Stoichiometric imbalances between soil microorganisms and their resources regulate litter decomposition

Litter decomposition is dependent on the requirements of decomposer communities and their ability to acquire energy and nutrients from their substrates (i.e. litter) and the surrounding environment (i.e. soil). However, knowledge about whether and how stoichiometric imbalance (i.e. the differences in C:N:P ratios between microorganisms and their substrates) regulate litter decomposition rates and whether it can be compensated by soil resources have rarely been evaluated, and even less across different decomposition stages over time. In this study, we conducted a reciprocal litter transplantation experiment using a stoichiometric gradient along the forest-steppe ecotone to evaluate mechanisms underlying litter-microbe-soil interactions at different moments during litter breakdown. We measured the C:N:P stoichiometry of litter, soil, microbes, enzyme ratios and soil microbial community composition (via metabarcoding) after 6 and 12 months of litter decomposition. We found that the stoichiometric imbalances between soil microorganisms and litter substrate controlled decomposition rates directly during the early phase of decomposition. In contrast, the stoichiometric imbalances between soil microorganisms and soil substrate regulated decomposition rates during the later phase of decomposition, but this was an indirect effect mediated via shifts in the saprophytic fungal community composition and enzyme allocation. These findings highlight that the stoichiometric imbalance between soil microorganisms and litter substrates can be partly compensated by the local soil resources over the course of the decomposition process. We conclude that the stoichiometric imbalance between soil microorganisms and their resources is a key mechanism that should not be ignored when predicting soil C and nutrient cycling in terrestrial ecosystems.Read the free Plain Language Summary for this article on the Journal blog.