1 / 22

Transpiration

Transpiration. Transpiration. the release of water vapor by plants to the atmosphere “is not an essential or an active physiological function of plants” a largely passive response to the “unquenchably thirsty” atmosphere.

ghazi
Download Presentation

Transpiration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Transpiration

  2. Transpiration • the release of water vapor by plants to the atmosphere • “is not an essential or an active physiological function of plants” • a largely passive response to the “unquenchably thirsty” atmosphere

  3. Stoma in a tomato leaf shown via colorized scanning electron microscope image. A stoma in cross section Images from http://en.wikipedia.org/wiki/Stoma

  4. The soil-plant-atmosphere continuum • 1 bar = 100 kPa = 1020 cm H2O • -100 bar = 93% relative humidity at 20C • -1000 bar = 48% relative humidity at 20C • The largest drop in water potential generally occurs between the leaves and the atmosphere

  5. Water status of plants • If transpiration exceeds root water uptake • the plant begins to wilt • the water potential inside the plant drops • transpiration decreases • common under high evaporative demand • If high evaporative demand is relieved • root water uptake can exceed transpiration • plant turgor is restored

  6. Root water uptake • limited by hydraulic conductivity, or • limited by the water potential gradient between soil and root • root water uptake lowers the conductivity and increases the gradient, until • the soil adjacent to the root is in equilibrium with the root • then the conductivity and gradients both decrease and uptake declines

  7. Transpiration rates for corn

  8. Water use efficiency • a ratio of biomass accumulation to water consumed during a given time span • accumulation can be expressed as: • CO2 assimilation • above-ground biomass • harvested biomass

  9. Water use efficiency (cont.) • water consumed can be expressed as: • transpiration • evapotranspiration • total water supply • time scale can be: • instantaneous • seasonal • annual

  10. Reading assignment • Sinclair, T.R., C.B. Tanner, and J.M. Bennet. 1984. Water-use efficiency in crop production. BioScience 34:36-40. http://www.jstor.org/stable/10.2307/1309424

  11. Ratio of assimilation to transpiration • Mc = mole weight CO2 • Mw = mole weight of H2O • e*L = saturation vapor pressure at leaf temperature • e = vapor pressure of the atmosphere • Pa = partial pressure of CO2 in atmosphere • Pi = partial pressure of CO2 in leaf • ra = aerodynamic boundary layer resistance • rs = stomatal resistance • prime notations signify resistance for CO2 rather than H20

  12. Ratio of assimilation to transpiration • e*L = saturation vapor pressure at leaf temperature • e = vapor pressure of the atmosphere • Pa = partial pressure of CO2 in atmosphere • c = 1-Pi/Pa = 0.3 for C3 plants and 0.7 for C4 plants

  13. Ratio of biomass to transpiration • B = above-ground biomass • e*a = saturation vapor pressure at air temperature • e = vapor pressure of the atmosphere • overbar represents daily mean during periods of transpiration • kd = constant for a given species at fixed Pa

  14. Tolk, J.A., and T.A. Howell. 2009. Transpiration and yield relationships of grain sorghum grown in a field environment. Agron. J. 101:657-662.

  15. Ratio of yield to evapotranspiration • E = evaporation from the soil, plant, and residue • ET = evapotranspiration • H = harvest index (yield/biomass) • assumes relatively constant seasonal conditions

  16. Yield versus evapotranspiration • plot Y versus ET • slope is transpirational water use efficiency • intercept is an estimate of evaporative losses

  17. Hochman, Z., D. Holzworth, and J.R. Hunt. 2009. Potential to improve on-farm wheat yield and WUE in Australia. Crop and Pasture Science 60:708-716.

  18. Pairwise growing season rainfall amount and wheat grain yield for 93 years across 18 counties in central-western Oklahoma. (Patrignani et al., 2012)

  19. Reading assignment • Soil temperature and heat flow • p. 215 - 218

More Related