Pollutants may destroy photosynthetic needle structure and affect stomatal activity. Toxic substances may change the structure of an entire tree, in particular its water transport system. The goal of the present paper is to find out whether such a disturbance reaches a level at which photosynthesis is inhibited.
The investigations were performed around the Severonikel mill in Monchegorsk (the Kola peninsula). Forty- to fifty-year-old Pinus sylvestris trees differing in growth dynamics and crown form were studied. Healthy appearing trees had 4 needle age classes while the poorest appearing trees had only 2 to 3.
A portable LI-6200 gas analyzer (LI-COR Instruments, USA) was used to study CO2 exchange. Seedling water potential was monitored by the pressure chamber method. Structural changes in the water transport system were studied by injecting dye into the xylem and following its path.
Prolonged influence of toxic substances changed the amount of sap-wood of experimental trees. Healthy trees had 17 living whorls and 17 annual rings of sapwood whereas in the poorest looking trees there were still 12 living whorls but only 5 rings fully transported moisture and 4 rings partially. Thus the leaf specific conductivity of xylem decreased. The xylem changes were associated with low morning water potential of seedlings (variation between 0.6 and 0.8 MPa). Registration of daily CO2 exchange rhythms under water deficit conditions revealed considerable disturbances in the course of this process. Water stress also influenced the pattern of light curves.
The influence of pollutants on the water transport system was discussed. Conclusions of its effect on photosynthetic production and needle longevity and tree mortality were drawn.
Key words: Pinus sylvestris, pollution, water transport, photosynthesis.
Correspondence: T.A. Sazonova, Forest Research Institute, Karelian Research Center, Russian Academia of Science, Pushkinskaja St., 11, Petrozavodsk 185610, Russia