Carbon Dioxide Exchange of Woody Plants in Urban Ecosystems

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The study of all factors that contribute to the carbon balance in the biosphere is of paramount importance due to the current increase in carbon dioxide content in the atmosphere. This article presents data on the carbon dioxide exchange for the needles of common spruce (Picea abies L.) and Douglas fir (Pseudotsuga menziesii L.) in an urban environment (based on the example of Moscow). It is established that the warm spell in autumn 2018 contributed to the prolongation of the period of carbon dioxide uptake by coniferous trees. Our analysis into the effect of environmental factors on the needle photosynthetic activity has revealed that the intensity of photosynthesis depends only on the level of illumination. The midday increase in air temperature failed to affect the photosynthesis intensity, which is probably explained by the adaptation of the plants to low night and morning air temperatures. A regression analysis has shown that the dependence of CO₂ assimilation on illumination represented a logarithmic curve (with the approximation validity coefficient (R²) of 0.8). The effect of environmental conditions on conifer photosynthesis in autumn has proven to be species-specific. Common spruce was the most resistant to environmental factors: its photosynthetic activity was 1.4 times higher than that of Douglas fir. Calculations revealed that the level of CO₂ assimilation was 3.6 and 2.7 times higher than the light respiration level for common spruce and Douglas fir, respectively, which indicates a positive carbon dioxide exchange and an important role of coniferous trees in regulating the carbon balance of an urban ecosystem.