川西亚高山不同海拔岷江冷杉树轮碳稳定同位素对气候的响应

Abstract

The tree-ring stable isotope technique is an effective approach to climate reconstruction and to establishment of tree responses to environmental factors.In this study,the tree-ring samples of Abies faxoniana from a sub-alpine forest of Wolong in Western Sichuan were used to develop the tree-ring width chronology and stable carbon isotope series based on the standard dendrochronology methods and the stable carbon isotope techniques.The Wolong Nature Reserve in Western Sichuan is located in a transition zone from the Chengdu plain to the Tibeten Platau,with a warm and moist summer andcold and dry winter.Abies faxoniana is the dominant tree species of the sub-alpine forests at the elevation of 2600—3200 m.Tree ring data were collected in 2010 along an elevation gradient(at 2750,2950,3150 m).Climate data were obtained from two nearby national climate stations,Dujiangyan(103° 34' E,30° 59' N) and Xiaojin(102° 21' E,31° N).Isotopic analyses were done at the Chinese Academy of Forestry.With the data and analyses,we established responses of Abies faxoniana tree-ring carbon stable isotope composition to several climatic factors(e.g.,precipitation,mean month temperature,and mean month relative humidity).The main results of this study are as follows:1) The carbon stable isotope series of Abies faxoniana(1904—2009) varied from-23.33‰ to-26.31‰ with the average value of-24.91‰,with the coefficient of variation ranging from-0.011 to-0.038.The carbon stable isotope series showed strong first-order autocorrelation(i.e.,0.651,0.936,and 0.333 along the elevation gradient).2) The tree-ring carbon stable isotope composition showed similar trends at the same altitude,while the isotope composition displayed different trends as altitudes change.However,the relationships between the tree-ring carbon stable isotope composition and climatic factors were complicated.The tree-ring detrend series(DS) values from the lower altitude showed a significant positive correlation to the mean monthly temperature of the December of the current year and the mean monthly relatively humidity of the August in the previous year(P0.05).The tree-ring DS values from the higher altitude showed a significant positive correlation to the mean monthly temperature of the April of the current year and the mean monthly relatively humidity of the August in the previous year(P 0.05).The tree-ring DS values from the mid-altitude showed a significant positive correlation to the mean monthly temperature of the February and November of the current year and the January and November in the previous year(P0.05).The most sensitive variable to the DS values was the winter temperature with a strong "lag effect".The results indicated that tree ring growth of Abies faxoniana in sub-alpine is mainly constrained by temperature with little dependence on rainfall.Thus,a warming climate should help improve the radial growth rate and the survival capability of Abies faxoniana,and this in turn should increase the stability of sub-alpine dark forests in Western Sichuan.The results should help alleviate the inadequacies of doing research in Qinghai-Tibeat plateau with fewer meteorological stations and shorter observation periods,and provide baseline data for studying responses of conifer trees to climate change in the region.