Limitações estomáticas e não estomáticas da fotossíntese em plantas de palma de óleo submetidas ao déficit hídrico

Abstract

From palm oil is extracted an oil which is applied in the food, pharmaceutical, cosmetic and energy industries. This palm tree has considerable sensitivity to water deficit, and exhibits reduced net CO2 assimilation rates (A) under drought. Thus, the aim of this research was to evaluate how A in young plants of oil palm can be negatively regulated by stomatal and non-stomatal limitations during the progress of water deficit. For this, oil palm plants were distributed in two treatments namely: Control, in which the plants were kept fully irrigated; and Water Deficit, whose irrigation was suspended for progressive stress induction. Each treatment was composed by five replicates distributed in a completely randomized design. The evaluations were performed at the time of differentiation of treatments (day 0) and after seven (day 7) and 21 days (day 21) of the differentiation of treatments, characterizing different severities of water deficit. Leaf water potential was reduced from -0.13 MPa to -1.56 MPa on day 7th and to -2.55 MPa on the 21st day. Under moderate water deficit, leaf water potential equal to -1.56 MPa, A was reduced by 85%, while chloroplastidic CO2 concentration decreased by 70% and mesophyll conductance by 84% Under severe water deficit, leaf water potential equal to -2.44 Mpa, A decreased by 117%, while maximum carboxylation velocity and carboxilation efficiency reduced by 120 and 114%, respectively, and photorespiration increased by 44%; in addition, potential activity of photosystem II decreased by 45%. Thus, it can be inferred that under moderate water deficit the downregulation of photosynthesis is due to stomatal or diffusive limitations, while under severe water deficit, the downregulation of photosynthesis is originated by non-stomatal limitations.