Dactylorhiza maculata, Platanthera bifolia and Listera ovata survive N application under P limitation

Increased nutrient availability is generally believed to be harmful for terrestrial orchids. However, no information is available on whether grassland orchids survive decades-long calcium (Ca), nitrogen (N), phosphorus (P) and potassium (K) application. We took advantage of sampling in one of the oldest long-term experiments in the world, the Rengen Grassland Experiment (RGE), which was established in Germany in 1941 on low-productive Violion caninae grassland, and we monitored orchids from 2005 to 2009.Dactylorhiza maculata, Platanthera bifolia and Listera ovata survived decades-long application of Ca and CaN fertilizer, but not CaN together with P. Cover of D. maculata was highest in areas of Ca treatment. The number of flowers per plant of L. ovata was significantly higher in the CaN treatment compared with the control indicating that enhanced N availability stimulated its growth. Long-term N application (NH4NO3 at an annual rate of 100 kg N ha−1) was not fatal to the studied orchids if not accompanied by P application. It is more likely that enhanced N availability can cause loss of studied orchids only where the availability of P in soil is high enough to enable the growth of productive species that can better compete for light on eutrophic soils.