| In the Loess Plateau,soil erosion in sloping farmland is serious and the use of reasonable conservation tillage is of great significance for improving the soil environment of farmland.Rhizobium can co-generate nitrogen fixation with legumes and promote plant growth and increase soil nutrients.In this study,we selected four different conservation tillage treatments in typical hilly areas of the Loess Plateau,including no-tillage(NT),straw mulching(SM),plastic film mulching(PM)and ridge mulching(RPM),while using conventional tillage as a control.We studied the effects on soil nutrient and crop growth,then analyzed the diversity of rhizobiales communities in non-rhizosphere,rhizosphere and nodule and the response of community structure to different tillage measures by combining traditional culture methods and high-throughput sequencing,which was in order to explore the relationship between soil environment and microbial community changes.The results are as follows:The microbial biomass,nutrient content and enzyme activity of rhizosphere soil were higher than non-rhizosphere,and there was a good rhizosphere positive effect.Different treatments increased the enrichment rate.The long-term conservation tillage measures increased carbon and nitrogen content,enzyme activities and microbial biomass in rhizosphere and non-rhizosphere soil and make pH lowerer,SM and RPM treatments are most effective.The community composition of rhizobiales in rhizosphere soil and non-rhizosphere soil was significantly different,showing a trend of increasing species richness from rhizosphere to non-rhizosphere,which indicated the filtration effect of crop roots on microorganisms.Many genus of nitrogen-fixing bacteria were detected in soil samples.Among them,Bradyrhizobium is abundantly enriched in the rhizosphere and is the dominant genus of this region.The tillage treatments had an effect on the enrichment of dominant genus of this region.The enrichment of dominant genus in RPM treatment was the most significant.The results of RDA showed that pH and inorganic nitrogen were the main factors affecting community composition.A total of twenty strains of bacteria were isolated from the obtained nodules in five treatments.The phylogenetic tree established by the 16 S rRNA sequence and the housekeeping gene sequence(recA,atpD,glnII)showed that the obtained strains belonged to Bradyrhizobium.daqingense,which is consistent with the enriched dominant genus in rhizosphere soil,indicating that the host obtained the dominant genus of nitrogen fixation from the soil through the action of root system.Plants were specific to the choice of rhizobium that established the symbiotic system and were not affected by tillage treatments.The phylogenetic tree of the nitrogen-fixing gene nifH sequence showed that the possible horizontal transfer of symbiotic genes at the species level.Conversational tillage managements reduced the water consumption of crops during the growing season and increased the water use efficiency of crops and crop yield.SM and RPM effectively increased the 100-grain weight,the number of seeds per plant,the number of pods per plant and biomass of above ground part.Crop growth and dry matter accumulation are more sensitive to changes in the rhizosphere soil environment.SM and RPM treatments had significant effects on improving soil water storage,soybean yield and water use efficiency,and effectively promoted soybean growth and development,providing the required moisture.In summary,soybeans grown in this area can establish an efficient symbiotic system with B.daqingense enriched from soil.The ridge mulching measure improves the soil environment,and the increase of nutrient content promotes the enrichment of the dominant Rhizobium genus,which significantly improves the water use efficiency and yield of the crop.The changes of Rhizobium community in soil were mainly affected by pH and inorganic nitrogen,and the growth of crops was significantly correlated with the changes of rhizosphere soil nutrients and microorganisms. |
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