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 leaching are affected by many factors, including anion dynamics. To determine the relationship of dissolved cations to NO3−, soil solutions were sampled monthly with ceramic tension lysimeters for up to 8 years from O, A, and B horizons in mature red alder (Alnusrubra Bong.) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands. Concentrations of Ca, Mg, and K, but not Na, displayed greater temporal variation under red alder, where nitrification-produced NO3− varied considerably, than under Douglas-fir, where NO3− was near zero. In red alder soil solutions, Ca and Mg were strongly positively correlated with NO3− at all soil depths (r2 = 0.94–0.83; p \u3c 0.000 01), while K and Na were not as strongly related to NO3− (r2 = 0.40–0.03; p = 0.0001 to \u3e 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 contrast, Ca and Mg were maintained at relatively high levels in the O and A horizons, possibly by increased levels of dissolved organic anions that partially offset the decline in anionic charge associated with the decrease in NO3−. In the O and A horizons following harvest, K was initially elevated but decreased to low levels during the following 4 years