Heterogeneous distribution of a floating-leaved plant, Trapa japonica, in Lake Mikata, Japan, is determined by limitations on seed dispersal and harmful salinity levels

• Published in: Ecological research Vol. 29; no. 5; pp. 981 - 989
• Main Authors: Nishihiro, Jun, Kato, Yoshikazu, Yoshida, Takehito, Washitani, Izumi
• Format: Journal Article
• Language: English
• Published: Tokyo Springer-Verlag 01.09.2014; Springer Japan; Springer; Blackwell Publishing Ltd
• Subjects: adverse effects; Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Behavioral Sciences; Biological and medical sciences; Biomedical and Life Sciences; Brackish; brackish water; Dispersal; Ecology; Ecotoxicology, biological effects of pollution; Evolutionary Biology; Flowers & plants; Forestry; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; General aspects; germination; laboratory experimentation; lakes; Life Sciences; Macrophyte; Original Article; Plant Sciences; Ramsar Convention wetlands; remote sensing; rivers; Salinity; seawater; sediments; Seed dispersal; Seed germination; Seeds; surveys; Synecology; Trapa; Trapa japonica; water salinity; Zoology; Sea of Japan; Japan; Asia; Far east; INW, Japan Sea; Japan, Honshu, Fukui Prefect., Mikata L; INW, Japan; Macrophyte; Seed dispersal; Ramsar Convention wetlands; Salinity; Seed germination; Seeds; Toxicity; Germination; Environmental factor; Dispersion; Freshwater environment; Limitation; Lakes; Aquatic plant; Wetland
• ISSN: 0912-3814; 1440-1703
• DOI: 10.1007/s11284-014-1186-6

Factors affecting the within-lake distribution of Trapa japonica were analysed in Lake Mikata, Japan, by integrating remote sensing analyses, field surveys, and laboratory experiments. The T. japonica bed has been expanding since 2006 and covered more than 60 % of the lake’s area from 2008 to 2010. However, two parts of the lake, the upper and lower areas, retained open water, even during recent years. A survey of lake-bottom sediments revealed a heterogeneous seed distribution. Although seed density exceeded 13 seeds/m² in the lake’s central area, no seeds were observed in the upper and lower areas. A seed-bag retrieval experiment showed that 75.6 % of seeds at the upper site germinated when seeds were artificially introduced, whereas 6.7 % of seeds germinated at the lower site. These results suggest that seed dispersal opportunities are the primary limitation on the distribution of T. japonica in the upper area. Brackish water was found in springs in the lower area, reflecting an adverse inflow of water from a downstream brackish lake. Laboratory experiments revealed significant adverse effects of water salinity on germination and early growth of T. japonica. Based on these results, we concluded that the heterogeneous distribution of T. japonica within the lake was determined by a combination of two factors: limitations on seed dispersal determined by the inflowing river and harmful salinity levels caused by inflows of seawater from the Sea of Japan via a downstream brackish lake.