THE INFLUENCE OF CARBON-DIOXIDE OR OZONE CONCENTRATION ON GROWTH AND ASSIMILATE PARTITIONING IN SEEDLINGS OF 9 CONIFERS

Seedlings of nine different conifers were exposed to 355 and 730 mu mo l mol(-1) CO2, or low (< 15 nmol mol(-1)) and elevated O-3 concentrati on (70 nmol mol(-1)) for 81-116 days. The experiments were conducted i n growth chambers placed in a greenhouse. Increased CO2 concentration enhanced the mean relative growth rate (RGR) and total plant dry weigh t by 4 and 33% in Larix leptolepis, by 4 and 38% in Larix sibirica, by 7 and 47% in Picea glauca and by 3 and 16% in Picea sitchensis, respe ctively. The growth rates and dry weights of Pinus contorta, Pinus mug o and Pseudotsuga menziesii were not significantly affected. Carbon di oxide enrichment enhanced RGR of two provenances of Picea abies by 4 a nd 6%, respectively, while a third provenance was unaffected. In Pinus sylvestris, only the RGR of one of three provenances was stimulated b y CO2 enrichment (4%). After two growth seasons CO2 enrichment enhance d RGR and total plant dry weight by 11 and 35% in Picea abies and by 1 2 and 36% in Pinus sylvestris, respectively. Elevated CO2 decreased th e shoot:root ratio in Larix leptolepis, and decreased the needle:stem ratio in Picea glauca, but increased it in Pseudotsuga menziesii. Elev ated O-3 significantly decreased the plant dry weight in Picea sitchen sis, Pseudotsuga menziesii and in one of three provenances of Pinus sy lvestris, while the other species and provenances were unaffected. Inc reased O-3 concentration increased the shoot:root dry weight ratio in one of three Picea abies provenances, in all three Pinus sylvestris pr ovenances and in Pinus contorta. The needle:stem ratio was enhanced by O-3 in seven of the nine species. The O-3 exposure caused chlorosis o f needles in all species except Pseudotsuga menziesii.