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The constant provision of plant productivity is integral to supporting the liability of ecosystems and human wellbeing in global drylands. Drylands are paradigmatic examples of systems prone to experiencing abrupt changes in their functioning. Indeed, space-fortime substitution approaches suggest that abrupt changes in plant productivity are widespread, but this evidence is less clear using observational time series or experimental data at a large scale. Studying the prevalence and, most importantly, the unknown drivers of abrupt (rather than gradual) dynamical patterns in drylands may help to unveil hotspots of current and future dynamical instabilities in drylands. Using a 20-y global satellite-derived temporal assessment of dryland Normalized Difference Vegetation Index (NDVI), we show that 50% of all dryland ecosystems exhibiting gains or losses of NDVI are characterized by abrupt positive/negative temporal dynamics. We further show that abrupt changes are more common among negative than positive NDVI trends and can be found in global regions suffering recent droughts, particularly around critical aridity thresholds. Positive abrupt dynamics are found most in ecosystems with low seasonal variability or high aridity. Our work unveils the high importance of climate variability on triggering abrupt shifts in vegetation and it provides missing evidence of increasing abruptness in systems intensively managed by humans, with low soil organic carbon contents, or around specific aridity thresholds. These results highlight that abrupt changes in dryland dynamics are very common, especially for productivity losses, pinpoint global hotspots of dryland vulnerability, and identify drivers that could be targeted for effective dryland management.

Despite the importance of microbial communities for ecosystem services and human welfare, the relationship between microbial diversity and multiple ecosystem functions and services (that is, multifunctionality) at the global scale has yet to be evaluated. Here we use two independent, large-scale databases with contrasting geographic coverage (from 78 global drylands and from 179 locations across Scotland, respectively), and report that soil microbial diversity positively relates to multifunctionality in terrestrial ecosystems. The direct positive effects of microbial diversity were maintained even when accounting simultaneously for multiple multifunctionality drivers (climate, soil abiotic factors and spatial predictors). Our findings provide empirical evidence that any loss in microbial diversity will likely reduce multifunctionality, negatively impacting the provision of services such as climate regulation, soil fertility and food and fibre production by terrestrial ecosystems. The role of microbial diversity in ecosystems is less well understood than, for example, that of plant diversity. Analysing two independent data sets at a global and regional scale, Delgado-Baquerizo et al . show positive effects of soil diversity on multiple terrestrial ecosystem functions.

Aridity, which is increasing worldwide because of climate change, affects the structure and functioning of dryland ecosystems. Whether aridification leads to gradual (versus abrupt) and systemic (versus specific) ecosystem changes is largely unknown. We investigated how 20 structural and functional ecosystem attributes respond to aridity in global drylands. Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.

Soils are the foundation of all terrestrial ecosystems 1 . However, unlike for plants and animals, a global assessment of hotspots for soil nature conservation is still lacking 2 . This hampers our ability to establish nature conservation priorities for the multiple dimensions that support the soil system: from soil biodiversity to ecosystem services. Here, to identify global hotspots for soil nature conservation, we performed a global field survey that includes observations of biodiversity (archaea, bacteria, fungi, protists and invertebrates) and functions (critical for six ecosystem services) in 615 composite samples of topsoil from a standardized survey in all continents. We found that each of the different ecological dimensions of soils—that is, species richness (alpha diversity, measured as amplicon sequence variants), community dissimilarity and ecosystem services—peaked in contrasting regions of the planet, and were associated with different environmental factors. Temperate ecosystems showed the highest species richness, whereas community dissimilarity peaked in the tropics, and colder high-latitudinal ecosystems were identified as hotspots of ecosystem services. These findings highlight the complexities that are involved in simultaneously protecting multiple ecological dimensions of soil. We further show that most of these hotspots are not adequately covered by protected areas (more than 70%), and are vulnerable in the context of several scenarios of global change. Our global estimation of priorities for soil nature conservation highlights the importance of accounting for the multidimensionality of soil biodiversity and ecosystem services to conserve soils for future generations. A global field survey that analyses samples of soil from all continents identifies hotspots for soil nature conservation, and shows that different ecological dimensions of soil are associated with different priority areas for conservation.

Understanding how drylands respond to ongoing environmental change is extremely important for global sustainability. In this review, we discuss how biotic attributes, climate, grazing pressure, land cover change, and nitrogen deposition affect the functioning of drylands at multiple spatial scales. Our synthesis highlights the importance of biotic attributes (e.g., species richness) in maintaining fundamental ecosystem processes such as primary productivity, illustrates how nitrogen deposition and grazing pressure are impacting ecosystem functioning in drylands worldwide, and highlights the importance of the traits of woody species as drivers of their expansion in former grasslands. We also emphasize the role of attributes such as species richness and abundance in controlling the responses of ecosystem functioning to climate change. This knowledge is essential to guide conservation and restoration efforts in drylands, as biotic attributes can be actively managed at the local scale to increase ecosystem resilience to global change.

We thank the researchers involved in the MUSGONET project for collection of field data. This study was supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN), and by the BES grant agreement No LRB17\\1019 (MUSGONET). We are grateful for the assistance of Yunyun Hao and Xuemei Han during soil sampling. We also thank Drs. Shuai Du and Xiuli Hao for their help in data analyses. M. D-B. is supported by the projects from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00) (SOIL4GROWTH) and TED2021-130908B-C41 (URBANCHANGE) funded by MCIN/AEI/10.13039/501100011033, and a project of the Fondo Europeo de Desarrollo Regional (FEDER) and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía (FEDER Andalucía 2014-2020 Objetivo temático “01 - Refuerzo de la investigación, el desarrollo tecnológico y la innovación”) associated with the research project P20_00879 (ANDABIOMA). Y-R. L. is supported by the National Natural Science Foundation of China (42177022). M.G.A.H is supported by the Swiss National Science Foundation (310030_188799). D.J.E. is supported by the Hermon Slade Foundation. F.B. and J.L.M. acknowledge support from the Spanish Ministry and FEDER funds for the project AGL2017-85755-R, the I+D+i project PID2020-114942RB-I00 funded by MCIN/AEI/10.13039/501100011033, the i-LINK+2018 (LINKA20069) from CSIC, as well as funds from “Fundación Séneca” from Murcia Province (19896/GERM/15). E.M.-J. was supported by an Experienced Researcher Fellowship of the Humboldt Foundation. E.M-J. and C.P. acknowledge support from the Spanish Ministry of Science and Innovation (PID2020-116578RB-I00). F.A. is supported by ANID FONDECYT 1220358. H-W.H. and J-Z.H. are supported by the project (DP210100332) from Australian Research Council. S.A. is funded by ANID FONDECYT 1170995 and ANID ANILLO ACT192027. MB is supported by a Ramón y Cajal grant from Spanish Ministry of Science (RYC2021-031797-I). The contribution of TG and TUN was supported by the Research Program in Forest Biology, Ecology and Technology (P4-0107) and project V4-3098 of the Slovenian Research Agency. T.P.M. would like to acknowledge contributions from the National Research Foundation of South Africa and cities involved in the South African survey. J.D. and A. Rey acknowledge support from the FCT (IF/00950/2014 and SFRH/BDP/108913/2015, respectively). JPV is thankful to SERB (EEQ/2021/001083) and DST (DST/INT/SL/P-31/2021) and BHU-IoE (6031)-incentive grant for research and development. MCR acknowledges support from an ERC Advanced Grant (694368). AM acknowledged financial support from the PMRF, Ministry of Education - Government of India, India.

Increasing the number of environmental stressors could decrease ecosystem functioning in soils. Yet this relationship has not been globally assessed outside laboratory experiments. Here, using two independent global standardized field surveys, and a range of natural and human factors, we test the relationship between the number of environmental stressors exceeding different critical thresholds and the maintenance of multiple ecosystem services across biomes. Our analysis shows that having multiple stressors, from medium levels (>50%), negatively and significantly correlates with impacts on ecosystem services and that having multiple stressors crossing a high-level critical threshold (over 75% of maximum observed levels) reduces soil biodiversity and functioning globally. The number of environmental stressors exceeding the >75% threshold was consistently seen as an important predictor of multiple ecosystem services, therefore improving prediction of ecosystem functioning. Our findings highlight the need to reduce the dimensionality of the human footprint on ecosystems to conserve biodiversity and function.The authors investigate relationships between various soil stressors that exceed critical thresholds and the maintenance of ecosystem services. They show that multiple stressors crossing a high-level threshold reduces soil functioning and can be consistently used to predict ecosystem functioning.

Soil samples collected from 224 dryland sites around the world show that aridity affects the concentration of organic carbon and total nitrogen differently from the concentration of inorganic phosphorus, suggesting that any predicted increase in aridity with climate change could uncouple the carbon, nitrogen and phosphorus cycles in drylands and negatively affect the services provided by these ecosystems. Aridity threatens nutrient balance in dry ecosystems It is thought likely that climatic change, such as the increased aridity predicted for many drylands, could disrupt the biogeochemical cycles of carbon, nitrogen and phosphorus during the twenty-first century. These elements are essential nutrients for biomass production in terrestrial ecosystems. This study finds that aridity has a negative effect on the concentration of global dryland soil organic carbon and nitrogen, but a positive effect on the concentration of inorganic phosphorus. This suggests a decoupling of nutrient cycles in response to an increase in aridity that could have a negative impact on biogeochemical reactions that control key ecosystem functions such as primary productivity. The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems 1 . It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes 1 , 2 , 3 , 4 , 5 . Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability 6 , 7 , 8 . The increase in aridity predicted for the twenty-first century in many drylands worldwide 9 , 10 , 11 may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients 12 , 13 , 14 . Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition 12 , 13 , 14 . Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

Fires alter the stability of organic matter and promote soil erosion which threatens the fundamental coupling of soil biogeochemical cycles. Yet, how soil biogeochemistry and its environmental drivers respond to fire remain virtually unknown globally. Here, we integrate experimental observations and random forest model, and reveal significant divergence in the responses of soil biogeochemical attributes to fire, including soil carbon (C), nitrogen (N), and phosphorus (P) contents worldwide. Fire generally decreases soil C, has non-significant impacts on total N, while it increases the contents of inorganic N and P, with some effects persisting for decades. The impacts of fire are most strongly negative in cold climates, conifer forests, and under wildfires with high intensity and frequency. Our work provides evidence that fire decouples soil biogeochemistry globally and helps to identify high-priority ecosystems where critical components of soil biogeochemistry are especially unbalanced by fire, which is fundamental for the management of ecosystems in a world subjected to more severe, recurrent, and further-reaching wildfires. Wildfires are intensifying as a result of rapid climate change. By integrating experimental observations with random forest model, the authors discovered that fires decouple soil biogeochemistry worldwide, providing critical insights for ecosystem management.

The increase in aridity predicted with climate change will have a negative impact on the multiple functions and services (multifunctionality) provided by dryland ecosystems worldwide. In these ecosystems, soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) play a key role in supporting multifunctionality. However, whether biocrusts can buffer the negative impacts of aridity on important biogeochemical processes controlling carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes remains largely unknown. Here, we conducted an empirical study, using samples from three continents (North America, Europe and Australia), to evaluate how the increase in aridity predicted by climate change will alter the capacity of biocrust-forming mosses to modulate multiple ecosystem processes related to C, N and P cycles. Compared with soil surfaces lacking biocrusts, biocrust-forming mosses enhanced multiple functions related to C, N and P cycling and storage in semiarid and arid, but not in humid and dry-subhumid, environments. Most importantly, we found that the relative positive effects of biocrust-forming mosses on multifunctionality compared with bare soil increased with increasing aridity. These results were mediated by plant cover and the positive effects exerted by biocrust-forming mosses on the abundance of soil bacteria and fungi. Our findings provide strong evidence that the maintenance of biocrusts is crucial to buffer negative effects of climate change on multifunctionality in global drylands.