Measured and modelled source water δ18O based on tree-ring cellulose of larch and pine trees from the permafrost zone

To identify source water for trees growing on permafrost in Siberia, we applied mechanistic models that quantify physical and biochemical fractionation processes, leading to oxygen isotope variation (delta O-18) in plant organic matter. These models allowed us to investigate the influence of a variety of climatic factors on tree-ring cellulose from two dominant species: Larix cajanderi Mayr. from northeastern Yakutia (69 degrees 22' N, 148 degrees 25' E, similar to 250 m a.s.l.) and Pinus sylvestris L. from Central Yakutia (62 degrees 14' N, 129 degrees 37' E, similar to 220 m a.s.l.). The climate of the region is highly continental with short growing seasons, low amount of precipitation and these forest ecosystems are growing on permafrost, which in turn impact the water cycle and climate variation in the delta O-18 of source water. We compared outputs of the Land surface Processes and eXchanges (LPX-Bem v. 1.3), and Roden-Lin-Ehleringer (RLE) models for the common period from 1945 to 2004. Based on our findings, trees from northeastern and central Yakutia may have access to additional thawed permafrost water during dry summer periods. Owing to differences in the soil structure, active thaw soil depth and root systems of trees at two Siberian sites, Larix cajanderi Mayr. trees can access water not more than from 50 cm depth, in contrast to Pinus sylvestris L. in Central Yakutia which can acquire water from up to 80 cm soil depth. The results enhance our understanding of the growth and survival of the trees in this extreme environment.