Aeration irrigation improving grape rhizosphere soil chemical properties and bacterial community structure in arid area

Abstract: In traditional agricultural irrigation, uptake of water of plant root and its own respiration are relatively contradictory. When the water content is satisfied, aerobic respiration can not fully carry out due to limited air supply in soil. Good soil aeration is beneficial for maintaining higher soil fertility and crop growth and development. Once air capacity in soil decreases and gas exchange is restricted, the soil physical and chemical properties would become deteriorated, which affects the normal growth of the crops, resulting in reduced production. Aeration irrigation is an improvement of subsurface drip irrigation (SDI), and it involves the delivery of oxygen or oxygenated material to the root zone of the crop through subsurface drip irrigation systems to improve soil aeration, and to meet the needs of root growth and development, thereby promoting growth and development of crops and improving crop yield and quality. Soil microorganisms are the most important and active part of soil ecosystems and reflect changes in soil quality in a sensitive, timely, and accurate manner. However, few reports have described the effects of aeration on soil microbial diversity. In this study, Red Globe grape planted in boxes was used as experimental material, self-designed integrated equipment of SDI with tanks of fertilizer-water-gas was involved as gas injection device, and high-throughput 16S genome sequencing was the key technique to study effect of aeration of rhizosphere under condition of SDI with tanks on the rhizosphere soil and bacterial community structure. The results showed that aeration of rhizosphere under condition of SDI with tanks could raise the pH values of soils, increase the contents of Olsen-P and available K in soil, and promote decomposition of organic matter in the 20-30 cm soil layer. Analysis of bacteria related to nitrogen, phosphorus and potassium metabolism showed that rhizosphere aeration can promote the Nitrosospira associated with nitrification，Pseudomonas and Bacillus associated with phosphorus and potassium metabolism, and inhibited Ralstonia associated with denitrifying bacteria. It showed that absorption of nitrogen, phosphorus and potassium in the plant maybe due to the increase of nitrifying bacteria and bacteria of decomposition of organic phosphorus and potassium. According to the analysis of microbial community structure, we learned that aeration of rhizosphere under condition of SDI with tanks promoted the growth of aerobic bacteria such as Nitrospirae, inhibited the growth of anaerobic bacteria Planctomycetes. Furthermore, Chao1 and Shannon index analyses indicated that aeration of rhizosphere under condition of SDI with tanks could change the abundance of bacterial community effectively. However, it had little effect on bacterial community diversity. In addition, for bacterial phylum, aeration treatment increased the abundance of actinomycetes and Nitrospira, which were 16.7% and 22.7% higher (P<0.01) with aeration treatment than that without aeration in the 40-50 cm soil layer, respectively, and reached extremely significant levels (P<0.01). Canonical correspondence analysis (CCA) and correlation analyses showed that the pH values of soils, Olsen-P and available K contents were important indicators of bacterial community structure when applying aeration of rhizosphere under condition of SDI with tanks. The results of this study showed that the SDI system can be used for aeration without extensive increases cost. This irrigation approach can improve soil aeration quality, optimize soil microbial community structure, and improve fertilizer use efficiency, which has certain application and promotion prospects. However, the frequency and intensity of aeration of rhizosphere under SDI with tanks need to be further optimized.