Effects Of Film And Straw Mulching On Soil Microbial Characteristics In Dry Loess Plateau Farmland

Soil microorganism is an important part of farmland ecosystem,which plays an important role in soil nutrient transport,energy conversion,ecological environment improvement and plant growth.Surface mulching can not only improve soil nutrients and physical and chemical properties by improving soil environment,such as soil temperature,moisture content,aeration and other soil structures,but also have an important influence on soil microorganisms,promote crop growth and development,and realize the sustainable development and utilization of farmland soil in dryland farming areas.This study is based on a long-term field positioning experiment set in the agricultural region of the Loess Plateau.With no mulching(CK)as the control,different mulching treatments(plastic film mulching(F)and high amount straw mulching(St90)in July,August and September each year were studied.Low amount straw mulch during whole growth period(S45);Effects of high straw mulch(S90)on soil nutrients,microbial activity and microbial community structure during whole growth period.Soil agricultural analysis methods,real-time fluorescent quantitative PCR,high-throughput sequencing and Biolog technology,and with the aid of redundancy analysis,correlation analysis and principal component analysis,quantitative analysis of the soil microbial community structure and function and soil physical and chemical properties,the relationship between the Loess Plateau farmland soil in order to choose reasonable cultivation way to provide the scientific basis and technical guidance.The main findings are as follows:(1)Long-term plastic film and straw mulching significantly reduced the contents of NH4+-N and NO3--N in the soil.Compared with CK,S90 treatment significantly increased soil organic carbon and available P contents.Soil microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)contents were decreased by all mulching treatments,and the contents of MBC and MBN were significantly decreased by F,St90 and S45 treatments.The soil microbial biomass(MBP)of St90 treatment was significantly higher than that of CK and F,while that of S45 and S90 treatment was significantly lower than that of CK and F.(2)The effects of mulching on soil microbial gene abundance were significantly different with different mulching methods and microbial species.F and S45 significantly decreased the gene abundance of soil archaea,ammonia-oxidizing bacteria,ammonia-oxidizing archaea,and nitrogenase ferritin,but significantly increased the gene abundance of soil bacteria.St90 significantly decreased the abundance of soil archaea,ammonia-oxidizing bacteria and nitrogenase ferritin genes.S90 treatment significantly reduced the gene abundance of soil archaea,ammonia-oxidizing bacteria and ammonia-oxidizing archaea.In addition,this study also found that each mulching treatment had little effect on the gene abundance of nitrite reductase,methane-oxidizing bacteria and alkaline phosphatase.(3)The results of OTU classification and a diversity analysis showed that soil microbial community was susceptible to different mulching methods,and the effects on soil fungal community structure and diversity were more obvious.The soil bacterial and fungal species richness and diversity were the highest under S45 treatment.Cluster analysis showed that there was little difference in microbial community structure among St90,S45 and S90 treatments under straw mulching,but there was a great difference between plastic film and straw mulching.Different mulching treatments had different effects on the dominant bacteria in soil,and each mulching treatment increased the relative contents of the dominant bacteria(Acidobacteria)and the dominant fungi(Ascomycetes and Morpheletes).In the dominant flora of soil bacteria,compared with F,straw mulching increased the relative content of Actinobacteria and Chloroflexobacteria,but decreased the relative content of Proteobacteria.Soil ammonium nitrogen,nitrate nitrogen and pH were the main influencing factors of soil microbial community under different mulching treatments.(4)Biolog data showed that soil microbial carbon source utilization activity(AWCD value)and functional diversity index were significantly increased under mulching treatments.The richness,dominance and evenness index of each mulching treatment were significantly increased.Among them,the functional diversity index of St90 treatment was significantly lower than that of F and other straw mulching treatments.Amino acids,carboxylic acids,sugars and amines are the main carbon sources of soil microorganisms.Soil pH,total nitrogen,nitrate nitrogen and water content are the main influencing factors of microbial carbon source metabolism variation.(5)In this study,medium active organic phosphorus(MLOP)was the main component,accounting for about 70%of the total organic phosphorus,followed by active organic phosphorus(LOP),medium stable organic phosphorus(MROP),and high stable organic phosphorus(HROP)accounted for the lowest proportion.F treatment significantly reduced the contents of LOP and MLOP;St90 treatment significantly increased MROP content;S45 treatment significantly increased HROP content,but decreased MLOP content.Soil organic phosphorus composition did not change significantly under S90 treatment.Soil microbial community structure and abundance and microbial biomass change had different correlations with the transformation of organophosphorus under different mulching methods.In summary,changes in soil carbon,nitrogen,phosphorus content,pH and other soil physical and chemical properties are important factors that affect changes in soil microbial communities.Plastic film mulching significantly reduces soil carbon and nitrogen content,and improves the ability of microorganisms to use carbon sources;the straw mulching treatment significantly increased the soil available phosphorus content.Among them,the St90 treatment significantly increased the soil organic phosphorus components and the MBP content,and effectively promoted the conversion of organic phosphorus by microorganisms.At the same time,the soil bacteria and fungal communities were particularly affected by the S45 treatment obvious.