Abstract:
At a spatially heterogeneous mixed-conifer forest in the central California Sierras, we quantified total
carbon (C) and nitrogen (N), inorganic N, and net N mineralization in organic (O) and surface (0–15 cm) mineral
soils, and in situ fluxes of inorganic N and ortho-phosphate using resin lysimeters under three patch types: closed
canopy conifer, sparsely vegetated open canopy, and Ceanothus cordulatus thickets. In O horizons, total N and
C pools ranked: closed canopy Ceanothus open canopy. In mineral soils, total N pools under Ceanothus
exceeded those under closed canopy patches by about 30%. For 2 years, nitrate concentrations and rates of net
N mineralization in O horizons were 4 greater under Ceanothus than under the other patch types. Similarly,
ammonium concentrations and net N mineralization in mineral horizons were more than 80 and 200% greater,
respectively, under Ceanothus than under the other patch types. In situ fluxes of nitrate were 4 greater beneath
Ceanothus for 1 year, and no differences were found among the patch types for another year. Despite the
interannual variability, our data suggest that Ceanothus contributes to a greater proportion of total N mineralized
than based on cover alone, and may be important for forest nutrition under current conditions and after forest
burning.
