No abstract

A method for assessing frost hardiness of plant tissues [using shoots of Picea rubens Sarg. syn P. riibra (Du Roi) Link] has heen developed based upon the rate of eleetrolyte leakage from shoots itnmersed iti distilled water after exposure to a range of freezing treatments. The relationship hetween cotiductivity (the electrolyte eotieentration in solution) and titne has heen shown to follow an asymptotic eur\-e, which may he represented hy a first-order equation: C,~C,^ = (C., -<"") (1 -'' ") where C, is the eonductivity at time /, f^ is the initial eonductivity, f' ,^,,,, is the conductivity after autoelaving atid k is the first-order rate constant (utiits time '). The rate of eleetrolyte leakage (k) varies directly with the extent of tissue damage. In P. rubens a rate of ()-4",, h ' distitiguished hetween sboots which eventually died, atid shoots whieh remained alive. A minimum of 3 eondueti\ ity tneasuremetits (after 1 day, 5 days and after autoelaving) is rec^uired for a reliable estimate of k. This objecti\ e, quatititative method of assessitig frost liarditiess may therefore be used directly to estimate L 1 ." values within a popuhitioti.

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.

No abstract

SUMMARVSeedlings of red spruee [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were exposed to mists containitig equimolar (NH,)., SOj and HNO., at pHs of 2-5, 2-7, 3-0, 3-5, 4-0 or 5-0. The mists were applied twiee each week, amounting to 2 mm pt-ecipitation equivalent on each oecasion, between July atid Deeember, to opeti-top ehamhers supplied with eharcoal-filtered air.Frost hardiness of shoots excised from seedlings was determitied on 6 oeeasions starting on 21 September, and was found to he strongly influeneed hy aeid mist treatments, seedlings suhjeet to the tnost aeidie mists heing the least frost hardy. On 21 September when the first sample was taken the lethal temperature for killing 50°,, of sboots (LT511) was -11 °C for the least aeidie (pH 5-0) mist and -7 °C for the most aeidie (pH 2-5). By 19 Oetoher, the LT.5,,s of pH 5-0 and pH 2-5 mists were -27 and -1 5 °C respeetively. All intermediate treatments ranked according to treatment concentration, with the smaller concentrations causing lower LT,,, values.The treatment at pH 3-0 provided S and N inputs to the seedlings similar to those experieneed hy red spruce at elevations of about 1000 m in the southern Appalaehians. At pH 3-0, the frost hardiness LT,,, during October was typically 8 °C higher than the pH 5-0 treatment, leading to a signifieant increase in the probability of frost damage at the LT^ level in an average Octoher.The proximity of minimum night temperatures during September to Deeemher to the L'P,,, temperatures of red spruce shoots receiving large inputs of SO.,-^", NO3 , NH,* and H* suggests that decreases iti frost hardiness eaused by intercepted eloud water eontainitig large eoneentrations of these tons tnay play a sigtiifieatit part in the ohserved decline at mountain-top locations.