Plants mitigate ecosystem nitrous oxide emissions primarily through reductions in soil nitrate content: Evidence from a meta-analysis.

Nitrous oxide (NO) is a potent greenhouse gas (GHG) and an ozone-depleting substance. The presence of plants in an ecosystem can either increase or decrease NO emissions, or play a negligible role in driving NO emissions. Here, we conducted a meta-analysis comparing ecosystem NO emissions from planted and unplanted systems to evaluate how plant presence influences NO emissions and examined the mechanisms driving observed responses. Our results indicate that plant presence reduces NO emissions while it increases dinitrogen (N) emissions from ecosystems through decreases in soil nitrate concentration as well as increases in complete denitrification and mineral N immobilization. The response of NO emissions to plant presence was universal across major terrestrial ecosystems - including forests, grassland and cropland - and it did not vary with N fertilization. Further, in light of the potential mechanisms of NO formation in plant cells, we discussed how plant presence could enhance the emission of NO from plants themselves. Improving our understanding of the mechanisms driving NO emissions in response to plant presence could be beneficial for enhancing the robustness for predictions of our GHG sinks and sources and for developing strategies to minimize emissions at the ecosystem scale.