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 ÀT 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.

Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (F(V)/F(M)), rarely accounting for the recovery of effective quantum yield (ΔF/F(M')) after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species' thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species' thermal tolerance thresholds (T 50) are related to the ability to recover from short-term heat stress in 41 Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T 50 and recovery capacity were positively correlated, the relationship was weaker for species with high T 50 values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.

We introduce the AusTraits database - a compilation of measurements of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 375 traits across 29230 taxa from field campaigns, published literature, taxonomic monographs, and individual taxa descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological parameters (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual-, species- and genus-level observations coupled to, where available, contextual information on site properties. This data descriptor provides information on version 2.1.0 of AusTraits which contains data for 937243 trait-by-taxa combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data to increase our collective understanding of the Australian flora.

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.

Why this research is novel and significant: We provide novel, mechanistic insight into how localised variation in microclimate drives intracanopy variation in thermal tolerance, providing a new consideration for whole plant function and optimisation. AUTHOR CONTRIBUTIONS: AL and EMC generated hypotheses and designed the thermal tolerance work; EMC collected and analysed the data; CAK provided advice and contributed fundamental intellectual input; EMC led the writing, with AL revising the final text.