Interactions between soil organic matter chemical structure and microbial communities determine the spatial variation of soil basal respiration in boreal forests

Abstract

Interactions between soil organic matter (SOM) composition and microbial communities determine soil basal respiration (BR, SOM-derived CO2). However, few studies have investigated the relative importance of SOM chemical structure, microbial community composition, and soil environmental factors to the spatial variability of soil BR on a large scale. Here, organic and mineral layer soils were collected along a 650-km boreal forest transect in Northeast China. Combining 13C-nuclear magnetic resonance spectroscopy and high-throughput sequencing techniques, SOM chemical structure, microbial community composition, and soil physicochemical properties were determined to investigate the biotic and abiotic drivers of soil BR. Soil BR, microbial communities, and soil physicochemical properties exhibited significant spatial heterogeneity across sites, but the variations were independent of latitude regardless of soil layer. Soil BR rates were significantly higher in the organic layer than in the mineral layer (0.82 vs. 0.31 CO2-C kg−1soil−1 h−1, P < 0.001). Multi-model averaging and partial regression showed that SOM chemical structure exhibited the strongest control on the spatial variation of soil BR (contributing 23.0 %), followed by the organic layer soil C/N ratio (contributing 17 %). However, only soil C/N ratio was the most important predictor of soil BR variation in the mineral layer. Copiotrophic bacteria had a higher impact on soil BR than oligotrophic bacteria. In addition, soil physicochemical properties (i.e. pH, mechanical composition) indirectly affected soil BR through regulating soil microbial composition, especially bacteria. Overall, these results highlighted that SOM chemical structure directly or indirectly affected the microbial decomposition of SOM, and contributed more relative to SOM quality. These findings should be incorporated into ecosystem process models to better predict the response of boreal forest soil C emissions to climate change.