Competition plays an important role in species interactions and community structure. More and more functional traits has been commonly used to explore plant strategies in competitive environments. The competition-trait similarity hypothesis and competition-trait hierarchy hypothesis have been widely discussed to explain the relationships between functional traits and competitive abilities. However, the two forms of competitive ability, competitive effect and competitive response were confounded in most of these studies, which limits our understanding on the role of functional traits in community structure. We conducted a greenhouse experiment with peatland plants to determine whether the relationships of functional traits and competitive ability were consistent when competitive effect and response abilities were detected separately, and which hypothesis can better explain the relationship between functional traits and competitive ability of peatland plants. We used one phytometer (Carex angustior) growing in competition with four wetland plant species separately to calculate competitive effect and response abilities under waterlogging and non-waterlogging conditions. Two above-ground (height, specific leaf area) and four below-ground (maximum root length, total root length, specific root length and root diameter) traits, and root/shoot ratio were measured. The Standardized Major Analysis was used to explore the linear relationship between functional traits and competitive ability.
Results/Conclusions
All the hierarchy trait distance we measured were consistently related with both competitive effect and competitive response abilities, indicating the species competitive interaction was driven by hierarchy trait distance. However, the slops of hierarchy trait distance to competitive response ability were steeper than those to competitive effect ability. The competitive effect ability significantly increased with the increasing similarity of most plant traits while the competitive response ability decreased, indicating the two forms of competitive abilities should be explicitly distinguished when the similarity hypothesis is discussed. We also found that the absolute values of those slops were bigger when competitive response ability was analyzed. Furthermore, the environmental condition affected the values of all slope we analyzed in this experiment, with steeper slopes in waterlogging condition than in non-waterlogging condition. Our research indicated that both the competition-trait hierarchy hypothesis and competition-trait similarity hypothesis could explain the competitive interactions among peatland plants. However, the role of competitive effect and competitive response in the relationship between plant functional trait and competitive ability was different. Competitive response ability was more sensitive to the differences of plant traits between competitors. These results have important implications for future research in plant competition and community structure.