Characteristics Of Soil Nematode Community And Its Influencing Factors In Soybean Continuous Cropping In Black Soil Region

Nematodes are widely found in soil and they play an important part in ecosystem,they are often used as sensitive indicators in agricultural ecosystem to characterize the health of soil.With the increase in soybean continuous cropping years,the soil showed inhibitory.It was related to the changes of soil physicochemical properties,microorganisms and nematode community characteristics.Based on the long-term experiment field in black soil area of Northeast China,the soil samples from soybean continuous cropping for 5 years(C5),10 years(C10),16 years(C16),20 years(C20),25 years(C25)and rotation(R)0?50 cm different soil layers(each 10 cm as a soil layer)and cultivation layer(0?20 cm)were collected.Morphological identification method and high-throughput sequencing technology were adopted to study the characteristics of soil nematode community,under the condition of different years and different soil layers:(1)to reveal the changes of soil nematode community structure and diversity;(2)to explore the correlation between soil bacteria,fungi and soil nematode community;(3)to identify the factors affecting the characteristics of soil nematode community in soybean continuous cropping.The results are as follows:1.Through the determination of soil physicochemical properties,with t he increase of soil depth,the pH value showed an increasing trend,and the soil nutrient content showed a trend of first increasing and then decreasing.The nutrient content of 10?20 cm soil layer was the highest,and there was no significant change in soil nutrient content below 20 cm.The soil pH value fluctuated between the different continuous cropping years,which were lower than that of R;soil organic matter(SOM)and available N,P and K increased first and then decreased with continuous cropping years;total nutrients changed insignificantly.The cultivation layer soil pH value and nutrient content of continuous cropping soybean in different years were lower than that of R.The contents of SOM,total K and available nutrients increased at first and then decreased with the extension of continuous cropping years.The 5-year continuous cropping declined,the 10-year continuous cropping showed an upward trend,and the20-year continuous cropping reached the highest.The contents of total N and total P decreased.The pH value,contents of SOM,alkali-hydrolyzed N(AN)and available K(AK)were significantly different in different continuous cropping years.2.The nematode community structure and diversity in 0?50 cm soil layer of soybean rotation and continuous cropping were studied by high-throughput sequencing technology.The results showed that 83 OTUs were obtained from all soil samples,belonging to 2 classes,9 orders,24families and 38 genera.The richness and diversity of soil nematode community increased first and then decreased with the deepening of soil layer.Among them,the difference between 0?10 cm and10?20 cm soil layers was large,while the richness difference between 20?50 cm soil layers was large,but the difference of community diversity was small.The abundance and diversity index of soil nematode community increased first and then decreased with the extension of soybean continuous cropping years.The dominant genus level groups changed greatly.The trophic groups were distribution balance.The same nematode genera were Aphelenchus?Oscheius?Pratylenchus and Paratylenchus,and the sum of relative abundance accounted for nearly 30%of the total genera.Nygolaimus increased first and then decreased with the extension of soybean continuous cropping years,and the relative abundance of R and C10 was higher.The soil nematode community(genus level)was significantly related to soil pH value,SOM,total N(TN)and AN content.3.Based on the morphological analysis of the changes of cultivation layer soil nematode abundance,community structure,ecological index and food net index in different soybean continuous cropping years,the results showed that the total number of nematodes in 100 g dry soil of different continuous cropping years was 597(the most)in cultivation layer of continuous cropping for 5 years(C5-c)and 251(the least)in rotation cultivation layer(R-c).There were 26genera of nematodes in the cultivation layer soil of different continuous cropping years,including5 genera of herbivores nematode,4 genera of fungivorous nematode,11 genera of bacterivores nematode(dominance)and 6 genera of omnivorous/predators nematode.There were significant differences in soil nematode community composition among different continuous cropping years,and the common dominant genus was Rhabditis.The nematode community was significantly correlated with pH value,SOM and AN.With the extension of soybean continuous cropping years,the diversity of soil nematode community showed a downward trend,the community structure was less affected by external disturbance,the changes of the characteristics of nematode community are caused by the herbivorous nematode and plant parasitic nematode,the disturbance degree of functional food web reduced,and the food web gradually became mature.The characteristics of cultivation layer soil nematode community in different soybean continuous cropping years were analyzed by high-throughput sequencing technology.The results showed that 58 OTUs were obtained,belonging to 2 classes,6 orders,21 families and 30 genera.The richness and diversity of cultivation layer soil nematode community increased first and then decreased with the extension of continuous cropping years,the 5-year continuous cropping had the lowest diversity index,the 10-year continuous cropping recovered,and the 20-year continuous cropping reached the highest,and the diversity of soil nematode community in continuous cropping was lower than that in R-c.The dominant families were Tylenchulidae,Hoprolaimidae,Rhabditidae,etc.,and the dominant genera were Paratylenchus,Hoprolaimus,Oscheius,etc.,the relative abundance of the same dominant family and genus was significantly different among different continuous cropping years.OTU level similarity analysis showed that the similarity of soil nematode community composition increased with continuous cropping years.The soil nematode community in cultivation layer was significantly correlated with pH value,SOM,TN and AN.Soybean continuous cropping led to the change of soil nematode communi ty structure in the cultivation layer.The change of abundance of plant parasitic nematodes and omnivorous/predacious nematodes is the reason for the emergence of inhibitory soil.4.The characteristics of cultivation layer soil bacterial community in di fferent continuous cropping years were analyzed by high-throughput sequencing technology,the 5-year continuous cropping had the lowest diversity index,the 10-year continuous cropping recovered,and the16-year continuous cropping reached the highest.The richness and diversity of soil bacterial communities increased first and then decreased with the extension of continuous cropping years,and the diversity of soil bacterial communities in the cultivation layer reduced during long-term continuous cropping.The dominant bacterial phyla were Acinobaracterita,Proteobacteria,Acidobaracterita,etc.among the different years of continuous cropping,and the dominant bacterial genera were Gailla,Sphingomonas,Bacillus and Rubrobacter.The correlation between soil bacterial community(genus level)and pH value,SOM,available N,P and K were significant.With the extension of continuous cropping years,the richness of soil fungal community fluctuated and the diversity decreased.The same dominant fungi phyla in different years of continuous cropping were Ascomycota,Mortierlomycota,Basidiomycota,and the same dominant fungi genera were Mortierlla,Solicoccozyma and Chaitomium.The soil fungi community(genus level)had significant correlation with pH value,TN,AN,available P(AP)and SOM.The difference of soil fungi dominant groups in long-term continuous cropping layer of soybean was significant,and the diversity index of community was higher than that of R-c.The relationship between soil nematodes,bacteria and fungi were analyzed at genus level.The results showed that fungi had more influence on nematode community than bacteria.Paratylenchus,Hoprolaimus and Nygolaimus were negatively correlated with the dominant bacterial genera,while Pratylenchus,Aphelenchoides and Aphelenchus were positively correlated with the dominant bacterial genera.Nygolaimus,Oscheius,Pratylenchus and Aphelenchoides were significantly negatively correlated with the dominant fungal genera,while Paratylenchus and Aphelenchus were significantly positively correlated with the dominant fungal genera.In addition to the dominant microbial genera,Rhizobium,Nitrospira of bacteria and Fusarium of fungi promoted or inhibited the occurrence of continuous cropping disorders.5.The contents of different forms of C and N in the cultivation layer soil of different soybean continuous cropping years were determined.The contents of dissolved organic C(DOC),easily oxidized organic C(EOC),particulate organic C,microbial biomass C(MBC),ni trate N(NO^3--N)and microbial biomass N(MBN)increased at first and then decreased with the extension of soybean continuous cropping years.There were significant differences among different continuous cropping years,and the content of R-c was the highest.The change of ammonium N(NH⁴⁺-N)content was opposite,and the C5-c was the highest.The richness index and diversity index of soil nematode community were positively correlated with DOC,EOC,MBC,NO^3--N and MBN,and negatively correlated with NH⁴⁺-N.Redundancy analysis showed that the dominant families and genera of soil nematodes were positively correlated with the contents of DOC and EOC,and negatively correlated with the contents of NH⁴⁺-N.It showed that the longer soybean continuous cropping years,the greater influence of C and N content on soil nematode community.In conclusion,the characteristics of soil nematode community under soybean continuous cropping in black soil area were surface aggregation with the change of soil depth,and restor ative with the extension of years.Soil depth had a greater impact on soil nematode community than continuous cropping years.The change of abundance of plant parasitic nematodes and omnivorous/predacious nematodes is the reason for the emergence of inhibitory soil.The fungal community had more influence on soil nematode community than the bacterial community,the dominant microbial genera,functional bacteria,and fungal pathogens played an important role in the defense of nematode diseases.Soil pH value,SOM,TN,AN,and different forms of C and N content had significant correlation with nematode community.The results of this study elucidated the characteristics of soil nematode community and its influencing factors under different time and space conditions of soybean continuous cropping in black soil region,which could provide a theoretical basis for revealing the status of soil nematode in the underground food web and its role in the farmland ecosystem,and for clarifying the mechanism of inhibitory soil in continuous soybean cropping,soybean continuous cropping soil disease and pest prevention,and reasonable planning of planting methods.It will provide scientific basis for soybean planting and sustainable development of modern agriculture in black soil region.