Estimation of ultraviolet radiation as a limiting factor for vertical distribution of plants by studying their ultraviolet resistance.

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1). Young Plantago asiatica grown in a growthcabinet.Only the plants derived from upper subalpine zone remarkably varied the amount of UV-B radiation absorbing substances after UV irradiation. Plantaginin among the substances was detected in all the plants only after a strong UV irradiation, and an unidentified substance after both a weak and strong UV irradiation. Some charactors of chlorophyll fluorescence after UV irradiation differed between the plants from low and high altitudes.2). Native species ill the field.UV resistance level of Polygonum cuspidatum shown as chlorophyll fluorescence was remarkably high. But, there seemed to be no relation between altitude and levels of UV resistance. --That of Trautvetteria japonica, however, becalae higher with the increase of its habitat's altitude. On 5 species of grasses growing in lower montane zone, UV resistance was the highest in P. cuspidatum, which distributes into the highest altitudes among these species.