This paper tests the hypothesis that Mg-deficient spruce suffers higher lea
ching loss rates of mineral elements due to increased cuticular permeabilit
y. To that end, it compares healthy looking and Mg-deficient declining adul
t spruce ill the Ardennes and young healthy and Mg-deficient spruce grown u
nder controlled conditions.
In the field, measured throughfall deposits and calculated needle excretion
s 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 intensitie
s were higher for Mg-deficient needles than for healthy needles. These diff
erences were adequately explained by a well structured epicuticular wax lay
er of healthy needles and malformed wax agglomerates of Mg-deficient needle
s. 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.