Plant Water Potentials/Plant Physiology

Physiological status of plants is monitored in conjunction with the sampling schedule outlined in Sevilleta Plant Demography. Several perennial life forms, including tree (Juniperus and Pinus), shrub (Larrea) and grass (Oryzopsis and Sporobolus), are being monitored at 1-3 of four sites which differ in elevation and topography as well as edaphic and annual precipitation characteristics. For the 1990 field season we are adding a spring annual, Lesquerella to our sampling efforts at these same sites. Currently, water status (xylem potentials, bars) is monitored twice a year, in spring (after the 'dry' season) and fall (after the 'wet' season). Three replicate measurements are made on each of 10-20 individuals per species per site. Three measurements are made at pre-dawn and midday to determine the diurnal range of values for each plant. For the 1990 field season, we will also be measuring peak photosynthetic rates for selected individuals by gas exchange measurements and porometry. Together with demographic data, this data set permits assessment of the physiological bases of plant growth and reproduction in response to short- and long-term changes in abiotic and biotic aspects of the environment.