The influence of interspecific competition on the distribution of an Alpine graminoid: Evidence for the importance of plant competition in an extreme environment

摘要

The importance of interspecific competition to plant distribution in an unproductive environment was investigated for two alpine tundra graminoids that differed in community of origin, Kobresia myosuroides from a resource poor dry meadow and Deschampsia caespitosa from a more resource rich moist meadow. It was hypothesized that Deschampsia is absent from the resource poor dry meadow due to competitive displacement by Kobresia, rather than low resource availability. A removal experiment was performed in the dry meadow, where Deschampsia growth, physiology, and mortality in response to both vegetation removal and N additions were examined. Water availability was monitored throughout the experiment. The effect of removal on Deschampsia was more pronounced than that of N addition. Removal resulted in a significant decrease in Deschampsia mortality, and significant increases in Deschampsia shoot and root biomass, tillering, biomass per tiller, root:shoot ratio, root N concentrations, water-use-efficiency and flowering. Soil moisture differences between intact and removal plots suggest that Kobresia is able to competitively displace Deschampsia from the dry meadow by reducing water levels below which Deschampsia can grow and reproduce. A second experiment, conducted in removal plots only, examined the mortality, growth, and physiology of Deschampsia and Kobresia in response to variations in neighbor and N availability. Kobresia exhibited no adverse response to competition with Deschampsia, even under high N conditions. These results demonstrate that a species of a resource poor community is capable of competitively displacing a species from a more resource rich community. Since this experiment was conducted in alpine tundra, these results illustrate that competition can be an important force structuring plant community composition in an extreme environment.