Mycorrhizal symbiosis benefited yield and fruit quality in Cabernet Sauvignon facing high temperatures combined with elevated CO2 in its first productive year

Abstract Aims Our objective was to assess whether mycorrhization could enhance the resilience of young Cabernet Sauvignon in its first year of production to elevated temperatures under current and future atmospheric CO 2 scenarios. Methods Two-year-old Cabernet Sauvignon grafted plants and divided into non-mycorrhizal and mycorrhizal, were subjected to four environments from fruit set to maturity: (1) ambient CO 2 and temperature; (2) ambient CO 2 and elevated temperature (ambient temperature + 4˚C); (3) elevated CO 2 (700 ppm CO 2 ) and ambient temperature; and (4) elevated CO 2 and temperature. Mycorrhizal fungi were co-inoculated with bacteria. Gas exchange, minerals and organic solutes in leaves were measured two weeks after fruit veraison. At maturity, yield and fruit quality were assessed. Results Mean maximum temperatures under ambient and elevated temperature were 32.4 and 36.6 °C, respectively. Photosynthesis increased under elevated compared to ambient CO 2 and temperature, especially in non-mycorrhizal plants. Cu, Zn and Fe decreased under elevated CO 2 and temperature in non-mycorrhizal plants. In mycorrhizal plants, Mn was higher under elevated CO 2 and temperature, and Cu and Fe were similar under elevated and ambient CO 2 and temperature. Yield, sugars and anthocyanins decreased in berries of non-mycorrhizal plants under elevated CO 2 and temperature, with an increase in antioxidant activity. Mycorrhization benefited yield and fruit quality under elevated temperature, especially when combined with elevated CO 2 . Conclusion Co-inoculation of mycorrhizal fungi and bacteria increased Cabernet Sauvignon thermoresistance by maintaining micronutrient levels under heat stress at levels similar to those at moderate temperatures, resulting in higher fruit yield and quality.