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，并受到快速气候变化和一些自然和人为干扰因素的影响。北方森林土壤中蕴藏着大量的有机碳(C)，对维持北方森林生态系统的碳平衡起着重要作用。然而，全球变化和干扰的影响，特别是它们对北方针叶林碳平衡的相互作用存在很大的不确定性。******在本研究项目中，我将1)研究不同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)研究与碳循环耦合的土壤氮(N)转化（如N2O排放）对各种扰动和全球变化机制的响应；3)将碳和氮过程相互联系起来，并与温室气体排放联系起来，这是一种对扰动-全球变化机制的反馈机制，因为温室气体排放的变化可能会增强或减缓全球变化。本研究将验证以下六个假设：1)土壤异养呼吸速率随干扰强度的增加而增加，因为受干扰系统中的有机碳受到的保护较少，更容易被微生物矿化；2)土壤有机碳和氮的稳定性随扰动强度的增大而降低；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)新植物物种入侵（气候变暖导致物种迁移）会加速土壤有机质分解，且活性氮速效度增加（正相互作用）会提高土壤有机质分解速率；5)地下启动对原生土壤有机质分解的促进作用大于地上启动；6)相对于控制条件（环境温度和无干旱条件），与干旱条件相关的温度升高将减少高C:N比有机质的矿化，导致对气候变暖的潜在负反馈。******本研究将培养大量高素质人才（HQPs），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HQPs的研究，该项目将改进在多种变化的环境和干扰制度下北方森林生态系统C和N循环的模型，并将使我们更好地理解这些多种变化制度如何相互作用，提高我们对物种迁移对生态系统C平衡的影响的理解。并为制定缓解北纬生态系统环境变化的政策和战略提供数据。

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.