N- and P-addition inhibits growth of rich fen bryophytes

Abstract

A greenhouse experiment was set up to investigate if infrequently and frequently occurring species respond differently to simulated habitat changes. Two frequently occurring (Bryum pseudotriquetrum and Calliergonella cuspidata) and two infrequently occurring (Hamatocaulis vernicosus and Paludella squarrosa) rich fen bryophytes were grown in mixed culture and subjected to rainwater or groundwater and three levels of N, ammonium nitrate (0, 1 and 3 mg N L–1) and P, potassium phosphate (0, 0.05 and 0.1 mg P/L). All species responded negatively to higher N-levels and three of the four species responded negatively to rainwater and higher P-levels. C. cuspidata had highest relative growth rate (RGR) in all treatments, and the infrequently occurring species had lower RGR and were more negatively affected by high levels of N than the frequently occurring species. A negative effect of rainwater seemed to be caused by higher background levels of N in rainwater compared to groundwater. We found a negative effect of high initial bryophyte density in three of the four species indicating density-dependent inhibition between species. We suggest that maintenance of oligotrophic conditions by recharge of nutrient-poor groundwater is vital for conservation of infrequently as well as frequently occurring rich fen bryophytes.