蚓粪对黑麦草吸收污染土壤重金属铜的影响

在长江冲积物形成的高沙土中加入CuSO4.5H2O模拟土壤污染,使Cu污染浓度分别为200、400、600 mg kg-1,并设置加蚓粪(15%)和加原土(15%)处理,二处理各设种植黑麦草(Lolium multiflorum)和不种黑麦草培养试验,研究蚓粪对黑麦草生长及对Cu吸收的影响,以揭示蚓粪在Cu污染土壤植物修复中的作用。结果表明:蚓粪显著增加了黑麦草的地上部和地下部的生物量(p<0.001**)以及根系的长度、表面积、体积和根尖数(p<0.05*),在Cu浓度为200 mg kg-1时促进作用最大;蚓粪还显著提高了黑麦草地上部Cu的浓度及累积量,但显著降低了地下部的Cu浓度(p<0.05*),而对地下部的铜累积量没有影响,显示蚓粪能促进Cu从根系向地上部的运移及在地上部的富集。通过对土壤的pH和Cu的形态特征分析,发现种植黑麦草处理降低了土壤的pH并增加了可交换态铜的含量,而且这种作用在加入蚓粪后更加明显。推测蚓粪主要通过促进黑麦草根系的生长和活性而影响根系周围环境,提高重金属铜的生物有效性进而增加植物对铜的吸收。

EFFECT OF EARTHWORM CASTS ON COPPER UPTAKE BY RYEGRASS IN COPPER POLLUTED SOIL

A pot experiment was conducted to examine effects of earthworm (Pheretima sp.) casts on copper uptake by ryegrass (Lolium multiflorum).The experiment had three levels (200,400 and 600 Cu mg kg^-1) of Cu contamination of the soil (Orthic aquisol) prepared by adding CuSO₄#5H₂ O,two treatments of soil amendments,earthworm casts (15%) and back-ground soil (15%) and two treatments of plantation,with ryegrass and without ryegrass.Results show that earthworm casts significantly increased biomass of shoots and roots (p<0.001),and length,surface area,volume and number of tips of the root system,and the effect was the highest when Cu content of the soil was 200 mg kg^-1.It also increased copper concentration and accumulation in shoots (p<0.05),but decreased copper concentration in roots.That means earthworm casts can promote copper transportation from roots to shoots and copper accumulation in shoots.In addition,analysis of soil pH and Cu fractions (BCR sequential extraction) show that plantation of ryegrass decreased soil pH and increased content of exchangeable Cu,and these effects could be strengthened by addition of earthworm casts.It could be inferred that earthworm casts promote copper uptake of ryegrass mainly by stimulating growth and act ivity of the roots,which in turn affects the rhizosphere environment and enhances bioavailability of copper.