| We studied the breeding system and pollination ecology of Meconopsis integrifolia (Papaveraceae), an alpine herb, for two consecutive years. Five plots (plot 1,4452 m. a.s.l:plot 2,4215 m a.s.l:plot 3,4081 m a.s.l:plot 4,3841 m a.s.l:plot 5,3681 m a.s.l) were established along an altitude gradient of the Balang Mountains. Flower longevity, stigma height and the highest stamen were recorded. The stigma receptivity and pollen viability were tested by Benzidine-H2O2 method and TTC method, respectively. The breeding system was tested by experimental approaches, and flower visitors were observed for the life span of the flower. Flower and environment temperatures were also recorded. In order to test the level of pollen limitation at different elevation plots, we also designed two treatments, meaning, supplemental hand pollitaion and intact.In natural populations, the early flowering season of M. integrifolia is in mid-late May, and then the full flowering stage is in the first ten-day period of June, afterwards, ending flowers in mid July. With the increase of altitude, flowering time in each stage of M. integrifolia existed a certain delay. Higher altitude, more obvious delay. Flower longevity in plot 1 and 2 was higher than that in longer than plot 3,4 and 5. Among the observational individuals, floral longevity of early blossom flowers in higher altitude plots is longer than those in lower altitude plots. However, there is no significant variations of late blossom flowers among different plots.The stigmas were higher than the anthers at the beginning of anthesis, and the distance between the stigmas and the anthers decreased gradually with the progress of flowing. The stigmas and the anthers came into touch in 65% of the sampled flowers when the corolla wilted, indicating an incomplete herkogamy. The stigmas became receptive before the dehiscence of anthers (protogyny). Under natural conditions, stigma receptivity lasted for 8 d and pollen viability lasted for 2 day. Flies and Thripidae spp could move within the flower, the latter finally resulted in "facilitated selfing". About 65% of the sampled plants could set seed by autonomous pollination.Hand-pollination experiments indicated that M. integrifolia was self-compatible and did not exhibit apomixis. Seed set was significantly increased after supplemental hand-pollination, suggesting the pollen-limitation of reproduction. Pollen limitations were evident in all plots due to the lack of sufficient outcrossing pollinators. Two different selfing mechanisms, unexplored here, may provide a partial compensation for the natural reproduction of this alpine species in the arid, alpine habitats.Contrast to intact treatment, supplemental hand pollination had significant increase seed set per fruit in all five plots. These indicated the reproductive success of M. integrifolia was limited by pollen transfer. Interestingly, the level of PL is rather uniform from plot 5 to plot 2, but PL index doubles in the highest altitude plot (plot 1). This difference may due to the increased severity of various ecological factors and decreased species richness that occur at altitudes over a certain value, which obviously limits the activity of pollinators, including the associated visitation rates. Above that value, the level of PL increases greatly. Insect visitation rates in plot 1 (the highest altitude population) is significant lower than other plots, these just confirm the view. Meanwhile, there is a significant negatively association between PL index and insect visitation rates. Also, high levels of PL can be attributed to the low incidence of autofertility.The pollinators in plot 1 and 2 were flies, and in plot 3,4 and 5 were flies and Thripidae spp. We observed that flies could move and transfer pollen between plants. There was a significant difference in the visiting frequency of flies between plots, with plot 1 being the lowest (0.15±0.09) and plot 2 the highest (0.59±0.04).At the same time of visitor observations, we calculated the flower temperature and environment temperature in all five plots. The results showed that:before 9:00 and after 18:00 daily, environment temperature was significantly higher than flower temperature; after 9:00, flower temperature and environment temperature increased gradually, but environment temperature increased faster, leading to environment temperature significantly higher than flower temperature during 12:00-15:00. Inetrestingly, the files number changed regularly with the temperature difference between flower temperature and environment temperature, meaning, when flower temperature was higher than environment temperature, more flies visit flowers; however, when flower temperature was lower than environment temperature, several flies visit flowers, or none flies. There were significantly negative associations between flies number and temperature difference in all five plots. Nectar has not been secreted by M. integrifolia, also, visitors do not feed on pollen. These results indicated that M. integrifolia could attract pollinators by providing them a warm shelter. |
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