Isotopocule signatures of N
2O (δ
15N
bulk, δ
18O and site preference) are useful for discerning soil N
2O source, but sometimes, N fertilizer is needed to ensure that there is enough N
2O flux for
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Isotopocule signatures of N
2O (δ
15N
bulk, δ
18O and site preference) are useful for discerning soil N
2O source, but sometimes, N fertilizer is needed to ensure that there is enough N
2O flux for accurate isotopocule measurements. However, whether fertilizer affects these measurements is unknown. This study evaluated a gradient of NH
4NO
3 addition on N
2O productions and isotopocule values in two acidic subtropical soils. The results showed that N
2O production rates obviously amplified with increasing NH
4NO
3 (
p < 0.01), although a lower N
2O production rate and an increasing extent appeared in forest soil. The δ
15N
bulk of N
2O produced in forest soil was progressively enriched when more NH
4NO
3 was added, while becoming more depleted of agricultural soil. Moreover, the N
2O site preference (SP) values collectively elevated with increasing NH
4NO
3 in both soils, indicating that N
2O contributions changed. The increased N
2O production in agricultural soil was predominantly due to the added NH
4NO
3 via autotrophic nitrification and fungal denitrification (beyond 50%), which significantly increased with added NH
4NO
3, whereas soil organic nitrogen contributed most to N
2O production in forest soil, probably via heterotrophic nitrification. Lacking the characteristic SP of heterotrophic nitrification, its N
2O contribution change cannot be accurately identified yet. Overall, N fertilizer should be applied strictly according to the field application rate or N deposition amount when using isotopocule signatures to estimate soil N
2O processes.
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