Journal of Weed Science and Technology
Online ISSN : 1882-4757
Print ISSN : 0372-798X
ISSN-L : 0372-798X
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Volume 51, Issue 3
Displaying 1-8 of 8 articles from this issue
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Original Reports
  • Water quality of macrophyte habitats in rural Japan
    Hiroyuki Kobayashi, Makoto Yamamoto, Makoto Kunihiro
    2006 Volume 51 Issue 3 Pages 133-138
    Published: September 22, 2006
    Released on J-STAGE: October 19, 2007
    DOIhttps://doi.org/10.3719/weed.51.133
    JOURNAL FREE ACCESS
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    This study is intended to clarify the effects of water quality on the ecological distribution of macrophytes. We studied the water quality of macrophyte habitats at 263 sites (106 cities) in rural Japan. Fifty-four species (22 families) were observed at the studied sites. The ecological distribution of these species differed according to their growth form. In general, water quality of emerged plant habitats was good and that of submerged plant habitats was poor in many water quality items, except for nitrogen and phosphorus. Habitats of some species that are ordinarily observed in good water were often markedly polluted by nitrogen and/or phosphorus. Almost all species were able to grow in good water. Data sets on water quality of 112 sites, and presence or absence data of 20 species were subjected to canonical correspondence analysis (CCA) for seeking correlations between water quality and distribution of macrohyte species. Consequently, CCA clarified some specific correlations between water quality items and macrophyte species: many submerged macrophytes correlated with DO and transparency, while some emerged macrophyes closely correlated with COD, BOD, SS, EC and Cl-. These results suggest that integrated evaluation based on data sets of many water quality items provides clearer comprehension of water quality of macrophyte habitats.
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  • Effect of emergence times and shading conditions on growth, seed production, and seed size of tropical spiderwort (Commelina benghalensis L.)
    Koji Yoshida, Mitsuhiro Matsuo, Hiroyuki Terao, Tsugufumi Ogawa
    2006 Volume 51 Issue 3 Pages 139-145
    Published: September 22, 2006
    Released on J-STAGE: October 19, 2007
    DOIhttps://doi.org/10.3719/weed.51.139
    JOURNAL FREE ACCESS
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    We investigated the seed size, growth, and seed production of tropical spiderwort (Commelina benghalensis L.), an annual weed in the Commelinaceae, under different emergence times and shading conditions. This species produces two types of seeds in capsules on its aerial and subterranean parts. We compared the sizes of a larger seed in the posticous locule of indehiscence and two to four smaller seeds in the anticous locule of a capsule. The large subterranean seeds were the longest, widest, and thickest of all the types of seeds, whereas the small aerial seeds were the shortest, narrowest, and thinnest. The plants that emerged from the aerial seeds in June were the tallest and had the most primary branches of those that emerged from March to September, reaching a maximum length of about 98 cm and having 12 branches per plant. The plants that emerged in May produced flowers the quickest, 21 days, and the plants that emerged in September took the longest, 42 days. It took 80 days for the plants that emerged in May to drop their seeds, which was the longest period, although seeds were not produced in those that emerged in September. Aerial seed production was the highest in the plants that emerged in April, producing about 720 large and 2,300 small seeds per plant. These April plants also produced the most inflorescences and large and small seeds born in the soil. The plants grown under 82% relative light intensity had the longest plant lengths and the most primary branches of all of the plants grown under shading or non-shading conditions, reaching about 54 cm length and having six branches per plant. These plants also produced the most aerial seeds, as each plant produced about 71 large and 143 small seeds, and the most inflorescences and large and small seeds born in the soil.
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