Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil

Published source details Perry L.G., Galatowitsch S.M. & Rosen C.J. (2004) Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil. Journal of Applied Ecology, 41.
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Summary

Manipulating nutrient availability to give native species a competitive advantage over invasive species might be an approach to effectively control invasive vegetation. This approach was evaluated for controlling invasion of wetland sedge meadow communities by reed canarygrass Phalaris arundinacea, a widespread invasive grass in North American. To test whether lowering nitrogen (N) availability would allow a native wetland sedge, porcupine sedge Carex hystericina, to suppress Phalaris competitively, Carex and Phalaris competition under a range of inorganic N concentrations in a glasshouse was investigated.

Soil preparation: Nitrogen (N) availability was lowered in a wetland soil (a clay loam collected in November 1998 from a drained wetland in Chanhassen, Minnesota) using carbon enrichment and repeated harvests of a cover crop (rye-grass Lolium perenne var. aristatum). In February 2000, to increase the volume of the N depleted soil, it was mixed with fresh soil, collected from the same source, at a depleted : fresh ratio of 4 : 1 by volume. This was steam-sterilized, and some used to fill 44, 47.5 × 35.5 × 13 cm basins. The remainder was amended with pine sawdust (i.e. carbon, C), at a soil : sawdust ratio of 2 : 1 by volume (9 : 1 by weight) and used to fill another 88 basins. The sawdust was 39.2% C and 0.21% N).

Nitrogen addition: A nitrogen gradient was created by applying NH₄-N to the soil. The two carbon treatments (sawdust added or none) were combined with four NH₄-N addition rates to give six soil N treatments. Basins with carbon added were subjected to addition rates of: 0.00, 0.025, 0.25 and 1.25 g N/week/basin. Basins without carbon added were subjected to two addition rates: 0.00 and 0.25 g N/week/basin. The six soil N treatments were combined with five competition treatments in a complete factorial design. Carex and Phalaris were each sown in monoculture at densities of 500 and 1,000 viable seeds/m², and in mixture at a density of 500 seeds/m² of each species.

In soil without carbon added, competition with Phalaris reduced Carex biomass by 91%. Conversely, in soil depleted of available N through carbon addition (sawdust added), competition with Carex reduced Phalaris biomass by 82%, while competition with Phalaris reduced Carex biomass by only 32%. This indicates that of the two species, Carex is the superior competitor for N.

Carbon enrichment lowered soil inorganic N by 10–30 mg/kg. NH₄-N addition mitigated the negative effects of carbon on Phalaris growth and competitive ability, indicating that carbon enrichment altered competitive outcomes by lowering N availability. Greater Carex N uptake efficiency under N-poor conditions appeared to account for the Carex competitive ability for N.

Conclusions: In this experiment, Carex hystericina dominance in carbon-enriched soil strongly suggests that lowering soil inorganic N to < 30 mg/kg in restored wetlands would allow establishing sedge meadow communities to suppress P.arundinacea.

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