Responses of soil background N₂O emissions to land use, soil properties, and climate parameters based on a global Meta analysis

Soil background N₂O emissions are the N₂O released from the soil without nitrogen fertilizer application or soil management during the planting cycle. With increased human activities, the amount of background N₂O emissions from soil has gradually increased, and its impact on the environment and climate is increasingly significant. However, the key driving factors and underlying mechanisms related to background N₂O emissions from the soil remain unclear. The distribution of the 282 studies included in this research was mapped based on field observation data of soil background N₂O emissions, as well as climate and soil factor data across the world, which were distributed across six continents and covered three predominant land use types, i.e., cropland, forestland, and grassland, to address this knowledge gap. The results showed that the global background N₂O emissions ranged from 0.01 to 19.80 kg(N)∙hm⁻²∙a⁻¹, with an average of 1.68 kg(N)∙hm⁻²∙a⁻¹. Among them, the range of soil background N₂O emissions in the grassland ecosystem was the widest, from 0.03 to 19.80 kg(N)∙hm⁻²∙a⁻¹. The soil background N₂O emissions in cropland and forestland ecosystems ranged from 0.01 to 7.10 kg(N)∙hm⁻²∙a⁻¹ and from 0.12 to 4.70 kg(N)∙hm⁻²∙a⁻¹, respectively. Furthermore, we conducted a systematic evaluation and in-depth investigation of various factors affecting soil background N₂O emissions, including soil pH, soil bulk density, soil total nitrogen, mean annual temperature, and mean annual precipitation, as well as the relationships between soil properties and climatic parameters with soil background N₂O emissions across different land use types. The main results were as follows: 1) compared with climatic factors, soil properties had a greater impact on soil background N₂O emissions; 2) soil background N₂O emissions under different land use types were different on a global scale; and 3) soil pH had significant effects on soil background N₂O emissions in cropland, forestland, and grassland ecosystems. This study provides valuable insights into the development and management strategies of sustainable agriculture and offers a scientific basis for mitigating N₂O emissions from the soil. It also provides critical support for reducing greenhouse gas emissions, protecting the ozone layer, and mitigating the impacts of climate change on ecosystems.