Effects of Laboratory Warming on Active Soil Organic Matter and Bacterial Diversity During the Long-Term Decomposition of Forest Litter in Soil Microcosms

To investigate the combined impacts of temperature and plant residues on the mineralization capacity of soil organic matter, in addition to the impact on the taxonomic composition and activity of the soil microbiome, a 364-day experiment involving gray forest soil (Greyzemic Phaeozem Albic) was conducted under controlled laboratory conditions. Three substrate treatments were applied, control (C), amendment with aspen leaves (L), and amendment with aspen branches (B), combined with three temperature regimes (2, 12, and 22 °C). The results showed that long-term experimental warming reduced microbial alpha diversity (number of species and richness), increased microbial respiration and decomposition rates, and altered community composition. Over the year, the percentage of mineralization of added carbon was higher for leaves (29.9%–57.8%) than for branches (20.1%–47.6%). The efficiency of organic matter decomposition increased by 1.5- to 2-fold between 2 and 12 °C. Across all treatments, Proteobacteria were found to be the dominant phylum. According to α-diversity analysis, leaves served as the most preferred substrate for enhancing species representation. β-diversity analysis results indicated that temperature was the most significant factor shaping the microbial community’s structure. Our research findings provide new insights into soil organic matter formation and highlight the need for further research on microbial functional genes.