What controls soil organic carbon stability and nitrogen transformation in boreal forest soils?

北方森林是地球上最大的生物群落之一，正受到快速气候变化和一些自然和人为干扰因素的影响。北方森林土壤是北方森林生态系统有机碳的重要储存地，在维持北方森林生态系统碳平衡方面发挥着重要作用。然而，全球变化和干扰的影响存在很大的不确定性，特别是它们对北方森林碳平衡的相互影响。 ** 在本研究计划中，我将1）研究各种干扰和全球变化情景下北方森林土壤有机碳（SOC）稳定性的机制; 2）研究土壤氮（N）转化对各种干扰和全球变化制度的响应（例如，N2 O排放），这是耦合到C循环;和3）链接C和N过程彼此和温室气体排放，这是一个反馈机制，干扰全球变化制度的温室气体排放的变化可能会增强或减轻全球变化。本研究将检验以下6个假设：（1）土壤异养呼吸速率随干扰强度的增加而增加，这是由于受干扰系统中的有机碳受保护程度较低，更易被微生物矿化;（2）土壤有机碳和氮的稳定性随干扰强度的增加而降低;（3）净初级生产力和净生态系统生产力随干扰强度的增加而降低; 4）新的植物物种入侵一个地点（变暖引起的物种迁移）将加速原生土壤有机质的分解，增加活性氮的有效性，其分解速率将更高（正交互作用）5）在促进原生土壤有机质分解方面，地下启动效应大于地上启动效应;（6）相对于对照（环境温度和无干旱条件），与干旱条件相关的较高温度将减少具有高C：N比的有机质的矿化，导致对气候变暖的潜在负反馈。** 本研究将培养一大批高素质人才（HQP），包括2名博士，3名硕士，10名本科生和2-3名博士后。通过整合HQP的研究，该计划将导致多种变化的环境和干扰制度下的北方森林生态系统C和N循环的改进模型，并将导致对这些多个变化制度如何相互作用的更好的理解，提高我们对物种迁移对生态系统C平衡的影响的理解，并为制定政策和战略以减缓北方纬度生态系统的环境变化提供数据。

The boreal forest is one of the largest biomes on the Earth, and is being affected by rapid climatic change and a number of natural and anthropogenic disturbance agents. The boreal forest soil represents a very large store of organic carbon (C) that plays a significant role in maintaining the C balance of the boreal ecosystem. However, there are very high uncertainties about the impact of global change and disturbance, and in particular about the interactive effects of those on C balance in the boreal forest. ******In this research program I will 1) investigate the mechanisms for soil organic C (SOC) stability in boreal forest soils under various disturbance and global change scenarios; 2) study the responses to various disturbance and global change regimes of soil nitrogen (N) transformations (e.g., N2O emission), which are coupled with C cycling; and 3) link C and N processes to one another and to greenhouse gas emission, which is a feedback mechanism to disturbance-global change regimes as changes in GHG emission may enhance or mitigate global change. The research will test the following six hypotheses 1) soil heterotrophic respiration rate will increase with increasing intensity of disturbance as SOC in the disturbed system is less protected and more subject to mineralization by microbes; 2) the stability of the SOC and N will decrease with increasing intensity of disturbance; 3) the net primary productivity and net ecosystem productivity will decrease with increasing intensity of disturbance; 4) new plant species invading a site (warming caused species migration) will accelerate native soil organic matter decomposition and the decomposition rates will be higher under increasing reactive N availability (positive interaction); 5) the belowground priming effect is greater than that from aboveground in enhancing native soil organic matter decomposition; and 6) warmer temperature in association with drought conditions will reduce the mineralization of organic matter with a high C:N ratio, relative to the control (ambient temperature and no drought condition), resulting in a potential negative feedback to climate warming. ******This research will train a large number of highly qualified personnel (HQPs), including 2 PhD, 3 MSc, 10 undergraduate students and 2-3 postdoctoral fellows. Through integrating the research of the HQPs, this program will lead to improved models of C and N cycling in boreal forest ecosystems under multiple changing environmental and disturbance regimes and will result in an improved understanding of how those multiple changing regimes interact, improve our understanding of the impact of species migration on ecosystem C balance, and provide data for developing policies and strategies for mitigating environmental change in ecosystems at northern latitudes.