Tree ring δ18O reveals no long‐term change of atmospheric water demand since 1800 in the northern Great Hinggan Mountains, China. Issue 13 (1st July 2017) - Liu, Xiaohong
Abstract: Global warming will significantly increase transpirational water demand, which could dramatically affect plant physiology and carbon and water budgets. Tree ring δ 18 O is a potential index of the leaf‐to‐air vapor‐pressure deficit (VPD) and therefore has great potential for long‐term climatic reconstruction. Here we developed δ 18 O chronologies of two dominant native trees, Dahurian larch ( Larix gmelinii Rupr.) and Mongolian pine ( Pinus sylvestris var. mongolica ), from a permafrost region in the Great Hinggan Mountains of northeastern China. We found that the July–August VPD and relative humidity were the dominant factors that controlled tree ring δ 18 O in the study region, indicating strong regulation of stomatal conductance. Based on the larch and pine tree ring δ 18 O chronologies, we developed a reliable summer (July–August) VPD reconstruction since 1800. Warming growing season temperatures increase transpiration and enrich cellulose 18 O, but precipitation seemed to be the most important influence on VPD changes in this cold region. Periods with stronger transpirational demand occurred around the 1850s, from 1914 to 1925, and from 2005 to 2010. However, we found no overall long‐term increasing or decreasing trends for VPD since 1800, suggesting that despite the increasing temperatures and thawing permafrost throughout the region, forest transpirational demand has not increased significantly during the past two centuries. Under current climatic conditions, VPD did not limit growth of larch and pine, even during extremely drought years. Our findings will support more realistic evaluations and reliable predictions of the potential influences of ongoing climatic change on carbon and water cycles and on forest dynamics in permafrost regions. Key Points: We reconstructed July–August vapor‐pressure deficit (VPD) based on tree ring δ 18 O in the northern Great Hinggan Mountains No long‐term trend in VPD was detected since 1800 VPD did not limit the growth of larch and pine in the study region