Needle permeability of Norway spruce (Picea abies (L.) Karst.) as influenced by magnesium nutrition

This paper tests the hypothesis that Mg-deficient spruce suffers higher leaching loss rates of mineral elements due to increased cuticular permeability. To that end, it compares healthy looking and Mg-deficient declining adult spruce ill the Ardennes and young healthy and Mg-deficient spruce grown under controlled conditions. In the field, measured throughfall deposits and calculated needle excretions were lower under healthy than under Mg-deficient declining spruce showing abnormal needle loss, eroded epicuticular wax structures of their needles and higher wettability. Laboratory experiments demonstrated that leaching and absorption intensities were higher for Mg-deficient needles than for healthy needles. These differences were adequately explained by a well structured epicuticular wax layer of healthy needles and malformed wax agglomerates of Mg-deficient needles. It was concluded that Mg-deficiency can explain high needle permeability as a result of malformed epicuticular wax structures. Enhanced throughfall and needle excretion of declining spruce in the field appeared to have at least partly the same origin.