Litter calcium content modulates litter decomposition by soil fauna in karst forest

Abstract

Litter decomposition serves as a fundamental ecological process for nutrient cycling in karst forest ecosystem, where soil fauna acts as a critical decomposer. Nevertheless, the regulatory mechanisms of litter nutrient stoichiometry, esp. calcium (Ca) content, on faunal-mediated decomposition remain poorly understood. To address this knowledge gap, we conducted a three-year decomposition experiment in a karst forest in southwestern China. Using litterbags with different mesh sizes (0.01 mm, 2 mm, 4 mm), we selectively excluded soil fauna by body-size classes to quantify their contributions to the decomposition of litter types varying in initial carbon-to‑nitrogen ratios (C/N) and Ca content. Results of the present study showed that high-quality litter, characterized by low C/N and Ca content, decomposed fast than low-quality litter. The importance of calcium exists on an equal footing with the C/N. Soil macrofauna contributed 12.39% to litter annual decomposition rate (k) on average, whereas mesofauna accounted for 11.63%. Random forest analysis indicated that mesofauna was the main factor affecting fauna-driven litter decomposition. Structural equation modeling elucidated that litter high Ca content and C/N directly suppressed macrofaunal decomposition activity, but not mesofauna. These findings highlighted that calcium-mediated litter stoichiometry drives functional divergence between macrofauna and mesofauna during decomposition, with implications for biogeochemical cycling in karst ecosystems.