© 2000 Heron Publishing—Victoria, Canada
Photosynthetic nutrient-use efficiency in three fast-growing tropical trees with differing leaf longevities
Ankila J. Hiremath (1, 2)
1. Department of Botany, 220 Bartram Hall, University of Florida, Gainesville, FL 32611, USA / 2. Harvard University, Biological Laboratories, Cambridge, MA 02138, USA (hiremath@oeb.harvard.edu) / Received October 28, 1999
Summary
Differences in nutrient-use efficiency have been attributed to differences in leaf habit. It has been suggested that evergreens,
with their longer-lived leaves, and therefore longer nutrient retention, are more efficient than deciduous species in their
use of nutrients. In tropical trees, however, leaf life span is not always a function of whole-tree deciduousness, leading
to the proposal that nutrient-use efficiency is better related to leaf life span than to leaf habit. It was predicted that
potential photosynthetic nutrient-use efficiency (maximum potential photosynthesis/leaf nutrient content) would decrease with
increasing leaf life span, whereas cumulative photosynthetic nutrient-use efficiency (carbon assimilated over a leaf's life
span/total nutrients invested in a leaf) would increase with increasing leaf life span. Potential and cumulative photosynthetic
nutrient-use efficiencies (with respect to nitrogen and phosphorus) were measured for three fast-growing tropical trees: Cedrela odorata L. (Meliaceae), Cordia alliodora (R. & P.) Cham. (Boraginaceae), and Hyeronima alchorneoides Allemão (Euphorbiaceae). Mean leaf life spans of the three species varied about threefold and ranged from 50 to 176 days.
The predictions were partially supported: Cedrela odorata had the shortest-lived leaves and the highest potential nitrogen-use efficiency, whereas Hyeronima alchorneoides had the longest-lived leaves and the highest cumulative nitrogen- and phosphorus-use efficiencies. Potential phosphorus-use
efficiency, however, was invariant among species. It is suggested that there are potential tradeoffs between leaf characteristics
that lead to high potential and cumulative nutrient-use efficiencies. High potential nutrient-use efficiency may be beneficial
in high-nutrient environments, whereas high cumulative nutrient-use efficiency may be of greater benefit to species in low-nutrient
environments.
Keywords:
Cedrela odorata, Cordia alliodora, Hyeronima alchorneoides, leaf life span, maximum photosynthesis, nitrogen, phosphorus.
