The vertical distribution pattern of microbial- and plant-derived carbon in the rhizosphere in alpine coniferous forests

Although the quantitative assessment of plant- and microbial-derived carbon (C) chemical composition in soil profiles has been initially explored, the vertical distribution pattern of these two C sources and their relative contribution in SOC formation based on the insights related to the rhizosphere are still lacking. We quantified the divergent accumulation of microbial-derived C (i.e., microbial residues), plant-derived C (i.e., lipids and lignin phenols) and SOC in the rhizosphere at various depths (0-10 cm, 10-20 cm and 20-30 cm) in the upper mineral soil and analyzed its control factors in an alpine coniferous forest (Picea asperata. Mast). We further revealed the relative contribution of plant- or microbial-derived C to rhizosphere SOC in the soil profile. The contents of microbial- and plant-derived C and SOC in the rhizosphere decreased with soil depth and were mainly regulated by root biomass and microbial biomass. Moreover, the contribution of microbial-derived C dominated by fungal residues to rhizosphere SOC at each soil depth (more than 62%) was much higher than that of plant-derived C (less than 6%), implying that the soil microbial C pump was intensely stimulated in the rhizosphere. These results indicated that microbial-derived C was the main contributor of rhizosphere SOC at various depths in the upper mineral soil. Our findings provide direct experimental evidence for assessing the relative contribution of microbial- or plant-derived C to SOC in the soil profile from the perspective of the rhizosphere.

Automated summary

Our study in an alpine coniferous forest revealed that microbial-derived carbon, especially fungal residues, contributed more significantly to the formation of soil organic carbon (SOC) in the rhizosphere compared to plant-derived carbon. Root biomass and microbial biomass were identified as the primary controlling factors for the contents of microbial- and plant-derived carbon as well as SOC in the rhizosphere.