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
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.
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