Spatiotemporal variability in tree ring's δ^(13)C of Picea crassifolia in the Qilian Mountains:climatic significance and responses to rising CO_2

The carbon isotopic composition (δ13C) of tree rings was used to assess changes in intrinsic water-use efficiency (Wi) to increasing atmospheric CO2 and climate change during the period of 1891-2003.Five Qinghai spruce (Picea crassifolia) stands were selected in the Qilian Mountains,growing along a precipitation gradient.All five δ13C were correlated to each other,but two sites (DDS and CLS),which are far from the main body of the mountains,show relative weak connections to other sites.Although trees at all sites had improved their Wi in response to increasing atmospheric CO2 concentration,spruce growing in the regions far away from the main body of the mountains were less sensitive to improved Wi than those of other sites.Based on the correlation between carbon isotope discrimination (Δ) and Palmer Drought Severity Index (PDSI),the drought history covering the period of 1891-2003 was reconstructed in the study region.The two most severe drought epochs of the late 1920s and the last decade were caused by reduced precipitation and climate warming,respectively.Our results will be useful in assessing any further spatial climate-related bioclimatic information.

Relative humidity reconstruction for northwestern China's Altay Mountains using tree-ring δ^(18)O

Relative humidity is an important factor in water and water vapor feedback cycles.In this study,we established a 222-year annual tree-ring δ^(18)O chronology for Siberian larch(Larix sibirica Ldb.)from the Altay Mountains in northwestern China.Climate response analyses revealed that the relative humidity was the primary factor limiting tree-ring δ^(18)O fractionation.Based on our analysis,tree-ring δ^(18)O can be used to reconstruct the July–August relative humidity based on both a reasonable mechanism of tree-ring δ^(18)O fractionation and a statistically significant regression model.We used this model to reconstruct variations in the July–August relative humidity,and the model explained 47.4% of the total variation in the measured relative humidity data from 1961 to 2011.The relative humidity in the study area increased from 1900 to the 1990s and decreased thereafter.Two regime-shift dry periods were detected during the study period(one from 1817 to 1830 and the other from 2004 to 2011).