The effects of climate warming and exogenous nitrogen input on soil N2O emissions from mangroves

The paucity of studies on nitrous oxide (N₂O) dynamics with rising temperatures and nitrogen (N)-based eutrophication makes it challenging to evaluate the role of mangroves in mitigating climate change. Here, a 3-year mesocosm experiment was conducted to investigate the effects of climate warming (+3 °C) and excessive N input (25 mg N L⁻¹) on soil N₂O emissions from two mangroves (Avicennia marina and Bruguiera gymnorrhiza). We found that warming and N input alone significantly increased soil N₂O emissions from both mangroves, while the interactive effects of warming and N input on soil N₂O emissions were affected by mangrove species. Warming mitigated the positive effect of N input on soil N₂O emissions from A. marina; and amplified the effect of N input on soil N₂O emissions from B. gymnorrhiza, suggesting that the response of soil N₂O emissions to these global change factors is species-dependent. Stable isotopic signature analysis revealed that both warming and N input significantly increased the relative contribution of nitrification to N₂O emissions from A. marina; whereas N input, rather than warming, significantly changed the relative contribution of nitrification in B. gymnorrhiza. This could be attributed to the differential changes in soil environmental conditions, plant growth and the microbial structure of the two mangroves. Overall, this study highlights the role of mangrove species in modifying the effects of warming and N input on soil N₂O emissions, which should be considered when accurately projecting N₂O emissions from mangroves. Furthermore, considering the low N₂O emissions from background sediments and the common N limitation across mangroves, our findings suggest that climate warming and exogenous N input may lead to a surge of N₂O emissions from mangroves, especially those that are seriously affected by human activities.