樟子松人工林细根生产、周转和碳归还对施氮的响应

在河北塞罕坝樟子松林, 设置对照样方、低氮(20 kgN/(hm²·a))、中氮(50 kgN/(hm²·a))和高氮(100 kgN/(hm²·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、pH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。

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

A N addition experiment was established with four treatments: control (no fertilization), low-N (20 kgN/(hm²·a)), medium-N (50 kgN/(hm²·a)) and high-N fertilization (100 kgN/(hm²·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 high-N 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 pH, while affecting turnover rate of fine root by root carbon and nitrogen content.