Shoot Population Dynamics of Carex kobomugi on a Coastal Sand Dune in Relation to its Zonal Distribution

Abstract

Shoot population dynamics of Carex kobomugi Ohwi, a rhizomatous perennial sedge with a guerilla-type growth form, dominating on Japanese coastal dunes, were examined to detect factors generating the zonal distribution pattern of the plant species. Relative growth rate of shoot (RGRS) and number of branching shoots formed by a mother shoot in a year (NBr) were measured in three populations occurring at three different distances from the shoreline. In 1992, Carex kobomugi shoots at the most inland site (90 m from the shoreline), where Imperata cylindrica var. koenigii dominated and soil-water salinity is always low, showed the lowest RGRS (0.0172 g g-1 day-1 from April to June and 0.00079 g g-1 day-1 in July) and the smallest NBr (1.3 shoots shoot-1 year–1 averaged for 3 years). Shoots of the species at the most seaward site (40 m from the shoreline), where the soil-water salinity is always higher than that of more inland sites, showed the highest RGRS (0.0228 g g-1 day-1 from April to June and 0.0093 g g-1 day-1 in July) and the largest NBr (2.5 shoots-1). However, Carex kobomugi population at the 40 m site had a high fraction of injured shoots (46% of total shoots sampled), which were recorded as shoots without any greenish above-ground part, and high mortality (0.34) due to temporal flooding of sea water caused by storms. In the intermediate site (70 m from the shoreline), Carex kobomugi had intermediateRGRS and NBr with low injury rate. The NBr value, however, showed a decreasing trend over the 3 years of observation, suggesting deteriorating effects of intraspecific competition on population dynamics. In the spring of the fourth year, shoots of Carex kobomugi at 70 m and 90 m from the shoreline produced 1.2 to 2.0 times higher number of buds per shoot than the 3-year-averaged NBrs. This suggests that some fractions of the buds were terminated or became dormant through intra- and/or inter-specific competition. The sparse distribution of Carex kobomugi at the 90 m site may be dictated by its competitive inferiority to Imperata cylindrica which has a denser root system and an aggressive growth form of a phalanx type.

Clonal and spatial genetic structure within populations of a coastal plant, Carex kobomugi (Cyperaceae)

“…It forms bulbs at nodes on rhizomes. About two to three rhizomes elongate from each original node (Ishikawa and Kachi, 1998). Annually, between autumn and winter, each rhizome forms a single node at its tip.…”

Shoot growth and distribution pattern ofCarex kobomugi in a natural stand

“…Furthermore, because C. kobomugi can produce many rhizomes when competition is less, this species can grow vigorously at the edge of the mean high-tide level where other plants cannot survive (Ishikawa and Kachi, 1998). However, Ishikawa and Kachi (1998) have also shown that, in areas that contain competitors such as I. cylindrica var.…”

“…Carex kobomugi is a pioneer and dominant species of unstable coast sand dunes (Nobuhara, 1967;Nobuhara and Miyazaki, 1974;Sasaki, 1987;Ishikawa et al, 1995;Ishikawa and Kachi, 1998). Despite having a low seed germination rate (Ishikawa et al, 1993), this species effectively reproduces by its plentiful rhizomes, which adapt their growth to sand movements.…”

“…I have previously reported shoot production from rhizomes as young as 5 years old (Min, 2004). With a guerilla-type growth pattern (Ishikawa and Kachi, 1998), this species can reproduce many shoots and widely propagate in a short time period even though it is generally inferior to phalanx-type plants in its ability to compete (Lovett Doust, 1981;Schmid and Harper, 1985;Bertness and Ellison, 1987). C. kobomugi exhibits three types of shoots: non-flowering, male-flowering, or female-flowering.…”

Genetic analysis of salt-marsh sedge Carex scabrifolia Steud. populations using newly developed microsatellite markers

“…Carex scabrifolia reproduces both sexually and asexually by elongating rhizomes and forming clonal ramets. Other members of the genus Carex show the same reproductive strategies as C. scabrifolia (e.g., C. kobomugi, Ishikawa and Kachi 1998;C. rugulosa, Ohbayashi et al in press).…”