Responses of soil microbial community characteristics and enzyme activities to different irrigation modes over four wheat-maize rotation seasons

Water scarcity in arid and semiarid areas highlights the importance of developing water-saving irrigation techniques. Soil extracellular enzyme activities (EEAs) and microbes are important for soil biochemical cycles and plant growth. However, little is understood about how soil EEAs, and microbial communities respond to water-saving irrigation systems and levels. Therefore, a field experiment was carried out over four consecutive wheat-maize seasons to explore the effects of surface irrigation (SI) and drip irrigation (DI) coupled with different irrigation levels (i.e. 65, 50, 35 and 20 mm/event, represents sufficient, mild deficit, moderate deficit and serious deficit irrigation, respectively) on the plant biomass, soil properties, soil EEAs, and bacterial community. The results revealed that mild deficit irrigation showed no significant impact on plant biomass, serious and moderate deficit irrigation significantly decreased crop biomass by 49.0 % and 26.6 %, respectively, compared with sufficient irrigation. However, the crop biomass of serious and moderate deficit irrigation under DI were 15.4 % and 17.4 % higher, respectively, than that under SI. Serious and moderate deficit irrigation significantly increased soil available K accumulation and soil urease activity, decreased bacterial richness, and shifted the bacterial community structure. No significant differences were found between mild deficit and sufficient irrigation. The relative abundances of Firmicutes, Gemmatimonadota, and Myxococcota significantly increased under serious deficit irrigation, while Acidobacteriota significantly decreased. Moderate deficit irrigation under DI did not shift bacterial community structure, while under SI did. Soil pH, electrical conductivity (EC), available K, and plant biomass were the major factors influencing the bacterial community compositions. Serious deficit irrigation reduced the complexity and stability of the soil bacterial co-occurrence network. The network of DI had more significant interactions among bacteria than the SI. Therefore, DI coupled with moderate deficit irrigation is more beneficial to maintain crop yield and the stability of bacterial community structure than SI.