Correlation of Photosynthesis and Water Regime of Pinus sylvestris L. Under Extreme Environmental Conditions of Pre-Baikal Area

The paper discusses variations in the photosynthesis and water regime for Pinus sylvestris L. under extreme conditions of the forest-steppe zone of the Irkutsk Region. The daily cycle of Pinus sylvestris L. is characterized by variations in net-photosynthesis, which reaches a maximum in the early hours, with a simultaneous decrease of gas-exchange intensity and transpiration. This is evidence of the substantial role the stomata plays in the regulation of these processes. The air temperature (r = –0.65±0.05, n = 12) is the principal negative factor for carbon dioxide gas exchange. The intensity of transpiration is determined by the level of solar radiation coming into the biocenosis. Insufficient soil moisture, and absolute air humidity (r = 0.70±0.04, n = 12) play a very important role in the processes of gas exchange and transpiration, together with such factors as cool cloudy weather. Therefore, with the solar radiation absorbed by the needles and the elevated air temperature, we observed not only an increase in air humidity in the sub-stomata cavities, but also an increase in th