%0 Articles
%T Kuusen karaistuminen boorinpuutoksessa
%A Räisänen, Mikko
%D 2008
%J Dissertationes Forestales
%V 2008
%N 75
%R doi:10.14214/df.75
%U http://dissertationesforestales.fi/article/1858
%X Dieback of boron (B) deficient trees has interested scientists for decades. Although decreased freezing tolerance has been hypothesized to be one of the reasons for dieback, there is no experimental evidence supporting that hypothesis.

A field experiment with boron (B) and nitrogen (N) fertilization treatments was established in a young Norway spruce (Picea abies L. Karst) stand with low B status. Freezing tolerance of experimental trees was studied during acclimation after one, three and five growing seasons after fertilization treatments. In addition, Norway spruce seedlings were cultivated at three B levels for two growing seasons prior to measuring freezing tolerance. Freezing tolerance of acclimated buds was also studied in three Norway spruce stands which differed in percentage of trees with growth disturbance. Freezing tolerance was studied by controlled freezing tests and electrolyte leakage (EL) and visual scoring, by differential thermal analysis (DTA) and by electrical impedance spectroscopy (EIS).

Cold hardiness in stem and bud (by DTA and EL) was decreased at B deficiency in cold hardened seedlings. Also results of EIS indicated that seedlings were more vulnerable to freeze drought at low B levels. In the field experiment, however, freezing tolerance of B deficient trees was not increased by B or N fertilization. In buds collected from field, no supercooling ability of buds was found when bud structure was malformed by B deficiency. There was also a slight effect of B on rapid dehardening and rehardening of cold hardened buds.

Freezing tolerance of cold hardy buds and stem in apical shoot was decreased when B status of spruce greatly below critical limits of B deficiency.  However, since effect of B was found in this study only in a small part of data and at very low B level, the increased risk for freezing injury in B deficiency may not have a primary role in the outbreak of growth disturbance.