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The Effect of Cold Nights on the Root-Regenerating Potential of Ponderosa Pine Seedlings

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The effect of low night temperatures on the root regenerating capacity of ponderosa pine was investigated in controlled environment chambers. Six groups of seedlings were grown for 180 days under a 24°C day, 18°C night schedule. During the next 150 days, each group was exposed to a different number of consecutive cold (6°C) nights, i.e., 0, 30, 60, 90, 120, 150, so scheduled that cold night exposures were all terminated together at the end of the 150 day period. Seedlings were then washed out of the containers in which they had been grown, root pruned to a length of 20 cm, transferred to a greenhouse, and planted in special water-tight containers filled with sandy loam which were in turn suspended in 20°C water baths. Thirty days later, seedlings were washed out of these containers and all roots that showed new growth of 1.25 cm or more were measured. The total number of these roots was used to express the root-regenerating potential for each treatment. When the root-regenerating potential was based on the number of old roots and newly initiated roots that elongated 1.25 cm or more, exposure to at least 90 cold nights was required to bring about a significant increase. When it was based only on the number of newly initiated roots that elongated 1.25 cm or more, exposure to 150 cold nights was required. Seedling top dry weight, top length, and stem diameter also were affected by exposure to cold nights, but root dry weight was not. These relationships and the possibility of using cold nights to precondition stock so that it would have a high root-regenerating potential on specific planting dates are briefly discussed.
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Document Type: Journal Article

Affiliations: Professor of Forestry, School of Forestry, University of California, Berkeley

Publication date: 01 December 1966

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