Scotch pine photosynthesis dependence on environmental factors in the Baikal forest-steppe

Photosynthesis, being the basis of production process, comes under the influence of ecological factors, adapting to their various combinations and intensity. During the vegetative period of 1976-1986 in 80 km to the northeast of Irkutsk in the for-est-steppe of the Baikal territory visible photosyn-thesis of needles of Scotch pine by a gas measur-ing method with the use of assimilatory chambers was investigated. In parallel with the standard methods environment factors were registered: solar radiation, temperature and humidity of the air and the soil. Day changes of visible photosynthesis of biannual needles were classified according to three types of curves. The first type was noted in mois-tening conditions, optimum or close to optimum, on sunny days, the second with several peaks was observed on cloudy days, the third type was regis-tered when the reserves of available soil moisture in the top of 50 centimeter, most root zone layer of soil was significantly exhausted. The intensity of visible absorption of CO2 in biannual needles of the pine was registered within 40-50 days of each vegetative period used for the determination of de-pendence of photosynthesis on environment fac-tors. Light curve of photosynthesis of needles at an optimum of soil moistening had a little stretched excess area, rather big tilt angle of an initial piece. The temperature of maximum of photosynthesis with the increase in the deficiency of soil moisten-ing was noted in the field of lower air temperatures (12-14 оС) in comparison with its size (20-22 оС) at optimum moistening. The types of day course and ecological dependencies of photosynthesis were presented by regression equations, using the poly-nomial function of the sixth order characterized by the approximation coefficient changing within 0.64-1.0. It was as much as possible approximated by polynomial function and dependence of day effi-ciency of photosynthesis of needles on a reserve of available soil moisture, i.e. ecological factor having direct impact on efficiency of photosynthesis of a pine ordinary in the forest-steppe of the Baikal terri-tory.