A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
A Look at Amazon Basin Seasonal Dynamics with the Biophysical ... A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
Water use efficiency increases in response to drought for Vismia guianensis in theoverstory of an Eastern Amazonian regrowth forestSteel S. Vasconcelos 1 , Daniel J. Zarin 2 , Stephen S. Mulkey 2 , Claudio José R. de Carvalho 3 ,Lucas B. Fortini 21 Projeto MANFLORA, Faculdade de Ciências Agrárias do Pará, P. O. Box 917, Belém,PA, 66077-530, Brazil, E-mail: manflora@amazon.com.br; 2 University of Florida, USA,E-mail: zarin@ufl.edu, mulkey@botany.ufl.edu, lucasfortini@usa.net;Amazônia Oriental, Brazil, E-mail: carvalho@cpatu.embrapa.br3EMBRAPAWe assessed the impact of drought on an abundant overstory species (V. guianensis) bymeasuring leaf water potential and leaf gas exchange in irrigated and control plots in anEastern Amazonian regrowth forest during the 2001 dry-season. Light-saturated CO 2assimilation rates (A max ) under PPFD of 1500 µmol m -2 s -1 and light response curves wereperformed with a portable photosynthesis system on young, fully developed leaves. Predawnand midday leaf water potential were measured with a pressure chamber. Irrigatedplants maintained higher leaf water potential in relation to control plants. A max valuesshowed a decreasing trend during the dry season and were similar between treatments onfive of six measurement dates; on one measurement date, irrigated plants showed higherA max than non-irrigated plants (16.4 ± 1.5 vs. 10.8 ± 4.6 µmol m -2 s -1 ). Stomatalconductance (g s ) values of irrigated plants were relatively constant during the whole dryseason; control plants were consistently lower and showed a very sharp decrease instomatal conductance from the mid to the end of the dry season. Instantaneous water-useefficiency (A max /g s ) values increased in control plants as the dry season progressed, whileremaining constant in irrigated plants. Light response curves obtained near the end of thedry season showed a trend of higher light compensation and saturation points in controlplants than in irrigated plants. These results suggest that V. guianensis is able to maintaingas exchange during moderate drought through regulation of stomatal water loss.
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W<strong>at</strong>er use efficiency increases in response to drought for Vismia guianensis in <strong>the</strong>overstory of an Eastern <strong>Amazon</strong>ian regrowth forestSteel S. Vasconcelos 1 , Daniel J. Zarin 2 , Stephen S. Mulkey 2 , Claudio José R. de Carvalho 3 ,Lucas B. Fortini 21 Projeto MANFLORA, Faculdade de Ciências Agrárias do Pará, P. O. Box 917, Belém,PA, 66077-530, Brazil, E-mail: manflora@amazon.com.br; 2 University of Florida, USA,E-mail: zarin@ufl.edu, mulkey@botany.ufl.edu, lucasfortini@usa.net;Amazônia Oriental, Brazil, E-mail: carvalho@cp<strong>at</strong>u.embrapa.br3EMBRAPAWe assessed <strong>the</strong> impact of drought on an abundant overstory species (V. guianensis) bymeasuring leaf w<strong>at</strong>er potential and leaf gas exchange in irrig<strong>at</strong>ed and control plots in anEastern <strong>Amazon</strong>ian regrowth forest during <strong>the</strong> 2001 dry-season. Light-s<strong>at</strong>ur<strong>at</strong>ed CO 2assimil<strong>at</strong>ion r<strong>at</strong>es (A max ) under PPFD of 1500 µmol m -2 s -1 and light response curves wereperformed <strong>with</strong> a portable photosyn<strong>the</strong>sis system on young, fully developed leaves. Predawnand midday leaf w<strong>at</strong>er potential were measured <strong>with</strong> a pressure chamber. Irrig<strong>at</strong>edplants maintained higher leaf w<strong>at</strong>er potential in rel<strong>at</strong>ion to control plants. A max valuesshowed a decreasing trend during <strong>the</strong> dry season and were similar between tre<strong>at</strong>ments onfive of six measurement d<strong>at</strong>es; on one measurement d<strong>at</strong>e, irrig<strong>at</strong>ed plants showed higherA max than non-irrig<strong>at</strong>ed plants (16.4 ± 1.5 vs. 10.8 ± 4.6 µmol m -2 s -1 ). Stom<strong>at</strong>alconductance (g s ) values of irrig<strong>at</strong>ed plants were rel<strong>at</strong>ively constant during <strong>the</strong> whole dryseason; control plants were consistently lower and showed a very sharp decrease instom<strong>at</strong>al conductance from <strong>the</strong> mid to <strong>the</strong> end of <strong>the</strong> dry season. Instantaneous w<strong>at</strong>er-useefficiency (A max /g s ) values increased in control plants as <strong>the</strong> dry season progressed, whileremaining constant in irrig<strong>at</strong>ed plants. Light response curves obtained near <strong>the</strong> end of <strong>the</strong>dry season showed a trend of higher light compens<strong>at</strong>ion and s<strong>at</strong>ur<strong>at</strong>ion points in controlplants than in irrig<strong>at</strong>ed plants. These results suggest th<strong>at</strong> V. guianensis is able to maintaingas exchange during moder<strong>at</strong>e drought through regul<strong>at</strong>ion of stom<strong>at</strong>al w<strong>at</strong>er loss.
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