Effects of root damage on the nutritional status and structure of Scots pine needles

In this experiment root damage was induced artificially in 35-year-old Scots pine trees growing on a nutrient-poor pine heath in northern Finland by cutting their surface roots at the beginning of the growing season. Nutrient concentrations in the needles were measured during the next growing season and the development of changes in the inner structure of the needles was observed. The needles were examined by light microscopy and at the ultrastructural level to reveal early symptoms of possible nutrient imbalances. Needle nutrient concentrations were lowered after root cutting, and changes in needle microscopic structure caused by nutrient imbalance were detected. Root reduction induced shorter needle length growth, and morphometric measurements with an image analyzer showed that the needle cross-sectional area, areas of various tissues and the sizes of certain cell types were reduced. Injury to the phloem tissue in the vascular bundle was indicative of a nutritional imbalance in the needles. The injuries to the mitochondrial structure and abnormally arranged chloroplast thylakoids at ultrastructural level pointed to P deficiency and the translucency of the chloroplast stroma to N deficiency. Vacuolization of the cytoplasm was induced, possibly indicating cold damage.