EFFECTS OF DETRITUS ACCUMULATION ON THE GROWTH OF SCIRPUS-MARITIMUS UNDER GREENHOUSE CONDITIONS

The effects of accumulation of dead belowground plant parts (detritus) of the emergent macrophyte Scirpus maritimus on the growth of this sp ecies were studied under greenhouse conditions. In the first experimen t, the growth of S. maritimus seedlings decreased when the thickness o f the detritus mat, covered by a layer of sediment, was increased. The position of a 5 cm thick detritus mat in a 15-cm column filled up wit h sediment had only a minor effect on the growth of this species. In t he second experiment, fragmentation of detritus turned out to increase the growth-reducing effects found in the first experiment. Unfertiliz ed seedlings with the lowest dry mass proportionally allocated most dr y matter to their roots. The supply of nutrients either did not or onl y partly compensated for differences in plant growth among substrate t ypes. Tn all instances the supply of nutrients strongly reduced the pr oportional dry matter allocation to roots, whereas differences in nutr ient concentrations in plants diminished. In most instances the soil r edox potential indicated a reduction of iron, but iron concentrations in the shoots never reached toxic levels. The most likely explanations for the poor growth of S. maritimus in its own detritus are the relea se of toxic compounds into the substrate and deficiency of oxygen to t he roots due to reduced substrate conditions.