Heatwave Effects on Irrigated Mediterranean Orchards

Extreme heat waves are expected to intensify in Israel, posing challenges for agricultural crops. Even in irrigated orchards, these events can damage plant function to the extent of impacting yield and hydraulic efficiency in the following seasons. In order to reveal how trees respond to periods of extreme evaporative demand, we measure water fluxes in the soil-plant-atmosphere continuum in two fruit species, Navel orange and Shelly mango. By monitoring sap flux and stem water content in a high temporal resolution, we first pair the measurable water stress on the plant with its causing climate event and establish causal relationship between the outer and inner dynamics of the continuum. We found that both species rely heavily on their internal stem water storage to sustain transpiration, showing significant nighttime sap flow during and following heat waves to replenish this source. It can take several weeks of regular irrigation to relieve the detrimental effects of hydraulic overdraft, as measured by stem water content. We quantify the resilience of each species to heat waves before and after irrigation onset. While the orange resilience increases after irrigation, that of the mango deteriorates over time due to cumulative damage. Finally, we show how a judicious irrigation scheme, devised with the help of a tree-level hydrodynamic model (FETCH3), can significantly alleviate the impacts of heat waves, compared to traditional irrigation scheduling.