N添加对林地土壤脲酶活性及动力学参数的影响

Impacts of nitrogen supply on enzyme activity and kinetics parameters of forest soil urease

为探讨不同施N量对土壤脲酶活性及动力学参数(V_(max)、K_m)的影响,以南京林业大学科研教学基地6年生墨西哥柏人工林(Cupressus lusitanica Mill.)为研究对象,设置N0(CK)、N1(24 kg/hm^2)、N2(48 kg/hm^2)、N3(72 kg/hm^2)、N4(96 kg/hm^2)、N5(120 kg/hm^2) 6个不同施N量处理,对其林地土壤进行了1年氮添加试验。结果表明:(1)与对照样地相比,土壤有机碳(SOC)随氮添加量的增加而显著增加,并在N4水平时达到最大值(19.06 mg/g)。氮添加对土壤C/N也产生显著影响。但氮添加并未对土壤全氮(TN),全磷(Tp)含量及N/p产生显著影响(P> 0.05)。(2)与对照样地相比,脲酶绝对活性(Ure)、单位有机碳脲酶活性(Ure/SOC)及V_(max)随N添加量增加而显著增加,并在N3水平下达到最大值。但在N4、N5水平下,Ure、Ure/SOC及V_(max)显著低于N3水平。K_m随施N量的增加显著增加,并在N5水平下达到最大值(21.195 g/L)。(3)冗余分析结果表明,Ure、Ure/SOC和V_(max)与TN,Tp,N/p呈正相关关系;但K_m与TN,Tp,N/p呈负相关关系。以上结果表明,氮添加通过改变森林土壤的环境因子,影响了土壤中脲酶活性及脲酶动力学参数,进而影响土壤氮素循环。

In order to investigate the responses of soil urease activity and kinetic properties(Vmax, Km) to increased nitrogen addition, a field experiment was conducted in a 6-year-old Cupressus lusitanica Mill. plantation in the Research and Teaching Base of Nanjing Forestry University in Nanjing, Jiangsu Province, China. Six treatments of nitrogen supply were designed, including N0(CK), N1(24 kg/hm2), N2(48 kg/hm2), N3(72 kg/hm2), N4(96 kg/hm2)and N5(120 kg/hm2). Each treatment comprised three replicate plots. We studied the soil physicochemical properties,urease activity and kinetic properties in response to 1 year of nitrogen addition. The results showed that:(1) The soil organic carbon(SOC) was significantly elevated with increased N(P<0.05, vs. Control) and peaked at the rate of N4(19.06 mg/g). Nitrogen addition had a significant effect on soil C/N. However, nitrogen addition had little impact on TN, TP and N/P(P>0.05).(2) Urease activity(Ure), Urease activity per. SOC(Ure/SOC) and Vmax were significantly elevated with increased N(P<0.05, vs. Control) and peaked at the rate of N3. However, values of Ure,Ure/SOC and Vmax in N4 and N5 plots were significantly lower than those in N3 plot. Km was significantly elevated with increased N and peaked at the rate of N5(21.195 g/L).(3) Redundancy analysis showed that Ure, Ure/SOC and Vmax was positively correlated with soil TN, TP, and N/P ratios while Km was negatively correlated with soil TN, TP,and N/P ratios. These results suggested that N addition could affect the soil nitrogen and nutrient flow by influencing environmental factors and microbial enzymatic activities in subtropical forest ecosystems.