Response patterns of net photosynthesis to moisture of mosses in xeric habitats
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The response patterns of net photosynthesis to moisture level of mosses in xeric habitats were compared with those in mesic habitats, in order to determine whether the former species are better adapted to the xeric condition with regard to carbon gain.
Moss species examined wereRhacomitrium lanuginosum andR. barbuloides in xeric open habitats andDicranum japonicum, Hypnum plicatulum, Ptilium crista-castrensis, Pleurozium schreberi andHylocomium splendens in mesic habitats on the coniferous forest floor in the upper subalpine zone of Mt. Fuji. Three additional xerophytic species collected at other localities,Ptychomitrium polyphylloides, Grimmia pilifera andHedwigia ciliata, were also examined.
Five species in the xeric habitats showed an optimum range of moisture level for net photosynthesis, 2 to 3g·g−1. On the other hand, species in the forest showed a wider optimum range, 3 to 8g·g−1. Net photosynthetic rate at the moisture level of 0.5g·g−1 was positive in xerophytic mosses, but negative in most forest mosses.
Moisture levels where external capillary water disappeared and drop of water potential began was determined by blotting water-saturated shoots with membrane filters. These moisture levels were low in the xerophytic mosses and high in the forest mosses, although there were some exceptions.
It was concluded that mosses in xeric habitats are better adapted for the efficient use of water for photosynthesis than those in mesic habitats.
Key wordsAdaptation Moisture Moss Net photosynthesis Water potential Xeric habitat
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