Abstract:

Aims: (1) To study effects of mean annual precipitation (MAP) on the diversity and community assembly of bacterial communities in the Gurbantunggut Desert; (2) Further our understanding of how bacterial communities respond to desertification.

Methods: We conducted the high-throughput sequencing data of bacterial communities from 30 soil samples (0-10 cm depth) collected from the Gurbantunggut Desert, where the MAP ranges from180 mm to 230 mm. We investigated the effect of MAP on the diversity of three defined categories of bacterial communities (whole, abundant and rare), and compared the compositions of the bacterial communities. Finally, we assessed the relative importance of deterministic and stochastic processes of the bacterial community assembly using the null model method.

Results: The results showed that MAP had no significant influence on the richness and Shannon index of whole and abundant bacterial taxa (P > 0.05). However, the indices of richness and Shannon diversity of rare bacterial taxa were significantly decreased with MAP reduction (P < 0.05). Moreover, MAP had a noticeable effect on the community composition of the whole, abundant and rare bacterial communities, with the rare bacterial taxa having the highest levels of community variation and spatial turnover followed by whole and abundant bacterial communities, respectively. The results indicated that the whole, abundant, and rare bacterial taxa in the Gurbantunggut Desert responded differently to MAP. Rare bacterial taxa showed strong sensitivity to regional precipitation differences, whereas whole and abundant bacterial taxa were resistant to MAP variation. The null model analysis showed that dispersal limitation dominated the bacterial community assembly process in the Gurbantunggut Desert (> 73.0%). In contrast, the rare desert bacterial taxa were subject to heterogeneous selection (43.0%), indicating that the desert precipitation differences enhanced the environmental selection or species competition of the rare bacterial taxa. In addition, spatial distance and MAP determined the whole bacterial community construction, and the abundant and rare taxa respectively. Particularly, MAP played an essential role in balancing the relative importance between deterministic and stochastic processes of the rare bacterial taxa.

Conclusion: Small-scale MAP differences in the Gurbantunggut Desert significantly alter the composition and assembly processes of the bacterial community. The community composition and turnover of rare bacterial taxa were affected strongly by MAP, which help mitigate the lag in the response of desert bacteria to environmental changes. Dispersal limitation isa stronger determinant of β diversity for whole and abundant bacterial taxa than for rare bacterial taxa, indicating that geographic distance explained more species turnover for desert whole and abundant bacterial taxa than for rare bacterial taxa, while the diversity distribution and ecological niche preference of desert rare bacteria were more precipitation-dependent than spatial geographic scale.

Key words: temperate desert, mean annual precipitation, abundant bacterial taxa, rare bacterial taxa, community assembly