Question: Do thick-twigged/large-leaf species have an advantage in leaf display over their counterparts, and what are the effects of leaf habit and leaf form on the leaf-stem relationship in plant twigs of temperature broadleaf woody species?
Location: Gongga Mountain, southwest China.
Methods: (1) We investigated stem cross-sectional area and stem mass, leaf area and leaf/lamina mass of plant twigs (terminal branches of current-year shoots) of 89 species belonging to 55 genera in 31 families. (2) Data were analyzed to determine leaf-stem scaling relationships using both the Model type II regression method and the phylogenetically independent comparative (PIC) method.
Results: (1) Significant, positive allometric relationships were found between twig cross-sectional area and total leaf area supported by the twig, and between the cross-sectional area and individual leaf area, suggesting that species with large leaves and thick twigs could support a disproportionately greater leaf area for a given twig cross-sectional area. (2) However, the scaling relationships between twig stem mass and total leaf area and between stem mass and total lamina mass were approximately isometric, which indicates that the efficiency of deploying leaf area and lamina mass was independent of leaf size and twig size. The results of PIC were consistent with these correlations. (3) The evergreen species were usually smaller in total leaf area for a given twig stem investment in terms of both cross-sectional area and stem mass, compared to deciduous species. Leaf mass per area (LMA) was negatively associated with the stem efficiency in deploying leaf area. (4) Compound leaf species could usually support a larger leaf area for a given twig stem mass and were usually larger in both leaf size and twig size than simple leaf species.
Conclusions: Generally, thick-twigged/large-leaf species do not have an advantage over their counterparts in deploying photosynthetic compartments for a given twig stem investment. Leaf habit and leaf form types can modify leaf-stem scaling relationships, possibly because of contrasting leaf properties. The leaf size-twig size spectrum is related to the LMA-leaf life span dimension of plant life history strategies.