Competition Among Grasses Along a Nitrogen Gradient: Initial Conditions and Mechanisms of Competition

摘要: We grew four perennial grass species (Poapratensis, Agropyron repens, Agros- tis scabra, and Schizachyrium scoparium) for 5 yr in monocultures pairwise com- petition plots on an experimental nitrogen gradient. The gradient contained ranging from 100% sand to black soil, plus that received additional N fertilizer. To examine the impact of initial conditions long-term outcome interspecific petition, three competitive situations were created: seed vs. competition (both planted simultaneously), invasions (each added as year-old monocul- tures other), vegetative (dividers separating adjacent two removed after 1 yr). Extractable soil NO3 NH4, measured test if differences concentration available monoculture (i.e., R* N, Tilman 1982) could predict competition. By year 5, displaced or greatly reduced biomass both Poa mixture (the mixed soils but not added-N plots) inde- pendent wide range starting conditions. On these soils, had significantly lower concentrations than either monocultures. Similarly, Agrostis by 5. N03- + NH4+, In contrast, no displacement occurred between Agropyron, persisted over yr. Monocultures did differ concentration, NH4+ NH4+. Thus, ability deplete successfully predicted all pairs If resource preemption asymmetric compe- tition been mechanism competition, would have affected Rather, results support reduction) model N. fertilizer plots, decreased with Agropyron. However, neither nor appeared advantage when they competed each other plots. For pairs, 5-yr which light availability because increased production litter accumulation, depended fourth pair, was treatments we cannot reject hypothesis competition) is important