| Cadmium(Cd)pollution in agricultural soil is a global environmental problem,which is related to sustainable agricultural production,food safety and the quality of people’s life.Phytoremediation is one of the most common techniques used to repair Cd contaminated soils.This paper takes Pennisetum sinese Roxb.,a plant with high biomass production and good performance in phytoextraction,as experimental material.Pot and field experiments were carried out to study the effects of aging Cd on growth,and Cd distribution as well as accumulation in different part of P.sinese,and to clarify the actural remediation effect of P.sinese to remove soil Cd.Soil environmental factors that affect Cd extraction efficiency were also studied in field experiment.The aim was to find the soil environmental factors that affect the effective transport of Cd in soil-plant system,and then lay the foundation of improving Cd phytoextraction efficiency with P.sinese.The main research contents and conclusions were as follows.In the pot experiment,a soil Cd concentration gradient(0.1,0.5,1,2,4,and 8 mg·kg-1)was used to assess growth,uptake and accumulation capacity of P.sinese in soils contaminated by Cd,and to explore changes in diversity and structure of rhizosphere soil bacterial communities in response to long-term Cd pollution.The results showed that the growth of P.sinese was inhibited markedly by Cd with a biomass reduction on the shoots when the Cd concentration was greater than 1 mg·kg-1 Cd.The Cd concentrations in P.sinese roots,stems,leaves,and shoots were increased with the increase of concentrations of soil Cd,and the highest Cd level was observed in roots at the same Cd treatment.When soil was treated by Cd with the concentration from 0 to 8 mg·kg-1,Cd concentrations in shoots and roots were 0.51-28.87 and 1.12-34.01 mg·kg-1,respectively,and total extraction amounts of Cd in P.sinese were 0.06-1.86 mg·plant-1.Most of the Cd was stored in shoots,accounting for 82.5-83.5%in the total extraction amounts.Durinng phytoextraction,the community composition of rhizosphere soil bacteria was affected by soil Cd concentration,but the relative abundance of main bacteria phyla,such as Chloroflexi,Proteobacteria,Acidobacteria and Cyanobacteria,were not affected by Cd concentration.In addition,the diversity and richness of bacterial communities were not significantly affected.In the feild experiment,the effect of different levels Cd pollution(0,0.25,0.5,1,2,4,8,and 16 mg·kg-1)on growth and Cd uptake of P.sinese during elongation stage and mature stage were studied in three different texture of soil(loam,sand loam,clay loam).The results showed that P.sinese maintained good growth,and the biomass of roots,stems and leaves was largely increasing from elongation stage to maturity stage in Cd contaminated soil with 0-16 mg·kg-1 Cd.In loam,sand loam,and clay loam,the total biomass of P.sinese was 668.73-895.73,693.26-942.33,and 831.19-1028.89 g·plant-1 at maturity stage,respectively.The Cd concentrations in P.sinese roots,stems,leaves,and shoots were increased with the increase of soil Cd concentrations.At the same concentration of Cd treatment,the Cd concentrations of shoots and roots showed an order of sand loam>loam>clay loam at elongation stage and sand loam>clay loam>loam at maturity stage,respectively.The extraction amounts of Cd in P.sinese shoots and roots increased from elongation stage to maturity stage in three different texture of soil.In loam,sand loam,and clay loam,total extraction amounts of Cd in P.sinese was 0.08-2.52,0.16-1.97,and 0.06-1.39 mg·plant-1 at elongation stage,and 0.09-3.14,0.22-10.08,and 0.23-5.37 mg·plant-1 at maturity stage,respectively.After making analysis of the relationship between soil physicochemical properties and Cd concentrations in different part of P.sinese in the three types of soil,the main impact factors affecting the availability of Cd in soil-plant system included soil total Cd concentration,DTPA-extractable Cd concentration,clay content,organic matter,and soil pH.In addition,the effects of Cd uptake of P.sinese differed in different growth stage. |
