Diversity of silicon release rates among tropical tree species during leaf-litter decomposition

Abstract

Leaf-litter is a significant source of biogenic Si, and differences among tree species in Si release rates during litter decomposition are important for quantifying Si cycles in forest ecosystems. We conducted two experiments to improve mechanistic understanding of Si release rates from dead leaves, using lowland tropical trees of Sarawak, Borneo. In the first experiment, we assessed Si leaching from leaf litter when they were shaken in water for four hours. In the second experiment, leaf litter samples were allowed to decompose in mesh bags in growth chambers for two months, in order to determine rates of decomposition and Si release, and to explore a relationship between decomposition rate and initial litter chemistry. Among the 12 species with large differences in initial leaf-litter Si concentration (0.72–80.0 mg Si g−1), Si leaching to water varied widely (0.04–0.16 mg Si g−1) and positively correlated with the initial Si concentration (R2 = 0.87; P < 0.001). Si release per unit leaf dry weight in the decomposition experiment was also positively correlated with initial litter Si concentration among six species (R2 = 0.998; P < 0.001). In contrast, proportion of initial Si content released did not exhibit a significant relationship with their decomposition rates, which were correlated with labile carbon content in leaf litter (e.g. hemicellulose). Our results suggest that Si release rates from decomposing leaf litter cannot be simply predicted from decomposition rates. The species differences in locations and stability of opal phytoliths and their resulting effects on Si dissolution rates should be considered.