Impact of Water Availability on Responses of Cucumis sativus Plants to a Short-Term Daily Temperature Drop

Impact of relative air humidity (RAH) and watering mode on responses of cucumber ( Cucumis sativus L.) plants to a daily short-term (2 h) temperature decrease to 10 o C (DROP treatment) was investigated. Plants were grown at comparably high (80%) or low (30%) RAH under conditions of normal watering or in the mode of artificially created “periodic drought.” It was found that RAH and watering mode exhibit strong quantitative and qualitative influence on plant responses to DROP treatment. Under high RAH, DROP treatment exhibits significant morphogenetic effect increasing plant biomass and compactness. Under the conditions of low RAH, effects of DROP treatment on plant compactness were leveled due to strong morphogenetic effect of the RAH itself and significant decrease in DROP-treated plant biomass under “drought”. Watering mode influenced on the effect of DROP treatment in a different manner depending on RAH. At high RAH, DROP treatment, together with “drought,” led to increase in plant compactness as well as their chilling tolerance. Besides, these plants became more tolerant to water stress induced by low temperature (4°C). At low RAH, no increase in compactness of DROP-treated plants was observed.