PARENT SESSION
Oral Session #57: Plant Competition I.
Presiding: T. Seastedt
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Competitive outcomes between halophytes shift when N and water levels are varied.

Morzaria-Luna, Hem Nalini^*,1, Zedler, Joy¹, ¹ University of Wisconsin-Madison., Madison, WI

ABSTRACT- Californian salt marsh vegetation often responds to nitrogen (N) enrichment; hence, differences in N utilization efficiency might shift plant dominance when nutrients are not limiting. We tested the interaction between Salicornia virginica (Sv); and Triglochin concinna (Tc) under three nitrogen levels (0, 15 and 30 g N/m²) and three water-level treatments (waterlogged, drained and dry), selecting these species because we observed opposite outcomes in experiments in the greenhouse (Tc reduces Sv growth) and field observations (Sv dominates most marshes). Our experiment followed a replacement design at one density. As hypothesized, outcomes differed with experimental conditions. Tc's ability to reduce Sv biomass was highest in waterlogged treatments, where abiotic stress was greater; while Sv exerted competitive dominance over Tc in treatments where N was added and abiotic stress was reduced. The intensity of the aboveground competition was greatest in pots with 15g/m²) added and least in pots with no N addition. When grown by itself, Tc biomass was highest in waterlogged conditions, a result that agrees with field observations. We suggest that competitive dominance of Tc over Sv occurs primarily when nitrogen is limiting and results from Tc's superior ability to sequester available N. Our results support current theory, that the intensity of competition is higher under benign abiotic conditions than in stressful environments.

KEY WORDS: competition, salt-marsh, nitrogen, interspecific-interactions