The water relations of red maple Acer rubrum L. ecotypes from contrasting hydrologic habitats

This project has two components. In the first, the response of red maple to water stress under controlled drought was examined to test for ecotypic differences. In the second, I developed and tested a novel tool for measuring sap flow in plant stems with the original intent of using this device to study differences in hydraulic conductivity among red maple families.; Chapter 1. Responses of eight red maple ecotypes were characterized in a common garden experiment. Wet and dry site ecotypes differed both in gas exchange characteristics and biochemical limitations to carbon assimilation. In comparison with dry site seedlings, seedlings originating from wet environments had a significantly higher maximum rate of carboxylation (Vcmax), maximum rate of coupled photosynthetic electron transport (Jmax), apparent quantum use efficiency (Qapp), light-saturated photosynthesis (Amax), stomatal conductance to water vapor (g s), and dark respiration (R).; Chapter 2. The response of growth, gas exchange, abscisic acid, and stable isotope discrimination (Delta) were investigated under well-watered and drought conditions. Under well-watered conditions, wet site plants grew faster and had higher Amax than plants from dry sites. None of the other variables measured differed between wet and dry site populations under well-watered conditions. Under drought stress, however, ecotypes from wet sites showed less of a decrease in absolute growth rate, greater reduction in gas exchange, and higher ABA levels than those that originated from dry sites. Instantaneous and integrated water use efficiency were not significantly different between ecotypes both under well-watered and water-stressed conditions.; Chapter 3. Osmotic adjustment was compared in leaves of well-watered and water-stressed red maple seedlings. Under well-watered conditions, wet site and dry site ecotypes were not significantly different with respect to osmotic potential at full hydration (Psipio), osmotic potential at the turgor loss point (Psipi tlp), relative water content at the turgor loss point (Rtlp), and average modulus of elasticity (epsilonavg). Under water-stressed conditions, only dry site ecotypes responded with slight osmotic adjustment and decreased Psi pio and Psipi tlp in response to water stress.; Chapter 4. Quantitative differences in abscisic acid (ABA) among red maple ecotypes were investigated. Leaves on well-watered plants responded to atmospheric vapor pressure deficits by increasing their ABA levels and reducing their photosynthesis and stomatal conductance. Moreover, red maple ecotypes showed characteristically different patterns of leaf synthesis of ABA.; Chapter 5. A system for measuring sap flow in real-time and without the need to puncture the stem was developed. The system uses a laser heat source and infrared detection system as an alternative to electrical resistance heaters and contact thermometers.