THE CALCIUM DEMAND OF THE CALCICOLE SEDGE SCHOENUS NIGRICANS

Growth and reproduction of the perennial sedge Schoenus nigricans from calcareous wet dune-slacks was investigated in response to increasing proportion of calcium carbonate in dune sand to test the hypothesis t hat a high calcium supply is necessary to ensure a full life cycle of this calcicole species and counteract the population decrease in wet d une slacks. Plant growth and nutlet quality, but nor reproduction per se were significantly lower in plants grown for 30 months at 0.03% Ca compared to all other concentrations from 0.25 to 2% Ca. Plants at 0.0 3% Ca had the lowest nutlet mass. With increasing Ca supply, the Ca co ncentration in the roots increased more than chat in leaves and shoots , where Ca was associated with the fractions being soluble in water an d acetic acid. Ca-oxalate was not present. The insoluble Ca fraction w as not affected by the external Ca supply, but was only related to the age of the tissue. A quotient of water-soluble calcium/water-soluble total cations of 0.15 seems to be sufficient for a good performance of S, nigricans in soils with 0.25% Ca or more, thus indicating a relati vely low calcium demand of this calcicole species which has a high deg ree of Ca-tolerance.