Scaling relationships between leaf petiole and lamina size of two Photinia species

Exploring the morphometric scaling relationships between lamina and petiole functional traits is important to our understanding of foliage and plant ecosystem dynamics. For this purpose, we examined the leaves of two evergreen species, i.e. Photinia x fraseri "Red Robin", which has relatively small leaves, and Photinia serratifolia, which has relatively larger leaves. Approximately > 320 leaves from each species were collected monthly from April to August during the growing season, and the t-test was used to determine the significance of interspecific differences in lamina and petiole traits. Reduced major axis regression protocols were used to fit the scaling relationships of petiole fresh mass (PFM) vs. lamina fresh mass (LFM), PFM vs. lamina area (A), petiole dry mass (PDM) vs. lamina dry mass (LDM), and PDM vs. A. The increase in PDM was positively correlated with increasing LDM. However, there was a temporal variation in PDM/LDM. Both PDM/LDM and PFM/LFM for P. serratifolia were significantly higher than those of P. x fraseri. There was a strong positive correlation between petiole size (as measured by PFM and PDM) and lamina size (as measured by LFM, LDM and A). These relationships reveal statistically robust scaling relationships between petiole size and lamina size for each of the two species, and provide additional support for the hypothesis called "diminishing returns", i.e. a disproportionate increase in one leaf trait (e.g. LDM) with respect to increasing another leaf trait (e.g. PDM).