Aridity drives the differentiation of soil bacterial communities in the Inner Mongolia steppe

Understanding the response of soil bacterial communities to precipitation and temperature gradients is crucial for assessing the impact of climate change on ecosystem structure and function. Here we investigated the spatial variations of bacterial community diversity and structure along a precipitation and temperature transect in the east Inner Mongolia steppe. Our results showed that the variations of bacterial diversity satisfied to the distance-decay rule along the sampled 451-km transect. Dramatic changes in bacterial community structure occurred at an annual precipitation of 261 mm (aridity index is 0.22), indicating different mechanisms driving bacterial community assembly in arid and semi-arid ecosystems. Temperature and plant coverage played more important role in shaping bacterial community structure in arid climate; however, precipitation and temperature played more important role in semi-arid climate. Microbial communities would use more energy for growth in the semi-arid steppe than those in the arid steppe. Competition for substrates may be more important for the bacterial community in the semi-arid systems while biological adaptation is more important in arid climate. Our results further showed that climate conditions had an important direct effect on soil properties and plants, and had indirectly effect on soil bacterial communities through the influences on soil and plants.