Changes in phenotypic variability of two tropical woody species due to short and long-term exposure to different irradiances

ABSTRACT Studies addressing the physiological and anatomical responses of plants under different light intensities normally are performed in short term. Thus, the present study includes a long term analysis. This study aims to verify whether the phenotypic variability off attributes in two woody tropical specieis, Paquira aquatica and Sterculia foetida, are compatible both under short term exposure to different light availability levels (full-light and half-light local irradiance) and long-term exposure in the same conditions. The study was developed in two phases: phase I (short term) and phase II (long term). The variables measured were referent to CO2 assimilation responses to light intensity, chlorophyll a fluorescence, chlorophyll content, morpho-anatomical attributes and phenotypic variability. In phase I, P. aquatica had differences between treatments in Amax (maximum net photosynthesis) and LCP (light compensation point), without differences in these attributes in phase II. S. foetida plants had differences only in phase I in Amax. In anatomical attributes, P. aquatica had a higher palisade and spongy parenchyma and mesophyll thickness compared to S. foetida plants, without differences between light treatments. In S. foetida, the aforementioned cell layers were thicker in full-light treatment. Both species showed a higher phenotypic variability in the same physiological attributes in phase I and similar attributes for mesophyll thickness of the abaxial epidermis in phase II. The species showed different anatomical and physiological strategies, however with plastic responses in similar attributes, only observable after a longer period of exposure. The results indicated the importance of lengthy exposure to light, mainly in tropical species, wich are naturally exposed to elevated irradiance levels for an extended period of time in the field.