Minireview Microbial nitrous oxide emissions in dryland ecosystems: mechanisms, microbiome and mitigation Hang-Wei Hu, 1 Pankaj Trivedi, 2 Ji-Zheng He, 1 and Brajesh K. Singh 3,4 * 1 Faculty of Veterinary and Agricultural Sciences, the University of Melbourne, Parkville, Victoria 3010, Australia. 2 Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA. 3 Hawkesbury Institute for the Environment, Western Sydney University, Penrith South DC, NSW 2751, Australia. 4 Global Centre for Land-Based Innovation, Western Sydney University, Penrith South DC, NSW 2751, Australia. Summary Globally, drylands represent the largest terrestrial biome and are projected to expand by 23% by the end of this century. Drylands are characterized by extremely low levels of water and nutrients and exhibit highly heterogeneous distribution in plants and biocrusts which make microbial processes shaping the dryland functioning rather unique compared with other terrestrial ecosystems. Nitrous oxide (N 2 O) is a powerful greenhouse gas with ozone depletion potential. Despite of the pivotal influences of microbial communities on the production and consumption of N 2 O, we have limited knowledge of the biological pathways and mechanisms underpinning N 2 O emissions from drylands, which are estimated to account for 30% of total gaseous nitrogen emissions on Earth. In this article, we describe the key microbial players and biological pathways regulating dryland N 2 O emissions, and discuss how these processes will respond to emerging global changes such as climate warming, extreme weather events and nitrogen deposition. We also provide a conceptual framework to precisely manipulate the dryland microbiome to mitigate N 2 O emissions in situ using emerging technologies with great specificity and efficacy. These cross-disciplinary efforts will enable the development of novel and environmental-friendly microbiome- based solutions to future mitigation strategies of climate change. Introduction: overview of nitrous oxide emissions from drylands Nitrous oxide (N 2 O) is a powerful greenhouse gas with 298 times greater global warming potential of CO 2 on an equiva- lent mass basis (IPCC, 2013), and is also a potent strato- spheric ozone depleting substance (Ravishankara et al., 2009). Over the past several decades, human activities have substantially enhanced atmospheric N 2 O concentra- tions by increasing the amount of reactive nitrogen (N) into the soil environment as a consequence of extensive use of synthetic N-based fertilizers (ca. 140 Tg N per year) and cultivation of N-fixing forages and crops (Del Grosso and Parton, 2012). Globally, terrestrial ecosystems emit approx- imately 6.8 Tg N 2 O-N per year into the atmosphere, and are the largest contributor (65%) to the global N 2 O budget (IPCC, 2013). An emerging body of evidence highlights that soil microbial communities are key drivers of terrestrial N 2 O emissions and N transformations, and modulate the effects of climate change on ecosystem functioning (Richardson et al ., 2009; Singh et al., 2010; Hu et al., 2015a). A mecha- nistic understanding of these microbial modulators and their direct linkage to N 2 O fluxes, therefore, is a prerequisite for improved estimation of global N 2 O emissions and develop- ment of innovative mitigation strategies. Drylands (including hyper-arid, arid, semi-arid and dry sub-humid ecosystems) are water-limited and drought- prone regions with an aridity index (defined as the ratio of the mean annual precipitation to potential evapotrans- piration) less than 0.65 (Safriel and Adeel, 2005). Received 14 March, 2017; Revised: 1 May, 2017; accepted 5 May, 2017. *For correspondence. E-mail: b.singh@ westernsydney.edu.au; Tel. (161) 2 45701392; Fax (161) 2 45701392. V C 2017 Society for Applied Microbiology and John Wiley & Sons Ltd Environmental Microbiology (2017) 19(12), 4808–4828 doi:10.1111/1462-2920.13795