Search

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.)

Nitrogen (N) and phosphorus (P) are limiting factors for crop production in Rwanda where food security is susceptible to inadequate agricultural techniques, especially fertilization. Understanding N and P footprints for food and their budgets under different fertilized scenarios may help to improve the nutrient use efficiency and crop yield in Rwanda, however, with little information available yet. Here, we estimated food N and P footprints and their budgets for agri-food system in Rwanda using adjusted N-P-Calculator model under fertilized, unfertilized and combined scenarios during 1961-2020. The total food N footprint per capita increased from 4.2, 3.8 and 6.4 (1960s) to 6.8, 4.9 and 9.9 kg N cap -1  yr -1 under combined, unfertilized and fertilized scenarios, respectively (2011-2020). The total food P footprint per capita increased from 0.19, 0.18 and 0.23 (1960s) to 0.31, 0.25 and 0.40 kg P cap -1  yr -1 under combined, unfertilized and fertilized scenarios, respectively (2011-2020). The total N input to croplands increased from 13.9 (1960s) to 37.0 kg N ha -1  yr -1 (2011-2020), while the total crop N uptake increased from 18.1 (1960s) to 32.5 kg N ha -1  yr -1 (2011-2020), resulting in N use efficiency decline from 99.1% (1960s) to 74.6% (2011-2020). Gaseous N losses of NH 3 , N 2 O, and NO increased from 0.9, 0.1 and 0.0 (1960s) to 7.5, 0.8 and 0.1 kg N ha -1  yr -1 , respectively (2011-2020). The total P removal in harvested crops increased from 2.9 (1960s) to 5.1 kg P ha -1  yr -1 (2011-2020). The results revealed large room for crop yield expansion; and low N and P inputs are major agricultural production limitations. We suggest N and P fertilizer improvement by focusing on better management of organic animal manure and ensuring high biologically N fixed through crop rotation of legumes and cereals; lastly to increase in moderation the use of synthetic N and P fertilizers in Rwanda., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)

Plants are either recognized to produce nitrous oxide (N 2 O) or considered as a medium to transport soil-produced N 2 O. To date, it is not clear whether in their habitat plants conduit N 2 O produced in soil or are a natural source. We aimed to understand role of plants in N 2 O emissions in field conditions. Therefore, rubber plants (Ficus elastica) were planted in the field; then plant and soil chambers were deployed simultaneously to collect gas samples, and 15 N site preference (SP) of N 2 O was evaluated. The mean SP values of plant and soil emitted N 2 O were -20.85 ± 2.8‰ and -8.85 ± 1.08‰, respectively, and were significantly different (p < 0.0001); while bulk 15 N of plant and soil emitted N 2 O were -10.83 ± 3.33‰ and -22.56 ± 3.37‰, respectively and were similar (p = 0.06). In the current study, soil always acted as a source of N 2 O, while plants were both source and sink. Plant and soil N 2 O fluxes had significant positive exponential relationship with both soil and air temperature. Soil water-filled pore space (WFPS) had significant negative linear relationship with only soil N 2 O fluxes. Plant N 2 O fluxes had significant positive linear relationship with plant respiration rates and negative linear relationship with plant surface areas. Based on the relationship between plant respiration rates and N 2 O fluxes, we suggest that mitochondria are the possible sites of N 2 O formation in plant cells while the relationship between plant surface areas and N 2 O fluxes suggests that roots are the parts of its formation in natural and field conditions. Our results suggest that plants are a natural source of N 2 O even at field conditions and challenge a view that plants are a medium to transport soil-produced N 2 O into the atmosphere., 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 © 2021 Elsevier B.V. All rights reserved.)