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GAS EXCHANGE IN QUERCUS RUBRA DURING A DROUGHT: ANALYSIS OF RELATIONS AMONG PHOTOSYNTHESIS, TRANSPIRATION, AND LEAF CONDUCTORS
Citation:
Weber, J. AND D. Gates. GAS EXCHANGE IN QUERCUS RUBRA DURING A DROUGHT: ANALYSIS OF RELATIONS AMONG PHOTOSYNTHESIS, TRANSPIRATION, AND LEAF CONDUCTORS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-90/472.
Description:
Development of water stress in leaves of mature Quercus rubra L. caused a marked midday depression in photosynthesis(A) and transpiration (E). t external CO2 partial pressures of 100-110 Pa, a constant temperature of 30 degrees C and a constant photosynthetic photon flux density of about 1000 umol -2s-1, A was 8 umol m-2 at low leaf water potentials (-1.5 to -2.0 MPa), whereas it was 20 umol m-2-1s in non-stressed leaves (-1.0 MPa). t lower external CO2 partial pressures, the effect of low leaf water potential on A was less. he midday depression in gas exchange was relieved by an overnight rain of 2.5 cm. o difference in carboxylation efficiency or CO2 compensation point was found between leaves before and after rain. he relationship between A and E was linear for a given external CO2 partial pressure, but the slope varied with CO2 concentration. odification of the model of stomatal response proposed by Ball et al. (1987) produced a linear relationship between leaf conductance and a factor incorporating A, relative humidity, and CO2. The data indicate that gas exchange in leaves of mature northern red oak respond rapidly to relief of drought with no indication of long-term photoinhibition.