Short-term response of soil bacterial and fungal communities to fire in rotational shifting cultivation, northern Thailand

Soil microbial communities are ubiquitous and essential for the functioning of the soil system. The use of fire is a common practice in rotational shifting cultivation (RSC) to clear land after cutting vegetation for cultivation. However, three main questions remain unanswered: (1) What is more sensitive to fire between bacteria and fungi in RSC fields? (2) What kinds of bacterial and fungal taxa are resistant to fire in RSC fields? and (3) Does fire affect the complexity of soil microbial networks in RSC fields? To address these questions, surface soil samples (0-2 cm depth) were collected from sites with 10 years of fallow in Chiang Mai Province, northern Thailand, at three different time points: before burning (BB), 5 min after burning (AB), and 1 month after burning (AB-1 M). The results revealed that bacteria exhibited greater sensitivity to fire compared to fungi. After one month of burning, bacterial richness and diversity increased significantly and recovered more rapidly than fungi, likely due to the rise in soil pH post-fire. Heat-resistant bacteria and fungi were detected following the fire event. Specifically, within the bacterial community, the phylum Firmicutes exhibited a substantial increase of around 95 % (BB = 0.63 %, AB = 96.31 %), while the genera Bacillus (BB = 0.16 %, AB = 38.53 %), Alicyclobacillus (BB = 0.14 %, AB = 17.10 %), and Aneurinibacillus (BB = 0.03 %, AB =10.48 %) showed over a tenfold increase after the fire. In the fungal community, the phylum Ascomycota (BB = 31.46 %, AB = 96.47 %) experienced a significant increase after the fire. At the genus level, Penicillium (BB = 4.99 %, AB = 54.14 %), Aspergillus (BB = 3.20 %, AB =14.50 %), and Hamigera (BB = 0.02 %, AB = 10.07 %) displayed dominant increases in response to fire. Co-occurrence network analysis revealed that fungi tended to form more complex networks compared to bacteria. The complexity of both bacterial and fungal networks declined after the fire but rebounded significantly after one month. Our study underscores the significance of fire disturbance in shaping the dynamics of soil bacteria and fungi in RSC fields.