采伐方式对森林土壤氮初级转化速率和净氮转化速率的影响

Effects of Cutting Methods on Gross and Net N Transformation Rates in Forest Soils

[目的]为探明不同采伐方式下森林土壤氮素的释放和保存能力,揭示采伐对森林土壤氮素循环的影响。[方法]本研究通过室内培养试验,采用^(15)N同位素成对标记技术和FLUAZ数值优化模型研究了择伐和皆伐方式下寒温带阔叶混交林土壤氮初级转化速率和净氮转化速率特征。[结果]保留带处理土壤氮初级矿化速率、净氮矿化速率、氮初级固定速率、初级硝化速率和净硝化速率分别为4.16、1.86、2.32、0.368和0.343 mg∙kg^(−1)∙d^(−1)。与保留带处理相比,择伐和皆伐处理土壤氮初级矿化速率分别显著降低了32.2%和61.8%,净氮矿化速率分别显著降低了43.1%和61.5%,氮初级固定速率分别显著降低了23.3%和63.4%。择伐对土壤初级硝化速率和净硝化速率没有显著影响,但皆伐处理土壤初级硝化速率和净硝化速率分别显著降低了23.6%和33.3%。相关分析结果表明,土壤有机碳和水溶性有机碳含量的变化是影响氮初级矿化速率和初级固定速率的主要因素,pH是影响硝化速率的主要因素。[结论]皆伐后土壤铵态氮固定速率的下降程度大于初级硝化速率,导致gn/ia和NO_(3)^(−)/NH_(4)^(+)值显著提高,增加了硝态氮淋溶风险。而择伐处理的gn/ia和NO_(3)^(−)/NH_(4)^(+)值与保留带处理没有显著差异,是一种相对可取的森林采伐方式。

[Objective]To explore the nitrogen release and conservation capacity of forest soil under different cutting methods,and reveal the impact of cutting methods on forest soil N nutrient cycle.[Method]A laboratory incubation experiment was conducted to study the effects of selective cutting and clear cutting on gross and net N transformation rates in broad-leaved mixed forest soil in cold temperate zone,using 15N paired isotope labeling technique and FLUAZ numeric model.[Result]In the reserved belt without any cutting,soil gross N mineralization,net N mineralization,gross N immobilization,gross nitrification,and net nitrification rates were 4.16,1.86,2.32,0.368,and 0.343 mg∙kg^(−1)∙d^(−1),respectively.In comparison with the treatment of reserved belt,soil gross N mineralization rates of the selective cutting and clear cutting treatments significantly decreased by 32.2%and 61.8%,respectively,soil net N mineralization rates significantly decreased by 43.1%and 61.5%,respectively,and soil gross N immobilization rates significantly decreased by 23.3%and 63.4%.Selective cutting had no significant effects on gross and net nitrification rates in soil,while clear cutting significantly decreased soil gross and net nitrification rates by 23.6%and 33.3%,respectively.The correlation analysis indicated that soil organic C and water soluble organic C were the main factors influencing gross and net N mineralization and immobilization rates in soil,and pH was the main factor influencing gross and net nitrification rates in soil.[Conclusion]Our results indicate that the decrease of gross ammonium immobilization rate is greater than that of gross nitrification rate after clear cutting,leading to the significant increase of ratio of gn/ia and NO_(3)^(−)/NH_(4)^(+)in soil,which increases the risk of NO_(3)^(−)leaching.However,the ratio of gn/ia and NO_(3)^(−)/NH_(4)^(+)in soil under selective cutting is not significantly different from that of the reserved belt,which is a desirable way of forest harvesting.