Seasonal variation in the ecophysiology of Littorella uniflora (L.) Ascherson in acidic and eutrophic habitats

Abstract

SUMMARYThe ecophysiology of the submersed aquatic macrophyte, Littorella unijiora (L.) Ascherson, has been compared at acidic and eutrophic habitats in the Lake District, 'I'he physico-chemical enYlronment (bulk-water and sediment-interstitial-water pH, CO^, O^, nutrient concentrations and PAR) have been related to seasonal photosynthesis (CAM activity, [COj]^ and CO^ and PAR response characteristics) and leaf growth rate of adult plants and ramets. In general, the environment was more favourable for plant growth at Esthwaite Water (the eutrophic site) than at Red Tarn (acidic). Although bulk-water pH was higher at Esthwaite, sediments were deeper and interstitial water CO^ concentrations greater. Concentrations of nitrate and ammonium, phosphorus and potassium were also higher. However, shading by phytoplankton blooms and epiphytes reduced PAR incident on Esthwaite plants. Photosynthetic characteristics and growth of L. uniftora followed the seasonal changes in PAR and temperature. However, Esthwaite L. unifiora showed greater CAM activity, and slightly higher [CO^Ji and photosynthetic capacity. Esthwaite plants also possessed more numerous, shorter leaves with greater chlorophyll and nitrogen content, and leaf growth rate and ramet production were greater than for Red Tarn plants, Esthwaite L. unifiora transplanted to Red Tarn showed higher rates of growth than native Esthwaite plants, while Red Tarn L. unifiora transplanted to Esthwaite performed poorly and retained the lower rate of ramet growth found in native Red Tarn plants. End of season productivit\-was greatest in Esthwaite to Red Tarn transplants and lowest in Red Tarn to Esthwaite transplants. The relationships between environmental conditions and plant performance at the two sites are discussed in the context of the disappearance of L. unifiora from acidic and eutrophic sites in N. Europe in recent years.

Adaptations for an amphibious life: changes in leaf morphology, growth rate, carbon and nitrogen investment, and reproduction during adjustment to emersion by the freshwater macrophyte Littorella uniflora

“…Littorella uniflora L. Ascherson (Shoreweed) is a common species at the margins of tarns, lakes and reservoirs throughout the UK, northern Europe and North America (see Fig. 1, and Clapham, Tutin & Warburg, 1981 ;Raven et al, 1988 ;Robe & Griffiths, 1992). This small perennial plant (4-6 cm high) has a rosette of cylindrical evergreen leaves, a short stem and a large root system.…”

“…In this paper we describe the changes which took place in leaf morphology (including stomatal density and lacunal volume), growth rate, dry-matter turnover and C and N investment as aquatic plants became terrestrial, flowered and set seed. We also draw on an earlier study of permanently submersed L. uniflora in lake and tarn habitats (Robe & Griffiths, 1992), to compare the costs and benefits of submersed vegetative proliferation with flower and seed production in the terrestrial environment.…”

“…Nitrogen requirements are reduced by N storage, a small life form and a slow growth rate (Robe & Griffiths, 1994). Plants growing permanently submersed produce approximately one ramet per plant per year (Sand-Jensen & Sondergaard, 1978 ;Robe & Griffiths, 1992).…”

“…No attempt was made to thin or weed round them. All existing leaves were identified using stainless steel washers attached with a loop of nylon cord, and their length and width were measured (Robe & Griffiths, 1992). The plants were re-examined at approx.…”

“…In Figure 5 b they are compared with those of plants growing submersed throughout the summer and autumn at Esthwaite Water, a lowland eutrophic lake, and Red Tarn, an upland oligotrophic tarn. Data for Esthwaite Water and Red Tarn L. uniflora, including environmental conditions at each site, were collected in a study in the Cumbrian Lake District in 1986 (see Robe & Griffiths, 1992). L. uniflora were planted in openwork plastic baskets which were relocated in the sediments in 0n25-0n4 m of water and could be removed for measurement.…”