Preliminary Responses Of Phenology And Growth Of Typical Dominant Species In Sub-alpine Timberline Ecotone To Simulated Global Warming, Western Sichuan

Global climate change characterized by global warming has been changing the structure and function of terrestrial ecosystem. According to International Panel on Climate Change(IPCC), global air temperatures are predicted to increase 1.8～4.0℃over the this century. It has been generally expected that the responses of terrestrial ecosystems in arctic and high mountain regions to global warming could be more sensitive and faster. Nevertheless, so far only very few experiments have been done to study the responses of vegetations in alpine ecosystems, especially in alpine timberline ecotones in middle latitudinal area to simulated global warming. Alpine timberline ecotones are considered to be the key zones in response to raising temperature. Low temperature is one of the most important factors constraining physiological activities and growth of alpine plants. There are many different functional species coexisting among short-distances in alpine timberline ecotone, so the responses of process of genetic exchange, individual migration and species competition etc to global warming could be more sensitive and faster. Phenology and growth of plants are two sensitive and readily-observed indicators in response to global warming, and play important roles in carbon budget. The sub-alpine forest ecosystems in the western Sichuan located at the transitive zone from Qinghai-Tibet plateau to Sichuan basin, are sensitive to global change. In this paper, the responses of phenology and growth of typical vegetations in timberline ecotone in Dawodang of Wanlang National Nature Reserve, Western Sichuan to simulated global warming were studied by using the open-top chamber (OTC) method. The results are as follows:1) OTC (Open-Top Chamber) increased mean air temperature (1.2 m) by 2.9℃throughout the growing season, and daily maximum temperature was 3.4～5.5℃higher in the OTC than in the CP. However soil temperature at the depth of -5 cm did not clearly differ between the OTC and CP throughout the growing season. Soil water content was 3.09 lower in the OTC than in the CP during the growing season.2) Abies faxoniana in the OTC showed earlier bud break. There were significant differences in bud break for Betula utilis between the OTC and the CP; however Betula utilis in the OTC showed later defoliation. Betula utilis had longer individual leaf longevity in the OTC than in the CP. Compared with ambient temperature, elevated temperature resulted in higher leaf and branch growth rates and relative growth rates of basal diameter for two species; Different responses (positive, negative or no effects) were found in branch length, branch number and leaf distribution pattern for two species.3) Compared with control plots, deciduous shrubs (Spiraea mongolica and Conicera hispida) and evergreen shrub (Daphne retusa) showed earlier bud break, flowing and fruit coloring; Flower longevity of all three target species and leaf life-span of deciduous shrubs (Spiraea mongolica and Conicera hispida) were extended. Evergreen shrub (Daphne retusa) in the OTC had higher leaf survival rate. No significant differences in number of flowers and fruits for others between OTC and CP were found except Spiraea mongolica. Elevated temperature stimulated branch and leaf growth. Leaf nitrogen concentration generally represented a trend of decrease in the OTC, however specific leaf area tend to increase.4) Allium prattii and Artemisia smithii in the OTC showed significantly earlier sprouting, flower-bud developing and flowering and later senescence. Elevated temperature had certain effects on leaf size and morphology for two observed species. Compared with control plot, the rhythm of scape of Allium prattii and Artemisia smithii in the OTC were accelerated and the response of Artemisia smithii appeared to be more sensitive. During the growing season 2007, leaf growth rate of Allium prattii in the OTC was advanced and total length of green parts of leaves was longer in the OTC than in the CP.5) No clear differences in responsive pattern were found among different functional types (tree seedling, deciduous shrub, evergreen shrub and herbage). Almost all target species represented earlier activities in spring phenophase and later autumn phenophase; vegetative growth was enhanced and reproductive parameters did not change clearly. But there was certain difference in responsive intensity among different functional types.