Cynomys ludovicianus) colony (PDC) and a grazing exclosure (EX), were grown in an environmental chamber to determine whether: (1) leaf silicon (Si) concentrations are greater in plant populations which differentiated under heavy grazing pressure, and (2) leaf silicification is inducible by defoliation. Mean shoot Si concentration of nondefoliated plants was greater in the PDC population (2.2%) than the EX population (1.9%) over the 18 wk experiment, largely as a result of differences in Si concentrations in leaf blades. However, leaf Si concentration was lower in defoliated plants of each population than in nondefoliated plants, indicating that leaf silicification was not an inducible herbivore defense mechanism in A. smithii. The higher leaf Si concentrations from the heavily grazed population may be associated with grazingrelated environmental stresses such as a warmer, drier microclimate or with morphological characteristics related to grazing tolerance or avoidance.
Article
For 5 plant species it was investigated whether or not the uptake of Si proceeds metabolically. A gradual transition was found from metabolic absorption to metabolic exclusion, depending on the Si concentration in the culture solution. Absorption of Si increased in the order soybean, sunflower, wheat, sugarcane, rice.
Article
Grasses and dung were collected in the Serengeti National Park and analyzed for silica content by wet ashing. Grasses from grasslands differing in the grazing intensities experienced were grown in the laboratory in a factorial experiment to determine factors controlling tissue silicification. Concentrations of silica in tissues of plants collected in the field were higher than have been reported for any other plants abundant in grazing ecosystems. Silica contents in the field were higher in more heavily grazed grasslands and in tissue produced earlier in the growing season. Animal dung contained substantial quantities of silica. Laboratory experiments indicated that tissue silicification was increased by defoliation, was higher in plants from more heavily grazed grasslands, varied in different organs and species in patterns confirming current hypotheses about plant defense, and was affected by the availability of soluble silica in the nutrient medium. Silica in the nutrient medium promoted the yield of unclipped plants substantially. Total yield was 18% higher than that of control plants, although hydroponic experiments with solutions prepared and handled in plastic indicated that silica was not a growth requirement, except, perhaps, at the ecologically unrealistic concentrations that might result from reagent contamination. Yield stimulation by silica was differentially distributed among organs, tending to promote photosynthetically active tissues and crowns. Flowering of one species was promoted by silica. Leaves of silica-fed plants were larger. Leaf blade chlorophyll concentrations were 15% higher in silica-fed plants from the more heavily grazed grasslands. The results suggest that complex patterns of grass silicification had a role in the radiation of grazing animals and grasses and may contribute to maintaining the biotic diversity of contemporary grassland-savanna ecosystems by influencing the partitioning of forage species and organs among grazers. Growth promotion by silica may be due to the substitution of mineral support for carbon-based support associated with the deposition of silica in the intercellular spaces of aerial tissues. Since soils of the Serengeti region commonly have pH levels above neutrality, where the availability of silica is low, silica supply could influence primary productivity and resultant energy and nutrient flow through the trophic web in the native environments of the plants.
Article
Silica is absorbed from the soil by many grasses in an active or passive manner depending upon the species involved. It is carried upwards in the transpiration stream and deposited throughout the plant where it polymerises to form amorphous silica gel. Deposition appears to be a passive process but some active mechanism may be involved. Deposition follows a set sequence and may be initiated before leaf expansion. Silica benefits most plants but may have adverse effects unpon herbivores ingesting this plant silica. A number of possible roles have been suggested for silica deposition in plants such as the 'light window' hypothsis or as a defence against large herbivores and these are discussed in the light of the available evidence. It is concluded that leaf silicification evolved in response to invertebrate herbivory and is oprimarily aimed at reducing tissue loss to these herbivores.
Article
In the past, discussion about grass-grazer interactions has tended to centre on whether they represent some sort of mutualism. However, intense grazing pressure is more likely to have selected for the presence of various antiherbivore defences in grasses. Many grasses contain silica, which functions in some cases as a physical defence. Others contain various secondary compounds which have negative effects on both invertebrate and vertebrate herbivores. Much recent evidence suggests that plants with higher levels of these defences deter herbivores more effectively than plants without them.
Article
1. To find out which properties enable plant species to dominate in nutrient-poor habitats and which properties benefit species in nutrient-rich habitats, we studied the growth and morphology of eight perennial grass species from habitats with contrasting soil fertilities in a pot experiment under controlled conditions in a glasshouse. 2. The species were grown under nutrient-poor and nutrient-rich conditions. Ranked from the least responsive to the most responsive to the supply of nutrients they were: Festuca ovina, F. rubra, Anthoxanthum odoratum, F. arundinacea, Alopecurus pratensis, F. pratensis, Arrhenatherum elatius, Lolium perenne. 3. The response correlated positively with the Ellenberg nitrogen number of the species. No differences in initial relative growth rate were found between the species, but after 4 weeks the plant dry weight increased with increasing nitrogen number as a result of variation in embryo plus endosperm weight. 4. Species characteristic of nutrient-rich hayfields are taller and show a more homogeneous vertical distribution of photosynthetic area than the species from nutrient-poor habitats, which have most of their leaf area below 15 cm. Species from the nutrient-poor habitats allocated less dry matter to the roots and consequently more to the shoot, than species from nutrient-rich conditions. However, leaf and root morphology seem to be most clearly adapted to the habitat. 5. Species from nutrient-rich habitats have a higher specific leaf area (SLA) than species from nutrient-poor habitats, while species from nutrient-poor habitats had more root length per unit root weight (SRL) than species from nutrient-rich habitats.
Article
Ash and silica contents and their depositional patterns in different tissues of 27 plants growing in the Ocean Springs area of Mississippi (many grow elsewhere), were determined. Silica content of dried plant parts varied from no more than 0 per cent in Borrichia frutescens (L.) D.C. stems to 18.76 per cent in Arundinaria gigantea (Walt.) Muhl. leaves. Ash content varied from 0·73 per cent in Cliftonia monophylla (Lam.) Britt. ex Sarg. stems to 44·02 per cent in Batis maritima L. leaves. Plants such as Batis maritima L., Borrichia frutescens (L.) D.C., Salicornia bigelovii Torr. and Salicornia virginica L. which grew in saline marshes had high ash contents due NaCl in their tissues. Morus rubra L. leaves had a high silica content for a dicotyledonous plant (3·12 per cent). Energy-dispersive X-ray analysis shows that the distribution of the element silicon is clearly related to certain epidermal structures such as ridges, cell walls, rows of irregular shaped structures lengthwise of the leaf, dumb-bell shaped ones and especially in trichomes. There was a high concentration of silica containing trichomes along the veins on the underside of Morus rubra L. leaves and this would protect them from insects. The outer parts of the inflorescences of Ctenium aromaticum (Walt.) Wood, Elymus virginicus L., Juncus polycephalus Michx. and phragmites communis Trin. were highly silicified. This should give the seed some protection from insects. The sharp particles would be irritating to oesophageal tissues and might be implicated in such a cancer. α-Quartz made up a considerable part of the silica in inflorescences and leaves of Ctenium aromaticum (Walt.) Wood.
Article
Silicon is the second most abundant element in soils, the mineral substrate for most of the world's plant life. The soil water, or the "soil solution," contains silicon, mainly as silicic acid, H4SiO4, at 0.1-0.6 mM--concentrations on the order of those of potassium, calcium, and other major plant nutrients, and well in excess of those of phosphate. Silicon is readily absorbed so that terrestrial plants contain it in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent, and in some plants to 10% or even higher. In spite of this prominence of silicon as a mineral constituent of plants, it is not counted among the elements defined as "essential," or nutrients, for any terrestrial higher plants except members of the Equisitaceae. For that reason it is not included in the formulation of any of the commonly used nutrient solutions. The plant physiologist's solution-cultured plants are thus anomalous, containing only what silicon is derived as a contaminant of their environment. Ample evidence is presented that silicon, when readily available to plants, plays a large role in their growth, mineral nutrition, mechanical strength, and resistance to fungal diseases, herbivory, and adverse chemical conditions of the medium. Plants grown in conventional nutrient solutions are thus to an extent experimental artifacts. Omission of silicon from solution cultures may lead to distorted results in experiments on inorganic plant nutrition, growth and development, and responses to environmental stress.
Article
Plants from four populations of three species of African grasses were collected from grasslands in Tanzania's Serengeti National Park that differ in the grazing intensity that they experience. Plants were grown in the laboratory in a factorial experiment in which variables were plant origin, species identification of plants, defoliation intensity, and supply of soluble silicate in the nutrient medium. All plants accumulated silica in leaf blades in the absence of soluble silicate from the nutrient medium. Plants native to the more heavily grazed grassland accumulated more silica in their leaf blades than did plants from the less heavily grazed site. Blade silica content was higher when plants were defoliated, indicating that silicification is an inducible defense against herbivores. The quantitative heterogeneity of this qualitatively homogeneous plant defense system may have contributed to the evolution of high species diversity in the grazing fauna.
In: Actes de l'Atelier Régional sur Cultures fourragères et Développement durable en zone subhumide
  • C Bodji N
  • Kore R
BODJI N.C. & KORE R., 1998. -Étude du comportement de quelques plantes fourragères tropicales herbacées et ligneuses dans la région de Touba (Cote d'Ivoire). In: Actes de l'Atelier Régional sur Cultures fourragères et Développement durable en zone subhumide. Korhogo, Côte d'Ivoire 26-29 mai 1997. pp. 31-40.
The anomaly of silicon in plant biology
  • Epstein E
EPSTEIN E., 1994. -The anomaly of silicon in plant biology. Proc. Natl. Acad. Sci. USA 90: 11-17.
  • Gali-Muhtasib H U C Smith C
GALI-MUHTASIB H.U. & SMITH C.C., 1992.-The effect of silica in grasses on feeding behaviour of the prairie vole Microtus ochrogaster. Ecology 73: 1724-1729.
Shearing strength as an additional selection criterion for quality in Brachiaria pasture ecotypes
  • R G Hugues N
  • Do
  • B Valle C
  • V Sabatel
  • J Book
  • S Jessop N
  • Herrero M
HUGUES N.R.G., DO VALLE C.B., SABATEL V., BOOK J., JESSOP N.S. & HERRERO M., 2000. -Shearing strength as an additional selection criterion for quality in Brachiaria pasture ecotypes. J. Agric. Sci. 135: 123-130.
The transport and function of silicon in plants
RAVEN J., 1983. -The transport and function of silicon in plants. Biological reviews 58: 179-207.
Strategies to reduce the ash content in perennial grasses
  • Samson R Mehdi B
SAMSON R. & MEHDI B., 2003.-Strategies to reduce the ash content in perennial grasses. Proceedings of Bioenergy 98: 1124-1131.
Silicon in C 3 -grasses: Effect on forage quality and sheep preference
  • E Shewmaker G
  • H F Mayland
  • C Rosenau R
  • H Asax K
SHEWMAKER G.E., MAYLAND H.F., ROSENAU R.C. & ASAX K.H., 1989. -Silicon in C 3 -grasses: Effect on forage quality and sheep preference. J. Range Manage. 42: 122-127.
Évaluation du bilan fourrager des parcours naturels et des exploitations agricoles en régions guinéo-soudanienne: cas de la ferme d'élevage de Samiondji en République du Bénin
  • Téka O
TÉKA O., 1999. -Évaluation du bilan fourrager des parcours naturels et des exploitations agricoles en régions guinéo-soudanienne: cas de la ferme d'élevage de Samiondji en République du Bénin. Mémoire Ing. Agro. FSA, Benin.
Le cycle bio géochimique du silicium sur roche acide : application à l'écosystème forestier tempéré (Vosges)
  • Bartoli F
BARTOLI F., 1981. -Le cycle bio géochimique du silicium sur roche acide : application à l'écosystème forestier tempéré (Vosges). Thèse. Doct. ULB/Université de Nancy I. UER-STMCM, France.