高水平氮素添加促进内蒙古温带典型草原生态系统碳固持

High-level nitrogen addition enhances carbon sequestration in Inner Mongolia typical temperate steppe

净生态系统生产力(NEP)直接反映陆地生态系统碳固持能力,是衡量碳汇或碳源的重要指标.目前关于氮沉降对NEP影响的研究大多数都采用2个水平的氮处理,而关于不同水平氮沉降速率对NEP的影响及其机制还鲜有报道.利用中国科学院植物研究多伦站在内蒙古温带典型草原建立的一项模拟多水平氮沉降影响的控制实验平台,通过对生态系统碳通量及其相关因子连续两年的观测,探讨温带典型草原NEP对不同水平氮素添加的响应机制.混合效应模型(Mixed effects models)显示:低水平氮素添加对总初级生产力(Gross primary productivity,GPP),生态系统呼吸(Ecosystem respiration,ER)和NEP均无显著性影响;高水平氮素添加更能促进温带草原生态系统碳固持.结构方程模型(Structural equation model,SEM)显示:GPP主要受到氮素添加量,群落盖度(Cover)和土壤湿度(SM)影响;而ER则受到氮素添加量,Cover,SM和土壤呼吸(SR)的影响.研究结果增加了全球气候变化条件下对温带草原生态系统净碳固持响应氮沉降的认识和理解,有助于预测陆地生态系统碳循环与全球变化的关系.

Net ecosystem productivity(NEP) reflects the ability of net carbon sequestration, which is used to determine carbon sink/source of terrestrial ecosystems. Most previous studies examine the impact of N deposition on NEP using only two levels of N treatments. Effects of multi-level N deposition on NEP are still unclear. A field manipulative experiment with multi-level N addition was conducted in a temperate steppe of Inner Mongolia, China to examine responses of ecosystem carbon fluxes to N addition rates via measuring ecosystem carbon fluxes and related indexes during the two growing seasons of 2015 and 2016. The mixed effect model showed that low levels of nitrogen addition had no significant effect on both gross primary productivity(GPP), ecosystem respiratory(ER) or NEP. Therefore, the carbon sequestration of the steppe is significantly enhanced by the high-level nitrogen addition. The structural equation model showed that GPP is mainly affected by N addition, plant coverage(Cover) and soil moisture(SM), while ER is mainly influenced by N addition, Cover, SM and soil respiration(SR). The results of this study can not only enhance the understanding of the responses of net carbon sequestration to nitrogen deposition in temperate grassland ecosystems, but also can help the prediction of the relationship between carbon cycle and global change factors in terrestrial ecosystems.