Effect of prescribed burning on the small-scale spatial heterogeneity of soil microbial biomass in Pinus koraiensis and Quercus mongolica forests of China

Prescribed burning can alter soil microbial activity and spatially redistribute soil nutrient elements. However, no systematic, in-depth studies have investigated the impact of prescribed burning on the spatial patterns of soil microbial biomass in temperate forest ecosystems in Northeast China. The present study investigated the impacts of prescribed burning on the small-scale spatial heterogeneity of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in the upper (0–10 cm) and lower (10–20 cm) soil layers in Pinus koraiensis and Quercus mongolica forests and explored the factors that influence spatial variations of these variables after prescribed burning. Our results showed that, MBC declined by approximately 30% in the 10–20 cm soil layer in the Q. mongolica forest, where there were no significant effects on the soil MBC and MBN contents of the P. koraiensis forest (p > 0.05) after prescribed burning. Compared to the MBC of the Q. mongolica forest before the prescribed burn, MBC spatial dependence in the upper and lower soil layers was approximately 7% and 2% higher, respectively. After the prescribed burn, MBN spatial dependence in the upper and lower soil layers in the P. koraiensis forest was approximately 1% and 13% lower, respectively, than that before the burn, and the MBC spatial variability in the 0–10 cm soil layer in the two forest types was explained by the soil moisture content (SMC), whereas the MBN spatial variability in the 0–10 cm soil layer in the two forests was explained by the soil pH and nitrate nitrogen (NO3–-N), respectively. In the lower soil layer (10–20 cm) of the Q. mongolica forest, elevation and ammonium nitrogen (NH4+-N) were the main factors affecting the spatial variability of MBC and MBN, respectively. In the 10–20 cm soil layer of the P. koraiensis forest, NO3–-N and slope were the main factors affecting the spatial variability of MBC and MBN, respectively, after the burn. The spatial distributions of MBC and MBN in the two forests were largely structured with higher spatial autocorrelation (relative structural variance C/[C0 + C] > 0.75). However, the factors influencing the spatial variability of MBC and MBN in the two forest types were not consistent between the upper and lower soil layers with prescribed burning. These findings have important implications for developing sustainable management and conservation policies for forest ecosystems.