Abstract: Soil freeze-thaw could affect nitrogen (N) availability. The N transformation is closely related with soil microbes. The effect of soil freeze-thaw on the soil bacterial communities in the temperate zone is still not clear. We hypothesized that freeze-thaw events could affect the diversity and composition of bacterial communities, thereby changing the contents of soil dissolved nitrogen pools as well as the N transformation process. In this study, microcosms with different freeze-thaw cycles (six and fifteen cycles) were designed, with the constant temperature at 2 ℃ as the control. The results showed that the contents of dissolved total nitrogen, dissolved inorganic nitrogen, microbial biomass nitrogen and net nitrogen mineralization rate were decreased significantly in response to increasing cycles of freeze-thaw. The number of freeze-thaw cycles did not affect bacterial α diversity. In contrast, the duration of incubation was positively correlated with bacterial α diversity including Chao1 and Shannon indices. Freeze-thaw treatment significantly affected the function and composition of bacterial communities, but the number of freeze-thaw cycles had little effect on the bacterial community structure. The partial redundant analysis showed that under freeze-thaw treatments, both the composition and function of bacterial community were significantly related to soil dissolved N pools and N transformation processes.

Key words: nitrogen transformation, bacterial community, freeze-thaw cycle, dissolved nitrogen, correlation