Yoder, Carolyn Kay (1993). Soil water utilization by herbaceous species of the southern Great Plains: evidence from isotopically labeled water. Master's Thesis.
Thesis
Understanding spatial and temporal patterns of soil water utilization by plants has broad implications for physiological, ecological, and hydrological processes. Water labeled with the stable isotopes deuterium ('H) or oxygen-18 ("'O) was injected at different depths (15 cm, 45 cm or 75 cm) into the sides of weighable, monolith lysimeters in order to determine spatial and temporal patterns of water utilization by selected species of the Rolling Plains of Texas, a component of the North American Great Plains. The species studied were: curlymesquite (Hilaria belangeri (Steud.) Nash); sideoats grama (Bouteloua curtipendula (Michx.) Torr); and annual broomweed (Amphiachyris dracunculoides (D.C.) Nutt). All three species are dominant in the plant communities of this region. Specific objectives of the study were to: 1.) Determine if both leaf and stem water reflected the pattern of utilization of labeled water from the soil profile; 2.) Document whether depth was a factor affecting the amount and rate of water taken up per unit of root, independent of soil water availability; and 3.) Determine if there were seasonal differences in the pattern of water utilization for three different growth forms. A correlation between the isotopic content of water in leaf versus stem tissue of annual broomweed was established (r = .86 for 2 H, r = .80 for 180) and indicated that water from either type of tissue may be used to determine patterns of water utilization.Normalizing for differences in root biomass, root length, and water availability between depths did not always remove the effect of preferential water extraction from the upper soil layer, and indicated that depth is a factor influencing the pattern of water extraction. Therefore, factors other than water availability, root biomass and root length should be considered when dealing with hydrological processes of plants. There were species specific seasonal variations in the pattern and rate of soil water extraction. These variations reflect differences in the abilities of these species to effectively access and utilize the water resource from different depths in the soil profile.
