Reproductive ecology of Bulbophyllum ambrosia (Orchidaceae)

doi:10.3724/SP.J.1258.2011.01202

Abstract

Abstract:

Aims Bulbophyllum ambrosia is an epiphytic orchid growing on rocks and trees in limestone seasonal rainforests and is commonly distributed in southern China. We found no fruit set of B. ambrosia during long-term monitoring of species diversity, reproductive phenology and pollinators of local orchid species in Green Stone Forest Park. Our objective was to determine barriers to fruit set in B. ambrosia.
Methods Flowering phenology and natural fruit-set were monitored once a week for three years. Floral morphology was studied during flowering time. We also investigated the rate of pollinia removal and deposition over two flowering seasons. To determine the self-compatibility system, different hand-pollination treatments were conducted over three years at the study site. We also observed floral visitors for 150 h over two years.
Important findings Unlike other myophilous species in the genus, B. ambrosia is fragrant and presents nectar as reward. Observations of floral visitors showed that honeybee (Apis cerana cerana) was the only efficient pollinator and regularly visited flowers with high frequency. In natural populations, the rates of pollinia removal and deposition were high, but there was no fruit set. The hinged labellum plays an important role in the process of honeybee pollination of B. ambrosia. No fruit was found in the selfing pollination treatment, and fruit set of crossing pollination treatments was >90% over two years, suggesting that B. ambrosia is self-incompatible. To our knowledge, this is the first report of a self-incompatible species in Bulbophyllum. Individuals of B. ambrosia have a mass of flowers opening simultaneously during anthesis because of its strong ability in cloning. Honeybees visited 4.29 ± 0.40 flowers ( n = 66) in average per visitation, which may lead to geitonogamy. Self-incompatibility causes no fruit set as the result of geitonogamy. These results provide useful implications for future conservation of B. ambrosia.

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Key words: absence of fruit set, Bulbophyllum ambrosia, geitonogamy, orchid conservation, self-incompatibility

CHEN Ling-Ling, GAO Jiang-Yun. Reproductive ecology of Bulbophyllum ambrosia (Orchidaceae)[J]. Chin J Plant Ecol, 2011, 35(11): 1202-1208.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2011.01202

https://www.plant-ecology.com/EN/Y2011/V35/I11/1202

Figures/Tables 5

Fig. 1 Niche, flower and visitors of Bulbophyllum ambrosia. A, B. ambrosia growing on tree or rock. B, The flower of B. ambrosia showing typical hinged labellum. C, Vespa basalis visiting a flower of B. ambrosia. D, Apis cerana cerana visiting a flower of B. ambrosia. Arrow indicates the pollinia of B. ambrosia.

Table 1 The floral traits related to pollinations of Bulbophyllum ambrosia

花部特征 Floral trait	样本数 Sample size	平均值±标准误差 Mean ± SE (mm)
通道长 Length of the access	20	19.13 ± 0.17
入口高 Height of the entrance	20	2.67 ± 0.09
唇瓣宽 Width of the lip	20	5.19 ± 0.12
唇瓣到蕊柱足距离 Distance between column foot and lip	20	2.43 ± 0.07
关节膜长 Length of the filmy joint	20	1.57 ± 0.05
关节膜宽 Width of the filmy joint	20	0.92 ± 0.03

Table 2 The fruit sets of Bulbophyllum ambrosia under different hand-pollination treatments

年份 Year	处理 Treatment
	对照 Control		自交 Selfing		异交 Crossing
	结实率 Fruit rate	样本量 Sample size	结实率 Fruit rate	样本量 Sample size	结实率 Fruit rate	样本量 Sample size
2008	-	-	0	55	90.2%	51
2009	0	134	0	32	0	33
2010	0	79	0	40	95.0%	20

Fig. 2 The mean number of Apis cerana cerana visiting per hour in 2009.

Fig. 3 The diagrammatic sketch of Apis cerana cerana pollinating a flower of Bulbophyllum ambrosia. A, A. cerana cerana with pollinia on its back lands the hinged labellum of B. ambrosia. B, The hinged labellum of B. ambrosia is pushed down. C, The hinged labellum rebounds and throws A. cerana cerana at the inside of flower. D, A. cerana cerana leaves flower of B. ambrosia and takes pollinia away.

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