Establishment And Regulation Of Soil Microbial Community For High Productivity Soil In Rice-wheat Rotation System Of South Jiangsu

Soils are considered to be the most diverse microbial habitats on Earth with respect to species diversity. Soil microorganisms are the basis of formation and maintenance of soil biological fertility. Improvement and maintenance of soil biological fertility, increase of the contribution rate of soil foundation fertility in grain production is the key to achieve higher grain yield and develop sustainable agriculture. Thus, the study of how to estabilish and regulate high-productivity associated soil microbial community is of utmost importance to improve soil biological fertility and increase crop yield.Fertilization can not only alter soil physiochemical and biological characteristics and change the bulk soil microbial community, but also shift the plant root exudate profiles and shape rhizosphere soil microbial community. This study was focused on the effects of fertilization and plant root exudates on soil microbial community and divided into three parts. Firstly, we compared the effects of different fertilizer regimes on crop yield and their components, found out the potential regimes to establish high-productivity associated soil microbial community. We further characterized the shifts of soil microbial community during the establishment process by these regimes and found out the biological indicators of these high-productivity associated soil microbial communities. Secondly, we collected and identified the root exudates of different growth stages of Arabidopsis. Then we set up soil experiments to study the effects of addition different root exudates on soil microbial community and try to find out the relationships between specific root exudate components and microbial taxa. Thirdly, we studied the effects of soil microbial community influenced by fertilization and plant root exudates on Arabidopsis biomass accumulation through soil slurry experiment. The main results were summarized as follows:1. Fertilization can influence crop yield and their components, increase soil available nutrient contents and enhance soil microbial biomass, and considered as the key factor in shaping the soil microbial community in agroecosystems. The application of chemical fertilizer plus pig manure organic-inorganic compound fertilizer (NPKMOI) and chemical fertilizer plus straw returning (NPKS) increased the number of productive spikes and yield of rice and wheat, respectively. Soil available nitrogen, phosphorus and potassium contents were significantly increased in all fertilizer treatments and were highest in the NPKMOI treatment. Soil microbial biomass carbon and nitrogen were significantly increased after fertilization and were highest in the NPKMOI treatment. Pyrosequencing results revealed that soil bacterial community was significantly influenced by fertilization and the changes of community structure were consistent in the rice and wheat seasons. RDA analysis showed that the bacterial community of NPKMOI treatment was markedly different with other fertilizer treatments and control,while bacterial community of NPKS treatment was similar with other fertilizer treatments but different with control. VPA analysis revealed that fertilizer regimes were contributed most to the variation of bacterial community,indicating that fertilization was the main factor in influencing soil bacterial community. Thus,NPKMOI and NPKS treatments were the potential regimes to establish high-productivity associated soil microbial community.2. Increases of microbial community diversity, functional diversity, microbial interactions and network stability are important biological indicators in the establishment process of high-productivity associated soil microbial community. BIOLOG analyses revealed that NPKS treatment significantly increased the microbial activity and carbon untilization diversity. Miseq sequencing results indicated that both NPKS and NPKMOI treatments increased soil bacterial and fungal alpha diversity. PCoA analysis showed that NPKS and NPKMOI treatments directionally shaped soil bacterial and fungal community structure,and the trend of these changes was consistent in the rice and wheat seasons.Network analysis revealed that NPKS and NPKMOI treatments had more bacterial and fungal interactions, and more stable microbial networks. Procrustes analysis revealed that soil bacterial community was significantlt correlated with fungal community, indicating that the effects of fertilization on bacterial and fungal community were consistent. Soil bacterial and fungal alpha diversity and community structure were positively and significantly correlated with rice and wheat yields. Therefore, soil microbial diversity and functional diversity can be considered as soil biological fertility indicator.3. The root exudate profiles of different growth stages of Arabidopsis were remarkably different. Arabidopsis root exudates of seedling, vegetative and bolting stage were collected using solution method under sterile condition. Overall, 534 compounds were detected and of 202 were identified by GC-MS. The identified compounds were further categorized as sugars (26),sugar acids (7),(sugar) alcohols (25),organic acids (60),nucleotides (12),amino acids (35), amides/amines (17) and others (20). PCoA analysis revealed that root exudate profiles of seedling, vegetative and bolting stage were significantly different. The seedling root exudates were dominated by sugars and organic acids while the vegetative root exudates were predominated by amiano acids. The compounds in each category of bolting root exudates were uniform and thereby the chemical richness and evenness were highest in the boting stage.4. To determine whether the root exudates can directionally manipulate soil microbial community, we develop an addition experiment including forward(seedling-vegetative-bolting) and reverse (bolting-vegetative-seedling) addition orders.Results showed that soil nitrate nitrogen, available phosphorus and available potassium contents increased along with the root exudates addition, and the contents of these soil properties were higher in the reverse addition order associated treatments. PCoA analyses showed that soil bacterial and fungal community structure followed distinct microbial succession paths in forward and reverse addition orders but finally assembled a similar bacterial and fungal community, indicating that the addition order of root exudates (driving force) did not alter the final microbial assemblages and the impacts of root exudates on soil microbial community were not stochastic. Thus, addition of suitable driving force could directionally regulate soil microbial community. Mantel test showed that root exudates profiles were positively and significantly correlated with soil available nutrient contents,bacterial and fungal community,5. NPKS treatment and bolting root exudates can establish and manipulate soil microbial community to increase Arabidopsis biomass accumulation. Under control conditions, soil experiment indicated that the Arabidopsis biomass was increased in the NPKS, NPKMOI and bolting root exudates associated treatments. Soil slurry experiment revealed that the soil microbial community in the NPKS treatment and rizhosphere soil microbial community in bolting stage of Arabidopsis promoted biomass accumulation.We studied the effects of fertilizer regimes and root exudates addition on soil microbial community and diversity, and investigated the effects of resulted soil microbial community on Arabidopsis biomass through soil slurry experiment. Results indicated that suitable fertilizer regimes and application of proper root exudates can establish and manipulate high-productivity associated soil microbial community, prodiving certain theoretical basis in future research of soil microbial community regulation.