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Aim Understanding species ability to withstand heat stress is paramount for predicting their response to increasing temperatures and decreasing rainfall. Arid systems are subject to climatic extremes, where plants, being immobile, live on the frontline of climate change. Our aim was to investigate whether: (1) warming tolerance [WT = the difference between a species physiological thermal damage threshold (T-50) and the maximum temperature within its distribution (T-hab)] for desert plants is higher at high latitudes, as has been shown for terrestrial ectotherms, and (2) if T-50 of desert plants better corresponds with broad climatic indicators or species native microhabitats.

Location The Australian Arid Lands Botanic Garden, Port Augusta, South Australia.

Methods Using chlorophyll fluorescence techniques, we measured T-50 for 42 Australian arid plant species native to different microhabitats based on water availability. WT was calculated (T-50 - T-hab) and each metric was compared against microhabitat and broad-scale climatic variables for each species.

Results T-50 was unrelated to macro-scale climate or latitude, whereas WT increased for species whose distributions extend into higher latitudes, a pattern hitherto not shown for terrestrial plants. We also found that species adapted to higher water availability in their native microhabitat had significantly lower T-50 and WT than species from drier microhabitats.

Main conclusions (1) Warming tolerance increased with latitude, but the strength of this relationship was related to the way WT was quantified, with T-hab and latitude being linked. (2) T-50 did not correlate with latitude, but both T-50 and WT were strongly related to their microhabitats. Specifically, water availability is important, such that even within a desert biome, species associated with ’wetter’ microhabitats, may be particularly vulnerable to heat stress. Thus, we show that local-scale patterns better capture plant physiological responses to temperature than broad-scale distributions.