模拟氮沉降对内蒙古典型草地碳固持效应及其稳定性的影响

Soil organic matter (SOM) is the most and labile carbon (C) pool in the earth surface, and understanding C sequestration and its mechanism of terrestrial ecosystems is very important scientific issues for global change study. Many researches have focused on the impact of global change (climate change, land-use change, nitrogen deposition) on SOM and its stability since 1990. Inner Mongolian grasslands of China have a large amount of carbon storage, especially in soil and have a potential as "C sink" to sequester atmospheric CO2. Currently, atmospheric nitrogen (N) deposition increased apparently since the mid of 20st century, and became the important approach of external-N input to terrestrial ecosystems nowadays. Therefore, the increases in external-N input by atmospheric N deposition will play more and more important roles in regulation to carbon storage and sequestration of Inner Mongolia grasslands in the future..In order to scientifically evaluate the effect of N deposition on the C sequestration of Inner Mongolian grasslands, we should consider the following questions. First, the extent to which future N deposition increase influence the C sequestration is considerably uncertain, and the underlying mechanisms are still not clear. Second, the stability of increasing SOM (C sequestration effect) is important. The C sequestration would become nothing at decade or longer scales if the stability of SOM decreased apparently under the future increasing N deposition conditions. Third, the effect of increasing N deposition on the stability of SOM in these long-term grazing-exclusion grasslands is very important to valuate their C sequestration, because many studies have showed that long-term grazing-exclusion is the most effective and economic approach to realize the C sequestration potential of Inner Mongolia grasslands, compared to controlling grazing intensity, fertilization, and so on. We assumed that if N deposition decreased apparently on the stability of SOM in these long-term grazing-exclusion grasslands, the real potential of C sequestration of Inner Mongolian grasslands would depressed significantly..In this study, we will use the long-term N addition experiment (simulating N deposition), 5 neighboring grasslands with different fenced times constituting a grazing-exclusion chronsequence, and the pare-experiment plots of long-term grazing exclusion and free grazing grasslands in four sites, by analyzed the total storage of C and N in SOM, roots, litter and aboveground biomass, the C and N storage in soil fractions, soil C mineralization rates (experimental incubation experiment), and the temperature sensitivity of soil C mineralization (Q10), to address above three questions in view of the magnitude of C sequestration and SOM stability, The results will provide scientific foundation to evaluate the C sequestration of Inner Mongolia grasslands in China.

陆地生态系统碳固持效应及其实现途径是当前全球变化研究的热点领域，并已成为新的国家战略需求。内蒙古典型草地是重要的碳库和潜在的"碳汇"。随着氮沉降日益增强，它已成为生态系统外源性氮输入的重要途径，并对内蒙古草地碳固持效应产生重要影响。为了科学地评估氮沉降对草地碳固持的影响，应考虑三个方面的因素：1）氮输入增加后草地碳固持量如何、其过程与机理如何？2）增加氮输入所获得的碳固持，其稳定性如何？3）未来氮沉降增加是会否影响到长期封育草地土壤有机质稳定性？本项目将分别利用氮添加实验、不同封育年限草地、不同地点长期封育-自由放牧成对草地，采用草地碳氮含量、土壤组分碳氮含量、土壤呼吸（原位）和（室内培养）土壤（组分）碳矿化量和温度敏感性（Q10）相结合的指标体系，从碳固持效应和土壤有机质稳定性相结合的角度，综合评估未来氮沉降加剧对温带草地碳固持效应的影响，为评价我国温带草地碳固持效应提供重要的科学依据。

1).6年野外控制实验表明：随着氮添加梯度（0–56 g N m–2 yr–1）草地碳贮量增幅为156.8 –1352.9 g C m–2；随着P添加梯度（0–12.4 g P m–2 yr–1）土壤碳贮量增幅为293.6–788.6 g C m–2；随着氮和磷添加梯度的增加其固碳效率显著下降。.2).整合51个站点数据发现：封育后内蒙古草地土壤很快就会表现为固碳，其固碳速率在前期较高并随着封育年限的增加而逐渐降低。草地封育恢复序列（0–31年），SOC、HAC、HUC、HAC/FAC和PQ随封育年限延长呈对数增加，草地封育11年后HAC/FAC和PQ显著增加，土壤肪族性增强，芳香性减弱，土体结构变得更加稳定且整体土壤品质提高。.3).封育年限、添加葡萄糖、培养温度和培养时间对土壤碳矿化速率具有显著的影响, 不同因素间存在显著的交互效应。长期封育会降低羊草草地土壤碳矿化速率、温度敏感性和激发效应， 使内蒙古长期封育草地土壤仍然具有碳固持能力。.4).温度、团聚体及两者的交互作用均对短期内碳矿化速率具有显著的影响，在团聚体层次分解速率表现大团聚体 > 粉-粘 > 微团聚体；温度敏感性（Q10）表现为大团聚体 > 土壤 > 粉-粘粒 > 微团聚体。.5).中国东北草地样带上0－20 cm和20－4 0cm土壤和不同土壤粒级内的碳氮含量与年平均降水（MAP）显著正相关、与年平均气温（MAT）显著负相关。0－10 cm土壤和不同土壤组分内的有机碳对MAT和MAP的响应明显高于20－40 cm。降水和温度均是影响内蒙古草地土壤碳贮量的重要因素，然而，不包括MAT的模型可以较好地拟合内蒙古草地碳贮量空间变化规律。.6).项目正式发表了科研项目24篇， SCI论文13篇（第一标注7篇）、CSCD论文11篇（第一标注6篇）；还有1篇论文在线发表。SCI论文主要发表在《Global Change Biology 》、《Agriculture Ecosystem & Environment》、《Journal of Geophysical Research》、《Ecological Engineering》、《Ecology and Evolution》、《Pedosphere》等期刊；CSCD论文主要发表在《生态学报》、《植物生态学报》等期刊。