Water addition-average

Investigating the responses of microbial communities to long-term water addition is helpful for facing the future global change with increasing precipitation amounts and extreme rainfall events. Here, we conducted an in-situ manipulative experiment with four levels of water addition treatments (ambient precipitation +0%, +25%, +50%, +100% of local annual mean precipitation) in a desert ecosystem of China. After nine-years of the water addition experiment, we used Illumina sequencing to analyze taxonomic compositions of the soil bacterial, archaeal and fungal community. The results showed that long-term water addition significantly increased microbial biomass carbon (MBC) and reached maximal values under 100% treatment. Moreover, bacterial diversity significantly increased along the water addition gradient. In particular,the relative abundances of several bacterial phyla, such as Proteobacteria significantly increased whereas that of some drought-tolerant taxa including Actinobacteria, Firmicutes and Bacteroidetes decreased. In addition, the phylum of Planctomycetes and Nitrospirae which associated with nitrification demonstrated positive responses to water addition. Archaeal diversities significantly decreased under 100% treatment. Alternations of archaeal community were mainly driven by changes in the relative abundance of Thaumarchaeota and Euryarchaeota. Fungal community composition was stable in response to water addition. The mantel test and structural equation models further suggested that water addition affected bacterial and archaeal communities in different ways, with directly influencing bacterial community composition by changing soil moisture and temperature while indirectly influencing archaeal community composition by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes.