Allocation and turnover of rhizodeposited carbon in different soil microbial groups

Abstract

Recent advances in soil organic carbon (SOC) formation indicate that labile plant C is disproportionately important for stable SOC pool because it is utilized more efficiently by soil microbes. Rhizodeposited C, accounting for 5–20% of photosynthates, are highly bioavailable and readily metabolized substrates for soil microbes. However, it remains poorly understood how different microbial functional groups contribute to transforming rhizodeposited C to SOC. Here, we synthesized 23 studies performing 13CO2 pulse labelling of plants in conjunction with stable isotope probing of microbial phospholipid fatty acids, and explored the fate of rhizodeposited C in different soil microbial functional groups. Among microbial groups, fungi (25.3%) and gram-negative bacteria (GN; 23.5%) took up most of the rhizodeposition-derived C, while the relative abundance of fungi (13.7%) was less than a half of GN (32.7%). These results suggest that fungi have a higher capability of acquiring rhizodeposition-derived C, which may be due to their hyphal growth form allowing them to obtain rhizodeposited C more effectively. The mean turnover rates of rhizodeposited C in microbial groups ranged from 0.04 to 0.13 day−1. We did not detect significant differences in the turnover rates of rhizodeposited C among microbial groups. Based on the distribution and turnover rate of rhizodeposited C in different microbial groups, we further revealed that GN (31.2%) and fungi (25.8%) produced the most microbial residues via rhizodeposition-derived C. Our results provided quantitative information about the roles of different microbial functional groups in competing for and processing rhizodeposition-derived C, which could help refine parameter estimation in modeling microbial transformation of plant C into SOC under global changes.