Conclusion
The present study quantified the photosynthetic thermal tolerance of
seven dominant evergreen trees from the hottest and most rapidly warming
forest site in the Amazonia. The key findings of this study are firstly,
that evergreen trees from the site exhibit a high level of PSII
thermotolerance. Although variations in thermotolerance was observed
between species, this was largely caused by data from one mid-storey
species, which showed exceptionally high thermotolerance (the highest
recorded in the tropics). A significant but weak seasonal acclimation ofT50 was observed that is consistent with the
literature (Sastry & Barua, 2017; Zhu et al., 2018). AlthoughT50 values were much higher than the absolute
maximum air temperature of the region, there is some evidence of
incipient loss of PSII function even under current conditions. Daily
maximum air temperatures during the dry periods at our study site in
recent years has reached levels that overlap with the range ofT5 measured in our study. The trees in the
hottest Amazonian forest site are therefore already sensitive and
experiencing temperatures close to the thresholds of their
high-temperature sensitivity.