Plastic Relationships between Reproductive and Vegetative Mass in Solidago Altissima.

To test several predictions of a model of linear, size-dependent reproductive output in plants, we analyzed the relationship between shoot vegetative (v) and reproductive (r) mass in five experiments on Solidago altissima from an invading population in Switzerland. There was large environmentally-induced and genetic variation in r and v. A large amount of variation in r could be explained by variation in v, using the simple linear model. There was a minimum size for sexual reproduction, and above this size, shoots devoted a relatively constant proportion (about one third) of their biomass to reproductive structures. We detected significant genetic variation for both the minimum size and the slope of the r-v relationship, but there was no evidence for an hypothesized trade-off between minimum size and slope. There was significant genotype-environment interaction for the slope of the r-v relationship. There were also developmental effects on the r-v relationship: plants grown from seeds behaved differently than those of the same genotype grown from rhizomes.