Latitudinal Patterns of First-Order Root and Leaf Litter Decomposition: Soil Microbial Networks Mediate Decomposition Dynamics of Coniferous Plantations

Aims First-order roots in forests exhibit high productivity and turnover rates, contributing to soil carbon accumulation to an even greater extent than leaf litter. However, the factors influencing first-order root litter decomposition, particularly the role of soil microbial communities in this process, remain poorly understood. Methods We conducted a three-year litter decomposition experiment using two dominant coniferous species in northeastern China, across four locations within their natural distribution range. This study aimed to investigate the differences in decomposition patterns between leaf and first-order root litter and to elucidate the influence of soil microbial network interactions on their decomposition dynamics. Results The decomposition rate of first-order root litter (13–22% per year) was significantly lower than that of leaf litter (23–31% per year). The decomposition rates of both litter types increased with decreasing latitude. First-order root litter decomposition exhibited a "home-field disadvantage," where locally sourced first-order root litter decomposed significantly slower than non-local sources, whereas leaf litter decomposition was independent of its origin. Additionally, we found that fungal network complexity in summer was positively correlated with the decomposition rates of both litter types, whereas bacterial network complexity in autumn exhibited a negative correlation. Climatic conditions modulate soil microbial network complexity, thereby influencing litter decomposition. Conclusions These findings demonstrate that while the decomposition dynamics of first-order root and leaf litter differ, both are influenced by soil microbial network complexity. Our study highlights the distinct and seasonally dependent effects of bacterial and fungal interactions within their respective networks on litter decomposition.