| Danjiangkou Water Conservation Area plays an important role in the South-to-North Water Diversion Project.Studying the characteristics and interaction mechanism of soil microbial and nematode community in conversion of cropland to grassland in Danjiangkou Water Conservation Area,which provides basic data for comprehensive analyzing and evaluating soil ecological effect of conversion of cropland to grassland,and supplies scientific basis for regional ecological environmental protection and sustainable land use.In September 2017,we chose three representtative Alfalfa(Medicago sativa)grassland(3 years)as the conversion of cropland to grassland plots in the upstream of Danjiangkou water conservation area,and with uncultivated corn(Zea Mays)field as a control.In this study,we examines the effect of returning farmland to grassland on soil microbial and nematode community.The results shows that,In Danjiangkou Water Source Conservation Area,conversion of cropland to grassland has a significant influences on soil microbial community structure.The amount of total PLFAs,actinomycetes,bacteria,fungi,gram-positive bacteria and gram-negative bacteria increased by 59.13%(P<0.05),64.35%(P<0.05),64.34%(P<0.01),135.19%(P<0.01),68.88%(P<0.05)and 85.83%(P<0.01)in 0-10 cm soil layer.The amount of total PLFAs increased by 62.58%(P<0.05)and fungi increased by 100.00%(P<0.05)in 10-20 cm soil layer.The effect of conversion of cropland to grassland on fungi is greater than that on bacterial community.Soil organic carbon(SOC),total nitrogen(TN)and nitrate nitrogen(NO3--N)had a positive correlation with total PLFAs(P<0.01).Conversely,soil p H and C/N had a significant negative association with total PLFAs(P<0.05).A total of 18307 soil nematodes belonging to forty-nine genera were identified in the converted alfalfa grass field,and 10706 soil nematodes belonging to forty-five genera in the maize field.Soil nematode was transferred from the short generation to the long generation of the c-p group,which indicated that returning cropland to grass has less disturbance to soil environment,improves diversity and stabilizes soil nematode community.The structure index(SI)and enrichment index(EI)indicates that conversion of cropland to grassland reduced the disturbance of soil environment,and the soil micro-food web tended to mature.The number of total soil nematode has a significant correlation with soil p H,water content,TN and NO3--N(P<0.01).Relative abundance of bacterivores and fungivores has a significant negative association with AP(P<0.01),and plant parasites and predators-omnivore have a significant relationship with SOC(P<0.01),ammonium nitrogen(NH4+-N)(P<0.01)and TN(P<0.05).As the main components of soil micro-food web,there is an interaction between nematodes and microbial community.Soil G-bacteria has a negative relationship with the abundance of bacterivores(P<0.05),and has a positive relationship with the abundance of fungivores(P<0.05).There is a significant positive correlation between G-bacteria and nematode ecological index(EI and SI)(P<0.05).The results shows that conversion of cropland to grassland changed the micro-food web structure,and soil nematode contributed more to the stability of soil micro-food web.In Danjiangkou Water Source Conservation Area,conversion of cropland to grassland affects soil environmental factors,changes soil microbial and soil nematode community,increases soil biodiversity and stabilizes soil micro-food network... |
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