Effects Of Irrigation And Fertilizer Measures On Farmland Soil Enzymes And Microbial Communities In Hetao Irrigation District

Water and nutrient deficiency are the two main factors that affect crop yields in arid areas.Therefore,irrigation and fertilization are widely used to increase soil moisture and nutrient content,thereby increasing crop yields.Microorganisms play a vital role in nutrient transformation,However,there are few studies on the relationship between soil microbes and farmland fertility and crop yield under different irrigation and fertilizer conditions in Hetao Irrigation District,especially the role of nitrogen-fixing bacteria,nitrifying bacteria and other nitrogen-transforming microorganisms on soil fertility and crop yield is still unclear.To solve this problem,this research takes spring corn from Shuguang Station in Bayannaoer City,Inner Mongolia as the research object.High-throughput sequencing,enzyme stoichiometry and other methods were applied to study the evolution characteristics of soil enzyme activity,microbial community structure and functional group interaction network under different irrigation and fertilizer treatments(low irrigation and low fertilizer(LI+LF),low irrigation and high fertilizer(LI+HF),medium irrigation and low fertilizer(MI+LF)),medium irrigation and high fertilizer(MI+HF),high irrigation and low fertilizer(HI+LF),high irrigation and high fertilizer(HI+HF control)),clarify the driving factors of soil microbial community structure changes,and clarify the role of microbes on soil fertility and crop yield,and provide a theoretical basis for farmland management measures in Hetao Irrigation District.The main results are as follows:(1)Irrigation and fertilization have significant effects on corn yield and soil chemical properties.Compared with other treatment groups,the corn yield,organic carbon content,and inorganic nitrogen content were higher under the treatments of medium irrigation with low fertilizer and medium irrigation with high fertilizer treatment,and also had a higher soil carbon to nitrogen ratio and carbon to phosphorus ratio.Irrigation significantly increased carbon limitation,while fertilization reduced the microbial nitrogen limition.The combination of medium irrigation and low fertilization resulted in higher C-acquisition enzyme activity and lower N-acquisition enzyme activity,suggesting the promotion of C limitation and alleviation of N limitation for microbes by this practice.Microbial C limitation strengthened the nitrification potential by increasing the abundance of amo A-AOA and amo A-AOB genes involved in nitrification.Microbial N limitation hindered the denitrification potential by reducing the abundance of nir K,nir S,nos Z,and nar G genes involved in denitrification.Increased microbial C limitation with irrigation was due to the elevated soil water content,which promoted the activity of C-acquiring enzymes and facilitated the ability of microbes to decompose organic matter.In general,the combination of medium irrigation and low fertilization reduced nitrogen loss by promoting microbial carbon metabolism and inhibiting microbial nitrogen limitation,and can effectively decompose organic matter.(2)Irrigation and fertilization significantly affected the Alpha diversity of bacteria and fungi,but the interaction between the two has no significant effect.Compared with other treatment groups,the treatments with medium irrigation with low fertilizer and medium irrigation and high fertilizer significantly increased the Shannon index and Chao1 index of bacteria and decreased the Shannon and Chao1 index of fungi.The dominant bacterial populations were mainly Gammaproteobacteria,Bacteroidia,Gemmatimonadetes,Alphaproteobacteria,and Anaerolineae.The top 5 fungal populations in relative abundance were: Sordariomycetes,Pezizomycetes,Dothideomycetes,Mortierellomycetes,Leotiomycetes.Compared with other treatments,the bacterial and fungal community composition of the medium-irrigation low-fertilizer and medium-irrigation high-fertilizer treatments were more similar and clustered more closely.The microbial community composition between the other treatments was significantly different.(3)Irrigation and fertilization had significant effects on bacterial and fungal community diversity,N-cycling potentials,and co-occurrence network patterns during the maize growth.The combined treatment of medium irrigation and low fertilization resulted in higher maize yields,bacterial diversity,nitrification,ammoxidation,N-fixation potentials,and network modularity,when compared with the other treatments.There were strong and positive associations between the soil N-cycling potentials,maize yields,and bacterial diversity.Structural equation modeling demonstrated that bacteria contributed more to soil fertility and maize yields than fungi,and irrigation and fertilization indirectly affected microbial functions by altering bacterial diversity and network modularization,which also affected soil fertility and maize yields.