title: A cost-benefit analysis of acclimation to low irradiance in tropical rainforest tree seedlings: leaf life span and payback time for leaf deployment.
abstract: The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.
authors.affiliation: 'Ecologie des Forêts de Guyane', Campus Agronomique de Kourou, 97387 Kourou, Guyane Française.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Coste
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Roggy
authors.forename: Heidy
authors.initials: H
authors.lastname: Schimann
authors.forename: Daniel
authors.initials: D
authors.lastname: Epron
authors.forename: Erwin
authors.initials: E
authors.lastname: Dreyer
mesh_terms: D002244:Carbon / Q000378:metabolism; D005616:French Guiana; D008027:Light; D010788:Photosynthesis; D018515:Plant Leaves / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D013045:Species Specificity; D014197:Trees / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects*; D014329:Tropical Climate
chemical_list: D002244:Carbon