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Leaf heat tolerance of 147 tropical forest species varies with elevation and leaf functional traits, but not with phylogeny
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  • Martijn Slot,
  • Daniela Cala,
  • Jorge Aranda,
  • Aurelio Virgo,
  • Sean Michaletz,
  • Klaus Winter
Martijn Slot
Smithsonian Tropical Research Institute
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Daniela Cala
Smithsonian Tropical Research Institute
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Jorge Aranda
Smithsonian Tropical Research Institute
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Aurelio Virgo
Smithsonian Tropical Research Institute
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Sean Michaletz
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Klaus Winter
Smithsonian Tropical Research Institute
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Abstract

Exceeding thermal thresholds causes irreversible damage and ultimately loss of leaves. The lowland tropics are among the warmest forested biomes, but little is known about heat tolerance of tropical forest species. We surveyed leaf heat tolerance of sun-exposed leaves from 147 tropical lowland and pre-montane forest species by determining the temperatures at which potential photosystem II efficiency based on chlorophyll a fluorescence started to decrease (TCrit) and had decreased by 50% (T50). TCrit averaged 46.7°C (5th–95th percentile: 43.5–49.7°C) and T50 averaged 49.9°C (47.8–52.5°C). Heat tolerance partially adjusted to site temperature; TCrit and T50 decreased with elevation by 0.40°C and 0.26°C per 100m, respectively, while mean annual temperature decreased by 0.63°C per 100m. The phylogenetic signal in heat tolerance was weak, suggesting that heat tolerance is more strongly controlled by environment than by evolutionary legacies. TCrit increased with the estimated thermal time constant of the leaves, indicating that species with thermally buffered leaves maintain higher heat tolerance. Among lowland species, T50 increased with leaf mass per area, so species with structurally more costly leaves reduce the risk of leaf loss during hot spells. These results provide insight in interspecific variation in heat tolerance at local and regional scales.