Effect of continuous photoperiod on growth and development of lodgepole pine seedlings and grafts

Abstract

Wind-pollinated seed and ramets from lodgepole pine (Pinuscontorta Dougl.) plus tree selections in British Columbia were established and maintained under 24-h photoperiods for 6 months. Subsequently, these trees were outplanted in the nursery and periodically assessed for height, diameter, and dry weight. Seedlings and grafts developed considerably faster than normal nursery-grown controls during the treatment period, and they maintained an accelerated growth rate during the two growing seasons following outplanting. Root growth was particularly enhanced, as evidenced by the sharply reduced shoot:root ratio of treated seedlings relative to controls. Large differences in growth response existed among wind-pollinated families but family × environment (greenhouse vs. nursery) interaction confounded interpretation. Family performances for treated and control seedlings of the same families were not well correlated (r = 0.24) after two growing seasons. The rapid growth and development of seedlings and grafts under continuous photoperiod can undoubtedly benefit tree improvement programs by ultimately reducing the establishment time of seedling and clonal seed orchards, particularly for slowly growing species such as lodgepole pine.