WATER AND NITROGEN MANIPULATIONS OF THE DESERT SHRUB LARREA-DIVARICATA SUBSP TRIDENTATA (ZYGOPHYLLACEAE)

Water supplementation of Larrea divaricata subsp. tridentata bushes gr owing under natural conditions affected the amount of resin, nordihydr oguaiaretic acid (NDGA) and soluble protein present in the leaves. Nit rogen fertilization had no effect on these parameters. The total resin and NDGA content also varied with the leaf production dates, but the NDGA concentration in the resin was not affected by either the treatme nt or the time of production. Herbivore activity, measured as a percen tage of the leaves eaten, was not affected by these manipulations, var ied with season (highest during the summer) and had a negative correla tion with the resin content of the plant.