Sodium limits litter decomposition rates in a subtropical forest: Additional tests of the sodium ecosystem respiration hypothesis

Our results showed that both 0.05 and 0.5% Na subsidies increased invertebrate detritivore decomposition of litter at least 1.5 fold, while it decreased the microbial contribution to litter decomposition by ≥7.2%. However, low-level Na subsidies (0.005%) increased microbial, but not detritivore, activity in recalcitrant litter. Despite enhanced litter mass loss from invertebrate detritivores, we found decreased microbial enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycling under high (0.5%) Na subsidies. This suggests that at 0.5% of Na, microbes experience Na-toxicity and mineralization of C, N, and P nutrients likely decreased in forest ecosystems. These results suggest that neither Na shortage nor Na excess would be unfavorable for carbon-release. As increased with anthropogenic input or climate change in the future, sodium may have multiple effects on soil organic matter dynamics, ecosystem biogeochemical cycling, and plant nutrition through regulating microbial processes in forests.