Nutrient use by Evergreen and Deciduous Shrubs in Southern California: II. Experimental Investigations of the Relationship between Growth, Nitrogen Uptake and Nitrogen Availability

Abstract

SUMMARY (1) Two laboratory experiments were conducted to test the hypothesis that growth of the drought-deciduous shrub, Salvia leucophylla is more closely coupled to soil nitrogen availability than growth of the evergreen chaparral shrub, Ceanothus megacarpus. (2) Seedlings were grown in sand culture for 50 days with four concentrations of N03-nitrogen and, in another experiment, were subjected to temporary increases in nitrogen. (3) Salvia had a greater relative growth rate, dry matter yield, leaf area, and concentration of nitrogen in its tissues than Ceanothus. Salvia also exhibited a linear response to increasing nitrogen concentration in terms of yield, leaf area, nitrogen content, and root absorption rate, whereas Ceanothus showed an asymptotic response to increasing nitrogen concentration. (4) Salvia showed a greater response during recovery from nitrogen stress and when supplied with a nitrogen flush, in terms of growth rate, nitrogen concentration, and root absorption rates. Its responsive, opportunistic pattern of growth and nutrient uptake appear to be adaptive to the nutrient conditions in the coastal sage scrub, the community in which it is common. (5) The limited response of Ceanothus to varying nitrogen concentration suggests an uncoupling of growth from nitrogen availability, as predicted from the field studies in the chaparral.