Monday, November 5, 2007 - 1:20 PM
61-2
Leaf Hydraulic Conductance and Increased Crop Water-Use Efficiency.
Thomas Sinclair1, Maciej A. Zwieniecki2, N. Michele Holbrook3, Andrew Fletcher1, and Thomas Carter4. (1) University of Florida, University of Florida, Agron. Phys. Lab, Bldg. 350, Gainesville, FL 32611-0965, (2) Arnold Arboretum, Harvard University, 16 Divinty Ave., Cambridge, MA 02138, (3) Organismic and Evolutionary Biology, Harvard University, 16 Divinty Ave., Cambridge, MA 02138, (4) ARS-USDA, 3127 Ligon St., Raleigh, NC 27607
Leaf gas exchange response to vapor pressure deficit (VPD) has been observed to differ among species. However, no such comparison seems to exist within a species, and the basis for such putative differences is unexplained. We originally undertook this study to understand the 'slow-wilting’ phenotype that expresses under water-deficit conditions. This trait has been observed in only a very few soybean genotypes. We found the slow-wilting phenotype in PI 416937 was associated with limited transpiration under high VPD conditions. A threshold VPD was reached at about 1.8 to 2.0 kPa above which there was no further increase in transpiration rate. Leaf regulation to limit transpiration rate to a low, maximum value meant that water loss was less than expected for high VPD conditions. Consequently, there was both water savings and an increased water-use efficiency when VPD was high. The basis for inhibited gas exchange at high VPD was traced to low hydraulic conductance in the leaves of PI 416937 as demonstrated in three, independent experimental methods. These results demonstrated that the ability of guard cells to be replenished with water lost via transpiration was limited in PI 416937. Therefore, and under high VPD transpiration rate was limited to the rate of water recharge of the guard cells. The low hydraulic leaf conductance offers a trait specifically for improved water-use efficiency under arid atmospheric environments and for increased yields when water-deficit conditions develop.