外源Cd胁迫对红壤性水稻土微生物量碳氮及酶活性的影响

研究外源Cd对红壤性水稻土微生物学指标的影响。采集湖南长沙红壤性水稻土,设置外源Cd胁迫浓度梯度为0、1、3、5、7 mg·kg~(-1)和10 mg·kg~(-1),进行室内模拟土壤Cd污染培养实验,测定土壤微生物生物量碳、氮和土壤酶活性指标。结果表明:土壤微生物生物量碳、氮含量随外源Cd胁迫浓度的增加表现为先上升后降低的趋势,当外源Cd胁迫浓度为1 mg·kg~(-1)时,土壤微生物生物碳、氮含量达到最大值;土壤脱氢酶、过氧化氢酶和脲酶的活性随着外源Cd胁迫浓度的增加而显著降低;而土壤蔗糖酶活性随外源Cd胁迫浓度的增加表现为先下降后上升再下降的趋势。由通径分析可知:外源Cd胁迫可以直接影响土壤微生物生物量,也可以通过酶活性间接影响土壤微生物生物量,Cd污染对酶活性的影响也有同样的作用机制;其中Cd胁迫对微生物生物量碳的直接抑制作用系数最大(-1.110),与脱氢酶的相关系数最大(-0.952~(**))。综上,外源Cd胁迫对土壤微生物生物量和酶活性均有不同程度的抑制作用,其中对脱氢酶活性抑制作用最为明显。

Effects of exogenous cadmium on microbial biomass and enzyme activity in red paddy soil

This study was carried out to investigate the effects of exogenous Cd on the microbial index in red paddy soil in Hunan Province. An indoor simulation experiment was conducted to study the effects of exogenous cadmium amendment (0, 1, 3, 5, 7, and 10 mg·kg^-1) on soil microbial biomass and enzyme activity. The results showed that soil microbial biomass C and N increased at first and later decreased with the addition of exogenous Cd. The highest concentrations of soil microbial biomass C and N were measured when the concentration of exogenous cadmium was 1 mg·kg^-1. Soil dehydrogenase, catalase, and urease activities decreased with increasing exogenous Cd concentrations, whereas soil invertase activity decreased firstly, then increased, and finally decreased. Path analysis indicated that the addition of exogenous Cd could affect the soil microbial biomass and enzyme activities directly or indirectly. The exogenous Cd concentration had the maximum direct path coefficient (-1.110) with microbial biomass carbon, and the maximum correlation coefficient (-0.952^**) was found between exogenous Cd concentration and dehydrogenase activity. These results suggested that exogenous Cd addition could restrain the soil microbial biomass and enzyme activities, and soil dehydrogenase activity might be the most sensitive index to exogenous Cd addition.