Physiological responses of young oil palm (Elaeis guineensis Jacq.) plants to repetitive water deficit events

Stomatal and non-stomatal limitations to photosynthesis and acclimation of the photosynthetic machinery to repetitive water deficit (WD) events were investigated in oil palms (Elaeis guineensis Jacq.). For this, well-watered plants (control treatment) were compared with plants subjected to one, two, and three WD events imposed by withholding irrigation until their predawn leaf water potential (psi pd) reached around -2.5 MPa. Treatment comparisons were performed over 28 days. The psi pd decreased equally between WD treatments. Decreases in net CO2 assimilation rate (A) were similar between stressed plants until day 7. In the following days, the A was higher in plants thrice stressed than in those stressed once. Stomatal conductance decreased similarly between WD treatments, but mesophyll conductance to CO2 was lower in plants subjected to a single WD. Chloroplast CO2 concentration decreased similarly between plants subjected to one and three WD events until day 14, but it was lower in the former on subsequent days. Plants subjected to a single WD event showed lower Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) activity, maximum rate of electron transport (Jmax), and higher rates of photorespiration and dark respiration than other treatments. Plants subjected to one WD event also showed lower maximum quantum efficiency of photosystem II (PSII) photochemistry and PSII maximum efficiency concomitantly with higher malondialdehyde content. The results support that repetitive WD events induce the acclimation of the photosynthetic machinery in oil palm through adjustments in carboxylase Rubisco activity, Jmax, photorespiration, and respiration rates, as well as attenuating oxidative damages to PSII and membrane lipids.