Sulphate and cation accumulation in mesophyll and endodermis vacuoles of spruce needles - effects on nutrient supply after SO2 fumigation

Three 10-year-old spruces were excavated with their root balls from a typical rhyolite site in the eastern Erzgebirge. The trees were fumigated for 6 months in a plant growth chamber with an average of 92 ppb(v) SO2. Trees of similar age from the same site served as control. The accumulation of SO42- and counter cations in vacuoles of the mesophyll and endodermis cells of spruce needles Picea abies (L.) Karst. was studied, applying low-temperature SEM and EDX. The element content in needles and the water-soluble proportions of the major nutrient elements were determined. The needles of the fumigated trees yielded 3-5 times higher S content than the control and increased total Mg and Mn values. The stomatal S uptake decreased with increasing needle age. The fumigation caused decreasing N, P, and S-org contents in the needles, and an increase of K+ in the youngest needles. Potassium, Mg2+, and traces of Mn2+ were identified as counter ions to the accumulated SO42- in the mesophyll vacuoles of the fumigated spruce. S concentrations were 3-4 times higher in the endodermis than the mesophyll vacuoles. Magnesium was the dominant counter ion in the endodermis. The endodermic P content of the fumigated spruce was significantly reduced as compared to the control. Relative to normal values, the needles showed a sufficient K+ and Mg2+ nutrition. Nutrient deficiency became obvious in the needles of the SO2-furnigated spruces when the cations fixed to SO42- in the vacuoles were subtracted. Our method of using plants with large root balls for fumigation successfully simulated real-world conditions. The experiments clearly show that the investigation of total element contents in needles is not sufficient to judge the nutrient supply and underlined the importance of the relative Mg2+ and K+ depletion to explain damage symptoms in the Erzgebirge.