Grantee Research Project Results
2005 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, 2005 through December 31, 2006
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 , Air , Climate Change
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 (PEP) carboxylase and pyruvate decarboxylase, 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 volatile organic compounds (VOCs) that is more accurate in its representation of the response of forest VOC emissions to future global change.
Progress Summary:
We produced 26 new genetically engineered lines of poplar plants that are designed to overexpress levels of leaf PEP carboxylase enzyme. These plants were produced in collaboration with workers at the Institute of Tree Physiology in Freiburg, Germany. So far, we have analyzed nine of these novel lines using molecular biological techniques to confirm the overexpression of the transgenic PEP carboxylase enzyme. We are currently in the process of applying for permits from the U.S. Department of Agriculture to import these trees into the United States for further experimentation and for use in testing some predictions of our modelling framework. If these transgenic poplars provide support for our central hypothesis, it will be the first time a tree that is important to U.S. agriculture has been produced with reduced isoprene emissions and thus less potential to cause ozone pollution.
Conducted experiments to verify that changes in the activity of PEP carboxylase (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. We will focus our development of new emissions models on the activity of this key enzyme. In addition, this is the first time that alterations in rooting-zone CO2/ HCO3ˉ levels have been found to directly impact leaf isoprene emission, providing new insights into the mechanisms by which below-ground components of global change may directly influence canopy isoprene emission.
We have cloned several PEPC genes from poplar leaves and cloned these into a variety of bacterial expression systems in an effort to produce highly purified and active recombinant PEPC enzyme from which we plan to measure the kinetic responses to PEP, bicarbonate, and other key allosteric effectors. Using these fundamental kinetic parameters, we will be able to include the role of PEPC activity in the new model we are developing. In addition, this purified recombinant protein will be used to develop highly specific antibody for use in quantifying PEPC levels in ongoing chamber experiments and planned field campaigns, as well as for efforts to purify native PEPC from poplar leaves.
We have begun to characterize the pyruvate decarboxylase (PDC) from poplar leaves and currently are comparing its biochemical properties with the PDC from poplar roots. We hypothesize that as with the root PDC the leaf PDC acts as a safety valve to prevent overaccumulation of pyruvate. We also cloned several poplar leaf-specific PDC genes and are working to over express these genes in Escherichia coli and characterize the recombinant PDC and also use the protein for antibody production.
Future Activities:
Principal Investigators Monson and Fall, along with postdoctoral fellow Rosenstiel, have planned three field campaigns to be conducted during May, June, and July 2006 in Texas, Tennessee, and Wisconsin at existing Free-Air Carbon Dioxide Enrichment (FACE) Experiment sites and manipulative experiments involving isoprene emitting trees. We will measure the rates of isoprene emission, photosynthesis, key enzyme activities, and mitochondrial densities for the leaves of oaks, poplars, and sweetgums. The isoprene emission rates will be measured across a range of atmospheric CO2 concentrations. This field-based data set will provide 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 intend to develop within the next year.
As part of the field experiments we also will use a proton-transfer reaction mass spectrometer to measure acetaldehyde emission rates from poplar leaves at the FACE facility in Rhinelander, Wisconsin.
We intend to measure the kinetic constants for PEPC and PDC enzymes obtained from our cloned gene products. These kinetic constants will be used in the modeling leaf isoprene and acetaldehyde emissions, which will be a primary focus of the studies during the next year.
Journal Articles:
No journal articles submitted with this report: View all 11 publications for this projectSupplemental Keywords:
molecular biology, poplar genome,, RFA, Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Ecological Risk Assessment, Chemistry, particulate matter, Air Quality, Atmosphere, Environmental Chemistry, Monitoring/Modeling, Air Pollution Effects, Atmospheric Sciences, Air Pollutants, air toxics, Chemicals, climate change, Environmental Monitoring, aerosols, atmospheric dispersion models, Global Climate Change, ambient aerosol, airborne aerosols, climate model, ecosystem models, atmospheric models, global change, aerosol formation, atmospheric chemistry, atmospheric transport, ecological models, emissions monitoring, climate models, environmental measurement, climate variability, atmospheric aerosol particles, environmental stress, BVOCs, meteorology, ozone, ambient air pollution, air quality models, atmospheric particulate matter, greenhouse gases, climatic influence, greenhouse gas, modeling, Volatile Organic Compounds (VOCs), monitoring of organic particulate matter, anthropogenic stress, climateRelevant 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.