Larch (Larix gmelinii) trees in the lowlands of the Indigirka River in northeastern Siberia were observed for five years (2009–2013). In situ photosynthesis was measured. Stem and needle-shaped leaf samples were collected to analyze individual mass, nitrogen content, and isotopic ratios of carbon (delta C-13) and nitrogen (delta N-15). Needle samplings were treated by acetone before delta C-13 measurement. Data for satellite-derived ecosystem indices and data for climatic factors for each site in 2009-2021 were also collected.