Abstract: [Objective] In forest community, the volatile pathway of allelochemical has a significant impact on its natural regeneration. Rhododendron delavayi, R. agastum and R. irroratum are the pioneer and dominant species in Baili Azalea National Forest Park in Guizhou province. Air samples are collected from pure forests of the three Rhododendron communities to analyze their allelochemical components, in order to provide a scientific basis for the natural regeneration of Baili Azalea National Forest Park.[Method] Field investigations of three major Rhododendron communities (R. delavayi, R. agastum and R. irroratum) under natural conditions were conducted using the method of typical sampling plots, Berger-Parker dominance index, Simpson's diversity index, and Pielou evenness index were calculated for each of the sample plots. Based on these parameters, biodiversity of the communities were characterized. Samples of volatile compounds were collected from the three communities using air bags. Components of the allelochemicals in the three communities were investigated and analyzed by using the solid phase microextraction (SPME) technique and the gas chromatography mass spectrometry (GC/MS).[Result] The Berger-Parker dominance index of the three communities from high to low was R. agastum, R. irroratum and R. delavayi, the Simpson index from high to low was R. irroratum, R. agastum and R. delavayi, and the Pielou index from high to low was R. delavayi, R. irroratum and R. agastum. There were respectively 17, 13 and 11 volatile allelopathy components in the air samples of R. irroratum, R. agastum and R. delavayi identified by SPME-GC/MS, and the main volatile allelopathy component was alkanes in all the three communities. Terpenes, organic acids, esters, ketones and phenols were also detected and they are allelochemicals or have inhibitory effects. The components of R. irroratum community were mainly alkanes, terpenes, ketones and phenols, and the highest component was 2,2,4,6,6-pentamethylheptane (30.81%), followed by 5-ethyl-2,2,3-trimethylheptane (19.87%), decane (11.71%), and dodecane (10.00%). The components of R. agastum community were aminly alkanes, terpenes, esters and organic acids, and the highest component was 2,5-dimethylhexane-2,5-dihydroperoxide (20.23%), followed by 5-ethyl-2,2,3-trimethylheptane (18.13%), dodecane (14.30%), and 2,2,7,7-tetramethyloctane (10.20%). The components of R. delavayi were mainly alkanes, phenols, esters and organic acids, and the highest component was decane (22.92%), followed by 2,2,4,6,6-pentamethylheptane (18.11%), γ-butyrolactone (16.82%), and palmitic acid (11.65%).[Conclusion] The three Rhododendron communities had higher dominance and evenness but lower diversity. The hierarchical structure of Rhododendron community was simple. When the canopy density exceeded more than 90%, the process of natural regeneration from seeds of alpine Rhododendron was difficult to complete. Air samples of the three Rhododendron communities were rich in allelochemicals, mainly including hydrocarbons and their derivatives. And the kinds of allelochemicals were positively correlated with community biodiversity. Further studies are required with focus on how the allelochemicals produce impacts in relation with the habitat conditions in the alpine Rhododendron communities.

Key words: alpine Rhododendron community, biodiversity, allelopathy, gas components, GC/MS