Understory N Application Overestimates the Effect of Atmospheric N Deposition on Soil N2o Emissions

Abstract

Deposition of atmospheric inorganic and organic nitrogen (N) may increase soil nitrous oxide (N2O) emissions. To simulate and quantify such effects in forest ecosystems, understory N application, usually directly to the soil surface, has been used. However, this approach overlooks N interception by forest canopies, resulting in overestimates of actual impacts from N deposition. To test our assumptions, we monitored soil N2O emissions over one year in a Moso bamboo (Phyllostachys edulis) forest using different N deposition simulation approaches (canopy vs. understory application) and forms of N (inorganic vs. organic N). Our results revealed that cumulative N2O emissions from understory N application treatments were 20–50% higher than the corresponding canopy treatments, with greater N2O emissions under inorganic N than organic N application. Our study underscores the importance of considering canopy processes in future studies on N deposition and soil N2O emissions.

Keywords: Canopy nitrogen deposition, Organic nitrogen application, Ammonium nitrate, amoA, nirK, nosZ