A simulation model of plant water relations and production in the alpine tundra, Colorado.

A model to predict the daily courses of leaf resistance, leaf water potential, transpiration, leaf temperature and net photosynthesis based on soil-plant-atmosphere continuum and energy budget concepts is presented. The principle water relations parameters required by the model are the minimum leaf resistance, the response curves of leaf resistance to light, temperature, and leaf water potential, and the relationship between leaf water potential and water deficit. Predictions of the effects of changes in soil water potential on the daily patterns of leaf resistance, leaf water potential, leaf temperature, and net photosynthesis in an alpine climate are examined. The model was tested using data from two alphine species, Bistorta bistortoides and Caltha leptosepala, that exhibited different daily leaf resistance and leaf water potential patterns as water stress developed. Agreement was found between predicted and observed patterns. Differences in the daily courses between the species are shown to be due to differences in the physiological parameters. The relevance of the daily leaf resistance patterns is discussed in the context of drought adaptability.