Contrasting contribution of fungal and bacterial residues to organic carbon accumulation in paddy soils across eastern China

Microbial residues are key components of stable soil organic C (SOC). However, the accumulation patterns of fungal and bacterial residues across climate regions are largely unknown, especially in paddy soils. In this study, the amounts of microbial-derived amino sugars (AS) with their constituents, glucosamine (GlcN), galactosamine (GalN), and muramic acid (MurN, a biomarker of bacterial residues) were quantified in paddy soils, which were collected from mid-temperate, warm-temperate, subtropical, and tropical climate regions across eastern China. The contents of total AS and fungal-derived GlcN (F-GlcN, a biomarker of fungal residues) were lowest in the warm-temperate region, but not significantly different among the other three climate regions. The MurN content and its contribution to SOC accumulation were higher in the warmer and wetter regions (subtropic and tropic) than in the cooler and drier ones (mid-temperate and warm-temperate). Consequently, the ratio of F-GlcN to MurN was lower in the warmer and wetter regions (8.5–15.4) than in the cooler and drier ones (12.8–28.8). These results illustrate that the bacteria participating in SOC transformation and stabilization in paddy soils exerted more prominent activities in the warmer and wetter regions than in the cooler and drier regions. Structure equation models emphasize that the contrasting patterns of fungal and bacterial residues’ contribution to SOC accumulation in paddy ecosystems along the latitudinal gradient were mainly attributed to their different responses to the climate factors of temperature and precipitation.