ИСТИНА

Modern climate change, accompanied by rapid increases in global air temperature, changes in precipitation patterns, increase in the frequency and severity of extreme weather events such as heat waves and droughts, heavy precipitation, and windstorms, may have significant impacts on forest functioning, growth, and primary production. How different forest ecosystems respond to these changes is a major challenge. The aim of our study was to assess the effects of extreme weather events (significant positive and negative anomalies in air temperature and precipitation) on carbon dioxide (CO2) fluxes in boreal and temperate forest ecosystems of the Northern Hemisphere. Experimental data from 26 greenhouse gas (GHG) flux monitoring stations of the FLUXNET database with the most continuous and longest time series were selected for the analysis of CO2 fluxes. The stations are located on different continents in forest ecosystems belonging to different biome types according to the IGBP classification. Meteorological data were collected from meteorological observations at the flux experimental sites and taken from the ERA5 reanalysis datasets. Analysis of the CO2 flux feedback to extreme weather events associated with high/low temperature and precipitation revealed a large diversity of flux responses in temperate and boreal forests, primarily related to forest type, but also varying with geographic location, regional climate conditions, plant species composition and age, as well as other biotic and abiotic factors. Positive CO2 flux anomalies were more frequent than negative anomalies in both summer and winter. Extreme weather conditions were mostly associated with increased CO2 emissions rather than CO2 uptake due to suppressed assimilation processes associated with extremely hot and dry weather conditions, greater reductions in gross primary production (GPP) at lower temperatures, and higher decomposition rates of soil organic matter resulting in higher autotrophic and heterotrophic respiration during wet periods. Extremely high air temperature in any season leads to increased CO2 release into the atmosphere in all forest types, with the largest response in coniferous forests. Negative air temperature anomalies in the warm season can have the opposite effect, leading to both increases and decreases in CO2 uptake by forest ecosystems, depending on the forest ecosystem type. No significant response of CO2 fluxes to extremely low temperatures in the cold season was found. During periods of heavy precipitation, a prevailing release of CO2 into the atmosphere was observed in most forest ecosystems. At the same time, during the warm season after prolonged rainfall, an increase in plant CO2 uptake was also detected, which may be associated with sufficient soil moisture conditions promoting an increase in plant photosynthesis. During periods without precipitation, increased CO2 uptake was observed in most forest types in both warm and cold seasons. This may indicate that soil moisture is not the limiting factor for photosynthesis in these ecosystems. Moreover, incoming solar radiation was greater during periods without cloud cover and associated precipitation, resulting in higher rates of plant photosynthesis.