Microbial mechanisms underlying active organic carbon pool increases via rhizodeposition by Moso bamboo under in situ crown 13CO2 enrichment

Abstract

Plant rhizodeposition strongly mediates plant-soil-microbe interactions and impacts the soil active organic carbon (C) pool. However, the mechanisms by which rhizodeposition affects the modulation of soil active organic C pool remain poorly understood. In this study, we investigated the effects of rhizodeposition on active organic C pool and microbial communities in Moso bamboo (Phyllostachys edulis), a clonal plant with rhizome-connected mother and offspring ramets. The crown of the mother ramet was enriched with 13CO2 to trace rhizodeposition and assess changes in soil organic C pool and the microbial community across different root systems (culm roots and rhizome roots) during key growth stages (early, peak, branching, and leafing). Our results showed that crown CO2 enrichment increased δ13C and the contents of microbial biomass C, dissolved organic C, and labile organic C (by 22.08 % to 43.67 %) in the rhizosphere, which significantly altered the bacterial community composition. Under crown CO2 enrichment, the abundance of bacterial taxa and genes associated with recalcitrant C decomposition decreased by 29.08 %–77.38 % and 30.75 %–56.85 %, respectively; while taxa and genes related to CO2 fixation increased by 51.22 %–267.00 % and 92.52 %–331.46 %, respectively. These microbial shifts contributed to an increase in the soil active organic C pool. In addition, the growth stage, rather than the root system, had a greater influence on rhizodeposition, with higher δ13C observed during the early and leafing stages compared to the peak and branching stages. In conclusion, our findings suggest that increases in the active organic C pool were primarily driven by enhanced C rhizodeposition, the stimulation of microbes involved in CO2 fixation, and the suppression of bacteria involved in recalcitrant C decomposition, while being highly dependent on the growth stage. This study provides valuable insights into the interactions between plant rhizodeposition, microbial functions, and soil active organic C dynamics.