Ecotypic variation in drought and salinity responses of bigtooth maples

Bigtooth maple (Acer grandidentatum Nutt.) is valued for its foliage fall color, wood and sap. Several ecological traits suggest that bigtooth maples could be popular landscape trees. Although bigtooth maple occurs on xeric and mesic sites, there is limited scientific information on the tolerance of the plant to environmental stress such as drought. Furthermore, many managed landscapes are on salt-affected soils or irrigated with saline water, but information on the tolerance of bigtooth maples to salt stress is virtually nonexistent.; I conducted three experiments to characterize and compare drought and salinity responses of bigtooth maple indigenous to locations in Arizona, New Mexico, Texas and Utah. In the first experiment, I compared drought responses of greenhouse-grown seedlings of bigtooth maple plants from 15 trees native to Arizona, New Mexico, Texas, and Utah. Plants were maintained as well-irrigated controls or exposed to drought and irrigated in cycles based on evapotranspiration. Variable to maximal fluorescence ratio (Fv/Fm) showed that bigtooth maples exposed to drought maintained photosystem II function near levels expected for non-stressed plants. Plants from the Guadalupe Mountains (GM3) in Texas maintained net assimilation rates at 61% of the well-watered controls. Plants from GM3 accumulated large amounts of root dry matter in both drought-stressed and well-irrigated plants which suggests that this source maintained tissues that could enhance survival in xeric environments.; Based on the results of the first greenhouse experiment, I selected the best four sources and one drought sensitive source and used a pot-in-pot field experiment to test the drought responses of those five sources. In this second experiment, trees native to the Lost Maples State Park in Texas (LMP5) had among the greatest leaf area (1236 cm2) while plants native to Logan Canyon in Utah (UW2) had among the smallest (216 cm2). Leaf area ratio was highest in plants from LMP5 (24.23 cm2.g -1). Plants from LMP5 had the highest leaf area/xylem diameter ratio (135 cm-2.mm-1) more than 5.8 times higher than of UW2, which suggest more carbon assimilation and better control of water transport in LMP5 than UW2 plants. Stomatal conductance (gs) was positively correlated to transpiration for both drought-stressed ( r2=0.801) and well-irrigated plants (r 2=0.759). Plants from New Mexico had the lowest transpiration rate (2.32 mmol.m-2.s-1), lowest g s (52.1 mmol.m-2.s-1), but largest xylem diameter (11 mm). Plants from Utah consistently showed more drought sensitive traits than the other four sources. Plants from LMP5 displayed the most drought-tolerant traits. (Abstract shortened by UMI.)...