Carbon Cycles in Forests

This chapter reports the distinctive features of leaf-scale photosynthesis, soil respiration, and net ecosystem exchange (NEE) of CO2, mainly based on long-term (1998–2014) observations in larch forests and their comparison with results obtained for other boreal forests. During the short growing season in eastern Siberia, the growth and development of woody plants are made possible by high levels of physiological processes (photosynthesis and transpiration), with relatively low dark respiration and night respiration rates supporting growth and maintenance. Soil respiration responses to the hydrothermal conditions of the soil layer are dependent on the season and precipitation regime; therefore, observations of the unique daily, seasonal, and interannual variation in these conditions were conducted. Differences in soil respiration between larch forests with different productivities were found to be influenced by soil physical properties, soil biota, length of the frost season, and hydrothermal conditions. According to long-term eddy-correlation data, the annual NEE in medium-productivity larch forest was 212 ± 34 g C m−2 year−1, that in high-productivity larch forest was 243 ± 23 g C m−2 year−1, and that in tundra was 75 ± 14 g C m−2 year−1. The contribution of Siberian forests (east of the Ural Mountains) to this CO2 sink was estimated to be 55–62% of that from all Russian forests. The annual sink of permafrost larch forests in Siberia was almost half that of all Russian forests (55%), and soil emissions were about 27% of those from all Russian forests.