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Harvard Forest REU Symposium Abstract 2012

  • Title: The Leaf Level Relationship Between Temperature, Leaf Nitrogen, Humidity and Photosynthetic Parameters in Five C3 Species
  • Author: Paul J Quackenbush (Middlebury College)
  • Abstract:

    Theoretical and empirical analyses have suggested that among the major terrestrial biomes, temperate forest ecosystems are an important global sink for atmospheric carbon dioxide (Tans et al., 1990; Ciais et al., 1995; Tans et al., 1995), storing up to a quarter of the CO2 added to the atmosphere annually by fossil fuel burning (http://www.lternet.edu/vignettes/hfr.html). Photosynthesis, which is governed by photosynthetic parameters including light saturated assimilation (Amax) and maximum carboxylation velocity (Vcmax), is the primary mechanism through which carbon enters ecosystems for possible storage by this important global sink (Sellers et al. 1997, Sellers et al. 1986). It is also a process that governs the fluxes of energy, mass and momentum between vegetated land surfaces and the atmosphere, with profound impacts on climatic conditions on earth’s surface (Sato et al. 1989, Margolis & Ryan 1997). Thus, understanding the factors and processes influencing seasonal variation in photosynthetic parameters is critical for accurate modeling of carbon dioxide exchange between vegetation and the atmosphere (Dang et al. 1998, Wilson et al. 2001,Tanaka et al. 2002, Kosugi et al. 2003, Misson et al. 2005), including important feedbacks to climate change (Woodwell & Mackenzie 1995). However, most forest carbon cycle models do not adequately consider how tree species contribute differently to carbon-cycle processes and how changing environmental conditions may differentially affect species (Bassow & Bazzaz 1998). This fits into a larger call for more plant- and species-level estimates of photosynthetic parameters under varying environmental conditions in order to tailor, refine, and improve popular models of photosynthesis such as the Farquhar model (Patrick et al. 2009). In light of this need for species level photosynthesis data, this study investigates the influence of two factors, nitrogen and temperature, on the photosynthetic parameters Amax and Vcmax in five temperate early successional species. These parameters are derived from light and CO2 assimilation curves taken over a 10 week period in a highly dynamic post-clearcut environment at the Harvard Forest Long Term Ecological Research Site (HF LTER) in Petersham, MA with the use of a Li-6400XT Portable Photosynthesis System. Preliminary results indicate a positive correlation between nitrogen content and Vcmax among the species studied. However, further experimentation is needed to confirm this trend. In addition to its applicability to forest carbon models, this work, when paired with vegetation and soil data for the HF LTER clearcut site, has the potential to be upscaled to the ecosystem for comparison with gross ecosystem productivity estimated with the eddy covariance method. This may provide a more holistic understanding of carbon, water, and energy fluxes in post-disturbance forest environments.

  • Research Category: Forest-Atmosphere Exchange

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