西双版纳思茅松(Pinus kesiya)年轮宽度和早晚材稳定氧同位素对气候因子的响应

Climate responses of tree-ring widths and stable oxygen isotopes of Pinus kesiya in Xishuangbanna,southwestern China

由于热带地区大部分树木缺乏清晰的年轮,因此树木年轮的研究相对较为薄弱。树轮稳定同位素较树轮宽度能更好地记录环境变化的信息,特别是研究年内稳定同位素可以提供气候变化的季节动态信息。本研究以西双版纳地区的思茅松(Pinus kesiya Royle ex Gordon)为研究材料,建立了1985—2018年的思茅松年轮宽度、早材和晚材稳定氧同位素(δ^(18)OEW和δ^(18)OLW)年表,分析了树轮宽度、δ^(18)OEW和δ^(18)OLW年表与温度、降水和标准化降水蒸散指数(SPEI)等气候要素的相关关系,并研究了思茅松δ^(18)OEW和δ^(18)OLW记录的降水、SPEI变化以及与大尺度季风环流的关系。结果表明:西双版纳地区思茅松树轮δ^(18)OEW和δ^(18)OLW的均值接近,并且均呈下降趋势,这种下降趋势可能与西双版纳地区的雾日减少有关。树轮宽度对气候因子响应不敏感,仅与上一年7月的温度呈显著负相关关系,与上一年7月降水呈显著正相关关系。δ^(18)OEW主要记录了生长季早期(4月和5月)的降水和SPEI信号,而δ^(18)OLW主要记录了生长季末期(8月)的降水和SPEI信号。δ^(18)OEW和δ^(18)OLW分别能很好地代表区域5月和8月的干湿变化。树轮δ^(18)O也受到了ENSO的影响,其中树轮δ^(18)OEW与3—12月厄尔尼诺呈显著正相关关系,树轮δ^(18)OLW与9—12月厄尔尼诺呈显著正相关关系(p<0.05)。该研究表明西双版纳地区的思茅松树轮早晚材δ^(18)O具有重建区域干湿变化的潜力。

Background,aim,and scope Due to the lack of clear ring boundaries in most tropical tree species,tree ring studies in tropical region are still rare.Tree ring stable isotopes variations generally record stronger climatic signals compared with ring width,thus have great potential in dendroclimatical study in tropical region.Moreover,intra-annual variations of tree ring stable isotopes could provide seasonal climatic information.The present study aims to investigate the potential of tree ring width and stable oxygen isotope variations of a tropical pine species in Xishuangbanna,southwestern China.Materials and Methods The present study developed tree ring-width and stable oxygen isotope chronologies in earlywood(δ^(18)OEW)and latewood(δ^(18)OLW)of Pinus kesiya Royle ex Gordon(Simao pine)in Xishuangbanna.We performed correlation analyses between tree ring width,δ^(18)OEW andδ^(18)OLW and climatic factors such as monthly mean temperature,monthly precipitation and Standardized Precipitation Evapotranspiration Index(SPEI)during the period 1985—2018.Spatial representatives were investigated by correlatingδ^(18)OEW andδ^(18)OLW with regional precipitation.The relationships between tree ring oxygen isotope and El Niño-Southern Oscillation(ENSO)were also investigated.Results The mean values ofδ^(18)OEW andδ^(18)OLW were 23.08‰and 23.83‰,respectively,and bothδ^(18)OEW andδ^(18)OLW showed decreasing trends.Tree ringwidth chronology of P.kesiya in Xishuangbanna correlated negatively with the temperature and positively with precipitation in July of the previous year.δ^(18)OEW chronology were negatively correlated with precipitation in the early growing season(May),whereasδ^(18)OLW mainly recorded precipitation signal at the end of the growing season(August).δ^(18)OEW was positively correlated with SPEI in April,and negatively correlated with SPEI in May,whereasδ^(18)OLW was negatively correlated with SPEI in August.Bothδ^(18)OEW andδ^(18)OLW were positively correlated with El Niño and negatively correlated with Southern Oscillation Index.Discussion Our study showed that tree growth of P.kesiya in Xishuangbanna is not sensitive to climate variables.The mean value ofδ^(18)OEW(23.08‰)andδ^(18)OLW(23.83‰)is similar,which may due to the low variability of rainfallδ^(18)O during the growing season.The decreasing trends of bothδ^(18)OEW andδ^(18)OLW could be related to the decreasing of the contribution of fog water to the tree water use in Xishuangbanna.δ^(18)OEW andδ^(18)OLW were negatively correlated with regional precipitation in May and August,respectively.Strong correlation between tree-ringδ^(18)O and regional precipitation confirmed that tree ringδ^(18)O has the potential to reconstruct regional precipitation variability in the tropical regions.Moreover,tree ringδ^(18)O showed high correlation with ENSO index,which implies that ENSO has an important influence on the hydro-climate in the study region.Conclusions Tree ringδ^(18)OEW mainly records precipitation signal in May of the early growing season,whileδ^(18)OLW mainly records precipitation signal in August at the end of the growing season(latewood formation period).Theδ^(18)OEW andδ^(18)OLW can represent the regional precipitation patterns in May and August,respectively.Tree-ring wasδ^(18)O mainly positively correlated with El Niño and negative correlation with the Southern Oscillation Index.Recommendations and Perspectives This study indicates that earlywood and latewoodδ^(18)O of P.kesiya in this region have high potential to reconstruct hydroclimate history in different seasons.