Results
T50 of the tropical forest species averaged 50.0 ± 1.5
°C (mean ± SD) and ranged from 45.8°C in Hedyosmum bonplandianum ,
a montane forest tree, to 53.7°C in Rhizophora mangle , the
pan-tropical red mangrove (Table S2), with 90% of observations falling
between 47.8 and 52.5°C. Even higher values were found in non-forest CAM
plants, with T50 of 55°C in Agave americana .
Within ecosystems there was also a considerable range in
T50 values: among the 117 lowland species, values ranged
from 47.7°C in Luehea speciosa to 53.5°C in Cecropia
longipes . TCrit likewise varied considerably, from
42.0°C in H. bonplandianum to 50.9°C in the palm Dypsis
lutescens , with an average of 46.7 ± 2.0°C and 90% of observations
falling between 43.5 a 49.7°C. Values of T50 were more
narrowly distributed around the overall mean than TCritvalues (Fig. S3). T50 and TCrit were
highly correlated (F1,150=231.2,p <0.001, r2=0.61).
T50 was on average 3.2°C higher than
TCrit. Fv/Fm declined
more steeply around T50 in species in which the decline
started at a higher temperature, i.e., the distance between
TCrit and T50 decreased as
TCrit increased. This was indicated by a decrease in the
b parameter—b becoming more negative—with increasing
TCrit (F1,150=62.2,p <0.001, r2=0.29).