Effects Of Long-term Unbalanced Fertilization On Microbial Community Distribution And Functions In Paddy Soil

The second largest food crop in the world is rice,which ensuring the survival of more than half of the population in the world.Balanced fertilization is an important agricultural production measure to maintain soil nutrients,soil microecology and rice yield.Unreasonable and unbalanced fertilization has become normal in global agricultural production,which has an impact on soil environment and crop yield.Analyzing the effects of unbalanced fertilization on crops and soil could provide guidance for accurate and reasonable fertilization.However,under long-term unbalanced fertilization,there is currently a lack of comprehensive understanding of the changes of rice yield and soil physicochemical properties,the responses of microbial community distribution and functions,and their contribution to yield.This study collected paddy soil from the long-term unbalanced fertilization experiment set up by Jiangxi Academy of Agricultural Sciences from 1983 after the rice was harvested in 2018.The experiment included five treatments: CK(no fertilization),-N(application of phosphorus and potassium fertilizers),-K(application of nitrogen and phosphorus fertilizers),-P(application of nitrogen and potassium fertilizers),NPK(application of nitrogen,phosphorus and potassium fertilizers).The community distribution and functional responses of soil microorganisms were analyzed by amplicon sequencing of bacterial 16 S r RNA,fungal ITS2 and archaeal 16 S r RNA genes,as well as soil metagenomic sequencing.The main results are as follows:(1)Long-term unbalanced fertilization changed rice yield and soil physicochemical properties.The annual rice yield of balanced fertilization was 11578.58 kg/ha,and the longterm lack of any nutrient element would significantly reduce the rice yield.Long-term NPK treatment reduced soil pH,resulting in soil acidification,but long-term N deficiency and P deficiency treatment slowed down soil acidification.Long-term balanced fertilization could more comprehensively maintain soil nutrients,and the contents of TOM,TN,TP,TK,AK,AP and AK in the soil were all increased.The long-term lack of nutrient elements would cause the decrease of corresponding soil nutrients.(2)The community distribution and community composition of microorganisms were affected by long-term unbalanced fertilization in paddy soil.Long-term unbalanced fertilization significantly affected the distribution of fungi and archaea.The lack of N and P significantly affected the fungal distribution(P<0.05),and the lack of N and K significantly affected the archaeal distribution(P<0.05).The composition of fungal community was more affected by unbalanced fertilization.The relative abundance of Chytridiomycota and Glomeromycota were significantly increased in the P deficiency treatment,and the Monochachytrium was significantly decreased in the K deficiency treatment(P<0.05).(3)Soil microorganisms were closely related to physicochemical properties under longterm unbalanced application.The community distribution of bacteria(23.0%),fungi(6.9%),and archaea(30.2%)were significantly affected by pH(P<0.05),and the explanation rates were the highest.Bacteria and archaea are more closely related to various soil nutrients than fungi,such as TOM,TN,AN,AP.(4)Microbial functions were regulated by long-term unbalanced fertilization.Long-term lack of P significantly increased the relative abundance of some nitrogen metabolism functions of microorganisms,such as nas B,nar H/nar Y/nxr B and nitrilase(P<0.05),and also enhanced more significantly different phosphorus metabolism functions than other treatments.Proteobacteria were mainly involved in functions related to nitrogen and phosphorus metabolism in paddy soil.(5)Soil physicochemical properties and microorganisms jointly contributed to the variation of rice yield under long-term unbalanced fertilization.The change of rice yield was mainly directly contributed by fertilization treatments.Microorganisms and physicochemical properties jointly contribute to the annual rice yield.Bacteria indirectly contributed to yield(?=0.27,P<0.001)through soil physicochemical properties(?=0.39,P<0.05),while fungi directly contributed to yield(?=0.19,P<0.01).In summary,bacteria,fungi,and archaea produced different responses in community distribution,community composition and metabolic function through pH adjustment to adapt to the changes of soil nutrients,and contributed to the annual rice yield by different mechanisms under long-term unbalanced fertilization.The results of this study expanded the understanding of soil microecological responses under unbalanced fertilization,and also provided a theoretical basis for appropriate and balanced fertilization to maintain stable crop yield and favorable soil environment.