Responses Of Microbial Community To Cadmium Pollution In A Oilseed Rape-soil System

Cadmium(Cd)is one of the most toxic heavy metals,and it can easily accumulate in plants and cause serious harm to human health through the food chain,which aroused the wide concern.Moreover,microorganisms are essential in biogeochemical cycling of heavy metals,with their diversity and abundance can serve as biological indicators of heavy metals such as Cd toxicity,so investigation to the influence of Cd on the microbial community is very important.In this study,the polluted agriculture environment was simulated with the pot experiment in greenhouse,with Cd as a contaminant and selecting two species of oilseed rapes(Brassica napus and Brassica juncea)as research objects.The accumulation in plants was measured and the impact of Cd on plant physiological properties and soil physicochemical properties were analysed.At the same time,response of phyllosphere,leaf endophyte,root endophyte,rhizosphere soil and bulk soil bacterial communities and soil fungal communities of two species of oilseed rapes to different Cd pollution concentrations(0,10 and 30 mg/kg)were investigated by high throughput sequencing technology.The main research results are as follows:(1)Cd is easy to accumulation in plant,and the accumulation amount increases with the increase of soil Cd concentration(274.07 mg/kg,266.17 mg/kg in leaves and 843.03 mg/kg,669.34 mg/k in roots for the highest respectively in B.napus and B.juncea).Cd pollution in soil suppressed plant growth and decreased chlorophyll content of two species of oilseed rapes.Meanwhile,Cd stress induced the changes of antioxidative enzymes activities.In addition,soil physicochemical properties would be changed under Cd stress.(2)Cd pollution could increase the number of soil total bacteria,especially in bulk soil of B.napus under 30 mg/kg Cd treatment.The ?-diversity of bacterial community in soils declined significantly under higher Cd concentration(30 mg/kg).In addition,soil bacterial communities composition and structure were altered in the presence of higher Cd concentration.The impact of Cd on soil bacterial communities was greater than plant bacterial communities(phyllosphere and endophyte).The analysis of CCA and Mantel showed that the bacterial community of bulk soil was significantly correlated with Cd,while the variation of rhizosphere soil bacterial community was markedly correlated with Cd and other enviromental factors of both soils and plants(height,weight and leaf area).The molecular ecological networks of soil bacterial community were also affected by Cd pollution.The stability of soil networks were increased and symbiosis of the networks in rhizosphere bacterial community were enhanced but weaken in bulk soil of two species of oilseed rapes under low Cd pullution.However,the stability of soil networks were decreased,but symbiosis were enhanced under higher Cd pullution.(3)Cd stress was not significant effect on rhizosphere soil fungal numbers,but it decreased the fungal numbers in bulk soil,especially under 30 mg/kg Cd treatment,the fungal numbers in bulk soil were significantly decreased.Soil fungal community composition and structure were altered in the presence of higher Cd concentration.However,there are almost not significant effect on ?-diversity of fungal community in soils under Cd treatment.The analysis of CCA and Mantel showed that the variation of rhizosphere soil fungal community in B.napus was markedly correlated with Cd and biomass,and fungal community in B.juncea rhizosphere soil was not only signifiantly correlated with Cd,but also with biomass,p H and TN.Meanwhile,the fungal community of bulk soil in B.juncea was significantly correlated with Cd and p H.The molecular ecological networks of soil fungal community were also affected by Cd pollution among which the stability and symbiosis of the networks of rhizosphere in B.napus were reduced,the stability of the networks of bulk soil in B.napus was increased,but symbiosis was reduced.At the same time,the stability and symbiosis of the networks of rhizosphere and bulk soil in B.juncea were increased.