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Engelhardt, K. A. M. and M. E. Ritchie. 2002. The effect of aquatic plant species richness on wetland ecosystem processes. Ecology 83:2911-2924. In a Nutshell: Problem - Rapid environmental changes have fostered debates on how to effectively preserve or restore ecosystem processes. One such debate deals with the effects of biodiversity, and the loss thereof, on ecosystem processes. While recent research highlights biotic controls on ecosystem functioning, studies are sometimes equivocal across ecosystems and among spatial or temporal scales, which has lead to sometimes heated discussion over the relative importance of biodiversity in affecting ecosystem functioning. What - A well-replicated outdoor mesocosm experiment tested alternative mechanisms that explain the effects of submersed aquatic plant diversity on wetland ecosystem processes. Findings - Algal biomass increased and phosphorus loss decreased as species richness increased. This result was caused by one of the weakest competitors, which facilitated algal growth and thereby filtering of phosphorus from the water column. The dominant competitor also appeared to decrease phosphorus loss through direct effects on phosphorus availability in the soil and water. Thus, the effects by one of the weakest and the most dominant competitors combine to produce a diversity effect on phosphorus loss. Macrophyte biomass was not enhanced, but converged towards the intermediate biomass of the most competitive species. This result may be produced when the most competitive species is not the most productive species owing to species-specific feedbacks and adaptations to the wetland environment. Potential Applications - The paper demonstrates that plant diversity may affect wetland ecosystem processes when inferior competitors drive system productivity and nutrient retention. To ensure coexistence of such species with superior competitors, wetland systems may need to be maintained in a non-equilibrium state, such as with hydrologic disturbances, which would maintain both higher diversity and enhance ecosystem functioning. |
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