Transpiration and conductance responses of salt-desert vegetaion in the Owens Valley of California in relation to climate and soil moisture

摘要

Work presented in this dissertation was performed in the salt-desert environment of the Owens Valley of California. The area experiences low-rainfall, hot summers, but has a high water table, seldom more than 5 meters from the surface. To test differences in plant species wateruse, a steady-state porometer was used for transpiration measurements while a 2-meter point-frame was used to estimate leaf area index on each species studied. The five species studied (Atriplex torreyi, Chrysothamnus nauseosus, Distichlis stricta, Sporobolus airoides, and Sarcobatus vermiculatus) varied with regard to photosynthetic pathways and leaf morphology. Water-use differences among species are hypothesized to be related to the differing physiological and morphological characteristics observed in the different species studied. This work focuses upon methods for integrating porometric transpiration rates and point-frame measured leaf area to estimate daily plant water-use. Daily water-use values are correlated with environmental growth conditions. A computer program was developed for scenario testing so that conclusions could be drawn concerning how given plants respond to different conditions of soil moisture and atmospheric evaporative demand. The computer-aided calculations led to conclusions that low water-use behavior characterizes A. torreyi, and high water-use behavior characterizes C. nauseosus. C4 photosynthesis and low leaf conductance may contribute to the success of A. torreyi on fine-textured soils when water transfer rates to roots are limiting to transpiration. Fine-textured soils may inhibit production in C. nauseosus because the species requires higher rates of transpiration to achieve optimal growth than soil hydraulic conductivity allows. These conclusions have implications for land managers who should recognize that climax plant communities in saltdesert regions are better at conserving water and stabilizing soil than is colonizing vegetation. Management should seek to maintain climax vegetation cover because restoration is difficult once vegetation disturbance occurs.