Study Of Different Ecological Regions And Deep Ploughing On Soil Microbial Community In Paddy Soil

Rice(Oryza sativa L.)is the most vital food crop in the world,which is of great importance to food security of our country.The cultivation of super-high yield hybrid rice varieties with high yield potential has made a great contribution to fulfilling the needs of China’s growing population.However,owing to the differences in climate and soil environment,there are differences of rice yield in different planting ecological regions.Microorganisms,as the major contributors of soil biogeochemical cycles,play a critical role in soil nutrient cycling,greenhouse gas production and emissions and crop yield in paddy fields.Therefore,it is essential to research the distribution characteristics and driving factors of bulk soil and rhizosphere microbial community structure,species and functional composition at a large scale in different rice planting ecological regions.At the same time,comparing the impacts of species and functional composition of microbial communities in different rice ecological regions and different root zones on rice growth is helpful for us to understand the rhizosphere microbial ecological mechanisms underlying yield differences between different ecological regions.Finally,it would be significant to further explore the microbial ecological mechanisms by which different tillage intensity enhance rice yield by affecting the structure and function of soil microbial community and related nutrient element cycling,in order to reduce rice yield differences between different ecological regions.The main findings are as follows:(1)The bulk soil and rhizosphere bacterial communities in rice under different ecological regions differed significantly in terms of structural construction,species composition and driving factors.The α andβ-diversity characteristics of rhizosphere microbial communities were significantly different from those of bulk soil microbial communities.At the meantime,the similarity of both bulk soil and rhizosphere microbial communities had a significant distance decay relationship with geographic distance,and geographic distribution characteristics.γ-Proteobacteria,Firmicutes,Myxococcota,Bacteroidota,Verrucomicrobiota were significantly correlated with geographical distance.In the community construction mechanism,the bulk soil microbial community construction mechanism was mainly dominated by deterministic process,in which homogeneous selection was the main process of deterministic process.The construction mechanism of rhizosphere microbial community was mainly stochastic process,in which undominated and dispersal limitation were the main processes of stochastic process.The SDER values for rhizosphere communities were significantly lower than for bulk soil communities.The driving degree of climate(mean daily temperature difference)and environmental factors(soil organic carbon)caused by latitude differences to microbial communities in different root zones affected the growth of rice in different ecological regions.(2)The "gatekeeper effect" of rhizosphere selective filtering in α diversity of microbial community was independent of region and soil type.The selective recruitment of different microorganisms was also independent of region providing the microbial source.The topological structure of microbial co-occurrence network was different in different regions,but key species in microbial network were similar across ecological regions(Proteobacteria,Desulfobacterota and Myxococcota).The dominant species drivers of bacterial communities in Gejiu were mean relative humidity,mean sunshine hours and mean temperature difference.The climatic drivers of dominant species in bacterial community at Xinyang were mean temperature difference and mean monthly temperature.Soil organic carbon,available phosphorus and available potassium were the environmental drivers limiting the differences in bacterial community structure between Gejiu and Xinyang.Microbial species and functions in different root zones had significant geographical distribution characteristics.The differential enrichment of microbial species and functions in different root zones may be an important factor affecting the growth and yield of rice in different ecological regions.For example,the differential bacteria were enriched in Gejiu,among which the species abundance of bacteria such as γ-Proteobacteria,Bacteroides and Desulfovibrio bacteria,which were quite different.In terms of potential functions,the two regions showed strong geographical differences.The bulk soil,rhizosphere and rhizoplane of Gejiu were enriched with higher levels of nitrogen-related microbial functions;the soil of Xinyang was enriched with methane cycle and iron respiration-related functions.(3)Based on above,deep tillage can alter the structure,species composition and function of soil microbial communities to improve rice yields.Tillage intensity can significantly affect microbial diversity and community structure.Deep tillage enriches the abundance of microbial species associated with the soil nitrogen cycle in rice fields,resulting in more complex and compact microbial co-occurrence network,richer and more competitive ecological functions,and was closely related to process of soil nitrification.Compared with shallow tillage,deep tillage can reduce the expression of denitrification process-related genes(nir S,nir K and nos Z),inhibit nitrate reductase(SNR)activity,reduce the intensity of soil denitrification,increase the intensity of nitrification potential,reduce N2 O emissions,promote nitrification intensity,increase soil NO3--N content,increase rice root volume,improve rice nutrient uptake utilization efficiency and increase crop yield.This study revealed the geographic distribution characteristics and community constructive mechanisms of microorganisms in different root zones of five rice growth ecological regions from north to south of China,and their effects on rice growth by using molecular biology,microbiomics techniques and various biometric methods.It is clear that the spatial distance,climate and environmental differences of different rice planting regions affect the microbial community assembly mechanism between rice rhizosphere and bulk soil,resulting in the enrichment differences of microbial community species and functions in different rice planting regions,thus influencing the growth and development of rice.Deep tillage treatment can improve the abundance of microbial species related to microbial nitrogen cycle,enhance the network interaction between microorganisms,inhibit the expression of related genes in soil denitrification process,promote the intensity of soil nitrification,reduce the emission of N2 O gas in paddy soil,promote the development of crop roots,and increase crop yield,which is of great significance to reduce the difference in rice yield between different ecological regions.