Response Mechanism Of Rhizosphere Soil Microorganism Of Cucurbitaceae Under Drought Stress

Drought is one of the abiotic factors that restrict the normal growth of plants and reduce the yield of crops.In recent years,frequent seasonal droughts have seriously affected the growth,development,yield and quality of crops.With the deepening of biotechnology and people's cognition of microbial function,it will be an important development direction of water-saving and drought resistant agriculture in the future to use the ecological effect of soil microorganisms to improve the drought resistance ability of crops.In this study,watermelon,muskmelon and cucumber were used as test materials,and normal irrigation and non-irrigation were treated as control(CK)and drought stress,respectively.The effects of drought stress on soil biological properties and microbial community structure in rhizospheres of Cucurbitaceae crops were analyzed.The purpose of this study was to elucidate the characteristics and functions of soil microorganisms in rhizosphere of Cucurbitaceae crops underdrought stress.The results are as follows:(1)The activities of ?-glucosidase,aminopeptidase in rhizosphere soils of watermelon and cucumber were decreased,and the activity of phosphatase was significantly decreased only in rhizosphere soil of muskmelon,under drought stress..As soil enzyme activity,is not only affected by environmental factors,such as drought stress,but also is affected by crop species,human measures and other factors.Therefore,the soil enzyme activity in rhizosphere,is not fit for using as an indicator of crop resistance under drought stress.(2)Under normal water supply conditions,the soil microbial biomass C,N and P,in rhizosphere of watermelon,muskmelon and cucumber,did not show the trend as theirresistant abilities against drought in field.However,on the contrary,they were all declined in rhizosphereof every crop under drought stress,respectively.Moreover,soil microbial biomass N and P in rhizospehre of different crop,showed a same trend in resistance against drought in field.It indicated that the soil microbial biomass,in particularly,the soil microbial biomass nitrogen and phosphorus in rhizosphere,were sensitively responesed to drought stress,could be used as the indicators for describing the drought resistance of crops.(3)Soil dominant bacteria,which classified at phylum level in rhizosphere of watermelon,muskmelon and cucumber,are Proteobacteria,Actinobacteria,Chloroflexi,Acidobacteria,Firmicutes,Patescibacteria,Gemmatimonadetes,Bacteroidetes,Rokubacteria and Cyanobacteria.At genus level,norank?f?Xanthobacceae,Gaiella,norank?o?Saccharimonadales,norank?c?Subgroup?6,norank?c?KD4-96,Chujaiibacter,norank?f?GJ30-KF-CM45,norank?o?Gaillales,Streptomyces and Nocardioids are the dominant bacteria in rhizospheres of watermelon,muskmelon and cucumber.And the percentage of Proteobacteria,Actinomycetes,Nocardioids and Streptomyces were the highest in rhizosphere soil of watermelon among these three crops.It suggests that higher enrichment of functional bacteria against drought in rhizopshere of watermelon,could bean important cause for watermenlon,which has higher resistant ability against drought than those of melon and cucumber.(4)Soildominant fungi,which classified at phylum level in rhizosphere of watermelon,muskmelon and cucumber,are Ascomycota,Ciliophora and Basidiomycota.At genus level,Chaetomium,Aspergillus,unclassified?f?Chaetomiaceae,Plectosphaerella,unclassified?p?Ascomycota,Thysanophora,unclassified?f?Microascaceae,norank?c?Leotiomycetes and Colpoda are the dominant fungi in rhizosphereof watermelon,muskmelon and cucumber.The fungi with good drought resistance,which belonged to Ascomycota,Basidiomycota and Chaetomium,could be found the highest abundance in rhizosphere of watermelon.This is an important reason for higher resistant ability of watermelon in fieldamong these three crops under drought stress.In conclusion,the activity of soil enzyme in rhizosphere of crops,is not fitfor using as an indicator of crop drought resistance.Soil microbial biomass,in particularly,the soil microbial biomass nitrogen and phosphorus in rhizosphere,were sensitively responesed to drought stress,could be used as the indicators for describing the drought resistance of crops.In addition,higher enrichment of functional microorganisms(bacteria and fungi)against drought in rhizopshere of watermelons,could be the important cause for its higher resistant ability againtst drought in these thress crops.