The effect of twig architecture and seed number on seed size variation in subtropical woody species.

This study aims to determine the effect of twig (current year shoot) size on seed size variation and to test whether a seed size vs number tradeoff occurs for the twigs of subtropical broad-leaved species. Fruit-bearing twigs were sampled for 55 woody species (including 33 evergreen and 22 deciduous dicot species) from a southwest Chinese forest. Twig size, fruit size and number, and seed size and number were measured for each species. The relationships among these functional traits were determined both across species and across correlated phyletic divergences. Total fruit mass and total seed mass were positively correlated with twig size. Seed size was positively associated with fruit size, which was, in turn, positively correlated with twig diameter, but negatively correlated with the ratio of twig length to diameter. The effect of twig size on seed size variation was not significant, possibly as a result of the large variation in seed number per fruit. Cross-species and across-phyletic divergence analyses revealed that seed size was negatively and isometrically correlated with seed number per twig mass in both the evergreen and deciduous species groupings, demonstrating the existence of tradeoff between seed size and number. A seed size vs number tradeoff is detectable in the twigs of woody species. Comparatively little of the variance in seed size was attributable to twig size variation.