Relationships between cation and nitrate concentrations in soil solutions from mature and harvested red alder stands

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Abstract
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 < 0.000 01), while K and Na were not as strongly related to NO3− (r2 = 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 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.

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