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Using Leaf Gas Exchange to Quantify Drought in Cotton Irrigated Based on Canopy Temperature Measurements

^a USDA-ARS, Plant Stress and Water Conservation Laboratory, 302 West I-20, Big Spring, TX, 79720
^b USDA-ARS, Plant Stress and Water Conservation Laboratory, 3810 4th Street, Lubbock, TX 79415
^c USDA-ARS, 1001 Holleman Drive East, College Station, TX 77840

View larger version (16K): [in this window] [in a new window]   Fig. 1. An example of leaf net assimilation (A) vs. photosynthetic photon flux density (PFD) for experimental plots that were either irrigated the previous day (wet) or that were not irrigated the previous day (dry). Wet and dry data sets were collected on three or four leaves on 8 and 11 Aug. 2003, respectively. Error bars are ± standard error. Regression curves are of the form y = y0 + a[1 – exp(–bx)] with R2 > 0.99 for both curves.

View larger version (14K): [in this window] [in a new window]   Fig. 2. Leaf net assimilation (A) and stomatal conductance (g) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. leaf temperature (TL) for wet and dry data sets collected in 2003.

View larger version (19K): [in this window] [in a new window]   Fig. 3. Leaf net assimilation (A) and stomatal conductance (g) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. leaf temperature (TL) for the 7.5 mm irrigation amount treatment in 2005. Numbers in parentheses are the number of days since the last irrigation or significant rainfall.

View larger version (25K): [in this window] [in a new window]   Fig. 4. Leaf net assimilation (A) and intercellular CO2 concentration (Ci) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. stomatal conductance (g). Different symbols represent different operators with different photosynthesis meters or different years.

View larger version (27K): [in this window] [in a new window]   Fig. 5. Leaf net assimilation (A) and stomatal conductance (g) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. leaf minus air temperature differential (TL – Ta).

View larger version (61K): [in this window] [in a new window]   Fig. 6. Three dimensional plot of leaf net assimilation (A) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. leaf minus air temperature differential (TL – Ta) vapor pressure deficit (VPDL). Equation for the fitted plane is y = 33.93 – 2.05(TL – Ta) – 5.24(VPDL) with R2 = 0.79, Sy.x = 3.64, and n = 166.

View larger version (60K): [in this window] [in a new window]   Fig. 7. Three dimensional plot of stomatal conductance (g) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m–2 s–1 vs. leaf minus air temperature differential (TL – Ta) and vapor pressure deficit (VPDL). Equation for the fitted plane is y = 1.08 – 0.09(TL – Ta) – 0.26(VPDL), with R2 = 0.80, Sy.x = 0.17, and n = 166.