Heat waves and drought stress impact grapevine growth and physiology

Abstract

Context and purpose of the study – Recurring heat and drought episodes during the growing season can produce adverse impacts on grape production in many wine regions around the world. Although the effect of these factors on plant physiology and growth has been investigated separately, little is yet known about their interactions and the variability of these effects among genotypes and phenological stages. The main aim of this study was to evaluate the response of two grape varieties to heat and drought stress and subsequent recovery at different phenological stages.

Material and methods ‐ Pot‐grown Cabernet Sauvignon and Riesling plants were moved to environmentally‐controlled growth chambers at bloom, pre‐veraison and veraison in 2018. For each phenological stage, a different group of plants were used to avoid cumulative treatment effects. After 7 days of acclimation in the growth chambers, different treatments were imposed: control (no stress), water stress, heat stress (10°C above control), and combined water and heat stress. Growth, gas exchange, leaf water potential, photosystem electron transport and energy dissipation were measured in both young and mature leaves of 6 plants per treatment before the stress episode, during 7 days of stress, and through 7 days of recovery.

Results ‐ At bloom, water stress decreased transpiration, stomatal conductance and photosynthesis in both varieties. Combined stress decreased gas exchange only in Riesling. During pre‐veraison, heat stress reduced leaf water potential, gas exchange and chlorophyll fluorescence, both in young and mature leaves. Combined stress drastically decreased most of the parameters compared to control plants. This decline was higher in Riesling than in Cabernet Sauvignon. During veraison, drought was the dominant factor that affected most parameters. Additionally, heat stress exacerbated the drought stress effect on the physiological parameters. During the recovery periods, no significant differences were found among treatments in any parameter, indicating that both varieties were able to recover fully from the imposed stresses. Water stress and combined stress decreased shoot length, number of main leaves, lateral leaves and total leaf area in both varieties.