Abstract
<jats:p>The objective of research is to identify promising tree species and cultivars for subsequent use in forest climate projects. The study was conducted using a systems approach and modern instruments for measuring respiration and photosynthesis activity. The objects of the study were tree genotypes of different ages: 4- and 10-year-old poplar (Populus L.), 4- and 46-year-old silver birch (Betula L.), and 4- and 50-year-old Scots pine (Pinus L.), which were grown on the experimental calibration site of the VSTU educational and experimental forestry enterprise. A CI-340 gas analyzer (SID Bio-Science, USA) was used to measure the rate of carbon dioxide absorption and emission by leaves in vivo. Online measurements of photosynthesis rates were taken on intact tree leaves in the morning from 8:00 AM to 11:00 AM, when cell water saturation is high and sunlight intensity and air temperature are close to optimal. Dark respiration activity was recorded from 11:00 PM to 1:00 AM. The leaves of fast-growing poplar exhibited the most active dark respiration, exceeding those of silver birch by an average of 21.0% and Scots pine by 26.3%. Species-specific differences in photosynthetic activity were identical. In 10-year-old poplar (variety 'E.s.-38'), the photosynthesis intensity and dark respiration rates were 9.6 and 15.8 % lower, respectively; in 46-year-old silver birch (variety Ug.-1), they were 32.6 and 13.3 % lower, respectively; and in 50-year-old Scots pine, they were 10.9 and 14.0% lower, respectively, compared to 4-year-old trees. Fast-growing poplar is the most promising of the studied tree species for the development of forest climate projects to improve the ecology of habitats and production.</jats:p>