The Ecological Significance of Pubescence in Saussurea Medusa, a High-Elevation Himalayan “Woolly Plant”

Abstract

Several members of the vascular plant genus Saussurea, which are found at elevations exceeding 5000 m, have dense layers of woolly trichomes on their leaves, bracts, and inflorescences, the function of which is not fully understood. Here we explore the thermal benefits of pubescence in Saussurea medusa, both in situ in the Chinese Hengduan Mountains and under controlled conditions. Mean daytime inflorescence temperature was 5.9 K above air temperature. Pubescence removal revealed that most of this warming is not related to pubescence but to radiant warming of the compact inflorescence itself (4.1 K warming in shaved plants, i.e. 1.8 K less). The effect of pubescence on nighttime radiative cooling was negligible. Our data indicated that the functional role of pubescence in these high-elevation plants cannot be attributed solely to producing warming tissues, but may also include other functions such as water repellency and reflection of short peaks of high radiation. These other functions must be specific to a small group of species, given that most other high elevation taxa do not exhibit this woolly character.

The Bracts of Saussurea velutina (Asteraceae) Protect Inflorescences from Fluctuating Weather at High Elevations of the Hengduan Mountains, Southwestern China

“…Additionally, there were no observed differences in the nighttime temperature between the control and treatment inflorescences in S. velutina, hence the hypothesized protection against radiative cooling by bracts in S. velutina was negligible. A similar situation was reported in S. medusa from the same region, where the dense bract hairs had little effect on heat retention and aerodynamic resistance within the inflorescence (Yang et al, 2008). In contrast, Omori and Ohba (1999) reported that inflorescences in R. nobile were maintained at 1.5 uC above surrounding air temperature during nighttime.…”

“…Changeable weather conditions and the short growing season are crucial factors that have influenced the evolution of alpine plants in this area (Ohba, 1988), most of which have specialized morphology for survival in this hostile habitat (Yoshida, 2005). For example, the highly pubescent bracts covering the inflorescence of Saussurea medusa (Himalayan ''woolly'' plant) assist in temperature control and water repellence in the cool humid summer Yang et al, 2008). For plant species growing at high elevations, solar energy absorbed by bracts assists in maintaining the temperature of reproductive organs above cold ambient levels, thereby promoting growth and development during brief intervals of warmth (Kö rner, 2003;Fabbro and Kö rner, 2004).…”

Phylogenetically balanced evidence for structural and carbon isotope responses in plants along elevational gradients

“…various Leontopodium species) or several species of Saussurea in Central Asia (Yang et al 2008). But many alpine plants show little pubescence, and it is quite unclear what the speciWc beneWts of higher pubescence in an alpine setting might be (Körner 2003).…”

Vascular and Cryptogam Richness in the World's Highest Alpine Zone, Tibet

“…Some high-alpine plants have special structures such as silky hairs all over the plant, as with Compositae (Saussurea spp. ), to avoid overheating and decrease transpiration (Gauslaa 1984), or to repel water and reflect short peaks of high radiation (Yang et al 2008). Other adaptational features such as succulent leaves for crassulacean acid metabolism photosynthesis, as in Crassulaceae (Sedum and Rhodiola spp.…”