Effects Of Digestate On Growth Characteristics And Rhizosphere Soil Microbial Characteristics Of Pennisetum Hydridum Under Cd Stress

Phytoextraction technique has great potential in remediating heavy metals contaminatedenvironment.Digestate,with properties of both fertilizer and soil amendent,has been widely applied to pomote crop quality and production,prevent and control plant diseases and insect pests,and improve soil environment,etc.,however there are few studies on digestate in combination with energy plant in remediating heavy metal-comtaminated soils.In the present study,swine farm digestate and large biomass Pennisetum hydridum were selected as research materials,pot experiment was carried out to explore the fesibility of digestate in combination with Pennisetum hydridum for remediating Cd contaminated soils.The effect of digestate on growth characteristics of Pennisetum hydridum were analyzed by measuring plant heights,tillerring numbers,fresh biomasses,the influence of digestate on enzyme activities,Cd bioavailabilities,and Cd accumulation capacity of tested plant was studied by collecting rhizosphere soils and harversting different tissues of Pennisetum hydridum.On above basis,Illumina Miseq high-throughput sequencing technology was adopted to explore the effect of digestate on microbial community structure and diversity in rhizosphere soil of Pennisetum hydridum under Cd stress.The main results were as follows:(1)Compared to the control treatment,digestate treatment increased the plant heights of Pennisetum hydridum under the stress of Cd 0,Cd 2,and Cd 8 by 41.83-56.41%,2.50-12.99%,and 6.91-28.95%,tillering numbers by 100-150.00%,7.85-38.57%,and 8.99-45.23%,fresh biomasses by 331.25-415.63%,18.18-41.82%,and 53.33-90.67%,respectively.However,excessive digestate irrigation did not exerted further promotion effect on the growth of Pennisetum hydridum,therefore the amount of digestate irrigation should be strictly controlled.(2)Compared to the control treatment,digestate increased the activities of urease,surcase,and dehydrogenase in rhizosphere soils of Pennisetum hydridum under the stress of Cd 0,Cd 2,and Cd 8 to varing degress,while that of alkaline phosphatase activity performed a decrease trend.(3)Under the stress of Cd 0,Cd 2,and Cd 8,digestate addition increased the bioavailable Cd concentration in rhizosphere soils of Pennisetum hydridum by 6.25-25.00%,1.38-8.33%,and 1.36-11.31%,respectively.Compared to the control treatment,digestate appication decreased the total Cd concentration of Cd 0 stressed-soils by 12.50-16.67%,while the total Cd concentration of Cd 2 and Cd 8 group increased by up to18.75% and 45.09%,respectively.The Cd contents in the stems and leaves of Pennisetum hydridum increased by multiple after digestate irrigated,while roots Cd content increased with increasing amount of digestate.The Cd transfer factors were close to 1,and almost all the Cd bioaccumulation factors were more than 1.(4)At phylum level,Proteobacteria,Chloroflexi,Actinobacteria,Acidobacteria,Gemmatimonadetes,and Bacteroidetes were the predominant bacterial communities with a relative abundance of more than 5% in digestate-irrigated rhizosphere soils of Pennisetum hydridum.At genus level,the bacterial community with a relative abundance of more than 3% in digestate-irrigated rhizosphere soils of Pennisetum hydridum was only Sphingomonas.Compared with the traditional treatment and the control treatment,the relative abundances of Chloroflexi,Actinobacteria,and Sphingomonas showed relatively higher in digestate-treated soils.Furthermore,digestate treatment greatly decreased the relative abundance of fungi at both phylum and genus level when compared with traditional treatment and control treatment,.