| Photinia magnoliifolia is distributed only in Qingshan lake, Lin’an. Its distribution area is extrem narrow and low number are found. The related researches of this plant remain blank. The aims of this research are to investigate the blossom biological characters of Photinia magnoliifolia through observing its phenology, the process of flower bud differentiation and floral dynamics; to investigate its breeding system and mechanism through measuring the pollen-ovule ratio( P/O), pollen viability, stigma receptivity and observation of structure of breeding system; compared with other three Photinia plants Photinia beauverdiana, Photinia beauverdiana var. brevifolia and Photinia subumbellata, it measured the light response curve of net photosynthetic rate, chlorophyll fluorescence parameters and related contents of chlorophyll of four plants to identify their photosynthetic characters. The results showed below:1. Field observation showed that Photinia magnoliifolia germinates and grows at the end of Febrary when the temperature rewarms each year, blooms in the beginning of May followed by bearing fruit and it becomes dormant in December. Flower bud differentiation mainly occurs between March and Apil and can be divided into six stages: undifferentiated stage, initial differentiated stage, sepal primordium differentiation stage, petal primordium differentiation stage, stamen primordium stage, pistil primordium differentiation stage. The bud time of Photinia magnoliifolia lasts about half month, it blooms mainly in May, which lasts around 15 days and less than 7 days each floweret. The bloom process can be divided into 6 stages: 0 green-bud stage, 1 white-bud stage, 2 initial-flower stage, 3 fullbloom stage, 4 terminal-flower stage and 5 flower-decline stage. Its long bud stage combined with rainy season leads to reduction of blossom to some extent, which could be one of the reasons being endangered.2. Research on breeding system and mechanism of Photinia magnoliifolia showed that its pollens have the highest viability at the full-bloom stage and nearly lost the viability at the flower-decline stage. This trend is consistent with alteration of stigma receptivity. Dichogamy is observed in Photinia magnoliifolia, maturation of stamen is earlier than that of pistil, which prevents its self-fertilize to some extent. On the other hand, dichogamy leads to florescence asynchronism of stamen and pistil. The low possibility that pistil develops into mature seeds has a strong impact on breeding of offsprings. This tallies with the natural phenomenon that there are no seeds in the undergrowth. Besides, pollen-ovule ratio of Photinia magnoliifolia is 837.2±220.7, so its breeding system belongs to compatible outcross. Its OCI is 3, therefore it belongs to partial self-compatibility, sometimes pollinators are needed, which could be ensurance of its reproduction to some extent.3. According to the identification of photosynthetic characters in these four Photinia plants, Photinia magnoliifolia has middle level on the maximum net photosynthetic rate, light saturation point and apparent quantum yield, lowest dark respiratory rate and light compensation point. Results of chlorophyll fluorescence parameters indicated that Photinia magnoliifolia has the highest Yield, higher level of Fv/Fm、Fv/Fm, q N and second highest contents of chlorophyll. These photosynthetic parameters infer that Photinia magnoliifolia is member of heliophytes with good shade-tolerance ability. It has higher actual photosynthetic ability with higher potential activity. However, its adaptability to hard light is poorer. The light condition of origin place of Photinia magnoliifolia is poor, which might be one of the reasons being endangered. |
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