Snider, John , Choinski, John S. Jr. .
Gas exchange and leaf temperature changes in Smooth (Rhus glabra L.) and Winged (Rhus copallina L.) Sumac.
Previous investigations of leaf development have shown that young, not fully expanded leaves have lower photosynthesis rates and stomatal conductance than more mature leaves suggesting that young leaves would also have higher leaf temperatures and leaf-air temperature differentials. To test this hypothesis, attached sumac (Rhus glabra, R. copallina) leaflets were measured from April-October 2006 at two sites in Arkansas using an infrared thermometer, a Licor data logger fitted with a temperature sensor, and a Licor IRGA. Daily patterns of leaf temperature and gas exchange were obtained through hourly measurements of illuminated (or shaded) young and mature leaflets from different leaves on the same shoot. When plants were sampled in April to June, young leaflets at midday had significantly higher adaxial temperatures, and lower leaf-air temperature differentials, stomatal conductance, and photosynthetic rates than mature leaflets. For example, in pooled data from 20 similar Smooth Sumac shoots measured from 1300-1500h on May 19, 2006, young leaflets (node 3; area = 5.5 + 1.7 cm2) were significantly (p < 0.05) warmer (31.6 + 0.51C), with lower leaf-air temperature differentials (-0.91 + 0.47 C), stomatal conductance (204.0 + 22.8 mmol m-2 s-1), and photosynthetic rates (5.2 + 0.73 μmol m-2s-1) than mature (node 8; area = 15.6 + 4.7 cm2) leaflets (30.0 + 0.34 C, -2.2 + 0.37 C, 372.5 + 26.0 mmol m-2 s-1, and 13.2 + 0.65 μmol m-2 s-1, respectively). In contrast, when measurements were taken from July to October in leaves in the same developmental stages as in the May readings, no significant differences in any parameter were observed. We conclude that photosynthesis in Sumac shows a plastic response influenced by seasonal conditions and that the higher surface temperatures and lower leaf-air temperature differences observed in young leaflets in the early spring may have an adaptive value in promoting growth and expansion when air temperatures are cooler.
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1 - University of Central Arkansas, Biology, Conway, AR, 72035, USA
Presentation Type: Poster:Posters for Topics
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM