Effects Of White Clover Returning To Apple Orchard On Soil Microbial Communities

The Loess Plateau is one of the dominant regions of apple production in our country.However,long-term utilization of chemical fertilizers has led to a decrease of soil fertility and organic matter in this region, which badly affects the improvement of apple quality, and limits the sustainable development of apple industry in this area. Orchard grass is becoming a new pattern of orchard management in recent years, orchard grass can not only inhibit weeds growth, but also play a role in conserving moisture and improving soil fertility. Previous studies have been focused on the effects of forage grass on fruit tree growth, soil fertility and microbial communities, while little attention has been paid to the utilization of forage grass. Practices have been proved that cutting forage grass and returning it back to orchards timely can improve physical and chemical properties of soil, increase the contents of organic matter, therefore, promote the soil fertility. The essence of forage grass degradation is the microbes involved enzymatic hydrolysis processes, and soil microbes are one of key factors to affect the transformation of soil mineral elements during forage grass degradation in apple orchard. In order to understand the effects of forage grass degradation in apple orchard on the soil microbial communities. White clover(Trifolium repens), which is the best orchard grass in the Loess Plateau, was used as objects. Fresh white clover was buried or covered in apple orchard by litter bag method, respectively. At 1, 3, 6 and 12 months of white clover degrading period, Biolog microplate method and highthroughput sequencing technology were performed to determine the functional and genetic diversities of soil microbial communities. The main results were as follows:Studies on the dynamic changes of functional diversities of soil microbial communities in different degradation stages after white clover covered and buried indicated that both covering and burying white clover can significantly elevate the soil microbial metabolism activities(P<0.05), the microbial Shannon diversity index and richness index(P<0.05), reduce the uniformity index(P<0.05) and change the microbial community structure of the soil. The effects of covering white clover were significantly greater than that of those burying. Besides, the duration of white clover degradation also had effects on soil microbial communities. Principal component analysis of soil microbial communities showed that the major differences between covering and burying were the utilization of carboxylic acids, and the major differences between each degradation period were the utilization of sugars.Studies on the dynamic changes of genetic diversities of soil microbial communities in different degradation stages after white clover covering and burying indicated large numbers of overlapping operational taxonomic units(OTUs) existing among different returning treatments in bacteria and fungi, meanwhile there were some treatment- and degradation period-specific OTUs. Nitrospira and Spirochaetes in bacteria were specific in covering and burying, degradation period-specific OTUs in fungi were mainly distributed in Zygomycota, Ascomycota, Chytridiomycota and Basidiomycota. After covering and burying grass, Chao index, ACE index and Shannon index in bacteria were all higher than those of control treatment. In fungi, Chao index and ACE index of covering and burying grass were higher than those of control, whereas Shannon index displayed opposite results. In bacteria, Chao index and Shannon index of burying grass were higher than those of covering grass. In fungi, ACE index and Chao index of covering grass were higher than those of burying grass in the early stage of degradation but lower than those of burying grass in the late stage of degradation, but Shannon index was higher in burying grass than that in covering grass. Returning white clover to orchard also influenced the abundance of the most 20 abundant species of bacteria and fungi, which was buttressed by a cluster analysis revealing that the abundance of the most 20 abundant species of bacteria and fungi were different between the early and late stage of degradation. Meanwhile, the abundance of the most 20 abundant species of bacteria and fungi varied in different degradation periods. According to the changes of abundance in different degradation periods, the most 20 abundant species of bacteria and fungi can be roughly divided into four clusters and the abundance of species in different clusters changed in different degradation periods of white clover. Principal component analysis of the most 20 abundant species revealed that species in Proteobacteria made the greatest contribution to PC1 and five species in Proteobacteria were the main contributors to PC2 in bacteria. In fungi, the species contributed most to PC1 and PC2 were mainly belonged to Dothideomycetes and Sordariomycetes.In conclusion, both covering and burying treatments can improve the functional and genetic diversities of soil microbial communities, which make the soil microbial ecosystem more stable.