Effect of fire on microbial necromass carbon content is regulated by soil depth, time since fire, and plant litter input in subtropical forests

Microbial necromass carbon (MNC) is regarded as a considerable source of soil organic carbon (SOC). However, the impacts of fire on MNC and its contribution to SOC remain unexplored in forest ecosystems. In this study, we aim to evaluate how fire affects over the long-term soil MNC and its contribution to SOC in subtropical forests.

We established a paired fire platform along a recovery time of 1, 5, 9, and 27 years, encompassing high severity burned and unburned plots in subtropical Pinus yunnanensis forests. Soil MNC, SOC, as well as physicochemical soil properties were measured.

Burning effects on SOC and MNC were observed solely in surface layer. Initially, the fire greatly reduced both variables, however, they recovered to pre-fire levels by 9 years post-fire and showed positive responses by 27 years post-fire. Interestingly, we found that fire strengthened the relationships between MNC and microbial α-diversity, as well as litter input. Additionally, reduced litter input resulting from fire, directly or through decreased soil nutrients, explained the loss of MNC across all sites at both soil depths.

Our work provides robust evidence that the effects of fire on MNC and its contribution to SOC largely depend on soil depth, time since fire, and plant litter input. These insights hold significant implications for fire management and post-fire recovery efforts in this and similar forest ecosystems.