Nutrient limitation in boreal plant communities and species influenced by scything

The nutrient status was studied in permanent plots Of four plant communities, two rich-fen communities and two wooded grassland communities, all formerly used for hay-making. The concentrations of N, P and K in plant material of dominant and subdominant species (above- and below- ground) were measured in plots experimentally scythed annually or biennially for two decades, and in plots unscythed for four decades. Three of the communities had an N:P ratio of 14 or less, indicating N-limitation; the most fertile grassland community had particularly low values for the N:P ratio (6-12), as did a majority of the species, including all tall-herb species. A species-rich community of fen-margin vegetation in the lowest productive rich fen, had an N:P ratio of 17-19 in the above-ground biomass, which indicates P-limitation of nutrients. Molinia caerulea and Thalictrum alpinum were found to be the vascular plants with the highest N:P ratio, indicating P-limitation of nutrients. Calculations of N:K and K:P ratios indicated possible K-limitation in the rich-fen communities, especially for Thalictrum alpinum., the species with the highest N:K value. No expected change from N- to P-limited growth was found; in contrast, a reduction in the N:P ratio was found in the annually scythed plots of the rich fens, suggesting that reduced biomass production is mainly a result of disturbance by scything. As expected, a reduction in the concentration of K was detected in the scythed plots.