Influence of deficit irrigation and warming on plant water status during the late winter and spring in young olive trees

Changes in rainfall patterns and increases in ambient air temperature (i.e., warming) are expected with climate change. Yet, little information is available on how plant water status will respond to the combination of water deficit and increased air temperature in fruit tree species. The objective of this study was to evaluate the individual responses of deficit irrigation and warming and their combination on plant water status during the late winter and spring in young olive trees. Two temperature and two irrigation levels were applied in open top chambers during the late winter and spring of 2018 and 2019 to two- or three-year-old, potted trees (cv. Arbequina in 2018; Coratina in 2019). The temperature levels were a near-ambient control and a warming treatment that was 4 °C above the control, while the two irrigation levels were 100% and 50% of irrigation needs. Midday stem water potential (Ψs), stomatal conductance, net leaf photosynthesis, transpiration, and leaf temperature were measured periodically, and the difference between leaf and air temperature (ΔT) was calculated. The Ψs generally decreased due to irrigation deficit and warming when applied individually. When both treatments were combined, an additive response was observed. In contrast, stomatal conductance and net photosynthesis were consistently decreased by deficit irrigation, but were less affected by warming. Irrigation deficit did not affect leaf temperature under our experimental conditions. As was expected, warming most often increased leaf temperature, but it also significantly decreased ΔT early in the season when leaf transpiration appeared to be greater due to warming. The results indicate that modifications in water management with global warming will likely be required given the mostly negative individual or additive effects of irrigation deficit and air temperature on Ψs and other variables.