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Multifunctional Bracts Enhance Plant Reproductive Fitness in Alpine Areas of Himalayas
source:Key Laboratory of Biodiversity and Biogeography, CAS     author:SONG Bo     2012-11-08

Although alpine areas are generally characterized by low temperatures, high solar radiation, strong winds, cloudiness, frequent precipitation, low levels of insect abundance and activity and etc., it harbours high biodiversity. Thus, how these plants reproduce successfully in hostile environmental conditions is the topic of evolutionary biology. Plants in these areas frequently exhibit highly specialized structures to cope with the various stresses, for example, greenhouse and snowball plants. However, the specific evolutionary adaptive mechanisms of these specialized structures are still unclear.

Recently, Ph.D student SONG Bo and Prof. SUN Hang, from Kunming Institute of Botany, Chinese Academy of Sciences, investigated the evolutionary adaptive significances of large and showy bracts in Rheum nobile, a giant herb endemic to eastern high Himalayas. Bracts increased flower and fruit temperature on sunny days, greatly decreased the intensity of ultraviolet-B (UV-B) radiation reaching flowers and fruits, and prevented pollen grains being washed away by rain. Pollen germination experiments indicated that high temperature could promote pollen germination, while pollen grains exposed to rain and UV-B radiation at ambient levels were seriously damaged. Furthermore, bract removal decreased the number of pollinators visiting flowers. When bracts were removed before or after flowering, fecundity and progeny quality were adversely affected, but seed predation by larvae of pollinators decreased. A cost–benefit analysis demonstrated that the cost of bracts, i.e., increased seed predation, is modest. Based on these results, it is suggest that the bracts of R. nobile promote pollen germination, protect pollen grains from rain and intense UV-B radiation, enhance pollinator visitation during flowering, and facilitate the development of fertilized ovules during seed development. It is concluded that multifunctional bracts of R. nobile are an effective adaptive strategy in hostile alpine environments and might have been selected for because of abiotic environmental conditions as well as for enhancing pollination success.

This results have been online published in Oecologia http://www.springerlink.com/content/w8uk2x52t03h7224), and supported by the National Natural Science Foundation of China (40930209) and Hundred Talents Program of the Chinese Academy of Sciences (2011312D11022).
Fig. 1  Rheum nobile (a-g). a: early flowering stage; b: flowering stage; c: late seed development stage; d: flowers concealed by bracts; e: bract removed before flowering; f: flowers protected by bracts, after rain; g: flowers with bracts removed, after rain. (Image by KIB)

 

Fig. 2  Flow chart of reproductive gains (solid lines) and losses (dotted lines) from flower to seed germination for Rheum nobile when bracts were either removed before or after flowering and compared to control plants. (Image by KIB)


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