Physiological variables related to photosynthesis are more plastic than the morphological and biochemistry in non-pioneer tropical trees under contrasting irradiance

Abstract

Contradicting the notion that non-pioneer tree species are less tolerant to high irradiance due to their lower plasticity, some non-pioneer tropical species have shown high capacities to adjust to full sun. This ability has been attributed to the greater plasticity related to photosynthesis variables rather than morphological variables. To test this hypothesis, we performed the present study to identify the phenotypic variables of greatest plasticity in the non-pioneer species Ca- riniana estrellensis (Raddi) Kuntze, Cedrela odorata L., and Manilkara salzmannii (A.DC.) H.J. Lam., which are very representative of the rainforests of Brazil and have a large potential for reforestation. After 150 days of cultivation in full sun (1,820 ± 110 lmol m -2 s -1 )o r shade (250± 84 lmol m -2 s -1 ), measurements were made of growth, chloroplast pigments, net assimilation rate (NAR), soluble carbohydrates (glucose, fructose and sucrose), catalase and ascorbate per- oxidase (APX) activity, and leaf and stem anatomy. The pig- ments and NAR showed greater plasticity than did the biochemical (carbohydrates and enzyme), growth or anatomy variables. Although the growth variables demonstrated low plasticity, the leaf area, specific leaf area (SLA), and leaf area ratio (LAR) had plasticity index values over 0.5. Cedrela od- orata was concluded to be the most plastic specie in leaf area, SLA, LAR, NAR, Carotenoids, APX, and the thickness of the periderm. The tolerance of Cariniana estrellensis, Cedrela odorata ,a ndManilkara salzmannii to full sun was attributed to the high plasticity of their physiological variables NAR and chloroplast pigments.