Changes in soil bacterial and fungal community characteristics in response to long-term mulched drip irrigation in oasis agroecosystems

Soil microorganisms are key drivers of soil nutrient cycling and agroecosystem sustainability. Despite their critical roles in soil evolution processes, the variation of soil microbial communities in cotton fields with different years of practicing mulched drip irrigation remains poorly understood. The objectives of this study were to investigate the effects of different years of mulched drip irrigation (i.e., CK, 11, 13, 15, and 21 years) on soil microbial communities and soil properties in cotton fields in an oasis by using high-throughput sequencing of the microbial 16 S/ITS gene. The results showed that soil EC decreased significantly after mulched drip irrigation and the lowest value occurred in 21-year treatment, decreased by 74.43%. Soil organic carbon, available nitrogen, available phosphorus and available potassium increased significantly with the length of years under mulched drip irrigation. The abundance of dominated bacterial phyla (Actinobacteria, Bacteroidetes, and Rokubacteria) significantly varied among different years of mulched drip irrigation, and no significant change was found in soil fungal community at the phyla level. The abundance of dominated fungal genera Cephalotrichum (21.82–68.96%) decreased significantly with irrigation years extension. Non-metric multidimensional scale analyses (NMDS) showed that soil bacterial and fungal communities significantly differed among different treatments (P = 0.001). The more positive co-occurrence relationships of bacteria to fungi, and the highest Shannon and lowest Simpson values were observed in the 13-year mulched drip irrigation. The abundance of bacteria and fungi was significantly correlated with soil EC, total nitrogen, total potassium, and soil organic carbon. Our results indicated that long-term mulched drip irrigation affected the structures and interactions of microbial communities in cotton fields by reducing soil salinity and regulating the soil nutrient concentrations, and 13-year mulched drip irrigation was capable of enhancing soil microbial diversity in this region.