Trocas gasosas e indicadores de estresse em plantas jovens de pau-debalsa [Ochroma pyramidale (Cav. ex Lamb.) Urban] e jatobá (Hymenaea courbaril L.) submetidos a dois ambientes de luz

Abstract

The main threat of tropical ecosystems’ diversity is the destruction of forest and the loss of habitats which turns the area susceptible to ecological degradation, causing damage to the flora and fauna. Among the strategies to restore the degraded ecosystems and facilitate the ecological succession is the planting of seedlings of pioneer and non-pioneer species randomly in rows or in densified groups, which makes important the study of ecophysiology for the monitoring of physiological responses of seedlings in the environment, in which the luminous intensity and air temperature affect the photosynthetic activity. The aim of this study was to analyze the ecophysiological behavior of pau-de-balsa [Ochroma pyramidale (Cav. ex Lamb.) Urban] and jatobá seedlings (Hymenaea courbaril L.) submitted to treatment in high and low irradiance environments at the National Institute of Amazonian Research (INPA), Campus V-8, Manaus. Pau-de-balsa and jatobá seeds were ceded by the Brazilian Agricultural Research Corporation – Embrapa/AM and the Experimental Farm of UFAM and put to germinate at INPA. The seedlings were put to acclimatize in nursery for three months and the first measurement was performed in this environment, then, thirty seedlings of each species were separated into two environments: at full sunlight (high irradiance) and in shadow of other trees (low irradiance). The photosynthetic performance was analyzed using the Infrared Gas Analyzer (IRGA) by the variables of maximum photosynthesis (A), stomatal conductance (gs), quantum yield (α), compensation irradiance (Ic), saturation irradiance (Is) and respiration dark (Rd); and the luminous stress was analyzed by fluorescence emission of chlorophyll a, which was measured by the yield of photosystem II (Fv / Fm) and by the amount of photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids). For data analysis, the means were submitted to the Shapiro-Wilk normality test and the Kruskal-Wallis analysis of variance, with a significance level of 5%. The results obtained demonstrate that pau-de-balsa obtained better photosynthetic performance when acclimatized at full sunlight, meanwhile, jatobá showed no difference in the photosynthetic rate between treatments of high and low irradiance, on the other hand, seedlings acclimatized at full sunlight obtained greater luminous stress when compared to the treatment of acclimatization to shaded environment.