干旱区生态环境知识资源中心

Paradoxically low nitrogen resorption efficiency in the drought-deciduous desert shrub Fouquieria splendens Engelm (ocotillo) triggered tests of the hypotheses that resorption is often low in this species and that resorption is influenced by zinc. Resorption efficiency and proficiency were measured in 1989 and 1994 at two sites in the Chihuahuan Desert in plants to which zinc, or zinc and nitrogen were added. Resorption of nitrogen, phosphorus, and zinc in unfertilized plants varied temporally and spatially, but was both efficient (66%, 49%, and 40%, respectively) and proficient (0.55%, 0.09%, and 9.4 mu g g-1, respectively) as determined by comparison to worldwide resorption patterns in a wide variety of other species. Applications of zinc had no significant effect on the resorption of nitrogen and phosphorus, but did influence the resorption of zinc. Resorption of zinc was significantly less efficient in zinc-treated plants than controls at only one of the two sites in one of the 2 years, yet resorption of zinc was significantly less proficient in zinc-treated plants than controls in both years and at both sites. This pattern of zinc resorption adds insight into the continuing debate regarding the relationship between fertility and resorption because the data used to fuel the debate have almost exclusively described macronutrients, not trace metals. The high variability in resorption among individuals, sites, and years observed for F. splendens may well be an attribute of many desert-dwelling, drought-deciduous plants. When senescence is controlled primarily by water availability rather than photoperiod, especially in a landscape characterized by unpredictable amounts and timing of precipitation, high variability in associated processes such as resorption may be inevitable.