Responses Of Soil Microbial Properties To Ecological Intensification Management In Maize Systems

Irrational fertilization and the resulting environmental problems have aroused widespread concern worldwide.Ecological intensive（EI）management,because of its using optimized management measures,such as high-yield crop varieties and their appropriate density,optimal nutrient management（e.g.,fertilizer right source,right rate,right time and right place）and other agronomic practices like tillage and cultivation practices,is proved to achieve the goal of high production and efficiency and protect the environment.To date,there have been many studies reported on agronomic performance under EI management,however,how soil microbial properties change under EI is not yet explored.Here we used field experiment integrated with high-throughput Illumina sequencing technology,quantitative polymerase chain reaction,phospholipid fatty acid analysis,fluorescence detection to determine the effects of EI management on 16s rRNA and 18s rRNA abundance,community composition and diversity,the abundance of genes involved in N cycling,extracellular enzyme activities involved in C,N,and P cycling.The main results obtained are as follows:1.Response of soil bacterial community composition and diversity to ecological intensification in spring maize and summer maize system.The results revealed that compared with FP,EI management with best agricultural practices successfully enhanced crop yield and alleviated pH decline,and maintained bacterial taxonomic diversity.Microbial taxa performing important ecological roles such as order Rhodospirillales and Bacillales were significantly enhanced in the EI approach,while Rhizobiales declined under FP.Proteobacteria,Actinobacteria,Acidobacteria,and Chloroflexi were the most dominant phyla in both locations.In fluvo-aquic soil,Rhodospirillales and Bacillales were significantly altered taxa in EI treatment.Conversely,Nitrosomonadales and Xanthomonadales were significantly altered in FP.In black soil,order subgroup₆ belonging to phylum Acidoacteria and Acidobacteriales were sensitive to N fertilization,and its abundance was highest in treatments without N.Across both soils,elevated N inputs have significantly reduced order Rhizobiales.Furthermore,both bacterial taxonomic diversity and community structure were tightly linked with soil available phosphorous（AP）in fluvo-aquic soil,whereas both bacterial taxonomic diversity and community structure were highly correlated with soil pH in black soil.2.Response of soil fungal community composition and diversity to ecological intensification in spring maize and summer maize system.The results indicated that,N application decreased fungal diversity,but EI treatment increased fugal gene copies in both black soil and fluvo-aquic soil.There was no significant difference found in the abundance major fungal phyla including Ascomycota,Basidiomycota,and Zygomycota between EI and FP.Interestingly,significant difference was found when we compared the abundance of major fungal phyla between fluvo-aquic soil and black soil for instance,Ascomycota and Zygomycota was more abundant in fluvo-aquic soil than black soil,while Basidiomycota was more abundanct in black soil over fluvo-aquic soil.Additionally,there was clear distinction in fungal communities at operational taxonomic unit（OTU）level between EI and FP for example,fungal community composition affiliated to EI clustered together and made separate groups from FP treatment.Meanwhile,the results showed that soil NO₃^-N and pH were key soil variables influencing fungal taxonomic diversity in fluvo-aquic soil and black soil respectively.Soil pH and NO₃^--N was positively linked with fungal community composition in both soils.3.Response of nitrogen transformation related gene expression to ecological intensification in spring maize and summer maize system.The results showed that N addition in both the EI and FP resulted in higher rates of potential nitrification activity（PNA）and potential denitrification activity（PDA）across the two soils.However,compared with FP,EI management has reduced rates of PNA and PDA.Similarly,N fertilization in both the EI and FP have increased the abundance of N cycling genes including ammonia oxidizing archea AOA,ammonia oxidizing bacteria AOB,nitrite reductase genes nirS,nirK,and nitrous oxide reductase nosZ across the two soils.However,compared with FP,EI management has reduced abundance of N cycling genes.Conversely,genes involved in N fixation nifH were significantly reduced under N enrichment in both EI and FP in the two soils.However,compared with FP,the extent of reduction in abundance of N fixation genes were less in EI management.Meanwhile,PNA significantly correlated with the AOA and AOB in the two soils.4.Response of soil extracellular enzyme activities and microbial community composition to ecological intensification in summer maize system.The results demonstrated that the activities of enzymes involved in carbon（C）,nitrogen,and phosphorus（P）cycling were significantly enhanced in treatments received N in both EI and FP.However,compared with FP,EI management had less C and N cycling enzyme activities.It was also found that enzyme activities involved in oxidative C cycling mainly,phenol oxidase and peroxidase significantly decreased following N fertilization,and compared with FP,EI management had higher reduction.Furthermore,total PLFAs and abundance of bacteria increased in those treatments received N in both seasons.Soil pH and soil organic carbon（SOC）were the most important soil variable causing shifts in soil bacteria.When compared with N-cycling enzymes,C-cycling enzymes were significantly affected by soil pH values and SOC.In summary,our study demonstrated that EI management preserved soil microbial diversity particularly fungal and bacterial diversity,lowered abundance of soil nitrification and denitrification genes,reduced N losses though lowering the rates of PNA and PDA,decreased the enzyme activities involved in C,and N cycling,increased crop productivity,and thus proved to be is a sustainable nutrient management approach.