RELATIONSHIPS BETWEEN CATION AND NITRATE CONCENTRATIONS IN SOIL SOLUTIONS FROM MATURE AND HARVESTED RED ALDER STANDS

Concentrations of dissolved cations available for plant uptake and lea ching are affected by many factors, including anion dynamics. To deter mine the relationship of dissolved cations to NO3-, soil solutions wer e sampled monthly with ceramic tension lysimeters for up to 8 years fr om O, A, and B horizons in mature red alder (Alnus rubra Bong.) and Do uglas-fir (Pseudotsuga menziesii (Mirb.) France) stands. Concentration s of Ca, Mg, and K, but not Na, displayed greater temporal variation u nder red alder, where nitrification-produced NO3- varied considerably, than under Douglas-fir, where NO3- was near zero. In red alder soil s olutions, Ca and Mg were strongly positively correlated with NO3- at a ll soil depths (r(2) = 0.94-0.83; p < 0.000 01), while K and Na were n ot as strongly related to NO3- (r(2) = 0.40-0.03; p = 0.0001 to >0.2). In the B horizon, dissolved Ca and Mg paralleled the decrease in NO3- that occurred during the 4 years following harvest of red alder. In c ontrast, Ca and Mg were maintained at relatively high levels in the O and A horizons, possibly by increased levels of dissolved organic anio ns that partially offset the decline in anionic charge associated with the decrease in NO3-. In the O and A horizons following harvest, K wa s initially elevated but decreased to low levels during the following 4 years.