残土処理場のオオバヤシャブシ幼齢群落における花粉生産

抄録

The production rates of pollen, male catkins, female strobili and seed cones in a young, 7-8 year old, Alnus sieboldiana community, growing on freshly dumped detritus with little humus, were studied in 1987 and 1988. The rates in terms of number and dry weight on an area basis were measured using litter traps and also by the clipping method. Pollen yields per catkin have been reported previously. Pollen production rates, obtained by multiplying the pollen yield per catkin (number and dry weight) by the number of open male catkins per m^2, were estimated to be 2.21×10^9 grains/m^2 and 29.58g/m^2 in 1987, and 2.42×10^9 grains/m^2 and 21.23g/m^2 in 1988. The pollen allocations, in terms of dry-matter production rates for male components, were 34.1% in 1987 and 37.8% in 1988. In the study community a large number of male catkins fell before flowering, accounting for 25.3% and 39.3% of the total number in 1987 and 1988, respectively. Dropping rates as high as about 70% were recognized in both years for female strobili and immature seed cones. As these dropping rates would have been affected by late frost damage, the potential production rates if all male catkins had flowered and all female strobili had matured, were estimated. The potential pollen production rates were estimated to be 3.0×10^9 grains/m^2 and 40g/m^2 in 1987, and 4.0×10^9 grains/m^2 and 35g/m^2 in 1988. The pollen dry-matter allocations in terms of the potential rates for male components reached 42% in 1987 and 46% in 1988, and those for male plus female components, reached about 27% in both years. The actual numerical ratio of pollen grains to ovules (P/Ov ratio) was 50〜60×10^3, compared with a potential ratio of 70〜100×10^3.