July 6, 2015

MBL Ecosystems PhD Student Xi Yang Defends Dissertation and Receives A Postdoc at Brown University

Jack Mustard (Brown), Joe Berry (Stanford/Carnegie Institute for science), Xi Yang (Brown-MBL), Jung-Eun Lee (Brown), Meredith Hastings (Brown), and Jim Tang (Brown-MBL).

Jack Mustard (Brown), Joe Berry (Stanford/Carnegie Institute for Science), Xi Yang (Brown-MBL), Jung-Eun Lee (Brown), Meredith Hastings (Brown), and Jim Tang (Brown-MBL).

Brown MBL PhD candidate Xi Yang defended his dissertation “The Times They Are A-Changin’: Scaling Seasonality of Plant Physiology from Leaf to Satellite and Implications for Terrestrial Carbon Cycle” on April 28th at Brown University. Xi, a former geography and geosciences student from Beijing began his PhD in the Department of Geological Sciences at Brown University in 2009. He is co-advised by Professor Jack Mustard from Brown University and Jim Tang, Assistant Scientist, at MBL.

Xi combined a detailed study of leaf optical properties with remote sensing and modeling techniques to understand the seasonality of plant physiology and its environmental drivers. First Xi used digital repeat photography to estimate the budburst date of trees in New England. Then he up-scaled a species-level phenology model to the New England area that reconstructed and predicted the changes of budburst dates. By collecting weekly sampled leaf traits such as chlorophyll concentration to interpret the data from digital repeat photography, he found a temporal mismatch between greenness index and chlorophyll concentration in the spring. In the fall, the redness index was a good indicator of vegetation senescence.  Xi used vegetation spectroscopy to successfully capture the seasonal variability of leaf traits and developed a system to continuously measure solar-induced fluorescence (SIF) over a temperate deciduous forest for the first time. His research found a strong correlation between SIF and vegetation photosynthesis, and absorbed photosynthetically active radiation.

Remote sensing studies such as Xi’s research can provide spatially explicit estimates of properties which are related to key ecological processes, while the mechanistic understanding of how environmental factors control these processes can help to understand how terrestrial ecosystem will respond to climate change.

Xi’s work was financially supported by the Brown-MBL Graduate Program in Biological and Environmental Sciences and the lab of Dr. Jim Tang, a Stanley Watson Fellowship from MBL and a Hartnett Fellowship from Brown University, the Brown–ECI phenology working group, and a Brown University Office of International Affairs seed grant.

In June, Xi will start work as a Post-doc with Dr. Jung-Eun Lee at Brown University in Providence, RI, and Dr. Joe Berry at the Carnegie Institute for Science using fluorescence to understand the response of tropical ecosystems to water stress.

List of Citations:

Yang X, Tang J, Mustard J (2014). Beyond leaf color: comparing camera-based phenological metrics with leaf biochemical, biophysical and spectral properties throughout the growing season of a temperate deciduous forest. Journal of Geophysical Research-Biogeosciences, DOI:10.1002/2013JG002460.

Yang, X., J. Mustard, J. Tang, and H. Xu (2012), Regional-scale phenology modeling based on meteorological records and remote sensing observations, Journal of Geophysical Research-Biogeosciences, 117(G3), G03029.