NITROGEN RETENTION ACROSS A GRADIENT OF15N ADDITIONS TO AN UNPOLLUTED TEMPERATE FOREST SOIL IN CHILE

• DOI: 10.1890/04-0415
• Publication Date: 2007-06-04T23:32:56Z
• Authors: Steven S. Perakis; Jana E. Compton; Lars O. Hedin
• Keywords: Temperate forest; Cycling; Nitrogen Cycle; Temperate rainforest; Sink (geography)

Accelerated nitrogen (N) inputs can drive nonlinear changes in N cycling, retention, and loss forest ecosystems. Nitrogen processing soils is critical to understanding these changes, since typically are the largest sink forests. To elucidate soil mechanisms that underlie shifts cycling across a wide gradient of supply, we added 15NH415NO3 at nine treatment levels ranging geometric sequence from 0.2 kg 640 N·ha−1·yr−1 an unpolluted old-growth temperate southern Chile. We recovered roughly half 15N tracers 0–25 cm soil, primarily surface 10 cm. Low moderate rates supply failed stimulate leaching, which suggests most unrecovered was transferred unmeasured sinks above ground. However, solution losses nitrate increased sharply >160 N·ha−1·yr−1, corresponding threshold elevated availability declining retention soil. Soil organic matter (<5.6 mm) dominated tracer low input, but coarse roots particulate became increasingly important higher supply. Coarse together accounted for 38% highest may explain substantial fraction "missing N" often reported studies fates Contrary expectations, additions did not gross potential nitrification, or ammonium oxidizer populations. Our results indicate nonlinearity resulted directly excessive relative sinks, independent plant–soil–microbial feedbacks. induce sharp decrease microbial biomass C:N predicted by saturation theory, could increase long-term storage lowering ratio net mineralization. All measured accumulated full suggesting short-term uptake kinetics, capacity, plant, pools.