Soil water uptake from different depths of three tree species indicated by hydrogen and oxygen stable isotopes in the permafrost region of Northeast China

Global warming has caused the gradual degradation of permafrost, which may affect the vegetation water uptake from different depths. However, the water utilization strategies of different vegetation species during the thawing stages of permafrost regions need further study. To elucidate these differences, we selected the permafrost region in Northeast China as study area. We analyzed the water uptake from different depths of <i>Larix gmelinii</i>, a deciduous coniferous tree, <i>Pinus sylvestris</i> var. <i>mongolica</i>, an evergreen tree, and <i>Betula platyphylla</i>, a deciduous broadleaf tree, using stable isotopes of xylem water, soil water, and precipitation from June to October 2019. The results showed that <i>L. gmelinii</i> primarily used shallow soil water (0-40 cm) with the highest proportion at 64.1%, <i>B. platyphylla</i> generally used middle soil water (40-110 cm) with the highest proportion at 55.7%, and <i>P. sylvestris</i> mainly used middle (40-110cm) and deep soil water (110-150 cm) with the highest proportion at 40.4% and 56.9%. The water sources from different depths exhibited more frequent changes in <i>P. sylvestris</i>, indicating a higher water uptake capacity from different soil depths. <i>L. gmelinii</i> mainly uptakes water from shallow soils, suggesting that the water uptake of this species is sensitive to permafrost degradation. This study revealed the water uptake strategies from different depths of three tree species in a permafrost region, and the results suggested that water uptake capacity of different tree species should be considered in the prediction of vegetation changes in permafrost regions under a warming climate.