Measurement of Photosynthesis from Space
A Department of Atmospheric and Oceanic Sciences Seminar featuring Dr. Joe Berry, Professor, Department of Global Ecology, Stanford University, Carnegie Institution for Science
Wednesday, October 30, 2013
The quantity of photosynthesis taking place on planet Earth places an ultimate limit on the size and activity Earth's biosphere. Our ability to predict the future of the biosphere depends in part on questions like; what is the photosynthetic productivity of Earth? Is it changing? And how will it respond to future climates? These are important questions, but we have limited tools to study photosynthesis on these geographically significant scales. I will introduce a new method based on the capacity to measure chlorophyll fluorescence from space. For a brief review of the technology and what it seems to tell us see: http://spie.org/x92267.xml . This new measurement is the flux of light re-emitted under mid-day illumination from the chloroplasts of plants covering the land surface. The fluorescence light is resolved from the much larger flux of reflected sunlight by taking advantage of Fraunhofer lines - narrow bands in the solar spectrum where sunlight is partially blocked by components of the solar atmosphere. The infilling of these lines by fluorescence can be resolved by high resolution spectrometers that were placed in orbit to measure atmospheric absorption lines of greenhouse gases. It is pure is serendipity that these instruments can be used to measure fluorescence. Interpretation of this measurement hinges on our understanding of fluorescence quenching mechanisms and their interaction with photosynthetic metabolism and environmental stress. As one of my colleagues at NASA describes it, “we have been handed the keys to a Ferrari but we didn’t expect it and we don’t have a driver’s license yet.” Empirical analysis of solar induced fluorescence (SIF) over large geographic areas indicates that it is approximately proportional to photosynthesis. Other methods for estimating photosynthesis involve the use of models driven by several independent plant and environmental data streams. Fluorescence is a simpler and more direct measurement. The global data sets of fluorescence provide interesting perspectives on regional differences in photosynthetic rates, on inter-annual variation in photosynthesis and may provide a useful constraint on total global photosynthesis. This appears to be a major breakthrough in remote sensing, and it is uniquely tied to our mechanistic understanding of photosynthesis.
SEMINAR at 3:30 PM
SEMINAR TEA: 4:30-5:00PM (MSB 7124B)