Reproductive Ecology Of Rhododendron Polylepis In Huaxi Sub-alpine Botanical Garden

Based on study of Rhododendron polylepis's flowering phenology, floral traits, pollen viability, stigma receptivity, breeding system and pollination biology, discussion on ecological adaptation mechanisms to protect reproductive success in the harsh environment of Alpine, is designed to provide data support the introduction and domestication for future work and to provide a scientific basis for species protection, and results showed that:(1) R. polylepis has large purple corolla, which contributes to attract pollinating insects in mountain areas' harsh environmental conditions. Herkogamy phenomenon (pistil is always higher than stamens) and slow movement of stamen is a mechanism of avoid self-pollination to improve the success rate of outcrossing. Viscin threads between R. polylepis's tetraded pollens bond pollen grain for pollination, reduced insect visits to remove all pollens needed within the anthers, improved pollinator pollination efficiency and pollinators rewards, and increased the possibility of all ovules which pollinated by the same pollen source, reduced the competition in non-homologous pollens.(2) The flowering period of R. polylepis was from early April to early May, and flowering duration period of species, individual, single flower level were 24?25 d,22 d,13?15 d and 7?9 d respectively. R. polylepis has a relatively high index of synchronous flowering 0.815, and its blooming process showed a single peak curve, showing a "substantial, concentrated" flowering pattern; individual relative flowering intensity frequency distribution is concentrated in 10%?50%.(3) The correlation analysis of flowering phenology indicators and fruiting number showed that initial flowering time showed significant negative correlation with flowering duration time, and flowering duration time was significantly positively correlated with fruiting number. The comparability of R. polylepis's flowering phenology among populations in different years showed that plant individual flowering phenology process was largely determined by genetic factors. "Centralized flowering mode", higher synchrony index and longer flowering duration were reproductive characteristics of R. polylepis to adapt to high mountain environment.(4) R. polylepis's, pollen viability reached more than 80% in the early flowering, and pollen viability was still about 60% on 5 d. And its stigma has long receptivity period from stigma exposure to 7th, the receptivity was more stronger in the first 5 days. Strong pollen viability and long stigma receptivity period were the reproductive compensation mechanism that formed in its long evolutionary process. Its pistil develops before stamen in the bisexual buds development process, and showed as protogynous. R. polylepis avoided selfing by protogynous phenomenon, and avoided mutual interference between male and female functions to ensure the genetic diversity of species and improve its adaptive capacity.(5) The breeding system of R, polylepis is outcrossing, partially self-compatibility and needing pollinators by Out-crossing index (OCI)?4, according to Danfi's standard; R. Polylepis's breeding system is facultative autogamy by its pollen-ovule ratio (P/O)= 248.25±44.57, according to Cruden's standard; bagging experiment showed that seed rate of CK was about 60%, and self-pollination rate was about 50%, artificial autogamy and outcrossing pollination seed were over 80%, so the characteristics of self-compatibility was confirmed and outcrossing had high seed rate, and artificial pollination could improve R. polylepis's seed rate, there was no apomixis phenomenon. In conclusion that the breeding system of R. polylepis is a mixed mating system, showed cross-pollinated plants, part of self-compatibility, needing pollinators, with outcrossing as the main breeding system and also retain the selfing way, which had a major reproductive significance for the continuation of natural populations.(6) The effective pollinators of R. polylepis were hymenoptera bumble bees and honeybees, not flies. The main purpose of flies visiting flowers was grazing style, filaments, petals and other floral organs, without real and effective contact with stigma. The efficiency of bumblebee pollination reduced the adverse effects of plant pollination on alpine environment, while it was a single species. In addition, R. polylepis'seed rate reached more than 80% by artificial pollination conditions, while was only 60% in natural conditions, so the seed rate did not reach the potential fertility, which indicated that there was a certain degree of pollination restriction under natural conditions. Lack of pollinators was the main pressure of R. polylepis to deal with alpine environment.