Oil yield components and biomass production responses to warming during the oil accumulation phase in young olive trees

Abstract

Global warming and olive expansion to new regions have increased interest in understanding how air temperature affects olive production. Thus, the objective of this study was to evaluate the responses of oil yield components, total biomass production, and its partitioning to a moderate temperature increase (3–4 °C) during the oil accumulation phase in young olive trees of two olive cultivars (cvs. Arbequina, Coratina). Young, potted olive trees were actively heated by 3–4 °C in open top chambers under outdoor conditions compared to near-ambient temperature in similar control chambers. The trees were warmed from final fruit set to the end of the oil accumulation phase (5 months) in one (2014–15 or 2015–16) or in two consecutive seasons. Oil yield and its components were obtained from fruit harvested at the end of the season, while the vegetative dry biomass produced was estimated from destructive harvests of entire trees before and after a warming period. Glucose equivalents (GE) were also calculated for both oil yield and vegetative growth. Warming during the oil accumulation phase in one season led to some significant temperature x cultivar interactions for oil components. Individual fruit dry weight was reduced by warming to a greater extent in cv. Coratina than in cv. Arbequina, while fruit oil concentration was decreased more in cv. Arbequina. Significant decreases in oil yield were also observed for both cultivars. Warmed trees had a greater net leaf area increase than control trees when heated during the oil accumulation phase for one season (2014–15 or 2015–16), and allocated more GE to vegetative organs than to fruit in 2015–16. However, total tree biomass was not affected by warming. Warming trees the first season led to reduced flowering the following spring, and directly contributed to a temperature x cultivar interaction for fruit number during the second warming period with a 66% reduction in fruit number in warmed trees of cv. Arbequina and very low fruit number in all cv. Coratina trees. In contrast to warming during one season, total tree biomass GE decreased across cultivars when warming was performed in the oil accumulation phase for two consecutive seasons. The results suggest that cultivars should be carefully selected for new, warmer growing regions and that global warming may ultimately reduce oil yields and affect cultivar selection.