外源微生物对土壤中镉形态及微生物多样性的影响

采用土壤盆栽模拟实验，研究接种氧化节杆菌、耳葡萄球菌、嗜麦芽窄食单胞菌对紫花苜蓿吸收土壤中Cd的作用效果．结果表明，3种微生物在土壤中Cd浓度分别为5、20、50mg?kg-1时均能增强紫花苜蓿对Cd的富集吸收，在3种加菌处理中紫花苜蓿地上部分的Cd积累量与单种植苜蓿处理相比分别显著提高了11.38%~20.67%、5.58%~16.54%、20.68~23.51%；地下部分分别显著提高了19.50%~32.30%、8.62%~19.38%、22.77%~39.23%．各处理中根际和非根际土壤Cd形态分布均为残渣态>交换态>碳酸盐结合态>铁锰结合态>有机结合态．紫花苜蓿可促进土壤中Cd向交换态EXC转化，与未种植物处理相比，其根际土壤中EXC态Cd显著提高了3.40%~6.51%；非根际提高了3.16%~5.48%．3种微生物加入显著增强了植物对土壤中Cd向EXC态转化作用，根际土壤中EXC态Cd与未种植物处理分别增加了11.23%~21.49%、6.37%~13.27%、10.78%~27.76%；非根际提高了7.71%~16.30%、4.64%~13.84%、9.62%~20.75%．BIOLOG ECO微平板法分析结果表明，外源微生物加入对Cd污染土壤中微生物数量、活性、多样性指数等均有显著性增大；主成分分析表明不同处理下土壤微生物利用碳源的种类和能力有所差异；聚类分析结果可合理地将各处理按对土壤中Cd有效态转化作用情况归类．

Effects of exogenous microorganisms on speciations of cadmium and microbial diversity in soil

Pot experiment was conducted to investigate the effects of different microorganisms on biosorption of Cd by alfalfa(Medicago sativa L.)in soil.The results showed that three stains,Arthrobacter oxydans,Staphylococcus auricularis and Stenotrophomonas maltophilia could significantly promote the plant alfalfa to remove and accumulate Cd from soil.These three strains all accelerated alfalfa’s ability to enrich and absorb Cd.when Cd concentrations in soil were 5,20 and 50 mg·kg-1, respectively.Compared with non-exogenous microorganism treatment,the three microbe-adding treatments notably increased Cd accumulation in the shoot of alfalfa by 11.38%—20.67%,5.58%—16.54% and 20.68%—23.51%,respectively,and in the root by 19.50%—32.30%,8.62%—19.38% and 22.77%—39.23%,respectively.The speciation of Cd in both rhizosphere and non-rhizosphere soil was in a sequence of residual form>exchangeable form>carbonate form>Fe-Mn oxide form>organic form in all treatments.Besides,alfalfa facilitated Cd in soil to transfer into exchangeable form,and EXC Cd in rhizosphere and non-rhizosphere increased by 3.40%—6.51% and 3.16%—5.48%,respectively,in contrast to non-alfalfa treatment.Furthermore,three strains remarkably enhanced alfalfa’s capability to transform Cd into exchangeable form in soil,with EXC Cd increased by 11.23%—21.49%,6.37%—13.27% and 10.78%—27.76% in rhizosphere and 7.71%—16.30%,4.64%—13.84% and 9.62%—20.75% in non-rhizosphere,respectively.The BIOLOG ECO experiments revealed that microbial community diversity,activity and diversity index in Cd-contaminated soil increased significantly by adding exogenous microbes.Principal component analysis demonstrated that under different treatments there existed differences in the type and ability for microbes in soil to utilize carbon source.The cluster analysis result indicated that clustering analysis was reasonable to classify each treatment according to its effect on the conversion of available Cd in soil.