Responses of an early and a late successional species of Polygonum to variations in resource availability.

The behavior of Polygonum pensylvanicum L., an early successional annual, and Polygonum virginianum L., a later successional perennial were compared on singlefactor gradients of light, nutrients and soil moisture and on a double-factor gradient of light and nutrients. The two species were grown together as well as alone. In most cases, the early successional species was more productive and allocated less of its biomass to belowground parts relative to its later successional congener. The early successional species was also more opportunistic in its utilization of resources as evidenced by its greater responsiveness to varying resource availability. The role of perenniality in the later successional species may be dual. Individuals of P. virginianum started from seed were more responsive to deficiencies in resources than were individuals started from rootstocks in these experiments. In the single-factor experiments where plants were started from seed, there were numerous significant interactions between levels of light, nutrients or moisture with competition in both species. In the double-factor experiment, however, there were no statistically significant interactions between light, nutrients and competition in the perennial started from rootstocks, but all possible interactions were significant in the early successional annual. The result of a large, underground reserve in the perennial was that the effects of resource availabilities of light and nutrients were uncoupled. The competitive superiority of the early successional species over the later successional species was greatly diminished when the later successional species was started from rootstocks instead of from seeds. Regardless of whether individuals of P. virginianum were started from seed or from rootstocks the results of competition between the two species indicate that the early successional species is competitively more competent when resources are abundant and that the later successional species is competitively more competent when resources are scarce.