Contribution of microbial necromass to soil organic carbon and its influencing factors during plantation recovery in a subtropical rocky desertification region

Abstract

Microbial necromass carbon (MNC) constitutes a significant portion of soil organic carbon (SOC). However, the contribution of MNC to SOC under different plantation recovery patterns in rocky desertification ecosystems remains poorly understood. Herein, we investigated MNC, along with its associated soil carbon (C) fractions, available nutrients, and microbial community composition across five stand types and unafforested land (control) in the Wuling Mountains of subtropical China. Establishing mixed forest and Cinnamomum camphora forest significantly increased SOC stock compared to the control. The highest microbial community biomass and MNC content were observed in the Cinnamomum camphora forest, being 1.64 and 1.16 times higher than the control, respectively. Soil fungal community biomass was lower than that of bacteria across all stand types, yet fungi contributed the majority of MNC (80.1 %). The contribution of MNC to SOC in the five stand types ranged from 31.7 % to 43.6 %, which was lower than in the control. Control soils, with low input of plant-derived organic matter, exhibited higher necromass accumulation coefficients (NAC). SOC content, microbial community biomass, and MNC content decreased with soil depth, whereas NAC and the contribution of MNC to SOC showed an opposite trends. The random forest and variance partitioning analyses revealed that soil available nitrogen, SOC, and fungal and bacterial community biomass were the primary drivers of MNC accumulation (p < 0.05), with their interactions explaining 83 % of the variance in MNC accumulation. Our findings demonstrate that afforestation enhances SOC stock in rocky desertification ecosystems, with microbial community biomass and necromass playing crucial roles in C transformation and sequestration.