Biogenic silica in tidal freshwater marsh sediments and vegetation (Schelde estuary, Belgium)
TL;DR: It is concluded that P. australis wetlands could be an essential, but unrecognised, sink for BSi in the biogeochemical cycling of Si in freshwater intertidal marshes.
Abstract: To date, estuarine ecosystem research has mostly neglected silica cycling in freshwater intertidal marshes. However, tidal marshes can store large amounts of biogenic silica (BSi) in vegetation and sediment. BSi content of the typical freshwater marsh plants Phragmites australis, Impatiens glandulifera, Urtica dioica, Epilobium hirsutum and Salix sp. was analysed year-round. All herbaceous species accumulated silica in their tissue during their life cycle. Of the live plants, P. aus- tralis contained the most BSi (accumulating from 6 to 55 mg g -1 ). Dead shoots of P. australis had the highest BSi content (up to 72.2 mg g -1 ). U. dioica (<11.1 mg g -1 ), I. glandulifera (<1.1 mg g -1 ), E. hirsutum (<1.2 mg g -1 ) and Salix sp. (<1.9 mg g -1 ) had a much lower BSi content. Except for P. aus- tralis rhizomes (<15 mg g -1 ) underground biomass contained low amounts of BSi (<6 mg g -1 ). Sediment BSi content decreased from the surface (9 to 10 mg g -1 ) to deeper layers (5 to 7 mg g -1 ). There was seasonal variation in sediment BSi. Dissolved Si in porewater was highest in summer (ca. 600 µM) and lowest in winter (ca. 400 µM). P. australis vegetation (aboveground and roots) con- tained up to 126 g m -2 BSi, while the upper 30 cm of sediment accumulated up to 1500 g m -2 , making sediment the largest BSi reservoir in the marsh. We conclude that P. australis wetlands could be an essential, but unrecognised, sink for BSi in the biogeochemical cycling of Si.
Citations
More filters
TL;DR: In this article, the authors show that wetland ecosystems may be as important for Si transport and processing as they are for other important biogeochemical cycles, such as nitrogen and phosphorus cycling.
Abstract: Recent research has emphasized the importance of terrestrial ecosystems in the global biogeochemical cycle of silica (Si). The production, retention, and dissolution of amorphous silica of biological origin in soils and vegetation effectively control terrestrial Si fluxes. However, surprisingly little is known about the role of wetlands in these processes. Wetlands are known hotspots for both nitrogen and phosphorus cycling, and there have been countless studies and numerous reviews on these nutrients worldwide. By bringing together previously scattered results, we show that wetland ecosystems may be as important for Si transport and processing as they are for other important biogeochemical cycles. Yet, the range of studied systems is small and incomplete. This constitutes a serious gap in our understanding of both coastal eutrophication and climate change, issues that are strongly linked to Si biogeochemistry. Ecosystem scientists and wetland biogeochemists around the world need to begin addressing these issues.
183 citations
TL;DR: The annual fixation of dissolved Si (DSi) into terrestrial vegetation has been estimated to range from 60 to 200 Tmole, or 10 to 40 times more than the yearly export of DSi and biogenic Si (BSi) from the terrestrial geobiosphere to the coastal zone as discussed by the authors.
Abstract: The annual fixation of dissolved Si (DSi) into terrestrial vegetation has been estimated to range from 60 to 200 Tmole, or 10–40 times more than the yearly export of DSi and biogenic Si (BSi) from the terrestrial geobiosphere to the coastal zone. Ecosystems form a large filter between primary mobilization of DSi from silicate weathering and its eventual export to the oceans, and a large reservoir of BSi accumulates in aquatic and terrestrial ecosystems. Although a number of synthesis activities within the last decade have discussed biological transformations in the terrestrial Si cycle, the timescales at which BSi is stored and recycled within ecosystems, BSi persistence and reactivity throughout soil profiles, the dependence of the BSi storage and recycling on ecological processes, the feedbacks to hydrology, the interaction with man’s activities and ultimately the global relevance in Si budgets are poorly constrained. Here we discuss 5 key controls on the ability of ecosystems to filter and control the export of DSi: ecosystem biodiversity, BSi dissolution rates and reactivity, hydrology, interaction with the geosphere and anthropogenic impacts. These controls need to be further studied to better quantify the global and local importance of the terrestrial biogeochemical Si cycle and specifically the BSi reservoir in ecosystems.
148 citations
Cites background from "Biogenic silica in tidal freshwater..."
...Recent research has also indicated the capacity of wetland and aquatic macrophyte communities to store BSi (Struyf et al. 2005; Schoelynck et al. 2010)....
[...]
TL;DR: Si appears to play a significant role in salinity tolerance even in a halophyte, which has other, specific salt-tolerance mechanisms, through diverse protective effects on the photosynthetic apparatus, water-use efficiency and mineral nutrient balance.
129 citations
TL;DR: The potential of silicon to impact plant growth and elemental stoichiometry and, by extension, to affect biogeochemical cycles in ecosystems dominated by Phragmites and other grasses and sedges is pointed to.
Abstract: Silicon is a non-essential element for plant growth. Nevertheless, it affects plant stress resistance and in some plants, such as grasses, it may substitute carbon (C) compounds in cell walls, thereby influencing C allocation patterns and biomass production. How variation in silicon supply over a narrow range affects nitrogen (N) and phosphorus (P) uptake by plants has also been investigated in some detail. However, little is known about effects on the stoichiometric relationships between C, N and P when silicon supply varies over a broader range. Here, we assessed the effect of silicon on aboveground biomass production and C:N:P stoichiometry of common reed, Phragmites australis, in a pot experiment in which three widely differing levels of silicon were supplied. Scanning electron microscopy (SEM) showed that elevated silicon supply promoted silica deposition in the epidermis of Phragmites leaves. This resulted in altered N:P ratios, whereas C:N ratios changed only slightly. Plant growth was slightly (but not significantly) enhanced at intermediate silicon supply levels but significantly decreased at high levels. These findings point to the potential of silicon to impact plant growth and elemental stoichiometry and, by extension, to affect biogeochemical cycles in ecosystems dominated by Phragmites and other grasses and sedges.
112 citations
Cites background from "Biogenic silica in tidal freshwater..."
...Abundant Si deposits in addition to phytholiths and several-fold higher concentrations of Si in leaf blades and sheaths compared to culms indicate massive Si transport into the leaves in the Si-100 treatment, in a range of Si in leaf blades, as described for natural sites (Struyf et al. 2005)....
[...]
...Therefore, variation in Si supply might not only affect the Si cycle in these ecosystems but also C and P cycling over large spatial scales (Derry et al. 2005; Struyf et al. 2005)....
[...]
TL;DR: The results suggest that tradeoffs exist between phenolic- and tannin-based defences and provide evidence that leaf silicification may be a more effective defence against some chewing herbivore groups than others.
Abstract: Silica is ubiquitous in plants and can constitute up to 10% of plant dry mass, varying with phylogeny and soil silicon availability. Plant silicon is an important alleviator of abiotic (salinity, heavy metal, drought) and biotic (herbivore and fungal pathogen) stress. As well as playing an important role in reducing the impact of abiotic stresses, silicon may be an alternative to carbon-based and other chemical defences. Knowledge of silicon function is predominantly derived from agricultural species and model systems. We investigated the abundance and role of plant silicon at a community level by comparing leaf silicon concentration with defence chemicals, carbon compound concentrations and invertebrate assemblages in vegetation communities from two different soil types with contrasting levels of plant available silicon. We found that the concentrations of silicon in the leaves did not reflect the silicon availability in the soil at a community level. The leaf silica concentration range in the vegetation communities was comparable to other diverse communities reported in the literature, suggesting that the species rather than the environment determine leaf silica concentration. Across sites, leaf silica concentration was significantly negatively correlated with concentrations of carbon, total phenols and weakly with tannins but not with other measured defence compounds. Leaf silica concentration was also negatively correlated with Coleoptera abundance, but not the abundance of any other invertebrate groups measured. Our results suggest that tradeoffs exist between phenolic- and tannin-based defences and provide evidence that leaf silicification may be a more effective defence against some chewing herbivore groups than others.
99 citations
References
More filters
TL;DR: 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.
Abstract: 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.
1,558 citations
"Biogenic silica in tidal freshwater..." refers background in this paper
...Roots in general contain low amounts of BSi, because Si absorbed is transferred from roots to shoots and deposition occurs at sites of greatest water loss (Epstein 1994)....
[...]
...Silicon uptake can positively influence plant growth and development, providing rigidity to plant structures and enhancing resistance to abiotic and biotic stresses, such as toxic metal accumulation and herbivory (Epstein 1994)....
[...]
TL;DR: For example, the accumulation of biogenic silica in estuarine deposits removes a maximum of 8 × 1014g SiO2/yr or 10% of the dissolved silica input to the oceans as mentioned in this paper.
1,128 citations
"Biogenic silica in tidal freshwater..." refers methods in this paper
...To extract BSi, 25 mg of sieved plant material was incubated for 4 h in 0.1 M Na2CO3 (DeMaster 1981)....
[...]
...BSi was calculated by linear extrapolation through the 3 extraction points in a time-extracted silica plot (DeMaster 1981)....
[...]
...BSi was extracted from the sediment (25 mg) in a 0.1 M Na2CO3 solution at 80°C. Subsamples were taken after 150, 210 and 270 min....
[...]
TL;DR: A number of lines of evidence suggest the intrinsic PSi(OH)4 of about 10‐10 m s‐1 in the plant cell plasmalemma, while relatively low, could maintain the intracellular concentration of Si( OH)4 equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h.
Abstract: Summary
A number of lines of evidence (Mr, number of -OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic PSi(OH)4 of about 10-10 m s-1 in the plant cell plasmalemma. While relatively low, such a PSi(OH)4 could maintain the intracellular concentration of Si(OH)4 equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super-saturated solution or the quantity of SiO2 required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)4 due to the intrinsic permeability of lipid bilayers to Si(OH)4 is never more than 10% of the cost of silicification.
In vascular land plants the entry of Si from the soil into the xylem can involve a flux ratio (mol Si/m3 water) that is less than (e.g. Leguminoseae) equal to (e.g. many Gramineae) or greater than (e.g. Oryza, Equisetum) the concentration (mol m-3) in the bathing solution. Even the low influx of the Leguminoseae cannot be accounted for by the ‘lipid solution’ value of PS(OH)4, but requires entry coupled (phenomenologically) to water influx with a reflexion coefficient of about 0.9. The situation in most Gramineae is described by such a coupling with a reflexion coefficient near O, while the accumulation of Si (relative to water) in Oryza and Equisetum involves an apparent reflexion coefficient which is negative, i.e. an active transport system stoichiometrically related to water flux. Even in Leguminoseae with a transpiration-stream concentration of Si(OH)4 of only 20 mmol m-3 (cf. the soil solution at 200 mmol m-3), the fact that only I % of the water in the xylem is retained in the plant means that Si(OH)4 at transpirational termini approaches saturation; super-saturation, and precipitation of SiO, occurs in Gramineae and Equisetum. SiO2 precipitation occurs mainly near transpirational termini but can also occur in the xylem vessels and endodermis of roots, for example. Si(OH)2 mobility in the phloem seems to be very restricted.
The energy costs of SiO2 relative to organic compounds as structural and defensive materials are in the ratio of 1:10-1:20 (on the basis of weight of material). The relative rarity of SiO2 as a structural material is discussed in the context of the evolution of Si(OH)4-transport mechanisms.
581 citations
"Biogenic silica in tidal freshwater..." refers background in this paper
...The role of Si in cell walls is similar to that of lignin, but it is energetically cheaper to incorporate Si (Raven 1983)....
[...]
TL;DR: In this article, the stable isotopes of sulfur, nitrogen, and carbon were used to trace organic matter flow in salt marshes and cstuarinc waters at Sapelo Island, Georgia.
Abstract: The stable isotopes of sulfur, nitrogen, and carbon were used to trace organic matter flow in salt marshes and cstuarinc waters at Sapelo Island, Georgia. Organic matter inputs from terrestrial sources as detrital input either from forests adjacent to the marshes or from rivers were not dctcctable by their isotopic signatures in estuarine consumers. The results suggest that there are two major sources of organic matter for the fauna of the marshes and estuarine waters of Sapelo Island: Spartina and algae. The long-standing debate about the relative importance of Spartina detritus and algae in supporting marsh and estuarine secondary production appears from this analysis to be a draw; both sources are important and their relative importance is determined by feeding mode, size, location, and trophic position of the marsh and estuarine consumers.
535 citations
"Biogenic silica in tidal freshwater..." refers background in this paper
...This can negatively influence the structure of coastal foodwebs, as diatoms are the most important energetic source in estuarine food chains (Peterson & Howarth 1987, Sullivan & Moncreiff 1990)....
[...]
TL;DR: It is suggested that the DOM pathway may be ecologically more significant than the POM (particulate organic matter) pathway and that processes analogous to those shown for lakes and rivers probably occur in estuarine and coastal waters.
Abstract: In both freshwater and marine habitats, vascular marine plants arc little used by animals that graze directly on them, because they have a relatively high content of indigestible fiber and a low content of nitrogen. The chief emphasis of detritus research in the 1970s was to show how microorganisms progressively reduce the content of fiber and increase the content of nitrogren in vascular plant detritus, rendering it nutritious for animals. Algal (seaweed, diatom, etc.) detritus starts with a lower fiber content and a higher nitrogen content. Many animals can use it directly, and a very short period of microbial colonization renders it highly nutritious. As a result, a high proportion of the algal carbon originally produced passes into animals via detrital food webs, while a low proportion of vascular plant carbon does so. Much more of the latter simply supports microbial respiration. In the 1980s it was shown, particularly for freshwater habitats, that the dissolved organic matter (DOM) released by plants while living or in the early stages of decomposition readily precipitates on surfaces and forms amorphous particulate matter with a low content of refractory material. These particles are highly nutritious for animals and are used directly by freshwater fish such as Sarotherodon (= Tifapia), which is commercially important, especially in Africa and South America. It is suggested that the DOM pathway may be ecologically more significant than the POM (particulate organic matter) pathway and that processes analogous to those shown for lakes and rivers probably occur in estuarine and coastal waters. There is much circumstantial evidence to suggest that planktonic food webs based on DOM are much more important than previously thought. The conversion of DOM to POM through the “microbial loop” and its utilization in higher trophic levels is a.n urgent topic for further study.
523 citations
"Biogenic silica in tidal freshwater..." refers background in this paper
...Coastal zones and shallow marine areas are among the most productive systems in the world (Mann 1988, Glantz 1992) and represent the main fishery grounds on Earth (Postma & Zijlstra 1988, Sherman et al. 1991)....
[...]