No drought memory in cotton despite evidence of drought acclimation

Plants are likely to experience multiple cycles of drought. However, physiological acclimation and stress memory may play key roles in reducing the detrimental effects of successive droughts. We investigated drought acclimation in cotton (Gossypium hirsutum) fertilized with low or high nitrogen (N) in a greenhouse factorial experiment. The cotton plants were subjected to one of four drought treatments applied during two 15-day periods, where plants were withheld water or were fully watered. We assessed CO₂ assimilation (A₄₀₀) and stomatal conductance (g_s400), maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO) carboxylation (V_cmax), maximum rates of electron transport for RuBP regeneration (J_max), and biomass at the time of harvest. Droughted and well-watered plants had similar rates of A₄₀₀, g_s400, V_cmax, and J_max during the first drought under low N. High N plants were larger in size than low N plants, which suggests that the additional N likely increased the severity of the drought, causing stomatal closure and a decline in photosynthesis. However, there were increases in both V_cmax and J_max for high N plants during the first drought. There was no evidence of drought memory, and plants exposed to both droughts responded similarly to plants exposed to only the second drought. Overall, our results indicate that cotton can acclimate under drought, and additional fertilization may result in severe drought stress.