Dynamics of Water Exchange of Pine Needles in Different Taiga Subzones

One of the parameters controlling the production process and the formation of the taiga zone stands is the moisture content. The integrated assessment of water exchange includes a number of indicators describing the content and limited needles water, and the water flow rate by transpiration. The results of observations of water regime of Scots pine needles (Pinus sylvestris L.) growing in sphagnum pine forests of the middle and northern taiga sub-zone are presented in the article. The regularities of the temporal organization of the pro-cesses of water exchange, the relationship with the other physiological processes and envi-ronmental factors are identified. The study of the water regime of pine on the territory of the Republic of Komi previously was carried out only in the pine forests of the Piceetum hylo-comiosum forest type groups of the middle taiga subzone. The work objective was to inves-tigate and give a comparative description of water exchange of waterlogged sphagnum pine forests. The research was conducted from 2008 to 2011. The measurements of the water regime of pine needles were carried out by conventional methods of ecophysiological field studies using a gas analyzer Li-Cor 6400. In the period of daily observations (July), the pro-cess of transpiration did not stop during a day. We registered a low dependence of the inten-sity of transpiration on a shade density in a sphagnum pine forest at night, and a close corre-lation in a sedge-sphagnum pine forest (northern taiga) between these parameters. This is due to the fact that the vegetation period in the northern taiga is behind by about two weeks. At this time there is a period of “white nights”, and the amount of solar radiation at night exceeds than that in the middle taiga subzone of almost twice. During the day the variation of transpiration coefficients (the ratio of transpiration rate to the rate of photosynthesis) in the middle taiga subzone has a wider range than in the North. This indicates a stronger de-pendence of these processes from external factors in the sphagnum pine forests (middle tai-ga). Needles water content in the investigated pine stands is close to its maximum water-holding capacity. Needles water deficit in the pine forests of both types is in the range of 16…18 %. In general, the photosynthetic apparatus of Scots pine in the waterlogged pine plant communities is characterized by stable moisture content and low water deficit. Changes in the intensity of transpiration and photosynthesis during the day have the same character.