Responses of Norway spruce (Picea abies [L.] Karst.) to water deficiency

The aim of the investigations was to comprehensively characterise the tree water regime of spruce trees in locations of higher elevation in Eastern Or e Mountains and its modification resulting from water deficiency and declin e. By means of an experimental simulation of water deficiency, concerning thre e 40-year-old spruce trees, physiological changes which occurred under long -term and extreme drought stress could be observed. Since the beginning of this experiment in spring of 1996 a continuously decreasing water supply ha s been detected by diminishing values of the pre-dawn water potential. This fact causes higher Values of diurnal water potential diminution (from pre- dawn until noon) in 1996 in comparison to the reference trees. During the s ubsequent growing season these Values decreased, while drought stress conti nued to occur. The decreasing sap flow rate and changing values of pre-dawn water potential, osmotic potential and turgor during the whole period from 1996 indicated different degrees of stress. The continued physiological activity and the obvious recovery of the experi mental trees in spite of long-term drought conditions with extinct water su pply from the soil suggest absorption of dew by needles as explanation This hypothesis is supported by a respective laboratory experiment. These resul ts emphasize the importance of dew, mist and short showers during drought p eriods for the water balance of trees.