Abstract
<jats:p> Boreal forests play a crucial role in maintaining the global ecological balance, acting as significant carbon sinks and mitigating the effects of climate change. This study examined how temperature affects photosynthesis in four boreal tree species – <jats:italic>Pinus sylvestris, Betula pendula, Populus tremula,</jats:italic> and <jats:italic>Alnus incana</jats:italic> – growing in a clear-cut of mid-taiga bilberry-type pine forest in southern Karelia, Russia. The Farquhar biochemical model was used to analyze key photosynthesis parameters, such as the maximum carboxylation rate by Rubisco ( <jats:italic>Vс</jats:italic> <jats:italic> <jats:sub>max</jats:sub> </jats:italic> ), the maximum photosynthetic electron transport rate ( <jats:italic>J</jats:italic> <jats:italic> <jats:sub>max</jats:sub> </jats:italic> ), and the triose phosphate utilization ( <jats:italic>TPU</jats:italic> ) rate, under different leaf temperatures ranging from 20 to 35°C and light conditions. The results revealed significant interspecific differences in photosynthetic responses. At a leaf surface temperature of 25°C, the lowest <jats:italic>Vc</jats:italic> <jats:italic> <jats:sub>max25</jats:sub> </jats:italic> , <jats:italic>J</jats:italic> <jats:italic> <jats:sub>max25</jats:sub> </jats:italic> , and <jats:italic>TPU</jats:italic> <jats:italic> <jats:sub>25</jats:sub> </jats:italic> values were obtained for the 1-year-old needles of <jats:italic>P. sylvestris</jats:italic> (38.8, 70.7, and 5.5 μmol m <jats:sup>-2</jats:sup> s <jats:sup>-1</jats:sup> ), whereas the values were 1.5- to 2.4-fold higher for the leaves of <jats:italic>B. pendula</jats:italic> (93.5, 172.1, and 12.7 μmol m <jats:sup>-2</jats:sup> s <jats:sup>-1</jats:sup> ), <jats:italic>A. incana</jats:italic> (86.1, 155.1, and 11.4 μmol m <jats:sup>-2</jats:sup> s <jats:sup>-1</jats:sup> ), and <jats:italic>P. tremula</jats:italic> (58.6, 122, and 9.3 μmol m <jats:sup>-2</jats:sup> s <jats:sup>-1</jats:sup> ). Meanwhile, <jats:italic>P. sylvestris</jats:italic> and <jats:italic>B. pendula</jats:italic> had a broader optimal temperature range for <jats:italic>Vc</jats:italic> <jats:italic> <jats:sub>max</jats:sub> </jats:italic> and <jats:italic>J</jats:italic> <jats:italic> <jats:sub>max</jats:sub> </jats:italic> (20–35°C), whereas <jats:italic>A. incana</jats:italic> and <jats:italic>P. tremula</jats:italic> had a narrower range (20–30°C), experiencing a decline at 35°C. In addition to having different levels of resistance to extreme temperatures, deciduous species also differed in their responsiveness to CO <jats:sub>2</jats:sub> enrichment. This could lead to shifts in the composition of boreal forest species under changing climate conditions. <jats:italic>P. sylvestris</jats:italic> demonstrated greater stability at low light levels and a strong response to elevated CO <jats:sub>2</jats:sub> , indicating its high adaptability to future climate change. These results highlight the importance of considering species characteristics when predicting the carbon balance of boreal forests. They can be used to model the resilience of forest ecosystems under climate change and to plan further investigations, including studies of mature trees and the effects of additional stress factors, such as drought. </jats:p>