THE INFLUENCE OF LIGHT QUALITY AND CARBON DIOXIDE ENRICHMENT ON THE COLD HARDINESS OF THREE CONIFER SPECIES SEEDLINGS

Pinus banksiana, Picea mariana and Picea glauca were grown in high and low red: far-red quantum flux ratios and CO_2 levels of 350, 700 or 1050μmol mol^<-1>. Following growth in long days then short days, the seedlings were hardened in a 6/-5℃ thermoperiod in ambient CO_2 levels and red rich light and placed in dark storage at-2℃. After storage, seedlings were cold stressed at various temperatures down to -25℃ and then rewarmed. Picea glauca was more cold hardy than Pinus banksiana which was more cold hardy than Picea mariana. Cold stressed Pinus banksiana grown in far-red rich light had greater triphenyl tetrazolium chloride reduction values than red grown plants but the red grown plants were evaluated as being of higher quality after regrowth following stress. The (P-O)/O chlorophyll fluorescence value for all three species was a good predictor of seedling quality following regrowth after cold storage and cold stress. Pinus banksiana and Picea mariana grown in red light at ambient CO_2 level had the greatest survival potential following cold storage and cold stress. Picea glauca survival was enhanced by doubling the CO_2 level in either light quality