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 Dr. Ann Stapleton Dept. of Biology and Marine Biology, University of North Carolina Wilmington and Dr. Melanie J. Correll Dept. of Agricultural and Biological Engineering, University of

Transpiration For each pound of solid material added to the plant 200 to 1,000 lb ( 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: ) Water use and availability major affects on crop yields and impact the global carbon and hydrological cycles (von Caemmerer et al., 2007)

H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Transpiration 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

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

H2OH2O CO 2 Guard Cell Intracellular Space Mesophyll Cells r bL rsrs r T = r bL + r s gbs = 1/r T = 1/(r bL + r s ) Boundary layer The stomatal pores determine the compromise between increasing CO2 fixation and reducing transpiration to prevent dessication

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/CO 2 Fixation Farquhar-von Caemmerer-Berry (1980, aka. FvCB) model (light saturating) ALa = V cmax *(Ci - gamma)/(Ci+KCO)

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

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

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

Acknowledgements iPlant Collaborative ( NSF IOS #

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 ModelDevelopment of a Gene-Based Ecophysiology Model contact: Melanie J. Correll, University of Florida at ext

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 CO 2