Methane Production Rate during Anoxic Litter Decomposition Depends on Si Mass Fractions, Nutrient Stoichiometry, and Carbon Quality

Hömberg A, Knorr K-H, Schaller J

Abstract

Abstract: While Si influences nutrient stoichiometry and decomposition of graminoid litter, it is stillunclear how Si influences anoxic litter decomposition and CH4 formation in graminoid dominatedfen peatlands. First, Eriophorum vaginatum plants were grown under different Si and P availabilities,then shoots and roots were characterized regarding their proportions of C, Si, N and P and regardingC quality. Subsequently the Eriophorum shoots were subjected to anoxic decomposition. We hypothesized;that (I) litter grown under high Si availability would show a higher Si but lower nutrientmass fractions and a lower share of recalcitrant carbon moieties; (II) high-Si litter would show higherCH4 and CO2 production rates during anoxic decomposition; (III) methanogenesis would occurearlier in less recalcitrant high-Si litter, compared to low-Si litter. We found a higher Si mass fractionthat coincides with a general decrease in C and N mass fractions and decreased share of recalcitrantorganic moieties. For high-Si litter, the CH4 production rate was higher, but there was no long-terminfluence on the CO2 production rate. More labile high-Si litter and a differential response in nutrientstoichiometry led to faster onset of methanogenesis. This may have important implications for ourunderstanding of anaerobic carbon turnover in graminoid-rich fens.