Irradiance triggers different morphophysiological responses in two neotropical tree seedlings with contrasting light demands

Abstract

Phenotypic plasticity occurs when plants acclimatize to contrasting conditions. Herein, we test the hypothesis that seedlings of a light-demanding species have greater phenotypic plasticity compared to seedlings of a shade-tolerant species under high irradiance. Thus, we investigate the growth, anatomical, and leaf gas exchange responses of Citharexylum myrianthum, a light-demanding species, and Poecilanthe parviflora, a shade-tolerant species, under full light and 60% shading. Under full light, the seedlings of both species were shorter, showed lower photosynthetic rates and specific leaf area, and thicker palisade parenchyma. In the same conditions, C. myrianthum showed increased number of leaves, and P. parviflora reduced leaf area and increased number of stomata and allocation of phloem and cortical parenchyma. Lower photosynthetic rates may negatively affect biomass allocation and growth, although C. myrianthum seems to show a higher tolerance to irradiance since it produced more leaves. P. parviflora seems to optimize heat dissipation, reduce water loss, and improve the allocation of photoassimilate transport and storage, which could increase performance during establishment in field conditions. The plasticity index of both species was similar. Thus, generalizations about the species plasticity and ecological group to which they belong should be avoided. Species-related responses of growth, anatomical, and gas exchange parameters were found, indicating that generalizations about the performance of functional groups should also be avoided. These findings may contribute to the success of forest restoration projects.