Interannual Variability and Climatic Determination of Carbon Balance in Spring Barley Agroecosystems on Soddy-Podzolic Soils of the Southern Taiga

Precise assessment of the sequestration potential of agroecosystems becomes a critical task under conditions of global climate transformation and the implementation of national low-carbon development strategies. This study analyzes the interannual dynamics of carbon dioxide fluxes (parameters NEE, GPP, and Reco) in spring barley (Hordeum vulgare L.) agroecosystems on soddy-podzolic soils in the southern taiga zone (Moscow oblast). The research is based on Eddy covariance measurements obtained during growing seasons with contrasting hydrothermal conditions (2013, 2016, and 2023). A non-linear response of carbon exchange to climatic drivers is revealed: the gross primary production was maximal in the warmest year of 2016 (GPP = 775 g C m−2), while the record net uptake was in 2013 (NEE = −245 g C m−2) under optimal moisture conditions. It is established that the determining factors for productivity include not only heat supply, but also the moisture regime and the proportion of diffuse radiation. The discovered pattern of decreasing carbon exchange efficiency (the GPP to Reco ratio) from 2.27 in moderately productive years to 1.25 in highly productive seasons indicates an outstripping growth of ecosystem respiration during the assimilation intensification. The results are of fundamental importance for the verification of carbon cycle models and the development of regional greenhouse gas monitoring systems.