Response To Soil Microbial Characteristics On Different Tillage Models In The Typical Farming Area Of Peak-cluster Depression,Northwest Guangxi

Farming areas,residents of the karst peak-cluster depressions live and produce intensively,carry great risk for rocky desertification and are focal regions of ecological conservation.How to maintain certain agricultural production under the condition of reducing the risk of rocky desertification and ecological security is of great significance for poverty alleviation and harmony between human and land in this area,which is also one of the key scientific problems to be solved for the sustainable use of land in karst area.Soil safety is the basis of sustainable land use and the comprehensive reflection of soil physical,chemical and biological properties.Therefore,it is very important to evaluate the ecological security of tillage activities in the peak-cluster depression area for maintaining the sustainability of agriculture and ecology.Soil microorganisms directly or indirectly participate in the soil biogeochemical cycle,which has a great relationship with the quality and health of soil ecosystem,and it is sensitive to environmental change,which has become one of the most important indicators to evaluate soil safety.Based on this,this study was conducted at the Guohua Karst Ecological Experimental Station in northwest Guangxi(a typical farming area in the peak cluster depression),to evaluate soil safety effects of different tillage models,based on the analysis of the soil physicochemical properties,PCR and Illumina hiseq high-throughput sequencing technology were used to analyze the community composition,structure and diversity characteristics of soil microorganisms(bacteria and fungi).Major types of croplands,including pitaya field(representing no-tillage,HF),maize field(representing plowing tillage,MF),sugarcane field(representing minimum tillage + straw return,SF),and paddy field(PF),were studied contrastively to forestland(artificial forest transformed from cropland,FL)and grassland(rehabilitated naturally from abandoned farmland,AF).The results were showed as follows:1.The soil physicochemical properties of different tillage models were significantly different,compared with the rehabilitated-land models(FL,AF),tillage activities(HF,MF,SF)reduced soil p H,soil organic matter contents(SOM),total nitrogen contents;increased soil C/N ratio,decreased soil N/P ratio;and in the aspect of soil particle size distribution(clay,silt,sand),clay contents showed an increasing trend,silt contents first increased and then decreased,sand contents first decreased and then increased.2.In the study area,dominant bacterial strains in soils were Actinobacteria,Proteobacteria,Acidobacteria,and Chloroflexi.The tillage models had obvious influence on the soil bacterial characteristics(?-diversity,?-diversity).Compared with the rehabilitated-land models,tillage activities(HF,MF,PF,except SF)increased the abundance-based coverage estimator index(ACE index)and diversity(Shannon index)of soil bacterial communities,both the ?-diversity index exhibited the indices declined as the soil depth increased.The analysis of ?-diversity showed that the bacterial community structure similarity existed among the HF and rehabilitated-land models,but different between MF,SF,PF and rehabilitated-land models.Soil bacterial community structure at 0-10 cm soil layers is similar to 10-20 cm,but these were largely different from that of the 20-40 cm depth.Soil p H and particle size distribution were important factors affecting soil bacterial community structure.The distribution characteristics of soil functional bacteria were affected by different tillage models,the no-tillage model improves the content of chitinolysis functional bacteria,MF and HF increased the number of nitrogen and sulfur transformation functional bacteria,SF and PF increase the content of decomposition of organic matter and anaerobic digestion of environmental substances transformation functional bacteria respectively.3.Dominant fungal strains in all soils were Ascomycota,Basidiomycota,Mortierellomycota;tillage activities did not change the species of dominant fungi,but affected their relative abundance.The responses of soil fungal community characteristics to tillage models were obvious.Compared with the rehabilitated-land models,tillage activities(except HF,MF,PF,SF)improved the richness and diversity of soil fungal community.With the increase of soil depth,the ?-diversity index of soil fungi in each tillage model was decreased.The similarity of soil fungal community structure existed among the dry tillage models(HF,MF,SF)and PF,and there was significant difference different from rehabilitated-land models were obvious.The soil fungal community structure was closely related to soil physicochemical properties,soil p H,C/N,N/P were important factors affecting soil fungal community structure.The results showed that the distribution of soil functional fungi was significantly affected by cultivation mode,and the content of saprophytic and pathotrophic fungi in cultivation mode was significantly higher than that in conversion mode;at the same time,the content of saprophytic and trophic fungi in SF was the highest,and that of symbiotic and trophic fungi in HF was the highest.In conclusion,the results show that no-tillage model(HF)has the similar soil bacterial community structure as the rehabilitated-land models,and the HF has the most abundant symbiotroph fungi and better soil physicochemical properties,it had positive ecological environment effect.The no-tillage model can be used as a low-risk farming model in the study area.