The phosphorus limitation in the post-fire forest soils increases soil CO2 emission via declining cellular carbon use efficiency and increasing extracellular phosphatase

Abstract

Wildfires cause severe disruptions to forest soils and modify the carbon (C) cycle in the post-fire soils. Yet, the contribution of abiotic and biotic drivers to CO2 emission in the post-fire forest soils is not well understood. This study investigated soil CO2 emission from the burned and corresponding unburned forest soils across a large latitudinal gradient of mean average precipitation (from 422 to 1640 mm) and temperature (from 0.20 to 25.8 °C). We compared the soil chemical properties (e.g., dissolved organic carbon, nutrients) and microbial properties (biomass, metabolic quotient (qCO2), and community diversity and composition) in the burned and unburned soils. Microbial metabolism was also addressed through extracellular enzyme activity and intracellular C use efficiency (CUE) using the stoichiometric modeling approach. Here, we showed that the wildfires: i) increased phosphorous (P) pressure to soil microbes (indicated by increased qCO2), ii) decreased microbial biomass, community diversity and abundance of some microbial groups (e.g., Phylum Actinobacteria), and iii) resulted in larger basal respiration due to lower cellular CUE and higher extracellular alkaline phosphatase (AP) ratio to other enzymes like β-glucosidase, Cellobiohydrolase and N-Acetyl-glucosaminidase. The latter indicated the wildfires-induced P:N imbalance (P-limitation) caused significant C loss via microbial exploitation of P from soil organic matter. The study highlights the ecological significance of intracellular and extracellular metabolisms in soil respiration and consequent C sequestration in post-fire forest soils.