title: Impacts of leaf age and heat stress duration on photosynthetic gas exchange and foliar nonstructural carbohydrates inCoffea arabica.
abstract: Given future climate predictions of increased temperature, and frequency and intensity of heat waves in the tropics, suitable habitat to grow ecologically, economically, and socially valuableCoffea arabicais severely threatened. We investigated how leaf age and heat stress duration impact recovery from heat stress inC. arabica. Treated plants were heated in a growth chamber at 49°C for 45 or 90 min. Physiological recovery was monitored in situ using gas exchange, chlorophyll fluorescence (the ratio of variable to maximum fluorescence,FV/FM), and leaf nonstructural carbohydrate (NSC) on mature and expanding leaves before and 2, 15, 25, and 50 days after treatment. Regardless of leaf age, the 90-min treatment resulted in greaterFV/FMreduction 2 days after treatment and slower recovery than the 45-min treatment. In both treatments, photosynthesis of expanding leaves recovered more slowly than in mature leaves. Stomatal conductance (gs) decreased in expanding leaves but did not change in mature leaves. These responses led to reduced intrinsic water-use efficiency with increasing heat stress duration in both age classes. Based on a leaf energy balance model, aftereffects of heat stress would be exacerbated by increases in leaf temperature at lowgsunder full sunlight whereC. arabicais often grown, but also under partial sunlight. Starch and total NSC content of the 45-min group significantly decreased 2 days after treatment and then accumulated 15 and 25 days after treatment coinciding with recovery of photosynthesis andFV/FM. In contrast, sucrose of the 90-min group accumulated at day 2 suggesting that phloem transport was inhibited. Both treatment group responses contrasted with control plant total NSC and starch, which declined with time associated with subsequent flower and fruit production. No treated plants produced flowers or fruits, suggesting that short duration heat stress can lead to crop failure.
authors.affiliation: Department of Forest Ecosystems and Society Oregon State University Corvallis OR USA.
authors.forename: Danielle E
authors.initials: DE
authors.lastname: Marias
authors.affiliation: USDA Forest Service Pacific Northwest Research Station Corvallis OR USA.
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Meinzer
authors.affiliation: Department of Forest Ecosystems and Society Oregon State University Corvallis OR USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Still
keywords: chlorophyll fluorescence; heat stress; nonstructural carbohydrates; photosynthesis; stomatal conductance