Plant physiological ecology. Current research areas: 1) Invasion, competition, and ecology of exotic annual grasses, especially cheatgrass and red brome, in arid ecosystems. 2) Effects of global changes on vegetation dynamics and on plant ecophysiology and productivity. 3) Dynamics of water and nutrients in native plant communities and their effects on carbon balance, water balance, rooting dynamics, and competition for soil resources. 4) Growth and physiological responses of fruits and vegetables to hoop house production environments.