Contrasting Effects of Nitrogen and Labile Carbon Addition on N2O Emissions from Andosols in Costa Rica and Chile Under Controlled Conditions

Our study analyzes nitrous oxide (N2O) emissions of two volcanic soils, from a tropical (Costa Rica) and temperate (Chile) environment. Volcanic origin soils are important for dairy production in both countries and understanding how they react to incubation conditions will aid our understanding of N2O production. A 21-day incubation experiment was carried out to estimate the N2O emissions under nitrogen (N) fertilization, and a labile C (LC) source (glucose), alone and in combination from two Andosols. In Costa Rica, N addition had no significant effect on the cumulative N2O emissions, compared to the control, while in Chile, N2O emissions were 100 times higher (P < 0.05). The addition of LC generated N2O emissions 2 times higher (P < 0.05) in Costa Rica, but no effect on Chilean soils. Finally, the combination of N and LC input produced N2O emissions significantly different to the control in both countries. The N2O fluxes in Costa Rica were linked to a drop in NO3- in the presence of LC, while in Chile the NO3- drop was present when N was added. In Chile, the rapid drop of NO(3)(-)was mirrored by an increment in NH4+ but not in the Costa Rican soil. Our results show that under controlled conditions N2O productions from Costa Rican soils are energy-limited, while in Chilean soils, they rapidly respond to N addition. This contrast suggests high rates of heterotrophic denitrification in Costa Rican tropical soils and the existence of an additional mechanism for N2O production in Chile (i.e., dissimilatory nitrate reduction ammonium (DNRA)). The insights on N2O process contribute to the design of adequate mitigation actions that could be differentially implemented in volcanic ash soils found under different environments.