Preliminary Studies On Niche And Reproduction Of Magnolia Sieboldii K.Koch

Magnolia sieboldii K.Koch,an endemic species of East and Northeast China,belongs to Magnolia of Magnoliaceae. It also occurs in Korean and Japan. Because of a rapid decrease in quantity and distribution area, it was listed in the third class of the national protection plant species. And the natural distribution area of Magnolia sieboldii is very narrow and disconnected. This dissertation is mainly dealing with its niche, pollination biology and seed biology. According to the results from this study, the factors that resulted in the present endangered situation of Magnolia sieboldii have been analyzed and several measures for effective protecting this species have also been proposed. The conclusions are as follows: 1. Based on the data from the plots investigation and using Levins, Shannon weiner and niche overlap formulas, the niche breadth values and niche overlap values of the main tree species were measured in the natural forestry of Magnolia sieboldii.The results showed that: The descending order of niche breadth value was to some extent in accordance with the descending order of important values, but Enkianthus chinensis is different from others for its strong adaptability ability. Niche overlap was relative to niche breadth, the populations with wide niche breadths usually had high overlap values and other populations, and the niche overlap among the populations with the same or similar environment requirements and similar biological properties also had a higher value. For example, Magnolia sieboldii and Enkianthus chinensis that both had the same shade-tolerant characteristic had high overlap value. There is a high degree of overlapping, a complex relationship and an obvious tread of sharing natural resources among populations. Through niche research of Magnolia sieboldii ,we draw a conclusion that Magnolia sieboldii was characterized by scattered distribution,poor regeneration and associated species in community, which made it have less competitive advantages, thus it was influenced easily by community variation .The author stated: populations with the same ecological characteristics could form a fine relation in the same habitat as resource was sufficient; and this supported Linsizu's theory that the relationship between niche overlap and competition was not positive correlated. 2.Its high altitude distribution shows its need for low temperature. Water condition is also the main ecological factor which affects the niche distribution of Magnolia sieboldii . 3. Age structure of Magnolia sieboldii was not integrity and its infancy was absent, which made population development get threatened. 4.The blooming time lasted about 20 days in the middle and last of May to the middle and the last of June,Full blooming time is from June 1 to June 5;The flower parts change distinctly in blooming time,Pollens are not mature as beginning flowering,but pistil has already matured,pistil stem elongated .After about 20 hours,the stigmas located at basal part is wet,but top stigmas has already turned black. After about another 40 hours,pollens turn to mature and anther become splitting;the stigmas located at basal and middle parts of the receptacle receive more pollens than those at the apical;Pollen lost vigor after 6 days; The pollination rate is 65%,The mean number of accepted pollen per stigma is 3.5;The rate of fruit set are as follows, 13.5% in nature conditions,20.1% in planting,11.3% as taking out perianth,10.7% if there is no stamen, 25.0% in condition of pollination by manpower;Magnolia sieboldii passes its pollens by insects and the pollination efficiency is low for its fewer visiting insects and fewer visiting frequency,Bee and a species of Aphididae insect are the most effective pollinators;The insect-visiting-rate is affected by others plant species in the same flowering phase ,such as Cornus controversa, and the visitation peak is different in different habitats and different weather conditions.The brighter the sky is, the higher the visitation rate and visiting peak comes earlier. 5.Its wooden seed coat make...