Recuperação fisiológica e retomada do crescimento em plantas jovens de palma de óleo submetidas a eventos recorrentes de déficit hídrico e reidratação.

Abstract

Under field conditions, the plants are subject to recurrent periods of water deficit and rehydration due to the frequency and distribution of rainfall. Some plant species have the ability to adjust their metabolism when exposed to periods of recurrent water deficit, leading to a faster response to stress in order to mitigate the incidence of cell damage. This metabolic adjustment is understood as memory to stress, having not been explored to the satisfaction of palm oil (Elaeis guineensis Jacq.). Thus, this work aimed to evaluate the time course of physiological recovery and the resumption of growth in young oil palm plants submitted to recurrent water deficit and rehydration events. For this purpose, physiological variables (water status, gas exchange and chlorophyll fluorescence) and morphological variables (number of leaf and mature leaves, stem diameter and plant height) were evaluated in plants previously submitted to one (C1), two (C2) and three (C3) water deficit events. Plants irrigated throughout the experiment were used as a control treatment. The experiment was carried out in completely randomized blocks (five blocks), each block being formed by four plants (i.e., one plant from each treatment). The evaluations started on the same day for all treatments, when the irrigation of the stressed plants was resumed (day 0). The full recovery of leaf water potential occurred on the 3rd day after the resumption of irrigation for all stress treatments. The recovery of the net CO2 assimilation rate (A) occurred on the 6th day of rehydration for C2 and C3 plants and on the 9th day for C1 plants. A similar pattern of recovery of stomatal conductance and sweating was observed for all stress treatments. The maximum efficiency of photosystem II (Fv / Fm) did not differ between control, C2 and C3 plants, but was significantly lower in C1 plants. After the resumption of irrigation, the recovery of Fv / Fm in C1 plants was only observed on the 6th day. Plants C1, C2 and C3 showed significant reductions of the same magnitude in the efficiency of capture of excitation energy by the PSII open when compared to the control, however, this variable was fully recovered on the 3rd day of resumption of irrigation for treatments C2 and C3 and on the 9th day for treatment C1. The recovery of the real quantum yield of electron transport from photosystem II, the electron transport rate (ETR), the photochemical dissipation coefficient and the non-photochemical dissipation coefficient followed the same pattern observed for A. ETR averages / A on day 0 and on the first day of resumption of irrigation were higher in the plants of treatment C1 than in C2 and C3, however, there was full recovery of this variable for all treatments on the third day of resumption of irrigation. During the rehydration of the plants, the release of leaves and the increase in the diameter of the stem was more faster in C2 and C3 plants than in C1 plants. It is concluded that the physiological recovery and the resumption of growth is faster in oil palm plants submitted to two and three previous events of water deficit rehydration than in those that experience stress for the first time.