The biomass and nutrient levels of Calamagrostis canadensis and Carex stricta under different hydrologic and fungicide regimes

We examined whether fungicide and the subsequent reduction of soilborne pathogenic fungi would differentially enhance the productivity and foliar nutrient content of two coexisting species, Calamagrostis canadensis (Michx.) Beauv. and Carex stricta Lam. This was tested under hydrologic regimes that simulated those in prairie wetlands and included a 32-d cycle (flooded 16 d, dry 16 d), 6-d cycle (flooded 3 d, dry 3 d), flooded, well-watered, and dry hydroperiods. Calamagrostis canadensis biomass increased 26%–45% in the wet hydroperiods (6-d cycle, well watered, and flooded) when fungicide was applied but remained fairly constant over all hydroperiods in nonfungicide treatments. Calamagrostis canadensis grown in the wet hydroperiods without fungicide produced the same biomass and growth rates as plants treated with fungicide in the dry hydrologic regime, suggesting that pathogenic fungi in wet hydrologic regimes have the same effect as major environmental stresses such as drought. In contrast, the biomass and growth rate of Carex stricta generally did not vary significantly with fungicide treatment. The only exception was in the rapidly alternating hydroperiod (6-d cycle), where Carex stricta treated with fungicide produced 48% more biomass and grew 46% faster than plants not treated with fungicide. Mean concentrations of foliar phosphorus generally were not significantly different between the fungicide and nonfungicide treatments for either plant species, while foliar nitrogen concentrations were higher in both species when treated with fungicide in the 32-d cycle, dry, and well-watered hydroperiods. The effect of fungicide on the biomass and foliar nutrients of these two co-occurring plant species depended on the species and the hydrologic regime, and our results suggest that seasonal and interannual changes in hydrologic regimes may confer a temporary advantage to one species or the other that, over the long term, allow them to coexist.Key words: benomyl fungicide, foliar nitrogen, foliar phosphorus, hydroperiod, marsh reed grass, wetland.