Provenance level differentiation in leaf and canopy temperatures
Temperatures of individual leaves recorded with handheld IR sensors ranged from 18.0 °C to 45.9 °C (Supporting information S6). When averaged to the plant level, mean Tleaf was 32.3 °C and ranged from 27.2 to 36.4 °C across all individuals. Mean ∆Tleaf was 4.1 °C and ranged from −0.7 to 8.1 °C (Figure 2a). For most plants mean ∆Tleaf was positive, except for H. novo-guineensis , which had multiple occurrences of Tleaf cooler than Tair (Figure 2b).
The mixed effects models found very strong evidence for provenance differences in ∆Tleaf for both T. microcarpa andC. australe . In T. microcarpa, ∆Tleaf was higher in the lowland provenance than the upland provenance (t (124) = 5.87, p < 0.0001), with a mean of 5.2 °C ± 1.17 and 3.4 °C ± 1.35, respectively (Figure 2b). The opposite was observed for C. australe , in which ∆Tleaf in the lowland provenance was lower than the upland provenance (t (121) = −3.79, p = 0.0002), with a mean of 4.8 °C ± 1.42 and 6.0 °C ± 1.68 respectively (Figure 2b). We found no evidence for provenance-differentiation in ∆Tleaf for M. elleryana or H. novo-guineensis (p > 0.05; Figure 2b).
For ∆Tcan, we found no evidence of provenance effects in any of the four species (Figure 2c).
Modelled leaf-to-air temperature differences (∆Tmod) represent the variation in potential leaf temperatures as resulting from the covariation between leaf width, leaf angle, and stomatal conductance. Across all individuals, mean Tmod was 29.1 °C and ranged from 27.1 to 31.0 °C. For T. microcarpa, we found moderate evidence for a provenance effect in ∆Tmod(t (10) = 2.39, p = 0.0381), with ∆Tmod higher in the lowland provenance than the upland provenance averaging 1.6 °C ± 0.69 and 0.6 °C ± 0.78 respectively. ForH. novo-guineensis , we found (only) weak evidence for provenance differences (t (10) = 1.81, p = 0.0996), with the lowland provenance also having a higher average ∆Tmod than the upland provenance, averaging 1.4 °C ± 1.0 and 0.3 °C ± 1.09 respectively. For the other two species, the data showed no evidence of provenance-differentiation in ∆Tmod.