Global Patterns and Influencing Factors of Mn Accumulation in Litter at Different Decomposition Stages—a Synthesis

Manganese (Mn) is an essential cofactor for lignin-degrading enzymes and crucial for nutrient cycling and ecosystem functions. During litter decomposition, Mn may accumulate to fulfill the microbial demand for degrading recalcitrant substances such as lignin, which is reflected in the relative increase in Mn in decomposing litter compared with its initial amount. However, a global-scale quantification of the patterns and factors influencing Mn behavior at different decomposition stages has not been conducted. Thus, we systematically synthesized 1,466 observations from 53 publications to assess the global patterns and influencing factors of Mn accumulation in litter across various stages of decomposition. Our findings are as follows: (1) Mn primarily accumulated during litter decomposition on a global scale, despite some variability among stages. Notably, Mn accumulation was lower in the early decomposition stage (<40 % mass loss) than in the intermediate and late stages. (2) Litter quality and soil properties were the primary factors influencing Mn accumulation in litter throughout most of the decomposition process, and climatic conditions were significantly correlated with Mn accumulation only in the intermediate stage (40-60 % mass loss). (3) During the early stage of decomposition (20-40 % mass loss), Mn accumulation in litter was significantly influenced by ecosystem and vegetation types, with higher accumulation observed in wetland litter than in upland litter and in tree litter than in shrub litter. Our study quantitatively synthesizes the global patterns and influencing factors of Mn accumulation in litter across different decomposition stages, thus enhancing our understanding of global Mn cycling and litter decomposition processes across different ecosystems and vegetation types. Furthermore, these findings highlight the necessity to incorporate Mn dynamics into global models of litter decomposition dynamics.