The genus Isoëtes in Scandinavia: An ecological review and perspectives

Information relating to the Scandinavian quillwort species, Isoëtes lacustris L. and I. setacea Lam. (syn. I. echinospora Durieu), is reviewed emphasizing their ecological adaptation to infertile and shaded habitats, where stress results from inadequate levels of light, available carbon and nutrients. In addition, their habitats can feature enhanced disturbance and stress arising from man-made and natural impacts; for example, acidification, eutrophication, water-level alteration, ice-scour and sediment instability. Quillworts have evolved a variety of mechanisms by which these adverse impacts can be mitigated. Such adaptations comprise carbon acquisition through crassulacean acid metabolism (CAM), high root biomass, slow turnover, resource reallocation on the vertical gradient of their habitat and other related features typical for an S-strategist (stress-tolerator). It is emphasized that success of this strategy by no means is guaranteed. In fact, the quillworts are ultimately victims of their own, insufficiently flexible, growth strategy under sustained adverse environmental impacts. Evidently I. setacea fares better than I. lacustris in this respect. This review identified a number of research areas which ought to be further advanced. Specifically we would like to emphasize the need for better insights into the extent and rate of vegetation changes driven by acidification. Contradictory evidence seems to exist on this issue. © 1989.