Interspecific differences in photosynthetic gas exchange parameters of woody species in shelterbelts of the dry-steppe zone

Shelterbelts in regions with low forest cover perform a range of soil-protective and environment-forming functions and at the same time contribute to greenhouse gas uptake, which determines their role under intensifying climate change. The capacity of plantations to absorb carbon is governed by the photosynthetic activity of tree species, realised through the assimilation apparatus. The aim of this study was to examine species-specific features of gas exchange parameters in five woody species growing in shelterbelts in order to assess their role in carbon uptake. The research was carried out at the Kachalino test site (Ilovlinsky District, Volgograd Region), located in the dry-steppe zone of chestnut soils, on five tree species of the same age class: English oak (Quercus robur L.), black locust (Robinia pseudoacacia L.), Siberian elm (Ulmus pumila L.), black pine (Pinus nigra Arnold.) and honey locust (Gleditsia triacanthos L.). Gasometric measurements were performed in the field on intact leaves using a portable LI-6800 system (LI-COR Biosciences, USA), recording CO₂ assimilation (A), transpiration (E), stomatal conductance (gsw) and intercellular CO₂ concentration (Ci). The results showed that the highest assimilation was recorded in English oak, amounting to 7.63 µmol CO₂·m⁻²·s⁻¹, and the lowest in honey locust (2.90) and black pine (2.93 µmol CO₂·m⁻²·s⁻¹). Ranking the measurements by photosynthetically active radiation ranges confirmed the consistency of the identified differences under comparable illumination. Statistically significant interspecific differences were established for all gas exchange parameters (p < 0.001). Correlation analysis revealed a strong positive relationship between assimilation and stomatal conductance (r = 0.75) and a strong negative relationship with intercellular CO₂ concentration (r = −0.71). The obtained results can be used in selecting tree species for protective afforestation in the dry-steppe zone, taking into account their photosynthetic activity, and in assessing the carbon uptake capacity of plantations. 125