Seasonal climate variations promote bacterial α-diversity in soil

Ecological theory suggests that temporal environmental fluctuations can contribute greatly to diversity maintenance. Given bacteria's short generation time and rapid responses to environmental change, seasonal climate fluctuations are very likely to play an important role in maintaining the extremely high α-diversity of soil bacterial community, which has been unfortunately neglected in previous studies. Here, with in-depth analyses of two previously published soil bacterial datasets at global scale, we found that soil bacterial α-diversity was positively correlated with both seasonal variations of temperature and precipitation. Furthermore, piecewise structural equation models showed that seasonal variations of temperature or precipitation directly promoted soil bacterial α-diversity in each dataset. However, it is noteworthy that the importance of seasonal climate variations might be underestimated in the above analyses, due to the high level of environmental variations irrelevant to climate seasonality among sampling sites and the lack of sampling across seasons. Supplementary analyses of a previously published wheat cropland dataset with samples collected in both summer and winter across North China Plain was conducted. Similarly, we found that bacterial α-diversity was positively correlated with seasonal climate variations, but much stronger, though the range of seasonal climate variations was much smaller compared to the two global datasets. Collectively, these findings implied that fluctuation-dependent mechanisms of diversity maintenance presumably operate in soil bacterial communities. Based on existing evidence, we speculated that the storage effect may be the main mechanism responsible for diversity maintenance in soil bacterial community, but rigorous experimental tests are needed in the future.