A study of the physiological ecology of Deschampsia flexuosa L. Trin. (Poaceae)
The phenology of D. flexuosa was followed through a growing season in both a grassland and a woodland habitat. A flowering tussock form in the open habitat contrasted with a non-flowering mat in shade. A major environmental difference between the habitats was in photosynthetically active radiation (PAR). Vegetative growth of tillers from the two habitats, grown under the same conditions in a glasshouse, was similar while showing a marked response to PAR. When nitrogen (N) and PAR were decreased, plants grown under summer glasshouse conditions produced less shoot dry weight through reduction in tiller numbers. Decreased PAR increased tiller dry weight, length, total leaf length, leaf weight, leaf number, leaf length ratio (= SLA) and leaf weight percentage. Decreased N increased tiller weight, leaf weight and leaf number. Deschampsia flexuosa required marked vernalisation for flowering. Plants grown at low PAR produced juvenile tillers which were unable to flower irrespective of vernalisation. In open grassland, tussocks flowered intermittently and this was probably determined by the level of PAR penetrating the tussock. Massed flower culms from previous seasons were a major barrier to PAR and when removed (naturally or artificially) the tussocks flowered again. Deschampsia flexuosa has a well-known tolerance of deep shade under woodland on dry acidic and nutrient-poor soil but it is also widespread on similar soils in open grasslands. In grassland, but not woodland, it can successfully flower and set seed. Deschampsia flexuosa should be seen ecologically as a species primarily adapted to open rather than shaded habitats.