Abstract:

Aims Trade-offs are fundamental to life-history strategies theory, and the leaf size and number trade-off is an important determinant of leaf-size evolution. It also has been proposed that this trade-off is dependent on habitat, but this is not well tested. Our objectives were to test whether the negative, isometric relationship between leaf size and number is conserved in different habitats and to explore the effects of altitude change on the relationship between the leaf size and number.
Methods Leaf area, mass and number and twig mass and stem mass of current-year twigs were measured for 61 deciduous broad-leaved woody species within three altitude-based habitats on Qingliang Mountain, southeastern China. The standardized major axis estimation method and the phylogenetically independent contrast method were used to examine the scaling relationship between leaf size (leaf mass and leaf area) and leafing intensity (twig mass and stem mass) within current-year twigs.
Important findings Significantly negative and isometric scaling relationships between leaf size and leafing intensity were found to be consistent in all three altitude-based habitats, regardless of whether leaf/twig size was expressed as area or mass. However, the intercepts of these relationships significantly decreased with increasing altitude, suggesting that habitats constrain the leaf size that can be supported by a given leafing intensity. The middle-attitude species usually had significant upper shifts along the common slopes relative to the high-altitude species. This suggested that the middle altitude is a more suitable habitat with high nutrients and moderate climate conditions for plants, compared to the high altitude with low temperatures and nutrients.

Key words: habitat, leaf size, lea?ng intensity, trade-off