Mineral ion, nitrogen and organic solute pattern in sedges (Carex spp.) - A contribution to the physiotype concept. II. Culture experiments

Field studies on Carex species (Choo and Albert 1999) suggest that this genus represents a uniform physiotype. In order to ascertain whether this physiological stability in the field can also be found under controlled conditions with a varied nutrient supply, five Carex species native to wet-acidic oligotrophic (C. rostrata, C. limosa), moist-eutrophic (C. acutiformis), mesotrophic flysch-sandstone (C. pilosa) and meso-eutrophic saline (C. distans) habitats were cultivated under three different nutrient regimes. In addition to plant matter and total N, plants were analyzed for inorganic ions (K, Na, Mg, Ca, Cl, NO₃, SO₄, P(i)), organic acids, low molecular weight carbohydrates, amino acids, and osmolality. While C. acutiformis, being adapted to nutrient-rich habitats, could not maintain a high growth under low nutrient availability, C. limosa and C. rostrata, being adapted to nutrient-poor habitats, were able to maintain or even to increase their growth. C. acutiformis and C. distans reduced the below-ground to above-ground biomass ratio under eutrophic conditions, while C. limosa maintained this ratio and C. pilosa even increased it. Despite differences in the nutrient regimes, changes in the main osmotica patterns of the investigated species were rather limited. The following trends were observed: levels of amino acids and total N increased with the nutrient supply, but were inversely correlated to sugar contents. Fluctuations of total amino acid levels were paralleled by changes of asparagine (Asn) contents, suggesting a key role for asparagine as a potential N-storage compound. Compared to oligo- and mesotrophic conditions, eutrophic plants generally showed the lowest total sugar contents. The ionic changes stemming from increased eutrophication showed the same pattern for all investigated species, indicating quite similar characteristics of the mineral ion and organic acid metabolism. Generally, Carex species under oligo- to mesotrophic conditions adequately met their ion demands by efficient metabolic uptake processes; on the other hand, under eutrophic conditions, a balanced uptake of nutrient ions was achieved by efficient regulatory processes that also prevent the uptake of potentially toxic amounts of ions. Based on these results as well as on those in Choo and Albert (1999), we assume that Carex species represent a relatively uniform physiotype enabling this genus to cope successfully with a broad variety of environmental conditions.