Is higher silicon availability increasing the mineralization of organic matter in fen peatlands?
Ecology and Biodiversity of Plants and Ecosystems
Final Report Abstract
Major controls on decomposition in peatlands are the water table, the availability of nutrients and electron acceptors and the quality of the litter. In fen peatlands, graminoids often are the dominant vegetation type. Graminoids, especially Cyperaceae, can accumulate large quantities of Si. This element can be intensely recycled between plant and peat and it has been shown that Si influences the C biogeochemistry and turnover in soils. A higher availability of Si could for example mobilize P and stimulate decomposition processes by provision of P, or may have further effects on decomposition through altering litter quality. The conditions under which Si has effects on P mobilization and greenhouse gas production, are yet not well understood. This project thus addressed the role of Si in the C cycle and the effects of a changed Si availability in peatlands. We hypothesized that (i) a higher Si availability will enhance the mineralization of organic matter via direct Si effects and indirect Si effects by increasing P availability, (ii) the higher mineralization rate of organic matter to both CO2 and CH4 due to direct and indirect Si effects will be achieved rather by bacteria than by fungi and fungal biomass will be lowered by Si addition, (iii) increased Si availability will increase P and N availability and uptake into plant biomass and thus lead to more labile litter, in turn accelerating carbon and nutrient turnover, (iv) both the quantity of DOC and of dissolved N increases due to direct and indirect effects of Si on organic matter mineralization, and (v) the direct Si effect on peat mineralization is more important compared to the indirect effect of Si via enhancing P availability. We conducted incubation experiments with Si additions and using untreated and Si-fertilized plant litter. Moreover, a mesocosm experiment with and without Si-amendment was conducted to replace a field experiment that could not be performed to extensive drought at the intended field site. On the basis of the conducted experiments we could not give a final statement on hypothesis (v), and also for hypothesis (ii) we could not provide a final answer, as we could not disentangle the activities of fungi and bacteria due to huge variation in mineralization rates with no clear differences between treatments. Nevertheless, higher Si availability stimulated CH4 production in most of our experiments, while for CO2 no effect could be verified. Moreover, Si fertilization lead to more labile plant litter, accelerating decomposition, as verified in incubations and qualitative analyses of the respective litter types. Finally, under certain experimental conditions, the quantity of DOC was increased, however, this could not be confirmed for dissolved nitrogen. In summary, our project revealed that Si is an important driver for the C-turnover in peatlands und certain conditions.
Publications
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Increased silicon concentration in fen peat leads to a release of iron and phosphate and changes in the composition of dissolved organic matter; Geoderma, Volume 374, September 2020, 114422
Annkathrin Hömberg, Martin Obst, Klaus-Holger Knorr, Karsten Kalbitz, Jörg Schaller
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Divergent effect of silicon on greenhouse gas production from reduced and oxidized peat organic matter; Geoderma, Volume 386, March 2021, 114916
Annkathrin Hömberg, Tanja Broder, Klaus-Holger Knorr, Jörg Schaller
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Methane fluxes but not respiratory carbon dioxide fluxes altered under Si amendment during drying rewetting cycles in fen peat mesocosms; Geoderma, Volume 404, December 15 2021, 115338
Annkathrin Hömberg, Tanja Broder, Jörg Schaller, Klaus-Holger Knorr
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Methane production rate during anoxic litter decomposition depends on Si mass fractions, nutrient stoichiometry, and carbon quality; MDPI Plants, 10, 618 on 24 March 2021
Annkathrin Hömberg, Klaus-Holger Knorr, Jörg Schaller
