Backgrounds — Chemical characteristics of acorns, seeds of oaks, have substantial influences on seed fates. Interestingly, they are highly diverse even among congeneric species. To understand why chemical traits of acorns differ so largely, it is insufficient to examine the effects of each chemical constituent solely on seed survival. It is also necessary to examine the presence of trade-offs among chemical constituents. To do this, we investigated seed chemical characteristics in ten oak species distributed in Japan.

Methods — Six species from subgenus Lepidobalanus and four species from subgenus Cyclobalanopsis were sampled. Chemical constituents measured are crude protein, NSC (nonstructural carbohydrates), total phenolics, condensed tannins, and PPA (protein precipitating ability of tannins). Five seeds from each of five sample trees for a species were analyzed individually (total 25 seeds).

Findings — 1) Cyclobalanopsis assayed higher in condensed tannins than Lepidobalanus. 2) The cluster analysis revealed that each species of Cyclobalanopsis formed the independent cluster, but those of Lepidobalanus did not. 3) Significant trade-offs between NSC and total phenolics or PPA were observed in six species. It indicates that the antagonistic relationship between growth and defense may exist in these species.