Effects of reed canary grass Phalaris arundinacea and nitrate-N addition on the establishment of wet prairie plant communities at University of Minnesota Horticultural Research Center, Minnesota, USA
Published source details
Green E.K. & Galatowitsch S.M. (2002) Effects of Phalaris arundinacea and nitrate-N addition on the establishment of wetland plant communities. Journal of Applied Ecology, 39
Published source details Green E.K. & Galatowitsch S.M. (2002) Effects of Phalaris arundinacea and nitrate-N addition on the establishment of wetland plant communities. Journal of Applied Ecology, 39
In North American prairie wetlands, enrichment by nitrate from agricultural runoff is thought to contribute to the increasing colonization and dominance of the invasive reed canary grass Phalaris arundinacea. If true, Phalaris might compromise the re-establishment of sedge meadow vegetation on sites reflooded with nutrient-rich agricultural drainage water. The primary objective of this study was to test if nitrate (NO3-N) enrichment of a restored prairie pothole community was associated with greater dominance of Phalaris over the native sedge meadow plant community after the first two growing seasons.
Study site: The experiment was conducted at the University of Minnesota Horticultural Research Center in Carver County, Minnesota,USA.
Experimental design: Native communities were grown in controlled mesocosms in a field setting and subjected to six treatments consisting of three NO3-N addition levels (0, 12 and 48 g/m²/year) and two invasion conditions: native community mixture (non-weed); native community plus Phalaris addition. Seed were sown in May-June 1998. The experimental design was a randomized incomplete block with each treatment replicated 10 times.
Data collection: Plant material was harvested in late August 1999, 15 months after seeds were sown. An effort was made to time plant harvesting with the time of maximum standing crop for a majority of the species. Species that did not appear to be at maximum standing crop at harvest were Aster spp., Eleocharis palustris and Eupatorium purpureum. Above-ground plant material was harvested from a 0.5 m² sampling area in each plot. Plant material was clipped 5 cm above the soil surface and sorted by species. Below-ground plant material was then taken from a 0.1 m² sampling areas. Below-ground plant material was removed with soil cores of 25 cm depth. The shallow depth to water table restricted roots to the top 25 cm of the sediment.
The total shoot biomass of the native community was suppressed by Phalaris presence at all nitrate levels, but suppression was significantly greater at the highest nitrate level (48 g/m²) where shoot growth of the native community was reduced by nearly 50%. The total root biomass was also suppressed by Phalaris when no nitrate was added.
As nitrate increased, the relative abundance of native graminoids declined while native forbs increased in communities with or without Phalaris. The most common graminoid, tall manna grass Glyceria grandis, was suppressed at all levels, but more so at the 48 g/m² nitrate addition, along with three other species. The two most common forbs, ice ballet milkweed Asclepias incarnate and water parsnip Sium suave, exhibited increases in growth corresponding to increases in nitrate but with overall suppression by Phalaris.
Community diversity and evenness declined with increasing nitrate levels, regardless of whether Phalaris was present.
Conclusions: The results suggest that reducing nitrate loads in prairie wetlands is essential for minimizing declines in plant diversity. If Phalaris is present, the restored sedge meadow community will not achieve levels of abundance that are possible when it is absent, regardless of enrichment conditions. However, increased suppression by Phalaris at the 48 g/m² NO3-N dose level indicates that the dominance over the native sedge meadow community is enhanced at nitrate input levels that are common in such agricultural landscapes.
The authors recommend curtailment of the use of P.arundinacea for soil conservation and other agri-environmental purposes because of the likelihood of detrimental impacts to wetland biodiversity in the region.
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