Plant carbon allocation, soil carbon and nutrient condition, and microbial community jointly regulate microbial biomass carbon accumulation

Abstract

Background and aims

Microbial biomass carbon (MBC) has a significant contribution to soil carbon (C) pool. It has been suggested that plant input, soil C and nutrient condition, and microbial characteristic play crucial roles in MBC accumulation. However, the primary driver of MBC accumulation remains uncertain.

Methods

To fill this knowledge gap, we conducted a greenhouse ¹³CO₂ labelling experiment by planting three pioneer species (Pinus tabuliformis, Betula platyphylla, Populus purdomii) in soils collected from three different depths, i.e., top-soil (0–10 cm), mid-soil (10–30 cm), and deep-soil (30–100 cm).

Results

We found that MB¹³C positively correlated with plant aboveground and belowground ¹³C. The effects of plant ¹³C on MBC accumulation were mainly mediated by fungal diversity and composition. Specifically, mycorrhizal fungi (e.g., Peziza) and toxigenic genera (e.g., Fusarium and Penicillium) were identified as crucial fungal taxa. Notably, plant ¹³C allocation (aboveground ¹³C, belowground ¹³C, proportion of aboveground ¹³C, and proportion of belowground ¹³C) explained a larger proportion (17.50%) of MB¹³C variation among treatments than did soil available phosphorus contents and microbial community structure (fungal diversity and composition) (1.98%).

Conclusion

Our study suggests that plant inputs are major determinants of soil C storage, as plant C allocation was identified as the primary driver of MBC accumulation. Given the different roles of fungi and bacteria, separating fungal and bacterial biomass C can refine our understanding of MBC accumulation.