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, and by converting sunlight into a form of energy that is useable by organisms, it forms the nearly universal foundation that supports the biodiversity and health of our ecosystems.
To understand how photosynthesis and plants influence Earth’s ecosystems, my research explores questions at the interface of ecosystem ecology, biogeochemistry, and climate change. This research is timely because it allows us to understand how ecosystems currently function, how they respond to land management practices and disturbance, and how they may slow future changes in Earth’s climate.
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, in-canopy field measurements, and models, to quantify how strongly atmospheric cloud conditions influence surface-level light and carbon cycling and to identify how this relationship changes across ecosystems with different canopy structures.
Learn more about this work at the links below!
- S.J. Cheng, A.L. Steiner, D.Y. Hollinger, G. Bohrer, and 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, and 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
Atmospheric Influences on Forest Energy Balance
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.
Plant Physiological Responses to Environmental and Ecological Change
Model calculations of forest CO2 uptake depend on how accurately models parameterize photosynthetic processes. Often, models use the same values for species within the same plant functional group to describe these processes. To test for species differences and to determine whether the future potential of forest CO2 uptake in the Great Lakes region will change as forests undergo succession, a REU student and I conducted in-situ photosynthesis measurements of early- and mid-successional tree species under different temperatures and at different canopy heights using a canopy-access vehicle.