Grantee Research Project Results
2006 Progress Report: New Biogenic VOC Emissions Model
EPA Grant Number: R831453Title: New Biogenic VOC Emissions Model
Investigators: Monson, Russell K. , Fall, Ray
Institution: University of Colorado at Boulder
EPA Project Officer: Chung, Serena
Project Period: January 1, 2004 through December 31, 2006 (Extended to December 31, 2007)
Project Period Covered by this Report: January 1, 2006 through December 31, 2007
Project Amount: $644,044
RFA: Consequences of Global Change for Air Quality: Spatial Patterns in Air Pollution Emissions (2003) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Climate Change , Air
Objective:
The objectives of this project are to better understand the biochemical basis for the response of isoprene and acetaldehyde emissions to elevated atmospheric CO2 concentration and climate warming. We are focusing on the role of key enzymes, phosphoenolpyruvate carboxylase (PEPC) and pyruvate decarboxylase (PDC), in the control of leaf isoprene and acetaldehyde emissions, respectively, and their responses to growth CO2 concentration. We intend to use the new knowledge we gain to construct a new biochemically-based model of the emissions of these two VOCs that is more accurate in its representation of the response of forest VOC emissions to future global change.
Progress Summary:
- Obtained 26 new genetically-engineered lines of poplar plants that are designed to over-express levels of leaf PEPC enzyme. These plants were produced in collaboration with workers at the Institute of Tree Physiology in Freiburg, Germany. So far, we have analyzed 9 of these novel lines using molecular biological techniques to confirm the overexpression of the transgenic PEPC enzyme. We obtained the necessary permits to import these lines to the U.S. and received representative plants of all lines in February 2007 to the Department of Biology, Portland State University (in the charge of Dr. Todd Rosenstiel). Using funds from the EPA grant, Dr. Rosenstiel and post-doctoral associate, Dr. Tami Sivi, initiated screening the lines for expression of the transfer vector and the transferred enzyme, PEPC. At present, we continue to characterize these lines. We anticipate initiating isoprene emission measurements on the lines later in the Fall of 2007 when the trees get larger. If these transgenic poplars provide support for our central hypothesis, it will be the first time a tree that is important to US agriculture has been produced with reduced isoprene emissions and thus less potential to cause ozone pollution.
- Wrote a manuscript with the results of an experiment conducted with funds from this grant. We conducted experiments to verify that changes in the activity of PEPC enzyme causes reductions in leaf isoprene emission in poplar trees. We conducted a series of experiments in which we treated the roots of poplar trees with elevated concentrations of bicarbonate (HCO3-), stimulating the trees to shift their nitrate reduction activities from the leaves to the roots, and concomitantly causing a dramatic reduction in both leaf PEPC activity and transcript levels. Consistent with our working model, this dramatic reduction in foliar PEPC activity, promoted a significant increase in leaf isoprene emission rate. Surprisingly, this increase in isoprene emission occurred despite a significant reduction in both the content and activity of the isoprene synthase enzyme. Results from this study provide strong support for our hypothesis that the activity of PEPC is a principal control regulating isoprene emission rate in vivo. A manuscript describing these results was submitted to the journal Plant Physiology in July 2007.
- co-PI Fall and an undergraduate student (Tam Ngyuen) have continued our efforts to characterize the PDC enzyme from poplar leaves, and are currently comparing its biochemical properties with the PDC from poplar roots. We have found that in cottonwood leaves the enzyme is highly concentrated in vascular bundles and not mesophyll cells, and PDC activity is highly induced by root flooding. We hypothesize that as with the root PDC the leaf PDC acts as a safety valve to prevent over accumulation of pyruvate in vascular bundle cells. We also cloned several poplar leaf-specific PDC genes, and are working to over express these genes in E. coli and characterize the recombinant PDC and also use the protein for antibody production.
- PI Monson, along with post-doc Rosenstiel and two graduate students (Nicole Trahan and Patrick Veres), conducted three field campaigns during May, June and July (2006) in Texas, Tennessee and Wisconsin at existing FACE sites and manipulative experiments involving isoprene emitting trees. We measured the rates of isoprene emission, photosynthesis, key enzyme activities and mitochondrial densities for the leaves of oaks, poplars and sweetgums. The isoprene emission rates were measured across a range of atmospheric CO2 concentrations. This field-based data set provides the fundamental data needed to parameterize (in the case of enzyme activities and mitochondrial densities) and validate (in the case of emission rates) the biochemical models we are developing. The results of our field campaign were published this past year in the journal Proceedings of the Royal Society of London (see below) and were presented at an international symposium in London on the topic of trace gas exchange and global change.
- As part of the field experiments we will also use a proton-transfer reaction mass spectrometer to measure acetaldehyde emission rates from poplar leaves at the FACE facility in Rhinelander, Wisconsin. These results are being prepared for publication.
- Post-doctoral associate Michael Wilkinson and graduate student Nicole Trahan conducted extensive measurements of isoprene emission from poplar leaves growing in four different atmospheric CO2 concentrations. Using these results, Dr. Wilkinson has developed a mathematical model of the response of isoprene emissions to elevated CO2 concentration. The model takes the form of an inverted Michaelis-Menten model, and seems to simulate the activity of the enzyme PEPC in different CO2 regimes. The model is being described in a publication at the moment, which will be submitted during the fall of 2007.
Future Activities:
Because we are in the final stages of this grant, we are most busy preparing our results for publication. We are writing a paper that describes our CO2 response model based on the growth chamber experiments with poplar. We are also preparing the data of acetaldehyde emission and response of both isoprene and acetaldehyde emission to ozone for a second publication. And, a manuscript is in preparation describing the properties of highly purified cottonwood leaf PDC and its induction by root flooding.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 11 publications | 3 publications in selected types | All 3 journal articles |
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Type | Citation | ||
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Monson RK, Trahan N, Rosenstiel TN, Veres P, Moore D, Wilkinson M, Norby RJ, Volder A, Tjoelker MG, Briske DD, Karnosky DF, Fall R. Isoprene emission from terrestrial ecosystems in response to global change: minding the gap between models and observations. Philosophical Transactions of the Royal Society A: Mathematical, Physical & Engineering Sciences 2007;365(1856):1677-1695. |
R831453 (2006) R831453 (Final) |
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Supplemental Keywords:
molecular biology, poplar genome,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, particulate matter, Air Quality, air toxics, Environmental Chemistry, Air Pollutants, Chemicals, Chemistry, climate change, Air Pollution Effects, Monitoring/Modeling, Environmental Monitoring, Atmospheric Sciences, Ecological Risk Assessment, Atmosphere, anthropogenic stress, aerosol formation, ambient aerosol, atmospheric particulate matter, atmospheric dispersion models, ecosystem models, environmental measurement, meteorology, climatic influence, emissions monitoring, biogenic VOC emissions model, global change, ozone, air quality models, climate, modeling, climate models, greenhouse gases, airborne aerosols, atmospheric aerosol particles, atmospheric transport, environmental stress, monitoring of organic particulate matter, ecological models, climate model, greenhouse gas, Volatile Organic Compounds (VOCs), aerosols, atmospheric models, Global Climate Change, atmospheric chemistry, ambient air pollution, climate variabilityRelevant Websites:
http://spot.colorado.edu/~monsonr/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.