增温和氮添加对亚热带杉木林土壤氮转化速率的影响

Effects of Warming and Nitrogen Addition on Soil Nitrogen Transformations in Subtropical Chinese Fir Plantations

温度和氮供应水平是影响森林土壤氮转化过程的重要驱动因子,因此增温和外源氮输入势必会改变土壤氮转化过程的速率和方向,而且二者的交互作用会使氮转化过程的响应更加复杂。为此,本研究依托亚热带杉木幼林增温×氮沉降模拟实验平台,设置了对照、增温、氮添加、增温×氮添加4种处理,以揭示增温和氮沉降及其交互作用对土壤氮矿化速率、硝化速率及氨化速率的影响。结果显示,土壤净氮矿化速率、净硝化速率及净氨化速率具有显著的季节变化特征。同时,增温整体上显著提高土壤净氮矿化速率、净硝化速率和净氨化速率,但是氮转化速率对增温的响应呈现明显季节性。氮添加整体上也显著提高土壤净氮矿化速率和净氨化速率,未显著影响净硝化速率,且氮转化速率对氮添加的响应也呈现明显的季节性。此外,增温×氮添加处理显著提高了净氮矿化和净硝化速率,但是未呈现协同效应;未显著影响土壤净氨化速率。上述结果表明,增温、氮添加及增温×氮添加处理促进土壤氮矿化和硝化作用,但是增温×氮添加未呈现协同效应,说明增温和氮添加处理会加速微生物氮循环,一方面可能会缓解亚热带森林生态系统植物氮限制,另一方面可能会加速森林土壤氮损失。

Warming and nitrogen(N)input would inevitably regulate the magnitude and direction of soil N transformations,as temperature and N supply are rate-limiting factor for N transformations.Meanwhile,the interactions between these two climate change factors would make the response of N transformations more complex.Hence,based on a simulation experiment platform including soil warming and N addition in subtropical Chinese fir plantations,four treatments are set,including control,warming,N addition and warming×N addition,trying to reveal the effects of warming and N addition on the rates of soil N mineralization,nitrification and ammonification.The results showed that all the N transformation rates exhibited significant seasonal variations.Meanwhile,warming generally increased soil rates of net N mineralization,net nitrification and net ammonification,and the responses of these rates to warming had seasonal variations.Moreover,N addition improved soil rates of net N mineralization and net ammonification in general,had no significant effects on the net nitrification rate,and the effects of N input on rates varied with seasons.In addition,warming×N addition significantly increased soil net N mineralization and net nitrification rates,but represented no synergistic effects on these rates.Overall,soil warming,N addition,and warming×N addition stimulated soil N mineralization and nitrification,while warming×N addition had no synergistic effects.This phenomenon suggested that these two climate changes factors could increase N cycling rate,which might mitigate plant N limitation and stimulate N loss in forest ecosystems.