Pollen production in an old-growth stand of Chamaecyparis obtusa
2008
Saito, H.(Kyoto Prefectural Univ. (Japan)) | Murao, M.
The production rates of male flowers, seeds and seed cones in an old-growth stand of Chamaecyparis obtusa in Koyasan, Wakayama, were studied by the litter-trap method during the period from 6th November 1991 to 23 November 1996. The number of C. obtusa trunks in the plot of 30 mX50 m located on a slope was 37 (297/ha), of which one half were trunks larger than 50cm in DBH, and one fifth were within a DBH range of 70- 112cm. Mean pollen yields of male flowers of C. obtusa, which we have reported previously, were 174x10E3 grains and 1.11mg. Pollen production rates, obtained by multiplying the pollen yield per flower by the number of open male flowers in the study stand, were estimated to be 0.21-27.6 (mean, 8.25) x10E12 grains/ha/yr and 1.37-176 (mean, 52.6) kg/ha/yr. 1995 was the most productive year, when it was recognized in old-growth and mature stands of Cryptomeria japonica that a great number of male flowers fell before flowering due to the abnormally hot and dry weather in 1994. In the study stand in 1995, the number of flowers that fell before flowering reached 81% of total flowers. These unopened flowers contained aborted pollen grains. The mean number of ovules in a 1-ha stand was estimated from the mean number of fallen immature plus mature cones per year based on a mean number of 32.45 ovules per cone, which we had obtained in female strobiles taken from three young C. obtusa trees. The numerical ratio (P/Ov ratio) of pollen grains to ovules in a 1-ha stand during the period 1992-1995 was 1.3x10E5. The investment of photosynthates or dry-matter production rate in sexual reproduction during the same period was 713kg/ha/yr, among which pollen allocation reached 7.4%.
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