Water stress interacts with early arrival to influence interspecific and intraspecific priority competition: A test using a greenhouse study

Abstract

Questions: Do species arriving early (priority effect) to a site have a competitive advantage over species arriving later? Does early arrival aid in species ability to tolerate water stress? Is intra- and interspecific competition different for early and late arrivers? Location: Greenhouse, University of Northern Colorado, Greeley, Colorado, USA. Methods: A 1-mo 'head start' in the greenhouse was used to simulate early arrival of Panicum capillare and Polygonum persicaria. We used a completely randomized design to examine the effects of water stress (drained, drought, flood) and priority competition (interspecific and intraspecific) in relation to species' cohort [older (established) and younger (novel) individuals planted in different combinations]. We calculated increases in root and shoot weights, total biomass, root/shoot ratios, height, leaf number and length of longest leaf. All dependent variables were analysed using MANOVA and individual GLM ANOVAs. Results: Increases in shoot and root biomass were significantly affected by water stress but the effects were species- and priority level-specific. Root biomass for established individuals was significantly reduced after flooding and drought. Shoot biomass was least for drought and flood treatments of both older and younger P. persicaria, but older and younger P. capillare were unaffected. There were species-specific priority differences (i.e. greater for older individuals) for shoot height and increases in leaf number; however, the opposite was seen for increases in leaf length. Conclusions: In terms of community assembly, neither species appears to have an advantage in relation to competition or water stress, as both seem plastic and are negatively affected by flood and drought stress. The greater impact of older P. persicaria on P. capillare is the only advantage P. persicaria seems to have in the greenhouse. Correlating this to natural conditions, it appears that chance in reaching a site first plays a major role in P. persicaria's colonization success. This study provides evidence of the impacts of arrival time on subsequent physiological and competitive abilities of plants. We simulated the dynamic colonization and stress of Mississippi River island community assembly, where competition often occurs among cohorts. Older individuals tolerated stress better and accrued more biomass regardless of competition, and first colonizer status gave one species a competitive advantage. This study gives evidence to the impacts of arrival time on subsequent physiological and competitive abilities of plants. © 2012 International Association for Vegetation Science.