|其他摘要||The vast Qinghai-Xizang Plateau is often called as the third polar region of the world. The Qinghai-Xizang Plateau is subsequently enclosed within an elliptical circle of mountain ranges, for example, the Himalayas, Kunlun Mountain, and Hengduan Mountain. “Hengduan” Mountain is a Chinese name which means “transverse cutting mountains”, and the region is characterized by formidable high parallel mountain ranges and deep gorges that are aligned roughly north-south. Climatically, the uplift of the Qinghai-Xizang Plateau and surrounding ranges resulted in a monsoon climate in this region that draws wet, warm winds towards the highlands from the nearby sea in summer and dry, cold winds form the highland in winter. Consequently, Hengduan Mountain has become one of the world’s biodiversity hotspots.
In the ragged and stony alpine environment of the Hengduan Mountain was commonly name as “alpine screes” which subjected to the high altitudes and a monsoon climate, characteristic dominant factors are general incessant cold rain or sleet and dynamic fluctuations in weather in a single day within short summers. The nature of the environmental factors has resulted in plants evolving rather unique adaptations to live in this region. Among several alpine plants having highly specialized life forms, three types are the most outstanding. Firstly, the “Woolly plant” having the inflorescence entirely covered with long wool-like hairs, such as Saussurea laniceps and S. medusa (Compositae). Secondly, the “Greenhouse plant” characterized by having the inflorescence cover by huge and semi-translucent bracts, such as Rheum nobile, R. alexandrae (Polygonaceae), Saussurea obvallata, and S. velutina (Compositae). Thirdly, “Cushion plant” , which are typically perennials that live for more than 100 years and develop a branched woody rootstock, forming a compact cushion to hemisphere-like structure, such as Androsace globifera (Primulaceae), Arenaria oreophila and A. polytrichoides (Caryophyllaceae). Their specialized morphology provides an opportunity for researcher to investigate the adaptive strategies of alpine plants in this region. The main aims of this study are to understand the ecological adaptability of those three highly specialized plant life forms to the alpine environment in the Hengduan mountain areas from population and community levels. The results show that:
1. Densely hairs covering the inflorescence of Saussurea medusa, one of the representatives of “Woolly plant” act as a heat trap. The warming effects of pubescence on the inflorescence of S. medusa accelerating the growth of the reproductive organ are an adaption to the extremely short growing season in the alpine screes of the Hengduan Mountain.
2. In addition to heat trap, densely hairs on the flower head of S. medusa act as a buffer against rapid fluctuations of temperature and incoming radiations. The buffer effects of hairs on the inflorescence of S. medusa ensuring a warm and constant phyto-climate for the development of inflorescence is an adaptation to the ever-changing weather conditions in the alpine life zone of the Hengduan Mountain.
3. High reflectance (20-40%) of hairs in S. medusa in the PA (photosynthetic active) range protects inflorescence underneath from extremely high incoming radiations which occurred in cloudy days in the high elevations of Hengduan Mountain. Therefore, the unique and specialized morphological feature of “Woolly plant” life form is an adaption to kinds of environmental stresses in the alpine screes of the Hengduan mountain areas.
4. Due to the peculiar anatomical and spectral characteristics, the yellow to red colored bracts in one of the representatives of the “Greenhouse plant”, Saussurea velutina, play an important role in warming up of flower head. The warming effects of bracts in S. velutina ensured seed set. In addition, the warming effects by bracts in S. velutina resulted in the faster growth of reproductive organ compared with manually opened treatment ones.
5. The warming effects and their mechanisms of bracts in S. velutina are almost identical with bracts in Rheum nobile and R. alexandrae (Polygonaceae). Therefore, the semi-translucent bracts in S. velutina, R. nobile, R. alexandrae and other systematically distant taxa inhabiting the alpine screes of the Hengduan Mountain, have evolved as a common morphological adaptation to the fluctuating and extreme weather conditions during the summer monsoonal climate of this region.
6. Cushion of Arenaria polytrichoides acts as nurse plant facilitating the establishment of other plant species on its surface. Positive spatial associations with cushion were more frequent at higher elevations. Therefore, the nurse effects of A. polytrichoides cushions become more pronounced with the increasing elevation.
7. Warmer substrate, greater water content and higher nutritional contents within A. polytrichoides cushions as opposed to outside are possible factors favoring strong plant recruitment on cushions at higher elevations in the harsh alpine environment in Hengduan Mountain.
In conclusion, the two plant life forms “Woolly plant” and “Greenhouse plant” can adapt well to the tough environment of the alpine screes in Hengduan Mountain which is contributing to their prominent and highly specialized morphology. Meanwhile, the similarities of adaptive strategy among systematically distant taxa within the same plant life form exhibit the harmonious relationship between plant functions and environments. Additionally, the increasing facilitation by A. polytrichoides cushions at higher elevations seems to be related to the modification of the harsh environmental conditions by cushions of A. polytrichoides. The striking altitudinal variation in association with A. polytrichoides cushions is of importance to clarify the impacts of the uplift of Himalayas on the adaptation and evolution of alpine plants in this region.|