Responses of nitrous oxide emissions to nitrogen and phosphorus additions in two tropical plantations with N-fixing vs. non-N-fixing tree species

Abstract. Leguminous tree plantations at phosphorus (P) limited sites may result in excess nitrogen (N) and higher rates of nitrous oxide (N₂O) emissions. However, the effects of N and P applications on soil N₂O emissions from plantations with N-fixing vs. non-N-fixing tree species have rarely been studied in the field. We conducted an experimental manipulation of N and/or P additions in two plantations with Acacia auriculiformis (AA, N-fixing) and Eucalyptus urophylla (EU, non-N-fixing) in South China. The objective was to determine the effects of N or P addition alone, as well as NP application together on soil N₂O emissions from these tropical plantations. We found that the average N₂O emission from control was greater in the AA (2.3 ± 0.1 kg N₂O–N ha⁻¹ yr⁻¹) than in EU plantation (1.9 ± 0.1 kg N₂O–N ha⁻¹ yr⁻¹). For the AA plantation, N addition stimulated N₂O emission from the soil while P addition did not. Applications of N with P together significantly decreased N₂O emission compared to N addition alone, especially in the high-level treatments (decreased by 18%). In the EU plantation, N₂O emissions significantly decreased in P-addition plots compared with the controls; however, N and NP additions did not. The different response of N₂O emission to N or P addition was attributed to the higher initial soil N status in the AA than that of EU plantation, due to symbiotic N fixation in the former. Our result suggests that atmospheric N deposition potentially stimulates N₂O emissions from leguminous tree plantations in the tropics, whereas P fertilization has the potential to mitigate N-deposition-induced N₂O emissions from such plantations.