Forest conversion induced variation of soil bacterial community across different seasons with more comprehensive information reflected by summer sampling

Purpose Soil bacteria are key component of forest ecosystem and are easy affected by changes in biotic and abiotic factors, such as vegetation and seasonal climate dynamics. When aiming to explore the differences in soil bacterial communities among various forest types, the influence of season should also be considered. Here, we aimed to explore the differences in soil bacterial communities after forest conversion and determine which season can best reflect these changes. Methods We investigated the soil bacterial characteristics from the O and A horizons in pure stands of Pinus massoniana forest, Cinnamomum camphora forest, and their mixed stands in Tieshanping, Chongqing, respectively sampled in four seasons. Results The results showed that after the conversion from coniferous to broad-leaved or mixed forests, soil bacterial diversity significantly increased (p < 0.05). Soil bacterial function was affected, evidenced by a reduction in functional guilds involved in the carbon (C) cycle (chemoheterotrophy, cellulolysis) and an increase in those involved in the nitrogen (N) cycle (e.g. nitrogen fixation, nitrification, nitrate reduction, aerobic ammonia oxidation) after forest conversion. Notably, samples collected in summer most effectively revealed the effects of forest conversion on soil bacterial community, as indicated by soil bacterial diversity, community structure and functional groups. Conclusion This study enhances our understanding of how different forest types impact soil bacterial communities and provides a guide for selecting optimal sampling seasons to cost-effectively investigate the effects of forest conversion on these communities.