关键词: 树枫杜鹃, 结实特性, 种子萌发, 种子形态变异, 光照条件

Abstract:

Objective: This study aimed to explore the fruiting and seed germination characteristics of Rhododendron changii and their response to environmental factors, so as to provide scientific basis for revealing the endangered mechanism and formulating conservation strategies. Method: Fruiting quantity characteristics of population and individual plants, cone and seed characteristics were investigated, and their correlations with environmental factors were analyzed. The effects of maternal plant traits, light intensity, fruit traits and seed morphological phenotype on seed germination were examined. Also, the influence of environmental factors such as different light and temperature during germination and seed soaking treatment with GA₃ at different concentrations were discussed. Result: 1) Fruiting characteristics of R. changii population growing in shrub and mossy dwarf forest were better than those in broadleaf forest (P < 0.05), and the percent of seed bearing mother trees ranged from 39.58% to 66.67% in four populations. The stratification effect of seed setting in canopy was obvious, and the fruit setting rate was between 43.90% and 58.62%, and the low seed plumpness rate varied from 9.89% to 15.71%. Morphological phenotype of seeds from the same maternal plant showed continuous variation, and the seeds with different morphological phenotypes possessed great breeding potential. 2)Fruiting was mainly affected by the limitation of light resources. The light condition of maternal plants was positively correlated with fruit setting rate, full-developed seeds rate and seed width (P < 0.01). The less light was, the lower percentage the full-developed seeds was and the more the oblong seeds (seed width/seed length < 0.4) were. 3)The seed germination characteristics were mainly affected by the morphological phenotype of seeds, followed by light condition and age of the maternal plant and the degree of fruit cracking. That is, the greater the ratio of seed width to seed length and the more sufficient lighting of the maternal plant, the higher the seed germination rate and vigor index of seedlings. The older the maternal plants and the more complete the fruit cracking, the lower the seed germination rate and vigor index of seedlings. In addition, the germination ability of oval seeds (seed width/seed length ≥0.4) was better than that of long-round seeds. 4)The seed of R. changii had light-requiring physiological dormancy. The germination rate under dark conditions was significantly lower than that under light conditions. The seed germination rate and seedling vigor index were positively correlated with light. The germination rate and seedling vigor index were significatly increased through seed soaking treatment with GA₃ in the suitable concentration range of 400-600 mg·L^-1. The seeds had a wide range of adaptability to temperature with germination just at 5 ℃, but the proportion of deformed seedlings was larger under low temperature conditions, and the optimum temperature for germination was 20-25 ℃. Conclusion: The intense light competition in the natural community leads to continuous decline of suitability of the habitat, and gradually tends to small populations. Limitation of light resources affects fruiting characteristics, causing the decline of seed yield and quality, and hence decline of the sexual reproductive ability gradually. Under the adverse natural conditions such as weak light under the forest, the transformation from seed to seedling is inhibited. Seeds germination starts at low temperature but with low germination efficiency, which increases the risk of population. Thus, forest trees should be thinned and surface litter should be cleared to improve the light condition of population and soil seed bank. In order to maintain the population development, artificial propagation should be implemented. The seedlings could be cultivated with yellowish-green fruit with slightly cracked capsules at the early stage of fruit ripening and oval seeds.

Key words: Rhododendron changii, fruiting characteristics, seed germination, seed morphology variation, lighting condition