We examined effects of elevated CO(2) and temperature on cold hardiness and bud burst of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Two-year-old seedlings were grown for 2.5 years in semi-closed, sunlit chambers at either ambient or elevated (ambient + ~ 4 degrees C) air temperature in the presence of an ambient or elevated (ambient + ~ 200 ppm) CO(2) concentration. The elevated temperature treatment delayed needle cold hardening in the autumn and slowed dehardening in the spring. At maximum hardiness, trees in the elevated temperature treatment were less hardy by about 7 degrees C than trees in the ambient temperature treatment. In general, trees exposed to elevated CO(2) were slightly less hardy during hardening and dehardening than trees exposed to ambient CO(2). For trees in the elevated temperature treatments, date to 30% burst of branch terminal buds was advanced by about 6 and 15 days in the presence of elevated CO(2) and ambient CO(2), respectively. After bud burst started, however, the rate of increase in % bud burst was slower in the elevated temperature treatments than in the ambient temperature treatments. Time of bud burst was more synchronous and bud burst was completed within a shorter period in trees at ambient temperature (with and without elevated CO(2)) than in trees at elevated temperature. Exposure to elevated temperature reduced final % bud burst of both leader and branch terminal buds and reduced growth of the leader shoot. We conclude that climatic warming will influence the physiological processes of dormancy and cold hardiness development in Douglas-fir growing in the relatively mild temperate region of western Oregon, reducing bud burst and shoot growth.

The contribution of N remobilization to the seasonal growth of field-grown Malus domestica (apple) trees was measured using two different techniques. 'Fuji' trees grafted on M.9 apple rootstocks were planted in the field and fertilized and irrigated for two growing seasons. During the second year, the trees received 15N-labelled fertilizer and destructive harvests were taken during the spring and summer to determine the pattern of N remobilization and uptake. At the same time, patterns of N translocation in the xylem were measured by sampling saps at each harvest and analysing them for their constituent amino acids and amides. Total water flux through the trunk xylem was also measured throughout the sampling period using the heat balance technique. The flux of amino compounds in the xylem was then calculated to see if this approach could quantify remobilization. Most of the N for leaf growth was provided by remobilization, which lasted for some 40 d following bud-burst. The labelled N was not taken up until 14 d after remobilization had started. The predominant amino compounds recovered in the xylem were Asn, Asp, Arg, and Gln, whose concentration peaked during remobilization, except for Arg whose concentration was highest at bud-break and declined thereafter. The amount of N translocated in the xylem as Asn, Asp and Gln correlated well with the amount of N remobilized (as measured by the recovery of unlabelled N in the new above-ground growth). The data suggest that Arg is translocated predominantly as a consequence of root uptake and they are discussed in relation to measuring N remobilization in field-grown trees.

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