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Nitrous oxide (N 2 O) is a potent greenhouse gas (GHG) and an ozone-depleting substance. The presence of plants in an ecosystem can either increase or decrease N 2 O emissions, or play a negligible role in driving N 2 O emissions. Here, we conducted a meta-analysis comparing ecosystem N 2 O emissions from planted and unplanted systems to evaluate how plant presence influences N 2 O emissions and examined the mechanisms driving observed responses. Our results indicate that plant presence reduces N 2 O emissions while it increases dinitrogen (N 2 ) emissions from ecosystems through decreases in soil nitrate concentration as well as increases in complete denitrification and mineral N immobilization. The response of N 2 O 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 N 2 O formation in plant cells, we discussed how plant presence could enhance the emission of N 2 O from plants themselves. Improving our understanding of the mechanisms driving N 2 O 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests that could appear to influence the work of this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Climate change is leading to the upward migration of treelines in mountainous regions, resulting in changes to the carbon and nitrogen inputs in soils. The impact of these alterations on the microbial mineralization of the existing soil organic carbon (SOC) pool remains uncertain, making it challenging to anticipate their effects on the carbon balance. To enhance our prediction and understanding of native SOC mineralization in Himalayan regions resulting from treeline shifts, a study was conducted to quantify soil priming effects (PEs) at high elevations above the treeline ecosystem. In laboratory incubation, soils were treated with a combination of 13 C-glucose and varying nitrogen rates, along with carbon-only treatments and control groups without any amendments. The addition of carbon with varying nitrogen addition rates exhibited diverse PEs on native SOC. A highly positive PE was observed under low nitrogen input due to a high carbon/nitrogen imbalance and increased L-leucine aminopeptidase (LAP) activity, coupled with low nitrogen availability and carbon use efficiency (CUE). In contrast, a positive PE declined following high nitrogen input due to a low carbon/nitrogen imbalance and LAP activity, coupled with high nitrogen availability and CUE. These findings support the concept that multiple mechanisms (i.e., microbial nitrogen mining and microbial metabolic efficiency) exist that regulate SOC mineralization under the addition of carbon with varying nitrogen rates. Thus, an increase in nitrogen availability fulfils microbial nitrogen demand, reduces the microbial carbon/nitrogen imbalance, decreases enzyme activity that requires nitrogen and enhances microbial metabolic efficiency. Consequently, this mechanism reduces the positive PE, thereby serving as a potential tool for stabilizing native SOC in above-treeline ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)