As climate change fuels more frequent heatwaves and cold spells, a plant's ability to tolerate temperature extremes is vital for its survival. Currently, scientists often assess this tolerance by measuring the chlorophyll fluorescence parameter Fv/Fm in darkness. But in reality, high temperatures often accompany strong light, while low temperatures coexist with weak light.
In a study published in Plant, Cell & Environment, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) and their collaborators showed that light intensity significantly influenced how well plants can withstand extreme temperatures, challenging current assessment methods conducted in darkness. This finding has crucial implications for understanding plant resilience under climate change.
The researchers tested the photosynthetic heat tolerance of 20 naturally grown tree species in XTBG. They measured the thermal tolerance of Photosystem II (PSII) under heat stress at different light intensities and cold tolerance under low light during cold stress.
They found that the effects of weak light (300 μmol·m⁻²·s⁻¹) on heat tolerance were species-specific. The strong light (1000 μmol·m⁻²·s⁻¹) significantly reduced heat tolerance in all tested species (except for a non-significant change in Psidium guajava).
Moreover, the critical temperature threshold for heat damage decreased by 1.96°C to 13.96°C under strong light. The temperature causing 50% damage decreased by 0.920C to 5.260C under strong light. Weak light (200 μmol·m⁻²·s⁻¹) significantly reduced the cold tolerance of all 10 tested species.
Species with higher maximum photosynthetic (Amax) and transpiration (Emax) rates showed greater resistance to light-induced damage during heat stress. Thicker leaves helped mitigate the reduction in heat tolerance caused by strong light and provided physical protection against light during cold stress.
According to the study, while measurements taken in darkness be used to compare differences between different species, they overestimate a plant's true temperature tolerance capacity in natural environments, where light is always present.
“This means assessments of plant thermal safety margins based solely on dark-adapted measurements may be inaccurate. Our results provide insights to how we should evaluate plant vulnerability to climate extremes. Future models predicting plant survival under heatwaves or cold snaps must account for the concurrent light conditions,” said LIN Hua of XTBG.
First published: 15 June 2025
