Nitrogen Fertilization of Lawns Enhanced Soil Nitrous Oxide Emissions by Increasing Autotrophic Nitrification

Abstract

As nitrous oxide (N 2 O) is one of the most important greenhouse gases, N 2 O emission pathways and regulation techniques in soils with different vegetation types have become a research focus. Currently, a diverse array of research exists on the N 2 O emissions from soils of different vegetation types, e.g., forest, grassland, and agriculture. Few studies have investigated the microbial processes of N 2 O emissions from lawn soils. Fertilization levels in lawn soils are often similar to or much higher than those in agricultural ecosystems, thus fertilized lawn is an important source of atmospheric N 2 O. In the study, we employed the 15 N-nitrate labelling method combined with the nitrification inhibition technique to distinguish microbial processes and their contribution to N 2 O emissions in long-term nitrogen fertilised lawns. We found that the N 2 O emission rate from the control treatment was 1.0 nmol g −1 h −1 over the incubation, with autotrophic nitrification contributing 60%. The N 2 O emission rate increased to 1.4 nmol g −1 h −1 from the soil treated with long-term N fertilization, and the contribution of autotrophic nitrification increased to 69%. N fertilization did not significantly increase the contribution of denitrification (24–26%) in the total N 2 O emissions. However, N fertilization substantially decreased the contribution of heterotrophic nitrification from 13 to 0.4% in the total N 2 O emissions. Co-denitrification to N 2 O was detected but the overall contribution was of minor importance (3–5%). The correlation analysis revealed that soil NO 3 − levels were the main influencing factors in the N 2 O producing microbial processes. Our results suggest that N fertilization altered both N 2 O production rates and the contribution pattern of microbial processes, and indicate the autotrophic nitrification and heterotrophic nitrification are more sensitive to N fertilization than denitrification and co-denitrification.