Kiwifruit plant physiological behavior to different levels of soil water depletion under semi-arid environmental conditions

Kiwifruit crop is known to be extremely sensitive to unbalanced soil water content, both excess and deficit, and irrigation is therefore a key factor to be properly managed. A field experiment was conducted in a commercial kiwifruit orchard (Actinidia chinensis var. chinensis ‘Zesy 002’) located in Metaponto (southern Italy) to evaluate the variation of vine water status, leaf transpiration and stomatal conductance under different water deficit levels, by increasing depletion of soil water content in the top soil layers (0-35 cm). Reduced soil water availability was achieved gradually, by imposing an irrigation treatment of water restriction (7 0 % of full crop requirements, ETc) for a limited period of the growing season (15 days), which was monitored by multi-profile soil moisture probes. Stem water potential (Ψ), leaf transpiration (E) and stomatal conductance (gsw) were evaluated during the water stress phase and the subsequent recovery phase (7 days) and compared to the control, in which irrigation supply was aimed at ensuring the soil water content in the volume of soil affected by irrigation remained between the field capacity (FC) and the lower readily available water (RAW) level. Leaf transpiration and gsw decreased during the water stress phase, reaching minimum values at midday approximately 60 and 7 0 % lower compared to control. Stem water potential became more negative due to the reduction in the soil water content, showing midday values of -14 bars at the end of the water stress phase. The prompt decline in E in response to Ψ lowering, occurring in the first days after the change in irrigation volumes, confirms a high sensitivity of kiwifruit vines to water deficit. During the recovery phase, a quick re-establishment of Ψ and a slow restoration of leaf activity and functionality were observed, making these parameters important indicators of the vine physiological status.