Grant: Discovery Grants Program - Individual

The terrestrial carbon (C) sink currently sequesters a third of anthropogenic carbon dioxide (CO2) emissions in vegetation and soil biomass, thereby exerting a pivotal control on atmospheric CO2 concentrations and climate change. However, the degree to which nutrients such as nitrogen (N) will constrain C sequestration under global change is unclear, especially as elevated atmospheric CO2 stimulates photosynthesis ("CO2 fertilisation") and correspondingly increases N demand. The role of N limitation in boreal forests is of particular importance because measurements of N cycling in boreal forests are rare and boreal forests are suggested to be strongly N-limited. However, it has been proposed that rising temperatures stimulate decomposition and permafrost thaw which could release available soil N. As such, the extent to which N will limit boreal forest growth under global change is highly uncertain. My research program will address the overarching question: To what extent will N limit terrestrial C sequestration in Canadian boreal forests under global change? My research will both enhance our fundamental understanding of boreal forest ecosystems and improve terrestrial biosphere models (TBMs), which are used within the framework of Earth System Models to simulate the terrestrial C sink and project climate change, as reported by the Intergovernmental Panel on Climate Change (IPCC). First, my research group will comprehensively examine N cycling across an established network of sites along a latitudinal gradient in northwestern Canada. This approach allows for the estimation of the degree of N limitation and how it varies with temperature and latitude in the Canadian boreal forest. These observations will then be used to directly evaluate and improve CLASSIC, which is the TBM component of the Canadian Earth System Model. CLASSIC will be used to simulate the extent to which N limits terrestrial C sequestration in Canadian boreal forests under a host of interacting global change drivers: elevated available soil N driven by rising temperatures, the influence of rising temperatures and variable precipitation regimes on forest growth and wildfires, alongside CO2 fertilisation and its intensification of N limitation. Second, my research program will examine N cycling in Canadian boreal forests across the suite of TBMs that contribute to the IPCC reports. Through my active involvement in various international model intercomparison projects, my research group will compare TBMs to evaluate how differences in N cycling between TBMs translate into differences in projected terrestrial C sequestration over the 21st century in Canadian boreal forests. Additionally, we will examine the future trajectories of N losses, which have significant socioeconomic consequences. Overall, my research will improve our understanding of the terrestrial biosphere with direct implications for improving climate change projections as well as Canadian and global climate policy.