Juvenile leaves of Rhus glabra have higher photosynthetic thermal tolerance than mature leaves

We have previously shown that juvenile leaves of Rhus glabra L. growing in a field setting were consistently 2–3 °C warmer than mature leaves during periods of high irradiance. An experiment was done to test the hypothesis that these differences in leaf temperature lead to increased photosynthetic temperature tolerance in juvenile leaves when compared with cooler, mature leaves. Significant differences were found between the leaf stages with detached juvenile leaves having a slightly higher T15 (the temperature causing a 15% drop in maximum photochemical efficiency) than mature leaves (43.5 vs. 41.1 °C). Additionally, measurement of the effect of temperature on actual quantum yield (ΦPSII) showed maximum activity at 35 °C for mature leaves, whereas juvenile leaves exhibited a broader temperature response with similar activities between 30 and 40 °C. The 2 °C difference in T15 roughly coincided with observed average differences between juvenile and mature leaf temperature we observed in the field, indicati...