Seasonal trend of photosynthetic parameters and stomatal conductance of blue oak (Quercus douglasii) under prolonged summer drought and high temperature

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OAK-B135 Understanding seasonal changes in photosynthetic parameters and stomatal conductance is crucial for modeling long-term carbon uptake and energy fluxes of ecosystems. Gas exchange measurements of CO{sub 2} and light response curves on blue oak leaves (Quercus douglasii H. & A.) were conducted weekly throughout the growing season to study the seasonality of photosynthetic capacity (V{sub cmax}) and Ball-Berry slope (m) under prolonged summer drought and high temperature. A leaf photosynthetic model was used to determine V{sub cmax}. There was a pronounced seasonal pattern in V{sub cmax}. The maximum value of V{sub cmax}, 127 {micro}molm{sup -2} s{sup -1},was reached shortly ... continued below

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13 pages

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Xu, L & Baldocchi, DD September 1, 2003.

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OAK-B135 Understanding seasonal changes in photosynthetic parameters and stomatal conductance is crucial for modeling long-term carbon uptake and energy fluxes of ecosystems. Gas exchange measurements of CO{sub 2} and light response curves on blue oak leaves (Quercus douglasii H. & A.) were conducted weekly throughout the growing season to study the seasonality of photosynthetic capacity (V{sub cmax}) and Ball-Berry slope (m) under prolonged summer drought and high temperature. A leaf photosynthetic model was used to determine V{sub cmax}. There was a pronounced seasonal pattern in V{sub cmax}. The maximum value of V{sub cmax}, 127 {micro}molm{sup -2} s{sup -1},was reached shortly after leaf expansion in early summer, when air temperature was moderate and soil water availability was high. Thereafter, V{sub cmax} declined as the soil water profile became depleted and the trees experienced extreme air temperatures, exceeding 40 C. The decline in V{sub cmax} was gradual in midsummer, however, despite extremely low predawn leaf water potentials ({Psi}{sub pd}, {approx} -4.0 MPa). Overall, temporal changes in V{sub cmax} were well correlated with changes in leaf nitrogen content. During spring leaf development, high rates of leaf dark respiration (R{sub d}, 5-6 {micro}mol m{sup -2} s{sup -1}) were observed. Once a leaf reached maturity, R{sub d} remained low, around 0.5 {micro}mol m{sup -2} s{sup -1}. In contrast to the strong seasonality of V{sub cmax}, m and marginal water cost per unit carbon gain ({partial_derivative}E/{partial_derivative}A) were relatively constant over the season, even when leaf {Psi}{sub pd} dropped to -6.8 MPa. The constancy of {partial_derivative}E/{partial_derivative}A suggests that stomata behaved optimally under severe water-stress conditions. We discuss the implications of our findings in the context of modeling carbon and water vapor exchange between ecosystems and the atmosphere.

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13 pages

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OSTI as DE00824572

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  • Journal Name: Tree Physiology; Journal Volume: 23; Other Information: Published in Tree Physiology: Volume 23

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  • Report No.: NONE
  • Grant Number: FG03-00ER63013
  • Office of Scientific & Technical Information Report Number: 824572
  • Archival Resource Key: ark:/67531/metadc781566

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  • September 1, 2003

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  • Dec. 3, 2015, 9:30 a.m.

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  • Aug. 4, 2016, 7:54 p.m.

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Xu, L & Baldocchi, DD. Seasonal trend of photosynthetic parameters and stomatal conductance of blue oak (Quercus douglasii) under prolonged summer drought and high temperature, article, September 1, 2003; United States. (digital.library.unt.edu/ark:/67531/metadc781566/: accessed August 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.