Our ecosystems are connected through a common set of processes that move energy, carbon, water, and nutrients across the globe. Photosynthesis is one of these processes; by converting sunlight into a form of energy that is useable by organisms, photosynthesis and plants form the foundation upon which our ecosystems and global biodiversity are built.
To understand how photosynthesis and plants influence Earth’s ecosystems, my research explores questions at the interface of ecosystem ecology, plant ecophysiology, and atmospheric science. Results from my research add to our knowledge of plant-atmosphere interactions and their representations in Earth system models–empowering us to better predict climate and climate change impacts. My work can also be used to support development of management programs for croplands, timber stands, and natural ecosystems.
Plant Ecology and Earth System Modeling
Model calculations of plant CO2 uptake and future climate depend on how accurately models parameterize plant processes that affect the atmosphere. Some of these processes include photosynthesis and plant uptake of nutrients added to ecosystems. I combine leaf and ecosystem-level field measurements with Earth system model experiments to test our understanding of how plants affect our atmosphere and climate and to find ways to improve the representations of plant ecology in models. To help facilitate better integration of field data and modeling experiments, I work on projects with modelers and empiricists asking questions about microbes, soils, plants, and land use change.
- S.J. Cheng, P.G. Hess, W.R. Wieder, R.Q. Thomas, K.J. Nadelhoffer, J. Vira, D.L. Lombardozzi, P. Gundersen, I.J. Fernandez, P. Schleppi, M. Gruselle, F. Moldan, C.L. Goodale. (2019). Decadal fates and impacts of nitrogen additions on temperate forest carbon storage: a data–model comparison. Biogeosciences.
- W.R. Wieder, D.M. Lawrence, R.A. Fisher, G.B. Bonan, S.J. Cheng, C.L. Goodale, A.S. Grandy, C.D. Koven, D.L.Lombardozzi, K.W. Oleson, R.Q. Thomas. (2019). Beyond static benchmarking: Using experimental manipulations to evaluate land model assumptions. Global Biogeochemical Cycles.
- D.L. Lombardozzi, N.G. Smith, S.J. Cheng, J.S. Dukes, T.D. Sharkey, A. Rogers, R.A. Fisher, G.B. Bonan. (2018). Triose phosphate limitation in photosynthesis models reduces leaf photosynthesis and global terrestrial carbon storage. Environmental Research Letters.
Impacts of Diffuse Light and Canopy Structure on Terrestrial Carbon Cycling
Plant canopy CO2 uptake is largely controlled by how much light leaves have to use for photosynthesis. However, maximum carbon uptake doesn’t necessarily occur on clear, sunny days. Scattered, diffuse light, formed when light interacts with clouds and aerosols in the atmosphere, can actually increase carbon uptake in ecosystems. This response occurs if diffuse light reaches deeper into canopies, reduces shadows, and changes distributions of light among leaves. Greater absorption by lower-canopy “shade” leaves on cloudy or high aerosol days would compensate for less absorption by light-unsaturated, upper-canopy “sun” leaves.
I use a range of tools, including AmeriFlux eddy covariance data, satellite data, and in-canopy field measurements, to quantify how clouds change surface-level light and carbon cycling, and how this relationship changes across ecosystems with different canopy structures.
Learn more about this work at the links below!
- P. Zhu, S.J. Cheng, Z. Butterfield, G. Keppel-Aleks, A.L. Steiner. (2019). The global influence of cloud optical thickness on terrestrial carbon uptake. Earth Interactions.
- S.J. Cheng, A.L. Steiner, D.Y. Hollinger, G. Bohrer, K.J. Nadelhoffer. (2016). Using satellite-derived optical thickness to assess the influence of clouds on terrestrial carbon uptake. Journal of Geophysical Research: Biogeosciences.
- S.J. Cheng, G. Bohrer, A.L. Steiner, D.Y. Hollinger, A. Suyker, R.P. Phillips, K.J. Nadelhoffer (2015). Variations in the influence of diffuse light on gross primary productivity in temperate ecosystems. Agricultural and Forest Meteorology.
- How Clouds Influence Forest Photosynthesis, “3 Minute Thesis” Competition 2nd place overall and Audience Choice winner (video below), 2013
Forest Energy Balance and Air Quality
Aerosols change the amount of diffuse light that reaches terrestrial ecosystems, which alters photosynthesis and transpiration rates. This in turn changes the ratio of sensible to latent heat in plant canopies. To explore how aerosols influence the partitioning of energy in forests, we used satellite measurements of aerosols with AmeriFlux measurements of energy exchange between forest canopies and the atmosphere.
Learn more about this work at the link below.
- Steiner, A.L., Mermelstein, D., Cheng, S.J., Twine, T.E., Oliphant, A. (2013). Observed Impact of Atmospheric Aerosols on the Surface Energy Budget. Earth Interactions.