PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal
Factors influencing the depth distribution of amphibious plants in an irrigation pond.
Ishii, Jun*,1, Kadono, Yasuro2, 1 University of Tokyo, Bunkyo, Tokyo, Japan2 University of Kobe, Kobe, Hyogo, Japan
ABSTRACT- Amphibious plants have physiological adaptations to life under fluctuating water level, but there are few studies on depth distribution and population dynamics in relation to water level fluctuation in natural communities. In Japan, amphibious plants are often dominant in irrigation ponds. We investigated the depth distribution of amphibious plants in an irrigation pond, Shin-ike Pond, in Hyogo Prefecture, western Japan, and analyzed the factors that influence the distributions. A survey of vegetation along three transects from the shoreline to deeper water revealed that the terrestrial and emergent plants were dominant around the shoreline, and that the floating-leaved and submerged plants had very low coverage in Shin-ike Pond. Amphibious plants were dominant in the inundated zone, although the water level was rather constant for three years including the study period. Both pH and conductivity were low, indicating that Shin-ike Pond was an oligotrophic pond. Moreover, most of amphibious plants were isoetids (e.g. Eriocaulon nakkasimanum, Eleocharis acicularis, Isoetes japonica and Schoenoplectus lineolatus) that typically have rosettes with a short stem and well-developed roots. Isoetids show adaptations to nutrient- and carbon- poor environments. We suggest that low nutrient availability may inhibit propagation of other aquatic plants, and amphibious isoetids may be dominant in water in an oligotrophic pond even if there is little fluctuation of the water level. Intensive studies of an amphibious isoetid, S. lineolatus (Cyperaceae) in Shin-ike Pond revealed much higher clonal growth and reproduction in terrestrial than in submerged environments. The dominance of amphibious isoetids, in particular of S. lineolatus, is probably due to high recruitment rates and fast population growth during rare phases of water drawdown in Shin-ike Pond.
Key words: amphibious plant, depth distribution, fluctuating water level, nutrient availability