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1. Allocation of biomass and nitrogen were studied for 1 year in experimental populations of Carex diandra, C. rostrata and C. lasiocarpa (species from mesotrophic fens) and C. acutiformis (a species from eutrophic fens). These species were grown at two levels of N supply (3 center dot 3 and 20 center dot 0 g N m to the -2 year to the -1, respectively). 2. At low N supply, total biomass did not differ between the species. At high N supply, the total biomass of C. lasiocarpa and C. acutiformis ('high-productive species') significantly exceeded that of C. diandra and C. rostrata ('low-productive species'). In all species, percentage nitrogen allocation to the leaves exceeded percentage biomass allocation to the leaves. 3. The high-productive species had a higher shoot:root ratio, a higher percentage biomass allocation to the leaves (leaf weight ratio, LWR), a higher total nitrogen content and a higher percentage nitrogen allocation to the leaves than the low-productive species. However, the low-productive species had higher leaf nitrogen concentrations (on a weight basis) than the high-productive species. 4. Parameters which are related to light interception, such as the specific leaf area (SLA: m squared of leaf per kg of leaf), the leaf area ratio (LAR: m squared of leaf per kg of plant), the leaf area index (LAI: m squared of leaf per m squared of soil) and the ratio between total leaf area and total root length, did not differ consistently between the high-productive and the low-productive species. 5. Compared with the high-productive species, the low-productive species invested relatively more biomass and nitrogen in plant parts which contribute to the acquisition of below-ground resources. 6. At low N supply, there was a decrease in all species of the shoot:root ratio, LWR, LAR, LAI, and the ratio between total leaf area and total root length. 7. The rank order of potential productivity of the species in this study did not match the rank order of nitrogen availability in their natural habitat. It is suggested that the distribution of these species is not only determined by their potential productivity, but also by specific demands on the water chemistry and by their competitive ability.

(1) The relative magnitudes of environmental vs. genetic influences on the growth of Scirpus americanus and Scirpus maritimus were examined in an intertidal marsh on the Fraser River Delta, British Columbia. Intraspecific comparisons at the high and low parts of an elevational gradient were made for shoot, inflorescence, root, rhizome and corm mass over a 16-month period. (2) S. americanus plants on the high marsh had greater shoot densities, flowering frequencies, above- and below-ground masses than plants growing on the low marsh. Shoot density of S. maritimus was highest on the low marsh but its flowering frequency, and above- and below-ground masses were greatest on the high marsh. At all sites sampled, vegetative reproductive effort exceeded sexual reproductive effort; within each species, total reproductive effort on the high marsh exceeded that measured on the low marsh. (3) Shoot growth rates were calculated after controlling for below-ground mass and the duration of tidal exposure. For both species, low-marsh stands had higher shoot growth rates per gram below-ground mass per hour of tidal exposure than high-marsh stands, but shoot mass [m.sup.-2] was greatest on the high marsh. Enhanced plant mass on the high marsh is associated with larger below-ground reserves, but is ultimately a product of prolonged aerial exposure. (4) Reciprocal field-transplant experiments indicated that the high- and low-marsh populations of S. americanus and S. maritimus consist of different genotypes which show similar phenotypes when grown in a common environment. Genotypes moved into new environments grew as well as the residents, suggesting that there is no local genetic differentiation.