Discussion
Provenance trials in tropical tree species are relatively rare, and as
such our understanding of how tropical forests acclimate or adapt to
environmental change is limited. Here we established and utilised a
provenance trial of tropical rainforest species in tropical Australia to
assess whether trees originating from the cooler upland provenances and
warmer lowlands differed in their leaf thermoregulatory traits, thermal
tolerance, and as a result operate with different thermal safety
margins.
With contrasting patterns of provenance-differentiation observed across
the four species tested, we found only partial support for our first
hypothesis that the lowland provenances have cooler leaf temperatures
than upland provenances when grown in a common garden (H1). Despite
this, we did find that variation of leaf thermal traits and plant height
was consistent with variation in Tleaf, supporting our
second hypothesis (H2). Finally, although we found limited
within-species association between Tleaf and
TÂcrit, these variables covary in such a way that
thermal safety margins did not significantly differ between provenances
supporting our third hypothesis (H3). Together, these results suggest
that despite variation in either Tcrit or observed
Tleaf, there was no provenance-level difference in
vulnerability to thermal stress as defined by the thermal safety margin.