NASA Astrobiology Institute (NAI)

Photosynthesis provides the foundation for nearly all life on our planet and produces unique life signs — atmospheric oxygen and pigment colors — that are detectable from space at the global scale. This project seeks to determine the adapative rules for why photosynthetic pigments absorb particular wavelengths of light, and to quantify what is the long wavelength limit for oxygenic and also anoxygenic photosynthesis. This work will allow us to predict the plausible spectral properties and detectable properties of photosynthesis on other planets, especially those orbiting M stars, where longer wavelengths of light dominate the planetary surface radiation.

For the period July 1, 2007 – June 30, 2008, the Life Modules section of the VPL accomplished the following, all of which are directly responsive to the NAI’s Goal 5: Evolution, Environment, and Limits of Life, and Goal 7: Signatures of Life.

Ent Dynamic Global Terrestrial Ecosystem Model (DGTEM) development: In cross-cutting research with NASA Earth Science, Modeling, Analysis, and Prediction (MAP) program, the Ent DGTEM is being developed for coupling of a terrestrial biosphere with the atmosphere to simulate fluxes of energy, water vapor, and biogenic trace gases, cycles of growth and decay, and migration of vegetation types with changing climate. This past year, Ent photosynthesis and vegetation conductance have been coupled to two atmospheric general circulation models (GCMs), and the modules for soil biogeochemistry and seasonal growth were successfully tested on field data for several vegetation types. More advanced canopy radiative transfer and dynamics of mortality, disturbance, and migration are being introduced this coming year. (Note that this work now replaces earlier efforts with the Community Land Model 3.0 of the National Center for Atmospheric Research). The VPL Life Modules group is currently collaborating with the Columbia Astrobiology Center (CAC) at Columbia University to couple an extrasolar version of the Ent DGTCM to the Terrestrial Planet Global Climate Model to allow 3-D modeling of extrasolar planet environments.

Energy efficiency limits of oxygenic photosynthesis: Additionally, we have started a new collaboration to work on “Thermodynamic efficiency of electron-transfer reactions in the Chlorophyll d-containing cyanobacterium, Acharyochloris marina.” to probe the long wavelength limits of oxygenic photosynthesis likely to be relevant for planets orbiting M stars. This work will be performed primarily by new NAI postdoctoral scholar Steve Mielke, under the guidance of Nancy Kiang and Robert Blankenship, and outside collaboration with David Mauzerall at Rockefeller University.