Cellulose 618O as a hydrological proxy: A case study for willows growing in Indigirka river lowland, Northeastern Siberia

During the last few decades, stable oxygen isotopic composition of cellulose (618Ocell) has been employed as a potential tool for understanding hydrological cycles on modern and past environments. In the present study, we measured the 618O values of stem water (618Osw) and the 618Ocell values of willows, which are growing on transects along the river with multiple water sources and different levels of humidity in Northeastern Siberia, further to evaluate the contribution of (1) the 618Osw values, (2) the ratio of ambient/intercellular water (i.e., ea/ ei), and (3) the 618O values of water vapor (618Ov), to the 618Ocell values. The results well demonstrate that the cross-plot of 618Ocell/618Osw can be used to evaluate the contributions of 618Osw values and ea/ei to the variation of 618Ocell values. Also, the contribution of the 618Ov values on the 618Ocell values are significantly increased, where the water vapor near the plants is isotopically equilibrated to large water pools (e.g., rivers, lakes, ponds, etc.) rather than the source water (e.g., precipitation) of plants. Based on these findings, we predict that full consideration of the above (1)-(3) permits us to enhance accuracy in our understanding of plant 618Ocell values with respect to hydrological cycles.