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.

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)

H2OH2O

H2O H2O

H2O

H2O

H2O

H2O

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

H2O

CO2

GuardCell

Intracellular Space

MesophyllCells

rbL

rs

rT= rbL + rs

gbs = 1/rT

= 1/(rbL + rs)B

ound

ary

laye

r

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 diffusionE = 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)

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. 566-631.

Acknowledgements

• iPlant Collaborative (www.iplantcollaborative.org)

• NSF IOS # 0920145

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

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