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The nitrogen decade: mobilizing global action on nitrogen to 2030 and beyond

2021; Elsevier BV; Volume: 4; Issue: 1 Linguagem: Inglês

10.1016/j.oneear.2020.12.016

2590-3330

Mark A. Sutton, Clare Howard, David Kanter, Luis Lassaletta, Andrea Móring, Nandula Raghuram, Nicole Read,

Atmospheric chemistry and aerosols

Despite its relevance to most UN Sustainable Development Goals (SDGs), nitrogen pollution still lacks broad visibility and coordinated global governance. A new goal to "halve nitrogen waste" by 2030 would save US$100 billion annually, contributing to post-coronavirus disease 2019 (COVID-19) economic recovery and multiple SDGs. The scientific community is working with the UN to coordinate and accelerate the necessary action. Despite its relevance to most UN Sustainable Development Goals (SDGs), nitrogen pollution still lacks broad visibility and coordinated global governance. A new goal to "halve nitrogen waste" by 2030 would save US$100 billion annually, contributing to post-coronavirus disease 2019 (COVID-19) economic recovery and multiple SDGs. The scientific community is working with the UN to coordinate and accelerate the necessary action. If every decade has its character, it seems reasonable that 2020–2030 will be remembered as the decade of coronavirus disease 2019 (COVID-19) and post-COVID-19 recovery. With a bigger global impact on gross domestic product than the 2008 financial crisis,1United NationsImpact of the COVID-19 pandemic on trade and development. Transitioning to a new normal. United Nations Conference on Trade and Development, Geneva, 2020, 2020https://unctad.org/system/files/official-document/osg2020d1_en.pdfGoogle Scholar the effects will be with us for years to come. It may look like reaching the 2030 Sustainable Development Goals (SDGs) has just become even harder. While you might think that there is already enough to worry about, we would like to add nitrogen to the mix. As scientists working with the UN to embrace nitrogen as the next big environmental challenge, we would say that nitrogen is not just another problem. Instead, we see it as part of the solution to the plethora of problems already faced. Many are aware of nitrogen as one of the most transgressed "planetary boundaries." What is less widely understood is that nitrogen also affects the exceedance of all of the other planetary boundaries. By massively increasing the supply of nitrogen compounds, humans are worsening air and water quality, contributing to climate change and stratospheric ozone depletion, and thereby threatening health, biodiversity, and livelihoods. At the same time, nitrogen compounds are vital building blocks of life, so we need them for food and bio-energy production. The core "nitrogen challenge" must be for society to recognize that nitrogen links all these issues. It points to the opportunity to reduce policy fragmentation and accelerate solutions for the many problems we know so well. If the world is to reach the SDGs, then we will need to get serious about sustainable nitrogen management. The key thing to remember is that nitrogen is both abundant and limited on planet Earth. In its low-energy state of atmospheric di-nitrogen (N2), it dominates Earth's atmosphere. By contrast, all other forms of nitrogen—from ammonia (NH3), nitrate (NO3−), amino acids, proteins, and DNA—can be considered as representing high-energy "reactive nitrogen" (Nr). Substantial energy is needed to create Nr—whether by lightning, fertilizer manufacture, or biological nitrogen fixation (BNF)—so that, collectively, Nr is a precious and limited commodity. This also means that Nr compounds naturally tend to revert to N2, supplying energy to soil bacteria, while producing other Nr gases along the way, such as nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). All together, these make for a cocktail of nitrogen pollution with pan-dimensional consequences. In addition to addressing the COVID-19 challenge, in our view, the years up to 2030 also need to become the decade of sustainable nitrogen management. To explain this, it is worth reflecting on the last 50 years of global environmental governance, where we highlight the problem of fragmentation between nitrogen threats across parallel UN activities (Figure 1). We start with the 1970s as the decade of international environmental awakening. The Stockholm Conference of 1972 became the first "Earth Summit," leading to the establishment of the UN Environment Programme (UNEP). In retrospect, it seems prescient that the world's first major environmental agreement already recommended that the Secretary General ensure "monitoring the environmental levels resulting from emission of carbon dioxide, sulfur dioxide, oxidants, [and] nitrogen oxides (NOx)."2United NationsReport of the United Nations conference on the human environment.https://digitallibrary.un.org/record/523249?ln=enDate: 1973Google Scholar In the decades since, carbon dioxide has become synonymous with climate change, and sulfur dioxide with acid rain. Looking ahead, if we are to overcome current barriers to achieving the SDGs and planetary boundaries, then nitrogen also needs global recognition and action. One of the first nitrogen-relevant environmental agreements to follow the Stockholm Conference was the UN Economic Commission for Europe (UNECE) Air Convention, established in 1979.6Bull K. Hoft R. Sutton M.A. Coordinating European nitrogen policies between international conventions and intergovernmental organizations.in: Sutton M.A. Howard C.M. Erisman J.W. Billen G. Bleeker A. Grennfelt P. van Grinsven H. Grizzetti B. The European Nitrogen Assessment. Cambridge University Press, 2011: 570-584https://doi.org/10.1017/CBO9780511976988.028Crossref Google Scholar It was an appropriate herald to the 1980s as the decade of acid rain. The convention's first major agreement was the Helsinki Sulfur Protocol of 1985, followed swiftly by the Sofia Protocol (1988) on NOx.6Bull K. Hoft R. Sutton M.A. Coordinating European nitrogen policies between international conventions and intergovernmental organizations.in: Sutton M.A. Howard C.M. Erisman J.W. Billen G. Bleeker A. Grennfelt P. van Grinsven H. Grizzetti B. The European Nitrogen Assessment. Cambridge University Press, 2011: 570-584https://doi.org/10.1017/CBO9780511976988.028Crossref Google Scholar In both cases, the focus was on large industrial combustion sources, including for electricity supply, whereas later agreements increasingly focused on NOx from vehicle engines. Although nitrogen compounds can be present in some fuels, NOx emissions are mostly a consequence of N2 oxidation at high temperatures to form a mixture of NO and NO2. The effect is similar to the way that lightning naturally splits N2 to make NOx but produces much larger amounts. Not only does NOx contribute to acid rain, but it also reacts with volatile organic compounds to make the "oxidants" (such as ozone [O3]) already mentioned in the Stockholm Declaration. The focus of the Sofia Protocol was on ecosystems and the air we breathe. In parallel, it was fast becoming recognized that NOx and N2O were important in the process of stratospheric ozone depletion.7Crutzen P.J. Influence of nitrogen oxides on atmospheric ozone content.Q. J. R. Meteorol. Soc. 1970; 96: 320-325https://doi.org/10.1002/qj.49709640815Crossref Scopus (1088) Google Scholar Concern led to signing the Vienna Convention in 1985, followed rapidly by the Montreal Protocol. However, whereas the Vienna Convention mentioned N2O, it was not included under the Montreal Protocol, which focused exclusively on solvents, coolants, and other manufactured chemicals. With chlorofluorocarbons and many other ozone-depleting substances largely banned as a result, N2O has now become the largest contributor to ozone depletion. The main source of N2O is soils, where N2O is produced by the soil bacteria that transform Nr back to N2. Humans have more than doubled natural Nr input through the agricultural use of industrially manufactured fertilizers, including NH3, ammonium (NH4+), and urea, and by increasing rates of BNF. The net result is massively increased N2O emissions from billions of fields. With the Montreal Protocol targeting quick wins in reducing fluorochemical products from a few major manufacturing companies, it might have seemed a step too far to deal with N2O, 70% of which is emitted from agriculture.8United Nations Environment ProgrammeDrawing down N2O to protect climate and the ozone layer: a UNEP synthesis report.http://hdl.handle.net/20.500.11822/8489Date: 2013Google Scholar Building on the successes with air pollution and stratospheric ozone, the 1990s fast became the decade of multi-lateral environmental agreements. In 1992, the year of the Rio Earth Summit, three major conventions were established: the UN Framework Convention on Climate Change (UNFCCC), the UN Convention on Biological Diversity (CBD), and the UNECE Water Convention. Each of these has become a busy marketplace in which the role of nitrogen pollution has often been overlooked. For example, as the third most important contributor to warming, N2O is included in the UNFCCC basket of greenhouse gases alongside carbon dioxide and methane. Yet whereas carbon and climate have become synonymous, N2O has received little attention in climate negotiations. Expressing all greenhouse gas emissions as "carbon equivalents" also underscores the idea that nitrogen is everywhere and invisible. Similarly, although the CBD does include nitrogen pollution within its extremely diverse set of Aichi Biodiversity Targets (COP/10/INF/12/REV.1, Target 8), because so many issues are competing in the CBD, nitrogen has struggled to find the visibility needed for substantive action. Beyond climate and biodiversity, nitrogen is also entwined in the water-food-energy-ecosystems nexus, since much wasted Nr from atmospheric deposition and farm inputs finds its way into watercourses, affecting water quality, ecology, and coastal fisheries. The UNECE Water Convention is therefore relevant, but it has not so far addressed nitrogen. The 1995 Global Programme of Action for the Protection of the Marine Environment from Land-Based Activities (GPA) is also relevant and has taken a global lead on nutrient pollution since 2012.9International Institute for Sustainable DevelopmentSummary of the Third Intergovernmental Review meeting on the implementation of the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities.Earth Negot. Bull. 2012; 24https://enb.iisd.org/vol25/enb2577e.htmlGoogle Scholar However, it has not agreed on any global goals, such as a 2011 proposal to increase nitrogen-use efficiency (NUE) by 20%.9International Institute for Sustainable DevelopmentSummary of the Third Intergovernmental Review meeting on the implementation of the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities.Earth Negot. Bull. 2012; 24https://enb.iisd.org/vol25/enb2577e.htmlGoogle Scholar,10Sutton M.A. Bleeker A. Howard C.M. Bekunda M. Grizzetti B. de Vries W. van Grinsven H.J.M. Abrol Y.P. Adhya T.K. Billen G. et al.Our nutrient world: the challenge to produce more food and energy with less pollution. Global overview on nutrient management. UK Centre for Ecology & Hydrology on behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative, 2013https://wedocs.unep.org/handle/20.500.11822/10747Google Scholar Despite multiple nitrogen-relevant UN agencies and conventions since 1972, global nitrogen waste has steadily increased, tripling in magnitude over the last five decades (Figure 1). In reflecting on these major environmental conventions, it is remarkable to see how fragmentation between multiple UN bodies has become an unintended barrier to joined-up management of the nitrogen cycle, where the individual nitrogen dimensions within each issue have often lacked the gravity needed to catalyze necessary change. Following up the Sofia Protocol on NOx, science activity in the UNECE Air Convention made major progress in linking nitrogen challenges. Work to establish the 1999 multi-pollutant-multi-effect Gothenburg Protocol highlighted the dual importance of NOx and NH3 emissions for particulate matter (PM) air pollution and ecosystem impacts.6Bull K. Hoft R. Sutton M.A. Coordinating European nitrogen policies between international conventions and intergovernmental organizations.in: Sutton M.A. Howard C.M. Erisman J.W. Billen G. Bleeker A. Grennfelt P. van Grinsven H. Grizzetti B. The European Nitrogen Assessment. Cambridge University Press, 2011: 570-584https://doi.org/10.1017/CBO9780511976988.028Crossref Google Scholar Substantial political barriers to abating agricultural NH3 emissions also pointed to the need for synergy across the nitrogen cycle to strengthen the case for action. In response, the UNECE Air Convention established the Task Force on Reactive Nitrogen (TFRN) "to develop a better understanding of the integrated, multi-pollutant nature of reactive nitrogen … which may be used by other bodies outside the Convention" (ECE/EB.AIR/91.Add1, decision 2007/1). The activity also drew on global science cooperation through the International Nitrogen Initiative (INI) to develop the European Nitrogen Assessment.11Sutton M.A. Howard C. Erisman J.W. Billen G. Bleeker A. Grennfelt P. van Grinsven H. Grizzetti B. The European Nitrogen Assessment. Cambridge University Press, 2011Crossref Google Scholar This work led directly to the inclusion of national nitrogen budgets under the revised Gothenburg Protocol of 2012 (ECE/EB.AIR/119), to guidance on ammonia mitigation,12Bittman S. Dedina M. Howard C.M. Oenema O. Sutton M.A. Options for ammonia mitigation: guidance from the UNECE Task Force on Reactive Nitrogen. UK Centre for Ecology & Hydrology, 2014http://www.clrtap-tfrn.org/content/options-ammonia-abatement-guidance-unece-task-force-reactive-nitrogenGoogle Scholar and to assessment of how eating less meat and dairy can reduce nitrogen pollution.13Westhoek H. Lesschen J.P. Rood T. Leip A. Wagner S. De Marco A. et al.Nitrogen on the table: the influence of food choices on nitrogen emissions and the European environment. European Nitrogen Assessment Special Report on Nitrogen and Food. UK Centre for Ecology & Hydrology, 2015http://nora.nerc.ac.uk/id/eprint/513111/Google Scholar The most recent product is a UNECE guidance document adopted on December 18, 2020—in the first ever e-session of the Air Convention's Executive Body—on integrated mitigation of NH3, N2, N2O, NOx, and NO3− and overall nitrogen losses (ECE/EB.AIR/2020/6). It includes all sorts of opportunities to save valuable nitrogen resources, from simple covering of manure to advanced processing for nutrient recovery. Global upscaling of this approach has been facilitated by the GPA, including its Global Partnership on Nutrient Management, leading to publications making the links across nutrients,10Sutton M.A. Bleeker A. Howard C.M. Bekunda M. Grizzetti B. de Vries W. van Grinsven H.J.M. Abrol Y.P. Adhya T.K. Billen G. et al.Our nutrient world: the challenge to produce more food and energy with less pollution. Global overview on nutrient management. UK Centre for Ecology & Hydrology on behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative, 2013https://wedocs.unep.org/handle/20.500.11822/10747Google Scholar climate, and the ozone layer.8United Nations Environment ProgrammeDrawing down N2O to protect climate and the ozone layer: a UNEP synthesis report.http://hdl.handle.net/20.500.11822/8489Date: 2013Google Scholar Cooperation among INI, UNEP, and the Global Environment Facility has since established the International Nitrogen Management System (INMS) as a science-led process for policy support across the nitrogen cycle.14Sutton M. Raghuram N. Adhya T.K. Baron J. Cox C. de Vries W. Hicks K. Howard C. Ju X. Kanter D. et al.The nitrogen fix: from nitrogen cycle pollution to nitrogen circular economy.in: Frontiers 2018/2019: Emerging Issues of Environmental Concern. United Nations Environment Programme, 2019: 52-65https://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concernGoogle Scholar,15Sutton M.A. Mason K.E. Bleeker A. Hicks W.K. Masso C. Raghuram N. Reis S. Bekunda M. Just Enough Nitrogen: Perspectives on How to Get There for Regions with Too Much and Too Little Nitrogen. Springer, 2020https://doi.org/10.1007/978-3-030-58065-0Crossref Scopus (4) Google Scholar Ultimately, the big idea is that global nitrogen governance needs to move beyond past fragmentation. In this way, coordinated action on nitrogen offers multiple benefits for the environment, health, and the economy. With GEF and UNEP having established INMS, global progress on nitrogen has rapidly accelerated. Learning from the UNECE, a partnership was formed in 2017 between INMS and the South Asian Cooperative Environment Programme (SACEP) to draft a first-ever UN Resolution on Sustainable Nitrogen Management, adopted by the Fourth UN Environment Assembly in March 2019 (UNEP/EA.4/Res.14). Agreement by ministers in the SACEP governing council enabled India to champion the resolution, which has given UNEP the mandate to work with member states in mobilizing nitrogen action globally. Among its provisions, the nitrogen resolution calls for the UNEP executive director to "consider the options for facilitating improved coordination of policies across the global nitrogen cycle at the national, regional and global levels, including consideration of the case for establishing an intergovernmental mechanism for coordination of nitrogen policies" (UNEP/EA.4/Res.14). Four options14Sutton M. Raghuram N. Adhya T.K. Baron J. Cox C. de Vries W. Hicks K. Howard C. Ju X. Kanter D. et al.The nitrogen fix: from nitrogen cycle pollution to nitrogen circular economy.in: Frontiers 2018/2019: Emerging Issues of Environmental Concern. United Nations Environment Programme, 2019: 52-65https://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concernGoogle Scholar,15Sutton M.A. Mason K.E. Bleeker A. Hicks W.K. Masso C. Raghuram N. Reis S. Bekunda M. Just Enough Nitrogen: Perspectives on How to Get There for Regions with Too Much and Too Little Nitrogen. Springer, 2020https://doi.org/10.1007/978-3-030-58065-0Crossref Scopus (4) Google Scholar were reviewed with member-state representatives during the high-level segment of the INMS-4 meeting at UNEP Nairobi in April 2019:Option 1: the status quo of nitrogen fragmentation across multi-lateral environmental agreements (MEAs).Option 2: leadership on nitrogen under one existing MEA.Option 3: establishment of a new international convention on nitrogen.Option 4: establishment of an interconvention nitrogen coordination mechanism (INCOM). Government representatives at the INMS-4 meeting gave a clear preference for option 4. Overall, there was a strong encouragement to work with existing MEAs, while some representatives recommended revisiting option 3 in the future. INMS is now following up with member states under a newly formed UNEP Nitrogen Working Group, preparing the basis for establishing INCOM. Under this approach, INMS provides nitrogen science support relevant across multiple MEAs (Figure 2). While the UNEA-4 nitrogen resolution represents a turning point for member states, UNEP, and the scientific community, it noticeably lacks any quantitative goal. This was essential to guarantee its adoption, while leaving the way open for champion countries to press for specific goals. In particular, Indian leadership on nitrogen drew on Prime Minister Modi's published suggestion (on November 27, 2017, through his regular radio address Mann ki Baat) to halve national use of chemical fertilizers by 2022. While reflecting a strongly motivated intent, such a goal was likely to be contentious in the international arena. Another goal was therefore needed to foster wider consensus. It is thus that in January 2018, in a tiny seminar room of New York University, was born the idea to "halve nitrogen waste." No one can object to reducing waste, where total "nitrogen waste" is the sum of all forms of Nr pollution plus denitrification to N2, which is equally a waste of Nr resources. The goal of halving global nitrogen waste is relevant both for countries with too much and too little nitrogen15Sutton M.A. Mason K.E. Bleeker A. Hicks W.K. Masso C. Raghuram N. Reis S. Bekunda M. Just Enough Nitrogen: Perspectives on How to Get There for Regions with Too Much and Too Little Nitrogen. Springer, 2020https://doi.org/10.1007/978-3-030-58065-0Crossref Scopus (4) Google Scholar and for intensive and agro-ecological farming given that reducing waste enables available Nr resources to go further. It is also more equitable than the earlier goal of increasing NUE by 20%10Sutton M.A. Bleeker A. Howard C.M. Bekunda M. Grizzetti B. de Vries W. van Grinsven H.J.M. Abrol Y.P. Adhya T.K. Billen G. et al.Our nutrient world: the challenge to produce more food and energy with less pollution. Global overview on nutrient management. UK Centre for Ecology & Hydrology on behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative, 2013https://wedocs.unep.org/handle/20.500.11822/10747Google Scholar because less waste means less action is needed. At the same time, it allows flexibility for national and local actors to tune according to their own priorities (by sector, source, nitrogen form, effect, etc.). Development of this idea with relevant stakeholder consultation allowed INI to launch its commitment to support the global goal at the Our Oceans Conference in October 201816UK Centre for Ecology & HydrologyINI commits to support a global goal to halve nitrogen waste by 2030.https://www.ceh.ac.uk/news-and-media/news/ini-commits-support-global-goal-halve-nitrogen-waste-2030Date: 2018Google Scholar in Bali, while adoping a 2030 target date linked to achievement of the SDGs. The process further accelerated with the launch of the UN Global Campaign on Sustainable Nitrogen Management in Colombo, Sri Lanka, in October 2019.17United Nations Environment ProgrammeLaunch of United Nations Global Campaign on Sustainable Nitrogen Management.https://papersmart.unon.org/resolution/sustainable-nitrogen-managementDate: 2019Google Scholar The resulting Colombo Declaration agreed on the ambition to halve nitrogen waste by 2030 as part of National Nitrogen Action Plans, while endorsing the UNEP Road Map for Sustainable Nitrogen Management. The new global goal is now taking on a life of its own, developing fresh character as it becomes more widely embraced. For example, in May 2020, the European Commission included the goal to "reduce nutrient pollution by 50% by 2030" in both its Farm to Fork and Biodiversity Strategies. In addition, the CBD is now considering future adoption of a similar target (CBD/WG2020/2/3). As Figure 1 shows, the goal of halving nitrogen waste is scarily ambitious. It is something to make everyone think. Can society really achieve it by 2030? The attraction of saving $100 billion worth of nitrogen resources annually is clear.14Sutton M. Raghuram N. Adhya T.K. Baron J. Cox C. de Vries W. Hicks K. Howard C. Ju X. Kanter D. et al.The nitrogen fix: from nitrogen cycle pollution to nitrogen circular economy.in: Frontiers 2018/2019: Emerging Issues of Environmental Concern. United Nations Environment Programme, 2019: 52-65https://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concernGoogle Scholar If the experience of past efforts is anything to go by, it will require a broad approach engaging all sectors and sources.8United Nations Environment ProgrammeDrawing down N2O to protect climate and the ozone layer: a UNEP synthesis report.http://hdl.handle.net/20.500.11822/8489Date: 2013Google Scholar,12Bittman S. Dedina M. Howard C.M. Oenema O. Sutton M.A. Options for ammonia mitigation: guidance from the UNECE Task Force on Reactive Nitrogen. UK Centre for Ecology & Hydrology, 2014http://www.clrtap-tfrn.org/content/options-ammonia-abatement-guidance-unece-task-force-reactive-nitrogenGoogle Scholar,13Westhoek H. Lesschen J.P. Rood T. Leip A. Wagner S. De Marco A. et al.Nitrogen on the table: the influence of food choices on nitrogen emissions and the European environment. European Nitrogen Assessment Special Report on Nitrogen and Food. UK Centre for Ecology & Hydrology, 2015http://nora.nerc.ac.uk/id/eprint/513111/Google Scholar It is also just the kind of economic target to stimulate innovation as part of post-COVID-19 green economic recovery. At the same time, it should contribute even bigger societal benefit in terms of reduced water and air pollution, less climate damage and stratospheric ozone pollution, and improved health, biodiversity, and soil quality.10Sutton M.A. Bleeker A. Howard C.M. Bekunda M. Grizzetti B. de Vries W. van Grinsven H.J.M. Abrol Y.P. Adhya T.K. Billen G. et al.Our nutrient world: the challenge to produce more food and energy with less pollution. Global overview on nutrient management. UK Centre for Ecology & Hydrology on behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative, 2013https://wedocs.unep.org/handle/20.500.11822/10747Google Scholar,18Van Grinsven H.J.M. Holland M. Jacobsen B.H. Klimont Z. Sutton M.A. Jaap Willems W. Costs and benefits of nitrogen for Europe and implications for mitigation.Environ. Sci. Technol. 2013; 47: 3571-3579https://doi.org/10.1021/es303804gCrossref PubMed Scopus (188) Google Scholar While the case for action on nitrogen is obvious to us as scientists, the emergent sapling of sustainable nitrogen management will require careful tending if it is to flourish in the marketplace of environmental ideas. It is therefore no surprise that the Colombo Declaration was agreed upon as part of the new UN Global Campaign on Sustainable Nitrogen Management.17United Nations Environment ProgrammeLaunch of United Nations Global Campaign on Sustainable Nitrogen Management.https://papersmart.unon.org/resolution/sustainable-nitrogen-managementDate: 2019Google Scholar Nitro-awareness will be needed by politicians, policymakers, businesses, farmers, civil society, and the public. If the nitrogen decade is to be a success, we will need every trick in the book. From the "Nitrogen Song" by Grammy Award winner Ricky Kej (available on YouTube) to the need for the Glasgow Summit (COP26) to "discover" nitrogen for climate and green recovery, hundreds of opportunities are awaiting. The only question remaining is, are you ready to join us? The authors acknowledge support from the Global Environment Facility though the UN Environment Programme for the "Towards INMS project," from UK Research and Innovation (UKRI) for the Global Challenges Research Fund South Asian Nitrogen Hub, from the UK Natural Environment Research Council for the SUNRISE program, and from the UKRI Newton-Bhabha Fund and the Indian Department of Biotechnology for the "NEWS India-UK" Virtual Joint Centre on Agricultural Nitrogen. L.L. acknowledges MINECO-Spain and an EC Ramón y Cajal grant (RYC-2016-20269) together with support from the Universidad Politécnica de Madrid.