镉在有机酸存在时对红壤中微生物生物量的影响

在预培红壤中加入定量的有机酸和不同浓度的Cd ,2 5℃培养 14d ,测定土壤微生物生物量C(Cmic)、N(Nmic) ,结果表明 ,存在有机酸时 ,土壤中Cmic和Nmic随着Cd浓度的增加而降低 ;Cmic/Nmic随着Cd浓度的增加而升高 .施加低分子量有机酸的土壤中 ,Cd浓度高于 2 5mg·kg-1土时 ,土壤中Cmic和Nmic均比未加有机酸时低 ,说明此时低分子量有机酸助长Cd的毒性 ,而Cd浓度低于 2 5mg·kg-1土时 ,土壤中Cmic和Nmic均比未加有机酸时高 ,说明此时低分子量有机酸可降低部分Cd的毒性 ;施加胡敏酸的土壤中 ,土壤中Cmic和Nmic均比未加有机酸时高 ,说明胡敏酸降低Cd的毒性并提供N源 .不含Cd时 ,加入有机酸导致土壤中Cmic和Nmic增加 ,其中胡敏酸最明显

Microbial biomass affected by cadmium with the occurrence of organic acids in red soil

Soil microbial biomass carbon and nitrogen were determined after adding fixed concentration of organic acids and changeable concentration of cadmium in pre-incubated red soil and 14-day incubation at 25 degrees C. The results show that soil microbial biomass carbon and nitrogen in the soil added with organic acids decreased with increasing concentration of cadmium. When the concentration of cadmium was higher than 25 mg.kg-1, the microbial biomass carbon and nitrogen in the soil added with low molecular weight of organic acids (oxalic acid, acetic acid, citric acid, tartaric acid) were lower than those without the addition of organic acids, indicating that low molecular weight of organic acids could increase the toxicity of cadmium. On the contrary, the microbial biomass carbon and nitrogen in the soil added with low molecular weight of organic acids were higher than those without the addition of organic acids when the concentration of cadmium was lower than 25 mg.kg-1, indicating that low molecular weight organic acids could decrease the toxicity of cadmium. The microbial biomass carbon and mitrogen in the soil containing humic acid were higher than those without the addition of organic acids, indicating that humic acid could decrease the toxicity of cadmium. However, the C:N ratio of soil microbial biomass was increased with increasing concentration of cadmium. Organic acids could increase microbial biomass carbon and nitrogen when soil was not added with cadmium.