Although stable carbon isotopic composition (δ¹³C) of plants has been widely used to indicate different water regimes in terrestrial ecosystems over the past four decades, the changes in the plant δ¹³C value under waterlogging have not been sufficiently clarified. With the enhanced global warming in recent years, the increasing frequency and severity of river floods in Arctic regions lead to more waterlogging on willows that are widely distributed in river lowland. To investigate the δ¹³C changes in plants under different water conditions (including waterlogging), we measured the δ¹³C values in the leaves of willows with three species,Salix boganidensis,S. glauca, andS. pulchra, and also monitored changes in plant physiology, under several major flooding conditions in Northeastern Siberia. The foliar δ¹³C values of willows varied, ranging from −31.6 to −25.7‰ under the different hydrological status, which can be explained by: (i) under normal conditions, the foliar δ¹³C values decrease from dry (far from a river) to wet (along a river bank) areas; (ii) the δ¹³C values increase in frequently waterlogged areas owing to stomatal closure; and (iii) after prolonged flooding periods, the δ¹³C values again decrease, probably owing to the effects of not only the closure of stomata but also the reduction of foliar photosynthetic ability under long period of waterlogging. Based on these results, we predict that plant δ¹³C values are strongly influenced by plant physiological responses to diverse hydrological conditions, particularly the long periods of flooding, as occurs in Arctic regions.

A stable carbon isotope ratio (δ¹³C) chronology for the past 100 years was developed from larch tree rings in eastern Siberia (near Yakutsk, 62°14′N, 129°37′E), to reconstruct past soil moisture water equivalent (SWE). Based on the correlation analyses between SWE and tree ring δ¹³C, we developed a linear regression model for SWE in the late growing period (LGP: 15 July to 31 August) using annual tree ring δ¹³C, which was calculated from the combination of latewood in a current year and earlywood in the following year, and then reconstructed SWE (LGP) for 1908–2007. Reconstructed SWE was compared with factors such as the output of the land surface model, annual precipitation, and Palmer Drought Severity Index for July. From the results, the reconstructed SWE appears reasonable and shows a large variation, including repeated occurrences of severe drought and an unprecedented high soil moisture event in 2006–2007 during the past 100 years. The reconstruction also captured a past documented record of severe drought in the 1940s. Despite the generally good performance of the reconstruction, by the 1930s the estimated SWE was higher than that expected from the annual precipitation. Tree ring width and δ¹³C were negatively correlated in most periods. However, the negative correlation was weaker for the period from 1919 to 1925, when relatively low air temperature was observed. This result suggests that the rate of photosynthesis, together with the degree of stomata opening, also affected the tree ring δ¹³C during cool periods.

Changes in winter precipitation (snow) may greatly affect vegetation by altering hydrological and biochemical processes. To understand the effects of changing snow cover depth and melt timing on the taiga forest ecosystem, a snow manipulation experiment was conducted in December 2015 at the Spasskaya Pad experimental larch forest in Eastern Siberia, which is characterized by a continental dry climate with extreme cold winters and hot summers. Variables including soil temperature and moisture, oxygen and hydrogen isotope ratios of soil moisture and stem water, foliar nitrogen and carbon contents and their isotopes, phenology, and soil inorganic nitrogen were observed at snow removal (SNOW−), snow addition (SNOW+), and CONTROL plots. After snow manipulation, the soil temperature at the SNOW− plot decreased significantly compared to the CONTROL and SNOW+ plots. At SNOW− plot, snowmelt was earlier and soil temperature was higher than at other plots during spring because of low soil moisture caused by less snowmelt water. Despite the earlier snowmelt and higher soil temperature in the SNOW− plot in the early growing season, needle elongation was delayed. Leaf chemistry also differed between the CONTROL and SNOW− plots. The needle nitrogen content in the SNOW− plot was lower in the middle of July, whereas no difference was observed among the three plots in August. The soil inorganic nitrogen content of each plot corresponded to these results. The amount of soil ammonium was lower in the SNOW− plot than in the other plots at the end of July, however, once production started in August, the amount of soil ammonium in the three plots was comparable. Extremely low soil temperatures in winter and freeze–thaw cycles in spring and dry soil condition in spring and early summer at the SNOW− plot may have influenced the phenology and production of soil inorganic nitrogen.