Plant trait expression responds to establishment timing.

Trait divergence between co-occurring individuals could decrease the strength of competition between these individuals, thus promoting their coexistence. To test this hypothesis, we manipulated establishment timing for four congeneric pairs of perennial plants and assessed trait plasticity. Because soil conditions can affect trait expression and competition, we grew the plants in field-collected soil from each congener. Competition was generally weak across species, but the order of establishment affected divergence in biomass between potmates for three congeneric pairs. The type of plastic response differed among genera, with trait means of early-establishing individuals of Rumex and Solanum spp. differing from late-establishing individuals, and trait divergence between potmates of Plantago and Trifolium spp. depending on which species established first. Consistent with adaptive trait plasticity, higher specific leaf area (SLA) and root-shoot ratio in Rumex spp. established later suggest that these individuals were maximizing their ability to capture light and soil resources. Greater divergence in SLA correlated with increased summed biomass of competitors, which is consistent with trait divergence moderating the strength of competition for some species. Species did not consistently perform better in conspecific or congener soil, but soil type influenced the effect of establishment order. For example, biomass divergence between Rumex potmates was greater in R. obtusifolius soil regardless of which species established first. These results suggest that plant responses to establishment timing act in a species-specific fashion, potentially enhancing coexistence in plant communities.