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

The above-ground standing crop and nutrient concentrations in plant ma terial were examined in 45 stands of mire vegetation in the Biebrza pe atland, Poland. The stands included flood-plains, rich fens, transitio nal fens and bogs. The pattern in nutrient concentrations in the above -ground plant material resembled the pattern in nutrient concentration s in peatwater and peat which had been investigated in an earlier stud y. Concentrations of N were quite uniform along the gradient. P-concen trations were highest in the transitional fen. Critical nutrient conce ntrations were defined on the basis of a review of nutrient concentrat ions in plant material from peatlands in which a fertilization experim ent 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 l ower 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 Bie brza fens and bogs appear to be primarily deficient in N. The growth o f the flood-plain vegetation does not appear to be restricted by nutri ents.