作为我国面积最大的人工林树种，杉木生长速度快，固碳能力强，对固碳减排、减缓气候变化具有重要作用。然而多代连作的杉木人工纯林出现了林分生产力下降和地力衰退等问题，也大大削弱了杉木林的固碳功能。低效针叶纯林阔叶化改造是改善林分结构、提高林地生产力和改善生态服务功能的有效途径，目前作为低效林生态修复的主要手段得到了大面积的推广应用。改造活动一方面可能会增加温室气体的排放，另一方面可能会扭转林分生产力下降的趋势而可望提高生物量固碳能力。但是，这种影响并未受到应有的关注。本项目拟研究不同杉木林阔叶化改造模式对土壤CO2、CH4和N2O三种温室气体通量、土壤有机碳储量与林分生物量碳储量的影响，从林分生长、土壤理化性质及土壤微生物特征的变化揭示阔叶化改造对温室气体通量和生态系统净碳汇功能的影响机制，探讨阔叶化改造提升低效杉木林固碳功能的潜力，为全面认识评估阔叶化改造的作用提供科学依据。

As the plantation tree species with the largest area in China, Chinese fir plays a significant role in carbon sequestration and mitigating climate change because of its rapid growth and strong carbon fixed capacity. Some problems have emerged in pure Chinese fir plantation during continuous planting, such as stand productivity declining and soil degradation. Its ability of carbon uptake is weakened. The mixed conifer and broadleaved-oriented transformation of low quality pure coniferous forest has been proved as an effective way to improve stand structure, production and ecological service function. At present, it has been popularized in large area as the major method of plantation ecological restoration with low effect. The stand transformation practices may increase soil greenhouse gas emission. On the other hand, it may improve carbon sequestration capacity through changing the downtrend of stand productivity. However, there are few researches focusing on such effects of stand transformation practices. In this project, we intend to examine the change in soil greenhouse gas (CO2, CH4 and N2O) emission, soil organic carbon storage and stand biomass carbon uptake in Chinese fir plantation ecosystem under different stand transformation models. It is expected to reveal the influence mechanism of stand transformation on soil greenhouse gas fluxes and net carbon uptake function of ecosystem, based on the changes of stand growth, soil physical and chemical properties, the composition and structure of soil microbes. And it will demonstrate the potential effects of stand transformation to increase carbon fixed capacity of low effect Chinese fir plantation. This study will provide the comprehensive scientific understanding and evaluation of the effects from stand transformation.