Germinação, emergência e crescimento de Ormosia arborea (Vell.) Harms (Fabaceae) sob alagamento

Abstract

Soil flooding restricts the availability of oxygen required for seed germination and plant growth; however, adaptive physiological, morphological, anatomical and / or metabolic adjustments involving phenotypic plastic responses of individuals are mechanisms that help occupy flooded areas and the wide range of strategies developed by plants to survive in these conditions depend not only on the species, but also on the intensity and duration of stress. Thus, this research aimed to evaluate the effect of different periods of flooding on the germination, emergence and growth of Ormosia arborea. For this, seeds scarified for 15 minutes in sulfuric acid or intact (without pre-germination treatment) were submerged for 0, 15, 30 and 45 days and, after each submersion time, the intact seeds were scarified by 0, 5, 10 and 15 minutes in sulfuric acid, to be seeded in tubes and Germitest® paper, to characterize emergence and germination, respectively. Seedlings were also flooded for different periods (0, 15, 30, 45 and 60 days) and at the end of each flooding period, they were drained for recovery evaluation 75 days after leaving the floodplain (post-flooding). It has been found that intact seeds are tolerant to submersion, but rapidly lose viability when integument dormancy is overcome. This response indicates that the waterproof and rigid integument of the seed is an important characteristic to tolerate adverse conditions and to prevent inviability. O. arborea seedlings survived under flooding, including post-flooding, with lenticel hypertrophy and changes in leaf angle, but during the longer flooding periods the seedlings reduced the quantum efficiency of PSII and gas exchange (except for the internal concentration of CO 2, which increased in this period). During post-flooding restoration the metabolism was resumed, however photosynthetic rates and carboxylilation efficiency were not fully recovered when submitted to prolonged flooding (60 days), neither recovery of stomatal conductance nor water use efficiency was observed at the level of control regardless of the flooding period. The leaf water potential and the leaf anatomy remained similar to the control seedlings, presenting only differences in the thickness of the central vein, vascular bundle, opening and index stomatal. These physiological and morpho-anatomical adjustments did not affect the growth of O. arborea, which did not stop accumulating dry mass during the experiment and invested in height post-flooding, demonstrating its phenotypic plasticity and indicating potential for survival and tolerance in temporarily flooded areas.