Distribution And Diversity Of Soil Microbial Community Response To Conservation Tillage And Its Mechanism

Dryland cropping is subjected to the special climate,terrain and water resources,with the unreasonable agronomic management,leading to the soil nutrient loss,serious degradation and the decline of soil productivity,and having a considerable impact on the regional agricultural sustainable development.Conservation tillage can improve soil structure,and conserve soil fertility and moisture effectively,so it is of great significance to study the functional mechanism of the conservation tillage in dryland cropping ecosystem.The study based on the dryland agriculture production and the current situation of agro-ecosystem,using the molecular biotechnique system(high-throughput sequencing technology and quantitative PCR)to study the response of the soil microbial community abundance,structure and ecological functional diversity to the conservation tillage,combinates with the knowledge of ecology and crop planting and cultivation,deeply analyze the time-space change law and the relationship with crop growth of soil microbial diversity under the conservation tillage.By conducting the experiment,we can identify a clear mechanism of the high yield of dryland wheat to provide the theoretic support for the efficient,ecological and sustainable conservation tillage technical system.(1)Our results show that conservation tillage increased the Simpson index by 378% and exhibited significantly dissimilar polygenetic diversity,with r of 1,and taxonomic diversity,of r higher than 0.49,compared to conventional tillage.This finding demonstrates that conservation tillage modifies soil bacterial diversity.Chisel plow and zero tillage increases the abundance of the genus Bacillus,including 85% of the phylum Firmicutes,and of Rhizobiales belonging to the Alphaproteobacteria.Overall conservation tillage increased the abundance of profitable functional bacteria species.Conservation tillage significantly influenced soil fungal diversity and phylogenetic composition by altering soil organic carbon content and texture.The fungal diversity and composition structure were similar for treatments causing higher soil perturbation,i.e.,chisel plow and plow tillage;zero tillage a less disruptive agriculture practice,preserved soil biological integrity.The most abundant phyla across all samples were Ascomycota and Basidiomycota,which are the main classical fungal decomposers in soils.These results suggested that conservation tillage can affect crop residue decomposition and the soil organic carbon content,leading to changes in soil fungal community distribution patterns.(3)Long-term conservation tillage had a significant effect on the soil environment,the abundance of soil fungi and bacterial communities have different effects with different tillage,they have different levels of response to the three tillages.In different tillage,microbial uneven spatial distribution,continuity is poor,higher spatial variability,showed a strong spatial aggregated distribution.The changes of soil microbial community abundance and physicochemical properties were mainly affected by tillage methods.Under the zero tillage,the content of soil clay,water and ammonium nitrogen significantly affected the distribution of soil bacterial community,and under chisel plow tillage,the content of soil soluble carbon and the activity of catalase significantly affected the distribution of soil fungal communities.(4)Our results showed that plant root decrease microbial alpha diversity and reduce catabolic diversity in response to conservation and conventional tillage.Microbial phylogenetic composition has stronger and significant effect on carbon substrate utilization as compared with membership.The relative abundance of Proteobacteria,Bacteroidetes,Capnodiales,Pleosporales fast-growing in rhizosphere helped to utilize amino acids,carbohydrates,and carboxylic acid responding to tillage practices.In addition,less variation in both microbial community and catabolic diversity is observed under zero tillage compared to plow and chisel plow tillage.This study suggested that plant root enriching soil nutrients condition increased copiotrophic microbial populations in rhizosphere thereby enhance metabolic capacities under tillage practices.(5)The response of plant growth was determined by measuring plant carbon and nitrogen accumulation from the wheat tillering stage to the flowering stage.Here,we show that variations in rhizosphere alpha and beta diversity throughout plant growth had the greatest contributions to distinguishing conventional plow tillage from conservation tillage.Additionally,zero tillage(dissimilarity: 11.3%)had less of an effect on the relative abundances of Proteobacteria(Alpha-,Beta-,Gamma-)and Bacteroidetes in the rhizosphere in response to plant growth as compared with plow tillage(dissimilarity: 21.7%).Furthermore,our study indicates that conservation tillage can modify the soil conditions and preserve rhizosphere bacterial memberships and enhanced stability of the plant growth-promoting rhizobacteria population.(6)Fungal alpha diversity in both rhizosphere and bulk were significantly higher under zero tillage during tillering,and tillage had no significant effect during the flowering stage.Instead,fungal alpha diversity was significantly different between rhizosphere and bulk soils during flowering,with bulk soil presenting the highest diversity.This was also reflected in the phylogenetic structure of the communities,as rhizosphere soil communities underwent a greater shift from tillering to flowering compared to bulk soil communities.In general,less variation in community structure was observed under zero tillage compared to plow and chisel plough treatments.Changes in the relative abundance of the fungal orders Capnodiales,Pleosporales,and Xylariales contributed the most to the dissimilarities observed.