Recoupling of Soil Carbon, Nitrogen, and Phosphorus Cycles along a 30 Year Fire Chronosequence in Boreal Forests of China

The biogeochemical coupling of soil carbon, nitrogen, and phosphorus (C-N-P) cycles is crucial for maintaining the ecological balance of boreal forests. Yet, the current understanding of wildfire disturbance is only based on changes in elemental contents, thereby lacking any within-ecosystem corroboration of biogeochemical coupling. Here, we conducted a field survey of microbial functional associations for 53 genes related to soil C-N-P cycling from 17 locations spanning a 30 year succession period after high-severity forest fires in the Greater Khingan Mountains (Inner Mongolia-China). We found that bacteria proliferated and dominated the competition with fungi by encoding genes for recalcitrant C decomposition, N fixation, and inorganic N cycling during the postfire early succession. Wildfire prominently decoupled the microbial functional associations of soil C-N-P cycling, particularly in organic-inorganic N turnover. However, over the 30 year succession period, these functional associations recoupled in both soil organic and mineral horizons. Notably, the decoupling of microbial functional associations recovered from a wildfire disturbance faster than the soil C-N-P imbalance. This strong resilience of the microbiome will aid in the recovery of the soil elemental balance and ecosystem stability from the increased intensity of wildfires projected for the boreal forests of China.