Diurnal and seasonal changes in the intensity of photosynthesis in stems of lilac (Syringa vulgaris L.)

It has been demonstrated that during the whole year the stems are photosyntheticaly active and capable of assimilating atmospheric CO2. The intensity of photosynthesis varies. During the vegetation period the registered net photosynthesis lasted up to 13 hours per day, and in the leafless period for 2–3 hours a day. Photosynthesis was registered also at temperatures below zero (−3 °C) as a reduced CO2 evolution in light in comparison with darkness. The maximal net photosynthesis values during the vegetation period amounted to 6 up 8 µmol (CO2)·m−2·s−1, and in the leafless period 0.5 – 1 µmol (CO2)·m−2·s−1, and they were close to being up to twice as big as the values obtained of darkness respiration. An increase of the photosynthetic activity of stems preceded the spring development of the leaves.