Influence of nutrient supply on spring frost hardiness and time of bud break in Norway spruce (Picea abies (L.) Karst.) seedlings

When spring frosts occur on recently planted forest sites, severe damage may occur to the seedlings. The aim of the present study was to test how different low levels of nutrient concentrations in Norway spruce ( Picea abies ( L.) Karst.) seedlings affected spring frost hardiness and time of bud break. Seedlings were grown in a greenhouse for one season and supplied with fertiliser containing 22, 43 and 72 mg N l(-1), respectively. The treatments resulted in needle nitrogen concentrations ranging from 0.9 to 1.8% in autumn. After winter storage at 0 degreesC, bud break was recorded on seedlings growing in the greenhouse, outdoors and in growth chambers at 12 degreesC and at 17 degreesC. Freezing tests were performed on seedlings directly removed from winter storage and following one week growth in the greenhouse. Seedlings receiving fertiliser with 43 mg N l(-1) had less freezing injury than the two other fertilisation treatments in the present study. The earliest bud break occurred in seedlings receiving 72 mg N l(-1).