Within-species leaf size–number trade-offs in herbaceous angiosperms

Abstract

Leafing intensity—number of leaves produced per unit of supporting (nonleaf, aboveground) dry mass—determines the size of a plant’s “bud bank”, i.e., the number of axillary meristems per unit plant body or shoot size. This in turn determines the plant’s capacity for flexible and economic meristem deployment strategies as vegetative or reproductive structures. From recent research, it is now widely established that leafing intensity has a strong and isometrically negative relationship with individual leaf mass at the between-species level for both woody and herbaceous species. In the present study of 24 natural populations of herbaceous angiosperms, we show that these two traits also have a general trade-off relationship at the between-plant level within a species. Smaller resident reproductive (i.e., mature) plants generally produced smaller leaves, and plants with smaller leaves generally had higher leafing intensity, in most cases involving an isometric trade-off. For several species, however, the trade-off was allometric—i.e., plants with smaller leaves, which also had generally smaller body sizes, had generally greater than proportionally higher leafing intensity. This parallels results of an earlier study at the between-species level suggesting that, when plant body size is relatively small, there may be a premium—in terms of maximizing fitness—on relatively high leafing intensity. The latter, it is proposed, may function in maximizing the capacity for “reproductive economy”, i.e., successful reproduction despite intense size suppression owing to competition.