Beyond a single temperature threshold: applying a cumulative thermal stress framework to plant heat tolerance

Abstract

Most plant thermal tolerance studies focus on single critical thresholds, which are arbitrary and phenomenological, limiting the generality of findings across studies. In animals and microbes, thermal tolerance landscapes describe the more realistic, cumulative effects of temperature. We tested this in plants by measuring the decline in leaf photosynthetic efficiency (F/F) of two species following a combination of temperatures and exposure times. As predicted by the thermal tolerance landscape framework, we demonstrate that a general relationship between stressful temperatures and exposure durations can be effectively employed to quantify and compare heat tolerance within and across plant species and over time. We also show how F/F curves translate to natural conditions, suggesting that natural environmental temperatures often impair photosynthetic function. Our findings provide more robust descriptors of heat tolerance in plants, and suggest that heat tolerance in disparate groups of organisms can be studied with a single analytical framework.