Effects of nitrogen supply on phenology and carbon assimilation in young Nothofagus fusca

Abstract

Measurements of stem, bud, and leaf growth and leaf loss were made on young Nothofagus fusca, grown in sand while irrigated with high (6 mM), medium (3 mM), and low (0.5 mM) concentrations of nitrogen, during two successive annual growth cycles. There were differences between treatments in the nitrogen concentration per unit leaf mass and area, and specific leaf area, in the first cycle but not during the second cycle. During the first cycle, increasing nitrogen supply resulted in increased leaf number, larger average leaf size, and the number and mass of buds. During the second cycle this resulted in increased leaf number, but not average leaf size, with increasing nitrogen supply. There were no differences in mafimum rates of photosynthesis or values for photosynthetic parameters between the treatments. The number of leaves falling during late summer and autumn increased with nitrogen supply. Support for this as a response to summer water deficit was provided from measurements of the carbon isotope ratios of the leaves.