Cellulose δ18O 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 (δ¹⁸O_cell) has been employed as a potential tool for understanding hydrological cycles on modern and past environments. In the present study, we measured the δ¹⁸O values of stem water (δ¹⁸O_sw) and the δ¹⁸O_cell 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 δ¹⁸O_sw values, (2) the ratio of ambient/intercellular water (i.e., e_a/e_i), and (3) the δ¹⁸O values of water vapor (δ¹⁸O_v), to the δ¹⁸O_cell values. The results well demonstrate that the cross-plot of δ¹⁸O_cell/δ¹⁸O_sw can be used to evaluate the contributions of δ¹⁸O_sw values and e_a/e_i to the variation of δ¹⁸O_cell values. Also, the contribution of the δ¹⁸O_v values on the δ¹⁸O_cell 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 δ¹⁸O_cell values with respect to hydrological cycles.