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

Most plant thermal tolerance studies focus on single critical thresholds,
which limit the capacity to generalise across studies and predict heat
stress under natural conditions. 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 (FV/FM) following a combination of temperatures
and exposure times, then modelled these physiological indices alongside
recorded environmental temperatures. 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. Importantly, we show how FV/FM curves
translate to plants under natural conditions, suggesting that
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 predictive framework.