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

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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.