Response of Texas and Florida live oak (Quercus virginiana) seedlings to water deficit treatments
Live Oak (Quercus virginiana) is a common landscape tree in much of the United States. Although in native areas live oak can be found in mesic and xeric climates, little research has been conducted to determine if provenance differences exist in the response of live oak to deficit irrigation. Therefore, this research investigated gas exchange in response to water deficit irrigation treatments of live oak seedlings from two mesic regions Groveland, Florida (USDA Hardiness zone 9) and Houston, Texas (USDA Hardiness zone 9) and one xeric region, Justiceburg, Texas (central Texas) (USDA Hardiness Zone 7). In May 2006, one-year old live oak seedlings from both Houston, Texas and Groveland, Florida were shipped to Texas Tech from Groveland, Florida. Acorns from Justiceburg, Texas were collected from several trees in October 2005. Acorns were germinated and planted according to standard nursery practices. To acclimatize seedlings, in June 2006 all seedlings were placed outside under shade cloth for two weeks and then in full sun for one month. When seedlings were in full sun weekly stomatal conductance and leaf temperature were measured and leaf to air vapor pressure difference was calculated weekly. After the acclimation period 21 seedlings from each location were brought into a greenhouse, assigned one of three watering treatments (control seedlings were watered every day, moderate water deficit seedlings were watered every other day, and severe water deficit seedlings were watered every fourth day), and arranged in randomized complete blocks. Prior to irrigation of severe drought seedlings, mid-day stomatal conductance and leaf temperature were measured. To calculate transpirational water loss, seedling leaf area was measured and prior to and after each irrigation seedlings were weighed. Outdoors, prior to irrigation treatments seedlings from Lake Alan Henry, Texas had greater mid-day stomatal conductance and lower leaf to air vapor pressure deficit when compared to seedlings from Groveland, Florida or Houston, Texas. In the greenhouse, seedling gas exchange was influenced by water deficit treatment and provenance. Mid-day stomatal conductance and leaf to air vapor pressure difference for Lake Alan Henry, Texas seedlings did not differ among water deficit treatments. However, Groveland, Florida and Houston, Texas seedlings exposed to severe drought had lower mid-day stomatal conductance and greater leaf to air vapor pressure difference when compared to seedlings exposed to control or moderate irrigation treatments. Regardless of irrigation treatment, seedlings from Lake Alan Henry, Texas had greater mid-day stomatal conductance, lower leaf to air vapor pressure difference, and less negative pre-dawn water potential when compared to Groveland, Florida or Houston, Texas seedlings. Lake Alan Henry, Texas trees also had greater water loss regardless of irrigation treatment. Our data indicate the response of live oak seedlings from Lake Alan Henry, Texas, Houston, Texas, and Groveland, Florida differ in their response to water deficit treatments and that live oak trees from Lake Alan Henry, Texas may be better adapted to xeric sites than live oaks from more mesic environments.