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Transpiration

Calculating Optimal Root to Shoot Ratio to Balance Transpiration with Water Uptake Rate and Maximize Relative Growth Rate.

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Transpiration

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  1. Calculating Optimal Root to Shoot Ratio to Balance Transpiration with Water Uptake Rate and Maximize Relative Growth Rate. Dr. Vincent P. Gutschick, Dept. of Biology, New Mexico State University (vince@nmsu.edu). Dr. Ann Stapleton (stapletona@uncw.edu), Dept. of Biology and Marine Biology, University of North Carolina Wilmington and Dr. Melanie J. Correll (correllm@ufl.edu) , Dept. of Agricultural and Biological Engineering, University of Florida.

  2. Transpiration • For each pound of solid material added to the plant 200 to 1,000 lb (90-450 kg or up to 120 gallons) of water are transpired per day (Columbia Encyclopedia, Sixth Edition. Columbia University Press) • Transpiration accounts for ¾ of the water vaporized on the global land surface (1/8 of water over entire globe; von Caemmerer et al., 2007) • A large oak tree can transpire 40,000 gallons (151,000 liters) per year (USGS: URL: http://ga.water.usgs.gov/edu/watercyclesummary.html ) • Water use and availability major affects on crop yields and impact the global carbon and hydrological cycles (von Caemmerer et al., 2007)

  3. Transpiration H2O H2O H2O H2O H2O • Transpiration provides: • driving force for water transport and nutrients from roots to shoots • Evaporative cooling for plants • Provides significant water vapor • for the global hydrological cycles H2O H2O H2O

  4. Why Model Transpiration and Water Uptake in Plants? • Critical for identifying crop productivity and irrigation scheduling events • Significantly impacts the global carbon cycle (Climate Change • Significantly impacts the global hydrological cycles (water wars) • Identifies areas of needed research (plant physiology/molecular biology) • Fundamental understanding of biology

  5. The stomatal pores determine the compromise between increasing CO2 fixation and reducing transpiration to prevent dessication Boundary layer rbL CO2 Guard Cell rs rT= rbL + rs gbs = 1/rT = 1/(rbL + rs) H2O Intracellular Space Mesophyll Cells

  6. Main Models used in This Exercise • Transpiration: Fick’s law of diffusion E = gbs*D/P E, transpiration per leaf area [mol m-2 s-1] D, vapor pressure deficit [Pa] P, total atmospheric pressure[Pa] • Photosynthesis/CO2 Fixation Farquhar-von Caemmerer-Berry (1980, aka. FvCB) model (light saturating) ALa = Vcmax*(Ci - gamma)/(Ci+KCO)

  7. Main Models used in This Exercise (con’t) • RGR= beta*alphaL*ALa/((1+r)*mLa)

  8. Where these Models Go… • Climate change • Crop Models • Plant physiology • Agronomists • Horticulturists • Molecular Biology

  9. References • Ball, J.T., Woodrow, I.E., Berry, J.A. (1987) A model predicting stomatal conductance and its contribution to the control of photosynthesis under different environmental conditions. In: Biggins, J. (Ed.), Progress in Photosynthesis Research, vol. 4. Proceedings of the 7th International Congress on Photosynthesis. Martins Nijhoff, Dordrecht, The Netherlands, pp 221–224. • Farquhar, G.D., von Caemmerer S., Berry J.A. (1980) A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species. Planta 149: 78–90 • Gutschick, V.P., Simonneau, T. (2002) Modelling stomatal conductance of field-grown sunflower under varying soil water content and leaf environment: comparison of three models of stomatal response to leaf environment and coupling with an abscisic acid-based model of stomatal response to soil drying, Plant Cell Environ. 25:1423–1434 • Jarvis, P.G. (1971) The estimation of resistances to carbon dioxide transfer. In: Plant Photoynthetic Production. Manual of Methods. Seztak, A., Catsky, J., and Jarvis, P.G., eds. Junk, The Hague. P. 566-631.

  10. Acknowledgements • iPlant Collaborative (www.iplantcollaborative.org) • NSF IOS # 0920145

  11. High School Teacher Opportunity • Summer Internship 2011 Paid Stipend at University of Florida to Work on an NSF Funded Project entitled Development of a Gene-Based Ecophysiology Model • contact: Melanie J. Correll, University of Florida at correllm@ufl.edu; 352-392-1864 ext 209

  12. Exercise • Part I: Identifying the water uptake rate of roots for a plant with baseline characteristics to balance transpiration and water uptake • typically 50% roots to shoot ratio baseline but some plants may have more efficient roots (i.e., more water uptake per root mass to balance transpiration) • Part II: Using the water uptake rate from Part I compare the effect of altering root to shoot ratio on relative growth rate, transpiration, and photosynthetic rate and internal leaf CO2

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