苏丹草根分泌物在有机氯农药降解过程中的作用

Effect of exudates from sorghum sudanense grass roots on degradation of organochlorine pesticides in soils

采用模拟修复实验的方法,研究了苏丹草(Sorghum sudanense)根系分泌物对根际土壤中有机氯农药(organochlorine pesticides,OCPs)各残留组分的降解特征及其对根际微生物群落特征(数量、组成、结构及功能)的影响,探讨了根际土壤中微生物碳、微生物氮和群落结构的变化差异.结果显示,供试OCPs含量(66.67~343.61mg/kg)范围内,根系分泌物介导下的土壤-微生物系统对OCPs污染物去除的促进作用明显:添加根系分泌物20d后,"根际"土壤(TR_2)中OCPs去除率在高达79.32%,比无根系分泌物的OCPs污染组(TR1)高36.86%,比灭菌处理组(CK)高60.63%;相同处理条件(污染水平、添加剂量)下,根系分泌物对HCHs、毒杀芬、HCB、艾氏剂、γ-氯丹等组分的强化去除率总高于对OCPs的强化率(P<0.05);对DDTs、灭蚁灵、硫丹Ⅰ、狄氏剂、环氧七氯等组分的强化去除率低于OCPs的强化率.相同污染水平下,"根际"土壤(TR_2)中土壤微生物碳、微生物氮也显著高于无根系分泌物的TR_1组;实验期间,细菌的磷脂脂肪酸含量占主导地位、真菌次之,其变化趋势与土壤中OCPs的降解特征相一致.可见,在OCPs降解过程中,根系分泌物改变了根际土壤中细菌、真菌等菌群的种群数量及群落结构,进而促进了OCPs的降解.

pot experiments was conducted to evaluate the potentials of exudates of sorghum sudanense in reinforcing the phytoremediation of organochlorine pesticides(OCPs),the removal efficiencies of OCPs and its main components in soils with initial concentrations ranging66.67to343.61mg/kg were determined,microbial ecological characteristics,including composition,numbers,and community structure and function,were investigated,and their influence on soil microbial biomass carbon,microbial biomass nitrogen and their phospholipid fatty acids(PLFA),as well as roles which root exudates played in the process of phytoremediation were discussed.Results showed that addition of the exudates significantly reinforced dissipation of OCPs in soils.During the entire experiment,the soil-microbe systems(treatment II,TR2)mediated by the exudates exhibited enhancement on OCPs degradation in soils.And,the highest OCPs removal rate at79.32%was achieved when the exudates were added in the presence of rhizospheric microbes(TR2);whereas,without the exudates(treatment I,TR1),the removal rate was merely40.46%,and it was18.69%in soils(CK)spiked with0.05%NaN3to suppress the microbial effect.Under the same treatment conditions,the enhanced removal rates of hexachlorocyclohexane(HCHs),hexachlorobenzene(HCB),toxaphene,aldrin andγ-chlordane were much higher than the total amount of OCPs while the extent of enhanced dissipation of dichloro-diphenyl-trichloroethanes(DDTs),mirex,endosulfanⅠ,dieldrin and heptachlor epoxide were always lower than that in the corresponding soils.Furthermore,soils microbial biomass carbon and nitrogen,increased increasing exudates concentration under the same level of the OCPs stress,and there were close relationship between OCPs degradation and soil microbes.In the test soils which PLFA probed by GC-MS,their microbial community was dominated by bacteria,and followed by fungi,and they had the same variation trend as the OCPs degradation,which indicated OCPs in soils were degraded mainly by bacteria and fungi,and influence of the exudates in OCPs degradation were mainly carried out through modifying bacterial and fungi population ecological characteristics.Thus,rhizosphere effect from of sorghum sudanense under the OCPs stress might encourage the growth of rhizospheric microbes and modify their community structure in the process of phytoremediation leading to the improved OCPs degradation.