| Here blooming phenology of Betula alnoides was observed in natural forests at JingxiCounty, Guangxi for two years since June, 2005 using plot method combined withsurvey on individuals. Meanwhile, reproductive modules were investigated taking siteand tree size into consideration. And some experiments such as pollen germination andstorage characteristics of this species were conducted. These studies were aimed toobtain evidences and prepare for pollination or hybridization and building orchard forthis species. The main findings were as follows:(1) According to the inflorescences of B. ainoides investigated, male infloresceneessprout out in the first half of July, and then grown slowly until at the end of Octoberwhen flowering began. After three days, mass flowering occurred and pollens werereleased, a bit earlier than leaves sprouting out. Mass flowering of male inflorescencelasted normally for about ten days, and then pollen dispersal was over.(2) The female inflorescences of B. alnoides sprout out at the same time for leaves on1st, November and grown much slowly. From fourth to tenth, November, the femaleinflorescence grown fast, while from eleventh to twenty-sixth this month, grown slowlyagain. On ninth, bract on female inflorescences began to open, and fully opened ontwelfth this month. The top of stigma fully curled on sixteenth which meant pollinationfinished.(3) Mass flowering of single tree lasted for ten days or so. And the mass floweringperiod of tree inside forests was longer than that at the edge of forests.(4) At the level of stand, mass flowering of B. alnoides forests lasted for about twomonths. There were no remarkable difference between interior and exterior forests, and between normal hills and limestone hills. While mass flowering at the normal hills lastedten days longer than that in the limestone hills.(5) The quantity of male inflorescence was three times larger than that of femaleinflorescence for a reproductive individual. The total number of inflorescence onindividuals at the edge of forests were remarkably larger than that of individuals insideforests (p＜0.05). For a single inflorescence, the number of little flowers on male one was0.45 time as that on female one. As a whole, there were much more male flowers thanfemale ones in the forests.(6) As to distribution patterns of reproductive modules within crown layers ofBetula alnoides, there were largest quantity of both male and female inflorescences intop layer, while smallest in bottom layer. For reproductive individuals inside forests, themajority of inflorescences were all in top and middle layer, their ratio were 66.2% and21.8%, respectively; the same law for individuals at the edge of forests, while 52.7% and29.4%, respectively.(7) Reproductive branches of B. alnoides were mainly located at the first-order andsecond-order branches. And about 90% of them were located at first-order branches.Among all branches investigated, 42% beard male inflorescences, 20% beard both maleand female inflorescences, 13% beard female inflorescences, and 25% beard noinflorescence. The ratio for top buds growing female inflorescence was remarkablylower than that of lateral buds on the reproductive branches. The ratio for second toeighth lateral buds growing inflorescences were all about 10%, while there was nosignificant difference between them.(8) As to pollen collection, when male inflorescence turned yellow and distancebetween bracts enlarged, branches beard this kind of male inflorescene were suggestedbeing collected and brought to laboratory and growing in water till pollens start todisperse. Pollen dispersal was over when male inflorescene turned deep brown.(9) The suitable media for in vitro pollen germination of Betula alnoides consist of15% sucrose and 200 mg.Kg-1 boric acid in distilled water, and optimized temperaturewas 30℃, and under these good conditions, the pollen germination rate and pollen tubelength become stabilized after three hours and seven hours, respectively. Thus three hours are reasonable for vigour test for this species.(10) To test rapidly pollen vigour for B. ainoides in the field, TTC method, with pHvalue of dye solution being 7.0, was screened out from TTC, I-KI and acetic acidcarmine methods, its results were remarkably in accordance with those of pollengermination.(11) Storage temperature has significant effects on preservation of pollen vigour ofB. alnoides (p＜0.05). The pollens survived only within four days under roomtemperature (18 to 30℃); they lost their vigour after one month stored undertemperature of 3℃; while their germination rate was still more eighteen percentageafter eighty three days under temperature of 10 and 20℃below frozen point. Under thesame low temperature, vigour of pollen treated by dryness and vacuum was higher thancontrolled one, but no significant difference was observed (p＜0.05). |
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