To explore the effects of long-term tillage on bacterial community structure in different soil layers of dryland wheat fields and its relationship with soil physicochemical properties, a long-term field experiment was conducted from 2016 to 2021 in Wenxi Experimental Demonstration Base of Shanxi Agricultural University, Shanxi Province. We studied the effects of no-tillage (NT), subsoiling-tillage (ST), and deep plowing (DP) on soil physicochemical properties; α and β diversity of the bacterial community; and dominant and different species of phyla and genera in different soil layers. Additionally, PICRUSt2 was used to predict the metabolic function of soil bacterial community. The results revealed that subsoiling-tillage and deep plowing significantly increased the soil water content in the 20-40 cm soil layer and significantly decreased the soil organic carbon content in the 0-20 cm soil layer compared with that under no-tillage for five consecutive years. Compared with that under deep plowing, subsoiling-tillage significantly increased soil water content, soil organic carbon content, dissolved organic carbon content, and dissolved organic nitrogen content in the 0-20 cm soil layer. Compared with that under no-tillage, subsoiling-tillage and deep plowing increased the α diversity of the soil bacterial community in the 0-40 cm soil layer, and subsoiling-tillage was higher than deep plowing. Compared with that under no-tillage, subsoiling-tillage and deep plowing significantly increased the relative abundances of Acidobacteria and Nitrospirae in the 0-20 cm soil layer and Acidobacteria, Chloroflexi, Gemmatimonadetes, Rokubacteria, GAL15, and Nitrospirae in the 20-40 cm soil layer. Compared with that under no-tillage, subsoiling-tillage and deep plowing significantly increased the relative abundance of Nitrospira in the 0-20 cm soil layer and Rubrobacter and Streptomyces in the 20-40 cm soil layer. Compared with that under deep plowing, subsoiling-tillage significantly increased the relative abundance of Acidobacteria and Gemmatimonadetes in the 0-40 cm soil layer. Redundancy analysis demonstrated that the contents of soil organic carbon, dissolved organic carbon, and dissolved organic nitrogen in the 0-20 cm soil layer exerted positive effects on Actinobacteria and Blastococcus, and the soil water content in the 0-40 cm soil layer exerted positive effects on Acidobacteria, Chloroflexi, and Gemmatimonadetes under subsoiling-tillage. The results of PICRUSt2 prediction showed that subsoiling-tillage and deep plowing significantly increased the relative abundance of amino acid metabolism and the metabolism of cofactors and vitamins but decreased the relative abundance of lipid metabolism of bacterial communities in the 20-40 cm soil layer compared with that under no-tillage. Compared with that under deep plowing, subsoiling-tillage significantly increased the relative abundances of amino acid metabolism in the 0-40 cm soil layer and other amino acid metabolism in the 0-20 cm soil layer. In conclusion, subsoiling-tillage or deep plowing could increase the soil water content, α diversity of the soil bacterial community, and their metabolic capacity in the dryland wheat fields during the summer fallow period. The relative abundance of Acidobacteria and Gemmatimonadetes and the ability of amino acid metabolism of the bacterial community were increased by subsoiling-tillage, and thus the contents of soil dissolved organic carbon and dissolved nitrogen can be increased.
Keywords: Illumina sequencing; bacterial community structure; dryland wheat fields; metabolic functions; summer fallow tillage.