樟子松人工林细根生产、周转和碳归还对施氮的响应

Fine Root Productivity and Turnover Rate Respond Nonlinearly to Increased Nitrogen Availability

在河北塞罕坝樟子松林,设置对照样方、低氮(20 kg N/(hm^2·a))、中氮(50 kg N/(hm^2·a))和高氮(100kg N/(hm^2·a))添加4种处理,分0~10,10~20和20~30 cm共3个土层,系统地研究细根生产、周转、碳归还以及细根生产力(NPPfr)占生态系统净初级生产力(NPP)的比例对不同程度氮可获得性的响应,结论如下:1)细根生产力在低氮下增大,高氮下降低;细根生产力占NPP的比例则相反,在低氮下降低,中氮下升高;2)随氮浓度增大,细根生物量逐渐降低,细根周转率增大,细根碳归还先升(低、中氮)后降(高氮);3)施氮对细根生产力的影响随土壤深度的加深无显著变化,施氮对细根周转率的影响在不同深度间则差异显著;4)结构方程模型表明,氮添加通过对土壤碳氮含量、p H的影响而改变细根生产力,通过对细根碳氮含量的影响改变细根周转率。

A N addition experiment was established with four treatments： control（no fertilization）, low-N（20 kg N/（hm^2·a））, medium-N（50 kg N/（hm^2·a）） and high-N fertilization（100 kg N/（hm^2·a）） in an N-limited Pinus sylvestris forest in Hebei Province, North China to study the production, biomass and turnover of fine root systematically. The results showed that fine root productivity（NPPfr） increased in low-N plots, decreased in highN treatment, while the proportion of NPPfr to net primary productivity（NPP） reduced in low-N addition and increased in medium-N addition. With the increase of N availability, root biomass decreased, turnover rate increased, and carbon returned to soil decreased at first and increased later. The influence of N availability on NPPfr didn＇t change with depth, while turnover rate varied among depth. N-addition made an impact on fine root productivity through soil nitrogen content, soil carbon content and soil p H, while affecting turnover rate of fine root by root carbon and nitrogen content.