CONTROLS OVER NUTRIENT RESORPTION FROM LEAVES OF EVERGREEN MEDITERRANEAN SPECIES

Nutrient resorption from senescent leaves, by minimizing nutrient losses, could be just as important as uptake in determining nutrient balance, especially in low-nutrient environments. To examine the relative importance of phenotypic and genotypic factors in controlling nutrient resorption, we sampled several mediterranean trees and shrubs growing in serpentine and nonserpentine soils in northern California. Plants growing in serpentine soils had smaller, thicker leaves than those growing in richer sites and had lower N and P concentrations and pools on a unit-area basis. Pools of nutrients resorbed and nutrients left in litter in rich-site leaves were larger than pools in poor-site leaves, but N resorption efficiency (percent of total leaf N resorbed) was higher in less fertile sites (65 vs. 46%). Differences in efficiency may be due to the ratio of soluble/nonsoluble proteins, which is higher at low-N sites. Trends for phosphorus resorption efficiency were not significant (47 vs. 46% in poor and rich sites, respectively). There were no significant differences among species adapted to poor vs. rich soils, nor between needle vs. broad-leaved species. We conclude that a high nutrient resorption efficiency is a phenotypic response to low-nutrient environments.