Discussion
We evaluated variation in heat tolerance of sun-exposed leaves among
tropical forest plants in Panama and show that irreversible damage to
leaves starts at temperatures about 10–15°C above current mean maximum
temperatures of the warmest month, but only a few degrees above the
highest leaf temperatures measured in the field (Doughty & Goulden
2008; Krause et al. 2010; Rey-Sánchez et al. 2016; Slot et al. 2016).
Heat tolerance of plants with C3 photosynthesis was
lower than that of the CAM species Agave americana andFurcraea cabuya , but had wide ranges nonetheless, with
TCrit being more variable than T50. As
hypothesized, interspecific variation in heat tolerance was underpinned
by differences in elevation and associated ambient temperatures across
sites, and related to differences in leaf functional traits associated
with thermoregulation and leaf construction costs within sites,
particularly among lowland species, while phylogeny played a smaller
role.