镉对北京城郊土壤潜在硝化速率的影响

采集北京城郊5个区县的3种土壤褐土、潮土和山地棕壤,通过急性毒性实验,研究了外源添加镉(Cd)对土壤潜在硝化速率(PNR)的影响。结果表明,5个采样点土壤的PNR分别随土壤中总Cd和有效态Cd含量呈先增后减的趋势。所有处理土壤的有效态Cd含量与PNR的相关关系(R2=0.42,p0.001)优于土壤总Cd含量与PNR的相关关系(R2=0.27,p=0.001)。在土壤总Cd含量和PNR的逐步回归分析中,引入土壤有机质和阳离子交换量(CEC)2个变量可提高其相关性。基于土壤总Cd的EC50(PNR降低至对照50%时的土壤Cd浓度)和有效态Cd的EC50的最大值与最小值之间分别相差2.3倍和3.3倍,而EC10(PNR降低至对照10%的土壤Cd浓度)的最大值与最小值之间分别相差8.5倍和10.8倍。基于总Cd的EC50最低值出现在CEC最小的丰台土壤,而最高值出现在有机质含量最多的灵山土壤,但这2个EC50值未达到显著性差异,表明5个采样点的土壤有机质和CEC虽然在一定程度上影响Cd对PNR的毒性,但不足以引起EC50的显著变化。

Influence of Cd Amendment on Potential Nitrification Rate in Suburban Soil of Beijing

Cinnamon soil, moisture soil and mountain brown earth from five districts of the suburban Beijing were collected to investigate the response of potential nitrification rate (PNR) to cadmium (Cd) stress in soil by acute toxicity test. The results showed that the PNR of five sampling sites firstly increased and then decreased with the content of total Cd or extractable Cd in soil. The correlation (R²=0.42, p<0.001) between the content of extractable Cd and the PNR was better than the correlation (R²=0.27, p=0.001) between the content of total Cd and the PNR. The introduction of soil organic matter and cation exchange capacity (CEC) could increase the correlation of stepwise regression analysis of the content of total Cd and PNR. The toxicity threshold of EC₅₀ (as defined as effective concentration of added Cd causing 50% inhibition) based on the total Cd and the extractable Cd varied 2.3-fold and 3.3-fold respectively, and the corresponding EC₁₀ (as defined as effective concentration of added Cd causing 10% inhibition) varied 8.5-fold and 10.8-fold respectively. The lowest value of EC₅₀ based on the total Cd content appeared in the Fengtai soil, which had the weakest CEC, and the highest value appeared in the Lingshan soil, which contained the highest amount of organic matter. But no significant difference was seen between the lowest value and the highest value, which indicated organic matter and CEC influenced the toxicity of Cd to PNR in some degree, but it was not enough to cause the remarkable variation of EC₅₀.