Soil Bacterial Community Response to Fire Varies with Slope Aspect at Zhenshan Mountain, East China

Wildfire is a crucial event in the regulation of the structure and function of forest ecosystems. The effects of fire on soil microorganisms is still poorly understood. Here, we compared soil properties and bacterial communities between burnt and unburnt soils on sunny and shady slopes 4 and 13 years after a fire in a warm temperate forest ecosystem at Zhenshan Mountain in Shandong, eastern China. Soil physicochemical properties and enzyme activity were more affected by fire than by slope aspect. Fire significantly altered bacterial beta-diversity but did not affect bacterial alpha-diversity. Co-occurrence networks showed that fire decreased the complexity, edge number, average degree, and average clustering coefficient of the bacterial communities. Available nitrogen content was the major factor explaining the differences in bacterial communities between the burnt and unburnt samples. Moreover, the impacts of fire varied with slope aspect and recovery time. The relative abundance of Spartobacteria, Gammaproteobacteria, TK10, and JG30-KF-CM66 differed significantly between sunny and shady slopes in burnt soil, and were all significantly correlated with soil pH. Differences in soil pH mediated by slope aspect drove the variation in soil bacterial community structure at burned sites. Within constant slope aspect, the soil bacterial community in burnt soil 4 years after the fire was significantly different from that in unburnt soil, and after 13 years of recovery it was similar to that before the fire. These results indicate that the slope aspect should be considered when predicting the response of soil microbial communities to fire.