Leaf age and methodology impact assessments of thermotolerance of Coffea arabica

Abstract

Mature Coffea arabica leaves were more heat tolerant than expanding leaves, longer recovery time yielded more accurate thermotolerance assessments, and photochemistry was more heat sensitive than cell membranes. Given future climate predictions of increased heatwaves in the tropics, suitable habitat to grow ecologically, economically, and socially valuable Coffea arabica L. is threatened. Accurate assessments of high temperature tolerance or thermotolerance are critical for understanding C. arabica responses to increased temperature. Thermotolerance curves of C. arabica leaf discs were constructed by measuring chlorophyll fluorescence (ratio of variable to maximum fluorescence, F V/F M; minimum fluorescence, F O) across three leaf age classes and two recovery times (15 min, 24 h) after 15 min exposure to temperatures from 25 to 58 °C. Thermotolerance measured with electrolyte leakage after 20 min at 25–65 °C was compared with F V/F M thermotolerance curves. The temperature corresponding to 50 % damage (T 50) was 49.0 and 58.6 °C for the chlorophyll fluorescence and electrolyte leakage methods, respectively. The critical temperature at which the F O rise began on F O-temperature curves (T crit) was 46.0 °C. We found that the 24 h recovery time yielded more accurate estimates of T 50, and that thermotolerance based on T crit increased with leaf age. Differences between the fluorescence and electrolyte leakage methods showed that photosystem II processes were more sensitive to temperatures above 40 °C than cell membrane stability.