The influence of basswood (Tilia americana) and soil chemistry on soil nitrate concentrations in a northern hardwood forest

In the Arbutus Lake Watershed in the Adirondack Mountains, New York, two nearly adjacent catchments (14 and 15) varied significantly in volume-weighted stream water nitrate (NO(3)) export (54 and 17 mu equiv..L(-1), respectively; P < 0.001). The most notable differences between the catchments were that Catchment 14 had significantly higher soil Ca concentrations and patches of basswood (Tilia americana L.). We evaluated the possible contributions of basswood and soil Ca concentrations to soil water NO(3) concentrations. Among the major overstory tree species, basswood leaf litter had the lowest C:N ratios, highest Ca concentrations, and among the lowest lignin:N ratios. Basswood basal area was significantly related to soil water NO(3) concentrations (R = 0.46, P = 0.01). Forest floor and mineral soil Ca concentrations were positively correlated with basswood basal area and negatively correlated with American beech (Fagus grandifolia Ehrh.) basal area. Our results suggest that a relatively low-density, calciphilic species such as basswood may create, given the proper soil conditions, hotspots with elevated soil water NO(3) concentrations. These hotspots result from the convergence of high soil Ca concentrations, due mostly to soil geology, with relatively labile litter substrate available for N mineralization and nitrification.