Comparison of ecophysiological responses to heavy snow in two varieties of <i>Aucuba japonica</i> with different areas of distribution

  • Atsushi Kume
    Department of Biology, School of Education Waseda University Tokyo 169‐50 Japan
  • Yoshio Ino
    Department of Biology, School of Education Waseda University Tokyo 169‐50 Japan

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<jats:title>Abstract</jats:title><jats:p><jats:italic>Aucuba japonica</jats:italic> varieties are common evergreen understory shrubs in Japan. <jats:italic>Aucuba japonica</jats:italic> var. <jats:italic>borealis</jats:italic> is distributed on the Sea of Japan side of Honshu and Hokkaido where heavy snow cover lasts for more than 3 months in winter. <jats:italic>Aucuba japonica</jats:italic> var. <jats:italic>japonica</jats:italic> is distributed in areas with shallow or no snow on the Pacific Ocean side of Honshu and Shikoku. The ecophysiological characteristics of var. <jats:italic>borealis</jats:italic> were compared with those of var. <jats:italic>japonica</jats:italic> to examine the effects of heavy and long‐term snow cover on the life cycle of var. <jats:italic>borealis</jats:italic>. Shoots of both varieties were shaded in crushed ice for 110 days, but their photosynthetic activities, chlorophyll contents and the chlorophyll <jats:italic>a/b</jats:italic> ratio was not affected. The leaves of var. <jats:italic>borealis</jats:italic> were no less frost tolerant than those of var. <jats:italic>japonica</jats:italic>. In spite of the difference in environmental factors, both varieties had similar characteristics in seasonal changes of photosynthesis, respiration and chlorophyll <jats:italic>a/b</jats:italic> ratio. These results suggest that var. <jats:italic>japonica</jats:italic> could survive in areas with heavy snow where it does not normally occur. Leaf net production (LNP) was estimated based on the microclimatic data and seasonal photosynthetic and respiration rates. The difference in the annual LNP between the two varieties was equivalent to the difference in the LNP during the snow season. One of the major effects of snow cover is to interrupt and reduce the production period of var. <jats:italic>borealis</jats:italic>.</jats:p>

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