Elevated precipitation modifies the relationship between plant diversity and soil bacterial diversity under nitrogen deposition in Stipa baicalensis steppe

Nitrogen (N) deposition and precipitation change are important phenomena in global climate change and they can strongly influence grassland ecology. Previous studies primarily focused on the impact of N deposition or precipitation on plant community and soil microorganisms separately. They did not account for the relationship between plant and soil microbial communities. To better understand how future climate change may affect the relationship between plant and soil microbial diversity, we simulated N deposition and precipitation change through artificial fertilization (0, 15, 30, 50, 100, 150, 200, 300 kg N. ha(-1).yr(-1)) and irrigation (no irrigation and irrigation equivalent to 100 mm extra summer rainfall) at a test area on the Stipa baicalensis steppe. We found that the plant primary productivity increased following N enrichment but the plant diversity declined. The composition, abundance and diversity of soil bacteria changed in the test scenarios. Under normal precipitation, the bacterial OTU richness increased at N100 (100 kg N. ha(-1) . yr(-1)) and the bacterial diversity increased at N100-N300 (100-300 kg N. ha(-1) . yr(-1)). When irrigation was applied, the bacterial OTU richness and diversity were improved at low N levels (15-50 kg N. ha(-1) . yr(-1)) but decreased at high N levels (N100-N300). This is probably due to water addition lead to the dissolution of more nitrates in soil and thus decreased the soil pH. A significant negative relationship was observed between plant diversity and bacterial diversity under normal precipitation. Under irrigation, the correlation was also negative at low N levels (N15-N50), but became significantly positive when the N level exceeded N100, which contributed to decrease in bacterial diversity resulting from significant decrease of soil pH. Our results clearly showed the elevated precipitation modified the relationship between plant and soil bacterial diversity under N deposition. We predict that as the global climate change further intensifies, the interaction between climate change factors may exercise complex impact on ecological properties and lead to unexpected consequences on the feedback in plant-microbe-soil system.