EFFECTS OF ELEVATED CO2, NUTRITION AND CLIMATIC WARMING ON BUD PHENOLOGY IN SITKA SPRUCE (PICEA-SITCHENSIS) AND THEIR IMPACT ON THE RISK OFFROST DAMAGE

Effects of elevated CO2, clone and plant nutrition on bud dormancy of Sitka spruce (Picea sitchensis (Bong.) Carr.) were examined. Sitka spr uce seedlings were fumigated with ambient or elevated (ambient + 350 m umol mol-1) concentrations of CO2 in open-top chambers for three growi ng seasons. In 1991 and 1992, elevated CO2 delayed bud burst in the sp ring and advanced bud set in the autumn. The effect of the open-top ch amber on the thermal requirement for bud burst was greater than the ef fect of elevated CO2 (50 and 30 day degrees (D(d)), respectively). In a second study, four clones of Sitka spruce taken from two provenances , at 43 and 54-degrees-N, were fumigated with ambient or elevated CO2. There was a large natural variation in the timing of bud burst and bu d set among the clones. Elevated CO2 had no effect on bud dormancy of the Skidegate a clone, but it reduced the growing season of the North Bend b clone by 20 days. In a third study, Sitka spruce seedlings grow ing in ambient or elevated CO2, were supplied with one of three nutrie nt regimes, low (0.1 x potential), medium (0.5 x potential) or high (2 .0 x potential), using a method and solution based on the Ingestad tec hnique. Elevated CO2 did not affect bud dormancy in the high-nutrient treatment, but it reduced the growing season of plants in the low-nutr ient treatment by 22 days. Increasing plant nutrient supply lengthened the growing season, plants flushed earlier in the spring and set bud later in the autumn. The effects of elevated CO2 plus a 0, 2 or 4-degr ees-C climatic warming on the timing of bud burst and the subsequent r isk of frost damage were assessed using a simulation model and meteoro logical data from three sites, Edinburgh, Braemar and Masset. The mode l predicted that (i) doubling the CO2 concentration in die absence of climatic warming, will delay the onset of bud burst at all three sites , (ii) climatic warming in ambient CO2 will hasten bud burst and (iii) climatic warming in elevated CO2 will hasten bud burst at Edinburgh a nd Braemar but to a lesser extent than climatic warming alone. At Mass et, a 4-degrees-C warming was required to advance the date of bud burs t of seedlings in the elevated CO2 treatment. At all three sites, elev ated CO2 and climatic warming increased the mean daily temperature on the date of bud burst, thus reducing the risk of subsequent frost dama ge.