Ecotypic variation in leaf thermoregulation and heat tolerance but not
thermal safety margins in tropical trees
Abstract
To avoid reaching lethal temperatures during periods of heat stress,
plants may acclimate either their biochemical thermal tolerance, or leaf
morphological and physiological characteristics to reduce leaf
temperature (T leaf). While emerging evidence indicates
that plants from warmer environments have a greater capacity to regulate
T leaf, the extent of intraspecific variation and
contribution of provenance is relatively unexplored. We tested whether
upland and lowland provenances of four tropical tree species grown in a
common garden differed in their thermal safety margins by measuring leaf
thermal traits, midday leaf-to-air temperature differences (∆T
leaf), and critical leaf temperature defined by
chlorophyll fluorescence (T crit). Provenance variation
was highly species- and trait- specific. Higher ∆T leaf
and T crit were observed in the lowland provenance for
Terminalia microcarpa, and in the upland provenance for
Castanospermum australe, with no provenance differences observed
in the other two species. Within-species covariation of T
crit and ∆T leaf led to a convergence of
thermal safety margins across provenances. These findings suggest that
when grown under common conditions, lowland and upland provenances may
not differ substantially in their vulnerability (defined here as thermal
safety margin) to heat stress, despite differences in operating
temperatures and T crit.