Effect of Drought on Browse from Three Oak Species.

The physiological response of plants to water stress provides insights into which species may survive in exceptional drought conditions. This study conducted on a remnant post oak savanna site in College Station, Texas, examined how drought affected the physiology of three native oak species. In June 2014, after a period of equal watering, we subjected three year old Quercus shumardii (Shumard oak; SO), Q. virginiana (live oak; LO), and Q. macrocarpa (bur oak; BO) saplings to one of two watering treatments: 1) watered, which received the equivalent of normal precipitation and 2) droughted, in which we reduced precipitation by 100%. Drought stress responses were evident after only one month of induced drought. Droughted trees displayed reduced (P≤0.05) predawn and midday leaf water potential (LWP), photosynthesis and transpiration rates, stomatal conductance, and leaf internal CO2 concentration in comparison to watered trees of the same species. LO saplings exhibited greater (P≤0.05) gas exchange but similar LWP to their respective watered and droughted BO and SO counterparts. Droughted LO exhibited gas exchange similar (P≤0.05) to watered BO and SO, and watered LO adjusted gas exchange rates best to changes in water availability during short-term drought. Results suggest LO may be more likely to withstand mortality in the face of drought than BO or SO. During drought leaf soluble sugar (SS) concentration may increase as consumption of SS for growth declines. SS concentration was greater (P≤0.05) in droughted than watered saplings, possibly confirming this phenomenon. Although SO and BO demonstrated similar photosynthesis rates, SS concentration was greatest (P≤0.05) in SO and least in BO. By displaying the greatest (P≤0.05) average photosynthesis rate, LO should have accumulated the greatest amount of carbon, but had an intermediate SS concentration. Results suggest species may differ in carbon allocation strategies.