Crescimento vegetativo em mudas de diferentes genótipos de açaizeiro (Euterpe oleracea Mart.) submetidos ao estresse hídrico.

Abstract

The açaizeiro (Euterpe oleracea Mart.) faces challenges associated with the expansion of plantations due to the demand for water demand. The present study analyzed the vegetative growth in young plants of different açaí genotypes subjected to water stress. Three genotypes (Anajás, BRS Pai D'égua and BRS Pará) were chosen to be analyzed under two water regimes (irrigated and non-irrigated) in a randomized block design with five replications. The biometric variables evaluated were: plant height, basal stem diameter, apical stem diameter, number of leaves, total leaf area, shoot dry mass and root dry mass; the physiological ones, separated into gas exchanges, were: water potential, net CO2 assimilation rate, stomatal conductance, transpiration, water use efficiency, ratio between internal CO2 and atmospheric CO2; and chlorophyll a fluorescence: maximum quantum yield of photosystem II (PSII), excitation energy capture efficiency of open PSII reaction centers, photochemical dissipation, non-photochemical dissipation, real quantum yield of PSII electron transport and rate apparent photochemical electron transport through PSII. Thus, the biometric variables showed that in situations of water deficit significant reductions of 56% and 50% in leaf area for BRS Pai d'égua and BRS Pará, respectively, as well as a 44% drop in shoot dry mass. for both genotypes. Regarding the physiological responses, they revealed that the three genotypes showed a reduction of up to 78% in photosynthesis, 92% in stomatal conductance and 92% in transpiration. However, only the cultivars BRS Pai d'égua and BRS Pará showed efficiency in water use with 47% and 65%, respectively. The anajás genotype showed lower efficiency in carbon fixation with a high rate of 74% in the ratio of internal CO2 and atmospheric CO2. BRS Pai d’égua and BRS Pará showed, in the same sequence, reductions in electron transport to PSII of 62% and 58%, and in photochemical transport through PSII of 63% and 57%. This suggests that they suffered some photoinhibitory effect, since the maximum quantum yield values of PSII, for the three genotypes, were below the threshold index of 0.75 quantum-1 electrons, consequently, causing a reduction in the photosynthetic processes of plants. With this, it is concluded that the vegetative growth in seedlings of young açaizeiro genotypes under moderate water stress, showed better morphological and physiological responses for the cultivars BRS Pai d'égua and BRS Pará. The plants reduced their growth in a mild way, as well as, their photosynthetic activity, but maintained a good photochemical efficiency.