Grantee Research Project Results
2001 Progress Report: Modeling Ozone Flux to Forests Across an Ozone Concentration Gradient in the Sierra Nevada Mountains, CA.
EPA Grant Number: R826601Title: Modeling Ozone Flux to Forests Across an Ozone Concentration Gradient in the Sierra Nevada Mountains, CA.
Investigators: Goldstein, Allen H. , Panek, Jeanne A.
Institution: University of California - Berkeley
EPA Project Officer: Chung, Serena
Project Period: August 1, 1998 through October 31, 2002
Project Period Covered by this Report: August 1, 2000 through October 31, 2001
Project Amount: $621,367
RFA: Ecological Indicators (1998) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The results of this research will contribute to the efficacy of forest health monitoring and enhance the general understanding of the relationship between ozone exposure and forest response in California ponderosa pine ecosystems.
Progress Summary:
Tropospheric ozone is a pollutant that is responsible for forest damage worldwide. There is a developing effort in the United States and Europe to replace current metrics of vegetation ozone exposure with metrics that reflect the more biologically meaningful ozone uptake by foliage. This requires measuring and modeling ozone flux across a wide variety of climates and ozone deposition regimes. There is a paucity of models describing physiology of forests (needed to estimate ozone uptake, because ozone uptake = ozone concentration x stomatal conductance to ozone) in seasonally drought-stressed forests, such as those in California. Therefore, we are measuring ozone flux both directly (through eddy covariance methods) and indirectly (from direct measures of leaf-level stomatal conductance) to ponderosa pine forests in the Sierra Nevada, CA, and developing a model to estimate ozone flux, which we hope to adapt for monitoring networks utilizing routinely measured ozone concentrations and meteorology. We also are exploring the utility of d13C as a proxy for stomatal conductance to estimate ozone flux.
We have completed 3 years of continuous meteorological measurements, three full growing seasons, one winter of measurements of tree growth, tree water potential, leaf level physiology (stomatal conductance, net photosynthesis, transpiration), and d13C at each of the four sites along an ozone concentration gradient transect. We continue to measure fluxes of CO2, water vapor, ozone, and energy at the canopy level using eddy covariance at the Blodgett Forest Research Station. We have developed a model for leaf-level stomatal conductance in ponderosa pine, which we use in combination with measured ozone concentration to determine ozone uptake in ponderosa pine.
Stomatal conductance dropped progressively at all sites from May through September in 1999 and 2000 (see Figure 1). This led to progressive decrease in ozone flux into the leaf via stomata over the summer season. The 2001 growing season showed the same pattern across all sites (data not shown). Winter stomatal conductance varied in response to temperature, light, and water availability. Mid-winter net photosynthesis and stomatal conductance values were similar to maximum summer values when the winter sun was out and temperatures were consequently high. This is in stark contrast to non-Mediterranean climates, such as the Northeastern United States, where conifers are dormant in the winter (see Figure 2).
A model (STOMATA) was developed with the data by collaborator Laurent Misson (Université Catholique de Louvain, Unité des eaux et forêts) to predict leaf-level physiology. STOMATA calculates leaf water potential, transpiration, photosynthesis, and stomatal conductance at the leaf-level based on continuous meteorological data. The model operates in three steps. First, it solves for maximum net photosynthesis and stomatal conductance taking into account only atmospheric variables. Second, it computes transpiration, soil and leaf water potential, and uses them to calculate a function of water stress. Third, it recomputes stomatal conductance, net photosynthesis, transpiration, and leaf water potential based on the water stress function. This approach takes advantage of the observation that conductance and photosynthesis vary together, and calculates conductance as a function of photosynthesis using the Ball-Berry approach (Ball, et al., 1987). Consistency was found between measured and modeled physiological variables in the first year of testing (see Figures 3 and 4). Other models, such as FORFLUX (Nikolov, 1995, 1997a, 1997b) are being tested for use in this climate with the data.
To separate the components of ozone flux measured by eddy covariance-foliar uptake, surface deposition, and gas phase chemical losses near the ground-canopy conductance was measured via sap flow from June 1, 2000 to September 30, 2000 (Kurpius, et al., submitted and in preparation). Evapotranspiration, transpiration, soil evaporation, and canopy conductance were modeled at the hourly timescale for measurement period using FORFLUX. FORFLUX is a multi-layer biogeochemical model designed to study diurnal and seasonal dynamics of all major fluxes of carbon and water in forest ecosystems (Nikolov, 1995, 1997a, 1997b). The FORFLUX model simulates short term dynamics of water vapor exchange between a terrestrial ecosystem and the atmosphere.
We found that this ponderosa pine plantation had an average daily water flux of 3 mm day-1. Transpiration accounted for roughly 55 percent of the total water flux, and soil evaporation accounted for the remaining 45 percent. Measurements from the sap flow system and eddy flux system corresponded in magnitude; however, there was more daily variability in the eddy flux system. Model results from FORFLUX were consistent with transpiration, evapotranspiration, and canopy conductance measurements at the daily timescale (see Figure 5), but did not simulate transpiration or canopy conductance well at the hourly timescale. Furthermore, the modeled transpiration and modeled canopy conductance differed from measured values in their response to the driving variables, vapor pressure deficit (VPD) and photosynthetically active radiation (PAR), at both hourly and daily timescales. Daily transpiration and canopy conductance rates remained steady throughout the summer, even with little rain. Our data suggest that strong coupling between: (1) the leaf surface and atmosphere, and (2) a low threshold for stomatal closure caused transpiration and canopy conductance to be limited on an hourly basis, but allowed the trees to remain active all summer.
Future Activities:
Data from the 2001 season are being finalized and integrated into the database. Data are being worked up for publication.
References:
Ball JT, Woodrow E, Berry JA. A model predicting stomatal conductance and its
contribution to the control of photosynthesis under different environmental
conditions. In: Biggins J, ed. Progression Photosynthesis Research. Nihjoff
Dordrecht, The Netherlands, 1987, pp. 221-224.
Nikolov NT. Mathematical modeling of seasonal biogeophysical interactions in forest ecosystems. Presented at Colorado State University, 1997.
Nikolov NT. Modeling spatial distribution of leaf area index, canopy conductance to ozone, and fluxes of CO2, O3, and latent heat at the San Joaquin Valley, CA. United States Department of Agriculture Forest Service, 1997.
Nikolov NT, Massman WJ, Schoettle AW. Coupling biochemical and biophysical processes at the leaf level: an equilibrium photosynthesis model for leaves of C3 plants. Ecological Modeling 1995;80(2-3):205-235.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
| Other project views: | All 19 publications | 10 publications in selected types | All 8 journal articles |
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Kurpius MR, McKay M, Goldstein AH. Annual ozone deposition to a Sierra Nevada ponderosa pine plantation. Atmospheric Environment 2002;36(28):4503-4515. |
R826601 (2001) R826601 (Final) |
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Kurpius MR, Panek JA, Nikolov NT, McKay M, Goldstein AH. Partitioning of water flux in a Sierra Nevada ponderosa pine plantation. Agricultural and Forest Meteorology 2003;117(3-4):173-192. |
R826601 (2001) R826601 (Final) |
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Law BE, Falge E, Gu L, Baldocchi DD, Bakwin P, Berbigier P, Davis K, Dolman AJ, Falk M, Fuentes JD, Goldstein A, Granier A, Grelle A, Hollinger D, Janssens IA, Jarvis P, Jensen NO, Katul G, Mahli Y, Matteucci G, Meyers T, Monson R, Munger W, Oechel W, Olson R, Pilegaard K, Pau U KT, Thorgeirsson H, Valentini R, Verma S, Vesala T, Wilson K, Wofsy S. Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation. Agricultural and Forest Meteorology 2002;113(1-4):97-120. |
R826601 (2001) |
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Panek JA, Goldstein AH. Response of stomatal conductance to drought in ponderosa pine: implications for carbon and ozone uptake. Tree Physiology 2001;21(5):337-344. |
R826601 (1999) R826601 (2000) R826601 (2001) R826601 (Final) |
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Panek JA, Kurpius MR, Goldstein AH. An evaluation of ozone exposure metrics for a seasonally drought-stressed ponderosa pine ecosystem. Environmental Pollution 2002;117(1):93-100. |
R826601 (2001) R826601 (Final) |
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Supplemental Keywords:
forest ozone damage, modeling forest response, carbon isotopes, forest physiological processes, carbon cycling, water cycling, ozone deposition, pollution stress., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Air, Geographic Area, Ecological Indicators, State, Ecosystem Protection, Forestry, Ecology, Environmental Chemistry, Ecosystem/Assessment/Indicators, tropospheric ozone, Ecological Effects - Environmental Exposure & Risk, California (CA), pine trees, carbon storage, stressors, meteorological fluctuations, ecosystem indicators, forests, Sierra Nevada Mountains, atmospheric contaminants, ozone flux, meteorology, ozoneRelevant Websites:
http://www.cnr.berkeley.edu/~ahg 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.