Impact of leaf removal on recovery of young grapevines under heatwave conditions: A study in an ecotron environment

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Abstract
One of the primary challenges of climate change faced by viticulture is the rising frequency of extreme weather events, including heatwaves. The aim of this study was to test apical leaf removal as a mitigation strategy during heatwaves based on the hypothesis that reducing total leaf area translates to lower transpirational water losses, thereby improving the water status of young grapevine plants under multiple stress conditions. Two-year-old Sauvignon blanc vines were subjected to progressive severe drought stress in combination with a heatwave (max air temperature 40 °C), which were simulated in a controlled environment. Key physiological parameters, such as pre-dawn water potential, stomatal conductance, Fv/Fm and net assimilation were measured before (acclimation), during and after (recovery) the heatwave. Drought stressed plants reached a maximum pre-dawn water potential of –1.4 MPa. Drought stress negatively affected all physiological parameters, especially stomatal conductance, which was reduced to almost zero for the duration of the stress. As a consequence, leaf temperatures during the heatwave reached up to 48.8 °C in drought stressed (WS) plants in contrast to well-watered (WW) plants, which reached a recorded maximum of 43.2 °C. Leaf removal had contrasting effects depending on water availability: in WW vines, it reduced cumulative transpiration by 15 %, whereas under drought stress, it had no impact due to near-complete stomatal closure. However, leaf removal positively influenced recovery, since WS leaf removal vines regained stomatal conductance values comparable to WW vines three days after rewatering. By the end of the 5-day recovery period, all physiological parameters in WS plants, whether leaf removal or control, returned to levels comparable to WW vines. Overall, this work proved that the success of apical leaf removal is highly dependent on water stress level. The practical relevance of this research lies in the necessity of finding ways to mitigate the effects of extreme weather events, especially in a context where irrigation water may be not available and with young vines that are characterised by a still undeveloped root system.

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