NUTRIENT CONCENTRATIONS IN MIRE VEGETATION AS A MEASURE OF NUTRIENT LIMITATION IN MIRE ECOSYSTEMS

The above-ground standing crop and nutrient concentrations in plant material were examined in 45 stands of mire vegetation in the Biebrza peatland, Poland. The stands included flood-plains, rich fens, transitional fens and bogs. The pattern in nutrient concentrations in the above-ground plant material resembled the pattern in nutrient concentrations in peatwater and peat which had been investigated in an earlier study. Concentrations of N were quite uniform along the gradient. P-concentrations were highest in the transitional fen. Critical nutrient concentrations were defined on the basis of a review of nutrient concentrations in plant material from peatlands in which a fertilization experiment had been carried out. Defined critical values for phanerogams were: 13-14 and 0.7 mg/g dry wt for N and P respectively. Concentrations lower than these values indicate deficiency. P/N ratios greater than or equal to 0.07 indicate N-deficiency and P/N ratios less than or equal to 0.04-0.05 indicate P-deficiency. According to these values the Biebrza fens and bogs appear to be primarily deficient in N. The growth of the flood-plain vegetation does not appear to be restricted by nutrients.