砷及重金属对土壤微生物的影响

砷及重金属污染土壤中微生物变化的模拟试验证实,土壤受砷及重金属污染后,细菌总数降低,随着砷及重金属浓度的递增而明显减少。本试验条件下,土壤砷浓度为10ppm、Hg为0.7ppm、Cd为3ppm、Cr为50ppm、Pb为100ppm时,细菌总数即开始减少。 砷及重金属对几种有益土壤微生物影响的纯培养试验表明,三价砷为5ppm、五价砷为10ppm时,对土壤固氮细菌(花生根瘤菌、大豆根瘤菌、紫云英根瘤菌、含脂刚螺菌、圆褐固氮菌)、解磷细菌(大芽孢杆菌、枯草杆菌)及纤维分解菌(木霉)均有抑制作用,其中三价砷的抑制作用尤为明显。不同菌种对砷的敏感性不同,紫云英根瘤菌和花生根瘤菌对亚砷酸钠敏感,木霉和大芽孢杆菌对砷酸氢二钠敏感。 Cd、Cu、Pb、Cr对大芽孢杆菌和枯草杆菌均有明显抑制作用,其中对大芽孢杆菌的抑制作用更为显著,低浓度Cd对枯草杆菌有刺激作用。 土壤受砷污染后,土壤呼吸强度降低,其CO_2的产量与土壤细菌总数呈正相关关系。

EFFECTS OF ARSENIC AND HEAVY METALS ON SOIL MICROORGANISMS

From model test of microorganism variation in arsenic and heavy metal polluted soils, it has been proved that after soils polluted with arsenic and heavy metals, the total counts of bacteria start to decrease, obviously as concentrations of arsenic and heavy metals increase. Under conditions of our experimental study, such as arsenic at 10 ppm, mercury 0.7 Ppm, cadmium 3 ppm, lead 100 Ppm and chromium 50 ppm, the total counts of bacteria are in the decrease.Our pure bacterium culture test shows that minimum concentrations of arsenic and heavy metals required for inhibiting effect on the bacteria which are beneficial to several kinds of soils are as follows: trivalent arsenic 5 ppm, pentavalent arsenic 10 ppni. They also possess inhibiting effects on nitrogen-fixing bacteria (Rhizobium arachis, Rhizobium japonicum, Rhizobium astragali, Spirillum lipoferum, Azotobacter chroocuccum), Bacillus phosphaticum, (Bacillus megatherium, Bacillus sbtilis) and cellulose-decomposing bacterium (Trichoderma sp.). Among them that of trivalent arsenic is especially outstanding. Different kinds of bacteria have different sensitivities to arsenic. Rhizobium astragali and Rhizobium, arachis are sensitive to sodium arsenite while Bacillus trichoderma sp, and Bacillus megatherium to disodium hydrogen arsenate.Cadmium, copper, lead and chromium all possess predominant inhibiting effects on Bacillus megatherium and Bacillus subtilis, especially on the former one. Cadmium in low concentration shows stimulating action to Bacillus subtilis. The respiratory intensity of arsenic-polluted soil is low. The amount of carbon dioxide produced is in correlation with total counts of soil bacteria.