Potassium Supplementation Promotes Osmotic Adjustment and Increases Water Use Efficiency in Sugarcane Under Water Deficit

Sugarcane (Saccharum spp.hybrids) yield and sustainability are constantly challenged by water deficit. High water use efficiency (WUE) and osmotic adjustment (OA) are considered strategies to drought tolerance, and potassium (K+) may be an inducer of these mechanisms. Thus, we tested the hypothesis if accumulation of K+ in leaves attenuates the effects of water deficit in sugarcane plants. The soil [K+] was increased allowing K+ accumulation in sugarcane leaves before exposing the plants to water deficit. The effect of [K+] on OA capacity, WUE, gas exchange and biomass accumulation was evaluated. Sugarcane plants (variety RB928064) were grown in pots in the greenhouse. The study design was randomized block with a 2 x 2 factorial scheme, regarding two [K+] (one recommended dose [131.4 mg KCl dm(-3)] and one twice recommended dose [262.8 mg KCl dm(-3)]) and two water conditions (well irrigated and water deficit), with n = 5. The analyses were done during the water deficit and rehydration periods. Pressure-volume (PV) curves were also performed to estimate the osmotic potentials at full (psi s(100)) and null (psi s(0)) turgor, OA, and the modulus of cell wall elasticity (epsilon). The plants with extra K+ maintained higher RWC and WUE, associated with lower psi s(100) and psi s(0), favoring higher OA and epsilon under drought. These combined traits allowed the maintenance of cell turgor and, may be associated with better resistance to water deficit in sugarcane plants, as observed by the greater biomass accumulation in plants containing higher leaf [K+].