NUTRIENT RESORPTION IN DESERT SHRUBS

Nutrient resorption is the physiological process that acta to conserve plant nutrients by withdrawing them from tissues undergoing senescenc e and sequestering them for future use. Speculation about this process has suggested that desert shrubs may rely heavily on resorption to co nserve specific nutrients that are often in short supply in arid lands . The objectives of this paper are to examine the efficiency of nitrog en and phosphorus resorption in desert shrubs and to comment on thc po tential interplay between resorption and desertification. Mean resorpt ion efficiencies for nitrogen and phosphorus were 57% and 53%, respect ively, in the seven species of desert shrubs for which resorption data were available. Corresponding efficiencies for non-desert woody peren nials were 52% and 43%. Desert shrubs also had a higher proportion of resorption efficiencies in the upper extremes of recorded resorption v alues than did non-desert plants. These data suggest that resorption m ay be more important to the nutrient economy of desert shrubs than it is to woody perennials inhabiting more mesic environments. A detailed consideration of litter nutrient content in desert shrubs, placed in t he context of functional resorption thresholds, provided further suppo rt for the hypothesis that resorption of nitrogen and phosphorus in de sert shrubs is as efficient, or more efficient, than resorption of the se nutrients in non-desert woody perennials. If the considerable trans port of surface litter in deserts caused by wind and water erosion aff ord desert shrubs a reduced probability of recuperating nutrients from abscised litter, then differences in the availability of mineralizabl e organic litter could account for the disparity in resorption efficie ncies between desert shrubs and non-desert woody perennials. The possi bility that the regulation of resorption efficiencies in desert shrubs may be quite complex was supported by the high degree of intersite an d interyear variation in resorption efficiency exhibited by Fouquieria splendens. Conclusions from previously published analyses suggesting that nitrogen in the litter of desert plants is substantially higher t han in non-desert plants were not supported by the data assembled here on desert shrubs. Speculation on the potential interplay between reso rption and desertification resulted in the conclusion that potential e ffects are reciprocal. Although high resorption efficiencies in the do minant plants of an area undergoing desertification could act to delay specific community-level effects of such a perturbation, environmenta l changes that often accompany the desertification process could also act to reduce resorption efficiencies.