The World's grasslands are under severe threat from on-going degradation, yet they are largely ignored in sustainable development agendas. This degradation is undermining the capacity of grasslands to support biodiversity, ecosystem services, and human wellbeing. In this Perspective, we examine the current state of grasslands worldwide and explore the extent and dominant drivers of global grassland degradation. We identify actions that are critical to the development of socio-ecological solutions to combat degradation and promote restoration of global grasslands. Specifically, we argue that progress can be made by: increasing recognition of grasslands in global policy, developing standardised indicators of grassland degradation, using scientific innovation for effective restoration at regional and landscape scales, and enhancing knowledge transfer and data sharing on restoration experiences. The integration of these strategies into sustainability policy should help to halt grassland degradation and enhance restoration success, and protect the socio-economic, cultural and ecological benefits that grasslands provide.Grasslands, comprising open grassland, grassy shrublands and savannah, cover about 40% of the Earth's surface and some 69% of the world's agricultural land area 1-3 . Not only do they serve as an important global reservoir of biodiversity, including many iconic and endemic species, but also, they provide a wide range of material and non-material benefits to humans and our quality of life. These benefits include a wide range of ecosystem services, such as food production, water supply and regulation, carbon storage and climate mitigation, pollination, and a host of cultural services 1-3 . Despite its importance, grassland degradation is widespread and accelerating in many parts of the world 4-6 with as much as 49% of grassland area worldwide having been degraded to some extent 5,7,8 .Grassland degradation poses an enormous threat to the hundreds of millions of people who rely on grasslands worldwide for food, fuel, fibre and medicinal products, as well as their multiple cultural values 9,10 . In terms of livestock production, the global cost of grassland degradation has been estimated at $6.8 billion 11 , with the impact on human welfare being particularly severe in regions where most the population is below the poverty line Grassland degradation also creates major environmental problems, given that grasslands play a critical role in biodiversity conservation, climate and water regulation, and global biogeochemical cycles 2,4 . For example, the conversion of tropical grassy biomes to arable cropland poses a significant threat to biodiversity given that they have a vertebrate species richness comparable to forests 12 , while the recent expansion of croplands in United States has caused widespread conversion of prairie grasslands, with considerable cost to wildlife 6 . Moreover, the conversion of grasslands to arable cropland and disturbance through overgrazing, fire and invasive species can lead to signif...

International audienceA broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms. We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning.Synthesis. Gaining a greater understanding of plant-soil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio-temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning