Diurnal dynamics of CO2 emission from soils of typical biogeocenoses in the north of Western Siberia

Abstract

Despite the widespread adoption of modern, high-precision methods for assessing ecosystem carbon budgets, most primary data for calculating monthly, seasonal, and annual gas fluxes are obtained through daily soil or ecosystem respiration measurements. The question remains whether such one-time, albeit regular, measurements can reliably reflect the average daily flux. The objectives of this study included assessing patterns in the diurnal dynamics of soil CO2 emissions for two northern taiga ecosystems (green moss pine forests and frozen hummocky peatlands) and three spotted-medallion tundra ecosystems (mineral spot, overgrown area, and dwarf birch area) in northern Western Siberia. In August2016 and 2017, CO2 emissions from the soil surface were measured every four hours for two days using a chamber method, as well as soil temperature and volumetric moisture at a depth of 10 cm. Significant diurnal dynamics were observed for all studied ecosystems, despite different absolute values of CO2 emissions. Minimum fluxes were observed in the pre-dawn hours, around 2:00 AM, for all sites. Maximum fluxes were recorded at various times but generally occurred between 2:00 PM and 6:00 PM. For most sites, the diurnal variation in emission values correlated with soil temperature, but a pronounced hysteresis was observed in this relationship. This phenomenon is explained by both biological factors—root respiration dynamics depend more on photosynthesis than on soil temperature—and physical factors—impeded gas diffusion in dense mineral horizons. The most favorable hours for measuring CO2 emissions, in terms of subsequent calculations of diurnal fluxes for most of the studied ecosystemsduring peak vegetation, are morning (before 10:00 AM) and evening (from 6:00 PM to 10:00 PM).

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