Effect of drought on growth and mortality of actively growing Norway spruce container seedlings planted in summer.Survival, root egress and height growth of 13-month-old actively growing Norway spruce (Picea abies (L.) Karst.) container seedlings exposed to preplanting drying treatments (0, 4, and 8 days) and postplanting drought periods (1, 2, 3, and 4 weeks) were studied in the eld between 5 July and 18 August 1999. The mortality of seedlings increased and the height growth and root egress decreased throughout the postplanting drought period. Postplanting performance was also affected by preplanting drying treatments. The results indicate that no risk of excessive mortality and growth restrictions occurs when actively growing seedlings are planted in summer, provided that seedlings are well watered before planting and the drought period does not exceed 3 weeks.

-Survival, root egress, height growth, xylem water potential, and chlorophyll fluorescence of dormant and growing Norway spruce (Picea abies (L.) Karst.) container seedlings exposed to postplanting drought periods (1, 2, 3 and 4 weeks) in the field were studied. Growth stages were created by terminating overwinter frozen storage 5 weeks (growing) or 5 days (dormant) before planting. Without postplanting drought, root egress of growing seedlings during the 6-week study period was twice that of dormant seedlings. When exposed to postplanting drought, growing seedlings showed a greater decline in root egress and xylem water potential than dormant seedlings. Postplanting drought had no effect on chlorophyll fluorescence in dormant seedlings, whereas in growing seedlings chlorophyll fluorescence decreased after the 3-week drought period. The results indicate that planting seedlings kept dormant by prolonged frozen storage in summer is beneficial only if very long dry periods occur after planting. chlorophyll fluorescence / drought / growth stage / Picea abies / root egress Résumé -Réaction physiologique et morphologique à la sécheresse après plantation de semis dormants ou en croissance de Picea abies cultivés en conteneurs. La survie, la production de nouvelles racines, la croissance de la pousse, le potentiel hydrique du xylème et la fluorescence de la chlorophylle ont été étudiés sur des semis de Picea abies (L.) Karst, dormants ou en croissance, cultivés en conteneurs et exposés à des périodes (1, 2, 3 et 4 semaines) de sécheresse après plantation au champ. Pour préparer les divers stades de croissance, le stockage hivernal des semis au froid a cessé 5 semaines (en croissance) ou 5 jours (dormants) avant la plantation. Quand les semis n'ont pas été exposés à la sécheresse après plantation, la production de nouvelles racines des semis en croissance a doublé comparativement aux semis dormants pendant les 6 semaines d'étude. Pour les semis exposés à la sécheresse après plantation, la production de nouvelles racines et le potentiel hydrique ont davantage baissé pour les semis en croissance que pour les semis dormants. La sécheresse après plantation n'a pas affecté la fluorescence de la chlorophylle des semis dormants, mais après une sécheresse de 3 semaines la fluorescence de la chlorophylle des semis en croissance a baissé. Les résultats montrent que la plantation des semis qui ont été conservés dormants par un stockage au froid plus long en été est bénéfique dans le cas où la sécheresse continue très longtemps après plantation. fluorescence de la chlorophylle / sécheresse / stade de croissance / Piceas abies / production de nouvelles racines

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The effect of preplanting drying of root plugs on survival, height growth and root egress of actively growing 12-month-old Norway spruce [Picea abies (L.) Karst.] seedlings was examined in dry and wet soil between 5 July and 17 August 2000. In addition, the response of seedling xylem water potential and survival to the decreasing water content of the root plug (v/v) was examined in the greenhouse. Most seedlings were dead when the water content of the root plug decreased to B/7% and xylem water potential to B/(/2.8 MPa. The higher the water content of the root plug at planting, the greater the height growth in both dry and wet soil. However, root growth was promoted by the increase in the water content of the root plug only up to approximately 30%. In wet soil height growth was greater but root growth poorer than in dry soil. All measured variables were strongly affected when the water content of the root plug decreased to B/20% at the time of planting.

Increasing use of frozen storage in nurseries at northern latitudes calls for thawing methods that are safe, economical and easy to apply on a large scale. The easiest and most economical method would be to thaw seedlings in the same boxes they were stored in. However, doing this safely requires more knowledge about how long and at what temperatures seedlings should or can be kept in the boxes without reducing field performance. In this study, 1-yr-old frozen-stored Norway spruce (Picea abies (L.) Karst.) container seedlings were thawed for 4, 8 or 16 days at 4 or 12 °C in cardboard boxes before planting on a reforestation site and on experimental field in mid-June. Some seedlings were also planted on these locations after thawing for only 7 hours at 12 °C in order to separate frozen root plugs. We found some evidence that planting seedlings after short thawing periods (7 hours at 12 °C and 4 days at 4 °C), under which conditions the root plugs remain completely or partly frozen, has a negative effect on field performance of Norway spruce seedlings. Thawing over a 4−8 day period in cardboard boxes at ca. 12 °C appears to ensure complete thawing of the root plugs and unaffected field performance, but is short enough to prevent the growth of mould.

Norway spruce (Picea abies (L.) Karst.) seed is collected from both forest stands after final felling and from seed orchards. To produce high-germinability seed lots that are easy to use in nursery sowing machines, empty, insect-damaged, and other poor-quality seeds are culled. Sorting is done typically by weight or size. Previous studies of conifer seed have indicated wide variation in seed weight between individual trees or clones. However, the intratree or intraclone variations have rarely been taken into account, and intracone variation in seed weight has not been examined. We collected cones from a forest stand and from a clonal seed orchard in central Finland. Each seed from each cone was extracted, weighed, and x-rayed to assess their quality. Trees and clones differed in terms of the proportions of different quality seed. Variance component analysis showed that the intracone variation explained a larger proportion of the total variation in seed weight than did the intercone/intertree or interclone variations. Thus weight-based seed sorting has less effect on the genetic diversity of a seed lot than previously believed. We also conclude that the large differences in proportion of full seed among trees and clones impact the contribution of genotypes in seed and, eventually, in seedling lots.

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Helenius, P. 2005. Extension of the planting period of Norway spruce container seedlings: risks related to the drought − growth stage dynamics and handling practices. Dissertationes Forestales 3. 46 p. The first aim of this study was to investigate the possibility of extending the planting period of Picea abies container seedlings from May to June and July without the risk of excessive mortality and growth restrictions due to drought. The second aim was to investigate risks related to thawing practices of frozen-stored seedlings. To achieve the first aim, 1.5-yr-old actively growing seedlings were exposed to different preplanting drying and postplanting drought periods. Seedlings kept dormant (sensu shoots not elongating) by prolonged frozen storage were also exposed to postplanting drought periods. To achieve the second aim, 1-yr-old frozen-stored seedlings were exposed to different thawing durations and temperatures before planting in mid-June. Height growth and root egress of actively growing seedlings planted in late June-early July decreased when exposed to postplanting drought as affected by the soil water content at planting and atmospheric evaporative demand during drought periods. Survival and growth under drought were also decreased by preplanting drying of root plugs and seedlings. However, mortality of actively growing, well-watered seedlings was negligible when exposed to drought periods not longer than 2 to 3 weeks. Prolonged frozen storage until late June had no observable negative effect on needle carbohydrate concentration and subsequent seedling outplanting performance. Contrary to actively growing seedlings, drought periods had no effect on root egress and chlorophyll fluorescence, and only moderate effect on xylem water potential of dormant seedlings. However, actively growing seedlings showed much greater root egress than dormant seedlings, except when exposed to very long (≥ 3 weeks) drought periods after planting. Frozen-planting may adversely affect seedling performance at soil temperatures prevailing in Fennoscandia in spring or early summer, especially when soil is dry. Thawing over 4 to 8 days at 9−12 °C ensures complete thawing of the root plugs and unaffected field performance of frozen-stored seedlings.