Research
The terrestrial carbon (C) sink currently sequesters a third of anthropogenic CO2 emissions in vegetation and soil biomass, thereby exerting a pivotal control on atmospheric CO2 levels and climate change. However, the terrestrial C sink requires nutrients such as nitrogen (N) to fuel C sequestration because nutrients form the building blocks of organisms alongside C. A major challenge has been resolving the degree to which nutrients will constrain C sequestration under global change, especially as elevated atmospheric CO2 levels stimulate photosynthesis and correspondingly increase nutrient demand (“CO2 fertilisation”). My research addresses the overarching question: To what extent will nutrients limit the terrestrial C sink under global change, and how does this feed back to climate change? Essentially, will the terrestrial C sink continue to sequester a third of anthropogenic CO2 emissions, or will this fraction increase or decrease given nutrient limitation? My research employs an interdisciplinary approach by scaling empirical ecology to Earth system models. My research seeks to both enhance our fundamental understanding of terrestrial ecosystems empirically and improve terrestrial biosphere models, which are used within the framework of Earth System Models to project climate change and inform climate change policy by the Intergovernmental Panel on Climate Change (IPCC). |
Global biogeochemical cycles
Sampling Robinia pseudoacacia
at Black Rock Forest |
Specifically, I am interested in how N and phosphorus (P) cycling is represented across terrestrial biosphere models and Earth System Models. In my postdoc at the Canadian Centre for Climate Modelling and Analysis (Environment and Climate Change Canada), I worked on the representation and analysis of N cycling in the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC) which is the land surface component of the Canadian Earth System Model (CanESM). I am also leading CLASSIC and the CCCma's contributions to the Inter-sectoral Impact Model Intercomparison Project (ISIMIP) and Global Nitrogen/N2O Model Intercomparison Project (NMIP). During my PhD, I worked on the representation of N cycling in the Geophysical Fluid Dynamics Laboratory Land Model (GFDL LM). Additionally, my PhD focused on how N-fixing trees, which are an important N source to terrestrial ecosystems and are commonly planted during agroforestry and reforestation, drive both carbon dioxide (CO2) sequestration in vegetation and significant nitrous oxide (N2O) emissions from soils.
I gave a talk at the Cary Institute of Ecosystem Studies on my research available at www.youtube.com/watch?v=YFjLMF61Kls
I'm also giving a series of talks for the Atlantic Geoscience Society Speaker Tour: https://scienceatlantic.ca/news/ags-speaker-tour-2023-2024/
I gave a talk at the Cary Institute of Ecosystem Studies on my research available at www.youtube.com/watch?v=YFjLMF61Kls
I'm also giving a series of talks for the Atlantic Geoscience Society Speaker Tour: https://scienceatlantic.ca/news/ags-speaker-tour-2023-2024/
Publications
- Anthropogenic-driven perturbations on nitrogen cycles and interactions with climate changes. Cheng Gong, Sian Kou-Giesbrecht, and Sonke Zaehle. Current Opinion in Green and Sustainable Chemistry (2024).
- The Impact of Climate Forcing Biases and the Nitrogen Cycle on Land Carbon Balance Projections. Christian Seiler, Sian Kou-Giesbrecht, Vivek Arora, and Joe R. Melton. Journal of Advances in Modeling Earth Systems (2024).
- Terrestrial Phosphorus Cycling: Responses to Climatic Change. Duncan Menge, Sian Kou-Giesbrecht, Benton Taylor, Palani Akana, Ayanna Butler, Kathleen Carreras Pereira, Savannah Cooley, Vanessa Lau, and Emma Lauterbach. Annual Review of Ecology, Evolution, and Systematics (2023).
- Allometric relationships for eight species of 4–5 year-old nitrogen-fixing and non-fixing trees. Kathleen Carreras Pereira, Amelia Wolf, Sian Kou-Giesbrecht, Palani Akana, Jennifer Funk, and Duncan Menge. PLOS ONE (2023).
- Evaluating nitrogen cycling in terrestrial biosphere models: a disconnect between the carbon and nitrogen cycles. Sian Kou-Giesbrecht, Vivek Arora, Christian Seiler, et al. Earth System Dynamics (2023).
- Compensatory Effects Between CO2, Nitrogen Deposition, and Nitrogen Fertilization in Terrestrial Biosphere Models Without Nitrogen Compromise Projections of the Future Terrestrial Carbon Sink. Sian Kou-Giesbrecht and Vivek Arora. Geophysical Research Letters (2023).
Media coverage: Carbon Sink Models Need Nitrogen (Eos). - Towards an ensemble-based evaluation of land surface models in light of uncertain forcings and observations. Vivek Arora, Christian Seiler, Libo Wang, and Sian Kou-Giesbrecht. Biogeosciences (2023).
- Tree symbioses sustain nitrogen fixation despite excess nitrogen supply. Duncan Menge, Amelia Wolf, Jennifer Funk, Steven Perakis, Palani Akana, Rachel Arkebauer, Thomas Bytnerowicz, Kathleen Carreras Pereira, Alexandra Huddell, Sian Kou-Giesbrecht, and Sarah Ortiz. Ecological Monographs (2022): e1562.
- Representing the dynamic response of vegetation to nitrogen limitation in the CLASSIC land model. Sian Kou-Giesbrecht and Vivek Arora. Global Biogeochemical Cycles (2022): e2022GB007341.
- A novel representation of biological nitrogen fixation and competitive dynamics between nitrogen-fixing and non-fixing plants in a land model (GFDL LM4.1-BNF). Sian Kou-Giesbrecht, Sergey Malyshev, Isabel Martínez Cano, Stephen Pacala, Elena Shevliakova, Thomas Bytnerowicz, and Duncan Menge. Biogeosciences 18 (2021): 4143-4183.
- Nitrogen-fixing trees increase soil nitrous oxide emissions: a meta-analysis. Sian Kou-Giesbrecht and Duncan Menge. Ecology (2021): e03415.
- N supply mediates the radiative balance of N2O emissions and CO2 sequestration driven by N-fixing vs. non-fixing trees. Sian Kou-Giesbrecht, Jennifer Funk, Steven Perakis, Amelia Wolf, and Duncan Menge. Ecology (2021): e03414.
- Nitrogen-fixing trees have no net effect on forest growth in the coterminous United States. Anika Staccone, Sian Kou-Giesbrecht, Benton Taylor, and Duncan Menge. Journal of Ecology 109.2 (2021): 877-887.
- Nitrogen-fixing trees could exacerbate climate change under elevated nitrogen deposition. Sian Kou-Giesbrecht and Duncan Menge. Nature Communications 10.1 (2019): 1-8.