Effects of elevated CO2, nutrition and climatic warming on bud phenology in Sitka spruce (Picea sitchensis) and their impact on the risk of frost damage

Effects of elevated CO(2), clone and plant nutrition on bud dormancy of Sitka spruce (Picea sitchensis (Bong.) Carr.) were examined. Sitka spruce seedlings were fumigated with ambient or elevated (ambient + 350 micro mol mol(-1)) concentrations of CO(2) in open-top chambers for three growing seasons. In 1991 and 1992, elevated CO(2) delayed bud burst in the spring and advanced bud set in the autumn. The effect of the open-top chamber on the thermal requirement for bud burst was greater than the effect of elevated CO(2) (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 CO(2). There was a large natural variation in the timing of bud burst and bud set among the clones. Elevated CO(2) 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 growing in ambient or elevated CO(2), were supplied with one of three nutrient 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 technique. Elevated CO(2) did not affect bud dormancy in the high-nutrient treatment, but it reduced the growing season of plants in the low-nutrient 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 CO(2) plus a 0, 2 or 4 degrees C climatic warming on the timing of bud burst and the subsequent risk of frost damage were assessed using a simulation model and meteorological data from three sites, Edinburgh, Braemar and Masset. The model predicted that (i) doubling the CO(2) concentration in the absence of climatic warming, will delay the onset of bud burst at all three sites, (ii) climatic warming in ambient CO(2) will hasten bud burst and (iii) climatic warming in elevated CO(2) will hasten bud burst at Edinburgh and Braemar but to a lesser extent than climatic warming alone. At Masset, a 4 degrees C warming was required to advance the date of bud burst of seedlings in the elevated CO(2) treatment. At all three sites, elevated CO(2) and climatic warming increased the mean daily temperature on the date of bud burst, thus reducing the risk of subsequent frost damage.