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.

O presente estudo avaliou o desempenho ecofisiológico das espécies Zea mays (milho), Sorghum bicolor (sorgo) e Brachiaria decumbens (braquiária) sob condições de déficit hídrico em casa de vegetação. O potencial hídrico foliar, trocas gasosas, fluorescência da clorofila a e variáveis bioquímicas do metabolismo fotossintético foram avaliados no máximo estresse e na reidratação. Aos 90 dias após a emergência e sob 21 dias com suspensão da irrigação o milho apresentou a maior redução do potencial hídrico (248%), condutância estomática (87%) e fotossíntese (53%) quando comparado às plantas bem hidratadas. O sorgo apresentou redução de 212%, 42% e 26%, enquanto a braquiária mostrou valores menores em 105%, 36% e 31%, respectivamente para os mesmos parâmetros. Entretanto, dois dias de reidratação foram o suficiente para todas as espécies recuperarem os valores apresentados pelos respectivos controles. A espécie que apresentou a menor queda relacionada aos parâmetros avaliados foi o sorgo, com redução em apenas 4 das 14 variáveis avaliadas, enquanto braquiária e milho reduziram 9 variáveis quando sob seca. O presente estudo destaca que, além da questão econômica, a tomada de decisão por parte de técnicos e pequenos agricultores de quais espécies devem ser utilizadas, sob baixa disponibilidade de tecnologia e alto risco de ocorrência de falta de água, deve-se levar em conta também o desempenho ecofisiológico.

The present study evaluated the ecophysiological performance of species Zea mays (maize), Sorghum bicolor (sorghum) and Brachiaria decumbens (Brachiaria) under water deficit conditions in a greenhouse. The leaf water potential, gas exchange, chlorophyll a fluorescence and biochemical variables of photosynthetic metabolism were assessed at maximum stress and rehydration. At 90 days after emergence and under 21 days under suspension of irrigation the maize showed the highest reduction of leaf water potential (248%), stomatal conductance (87%) and photosynthesis (53%) when compared to well watered plants. Sorghum decreased by 212%, 42% and 26%, while the brachiaria showed lower values in 105%, 36% and 31%, respectively for the same parameters. However, two days of water supply were enough for all species recover the values showed by the respective controls. The species with the smallest decrease related to the variables evaluated was sorghum, which reduced 4 among 14 variables evaluated, while brachiaria and maize decreased 9 variables when under drought. The present study highlights that beyond economics, decision making by small farmers and technicians, about which species should be used under low availability of technology and high risk of water shortages should take into account also the ecophysiological performance.