Effects of microtopography and nutrients on biomass production and plant species diversity in experimental wetland communities.
We performed a mesocosm study to examine the effects of microtopography and nutrients on biomass production, plant species diversity, and the relationships between these indices in wetland ecosystems. Although we found significant contributions (p < .05) of microtopography toward shoot coverage, above-ground dry weight, and total dry weight, the effects of nutrients on most indices of biomass production and diversity were more prominent (p < .001) than those of microtopography. Relatively low biomass production and high diversity were found under low nutrient conditions, whereas directly opposite results were obtained under fertilized conditions, indicating negative linear correlations between biomass production and diversity. Relatively short species such as Eleocharis congesta and E. yokoscensis were more frequent under low nutrient conditions, whereas relatively tall species such as Echinochloa crus-galli, Panicum dichotomiflorum, and Persicaria hydropiper were more common under fertilized conditions. In particular, an invasive species (Paspalum distichum) also showed relatively high importance value under fertilized conditions. In the context of wetland construction, restoration and management, we suggest that nutrient status should be considered before microtopography, particularly in wetland ecosystems under the early phase of secondary succession. Oligotrophic status should be maintained particularly for the co-existence of diverse plant species including rare species.