Plant phenolics play a key role in plant defence mechanisms against both biotic and abiotic stressors. However, their responses to environmental variables and grazing pressure across large geographical scales remain poorly understood. Using data from a global survey of 325 plots spanning six continents, we examined how climatic factors, soil properties, leaf nutrients and grazing pressure shape leaf phenolic concentration in 1854 plant species (1280 herbaceous and 574 woody) across global drylands. Our findings reveal that leaf phenolic concentration in herbaceous plants was mainly influenced by grazing pressure and its interactions with leaf nitrogen and iron, which together explained over 50% of observed variation across global drylands. Conversely, phenolic concentration in woody plants was strongly associated with climatic factors, particularly mean annual precipitation (MAP) and mean annual temperature (MAT), which accounted for 80% of the observed variation. While MAP had a positive effect on leaf phenolic concentration in woody plants, grazing pressure buffered this relationship by reducing the influence of MAP. Synthesis. Our study advances the understanding of how biotic and abiotic stressors shape plant defence strategies in global drylands. Our findings shed novel insights about how plant secondary metabolites and their associated functions shift in response to changes in climate and grazing pressure, two key global change drivers with significant implications for ecosystem resilience in drylands worldwide.

Drivers of non-native plant success in drylands are poorly understood. Here we identify functional differences between dryland native and non-native perennial plants and assess how biotic, abiotic and anthropogenic factors shape the success of the latter. On the basis of plant community and functional trait data from 98 sites across 25 countries, we report a total of 41 non-native plant species at 31 sites. Non-natives tend towards faster growth strategies than natives. Non-native plant richness is higher at sites with greater grazing pressure and under environmental conditions associated with higher soil fertility, decomposition and fungal richness-conditions that tend to occur in less arid regions-and lower where native plant and herbivore richness are greater. Non-native plant cover correlates positively with grazing pressure and negatively with native plant richness. Taken together, our results suggest that non-native plant success in drylands is facilitated when high grazing pressure coincides with elevated resource availability. Such context-dependence of non-native plant success and linkages with native plant and herbivore diversity highlight the need for managing grazing and conserving biodiversity across the world's drylands.

Abstract Reliable predictions of dryland carbon fluxes require understanding the persistence and turnover of soil organic carbon (SOC). We measure radiocarbon to quantify the age of SOC and CO2 released from soil respiration at 97 dryland sites across six continents. Here we show that bulk SOC contains little C fixed in the past 60 years, while respired CO2 originates from both bomb-derived recent C and millennia-old C, challenging the idea that old C is chemically or physically protected. Radiocarbon suggests mean ages of ~2100 years for bulk SOC and ~520 years for respired CO2, the latter far older than machine-learning (<50 years) or Earth system models predict. Aridity, net primary productivity, and SOC content are dominant predictors for radiocarbon signatures, with abrupt shifts to older C beyond an aridity threshold of ~0.87. Our findings underscore the need to incorporate the vulnerability of older carbon into models and land management strategies.

In the current process of widespread depopulation in Mediterranean rural ecosystems, agroecosystems are undergoing a process of passive rewilding due to the abandonment of agricultural practices. This study evaluates the effect of the factors involved in multi-trophic biodiversity changes associated with the rewilding process. A network of paired plots (areas abandoned more than 20 years ago and controls with no history of cultivation) in 40 municipalities in Aragon that have lost population in recent decades was used. Specifically, the effect of environmental factors, at local and regional scale, on the diversity of primary producers (plants), herbivores (orthoptera) and predators (spiders) measured in these plots was evaluated. Agricultural abandonment did not have a significant effect on species richness, although it did modulate the effect that environmental factors had on it. Each trophic group showed different responses to the environment, with local (soil) factors being more important for plants and spiders, and regional factors (human population) being more important for orthoptera. The study suggests that both local and regional factors influence the process of multi-trophic rewilding, highlighting the complexity involved in managing the consequences of depopulation on the natural environment.

Understanding the mechanisms that shape ecosystem resistance to increasing livestock grazing pressure, a major driver of land degradation, is essential for predicting its impacts and informing sustainable land management strategies. This issue is particularly relevant in drylands, which host half of the world's livestock production and are highly vulnerable to desertification caused by overgrazing. Here we conduct a standardized field survey across 73 dryland sites in 25 countries to simultaneously evaluate how climatic, edaphic, vegetation and grazing-related factors influence ecosystem resistance-defined here as the capacity to maintain vegetation cover under increasing grazing pressure. We found that increasing grazing pressure reduced vegetation cover in 80% of sites, with an average decline of 35%. Plant species richness emerged as the strongest predictor of ecosystem resistance, with higher richness associated with lower vegetation cover loss. Functional trait data indicated that this positive effect was mainly explained by complementarity in trait values among plants, rather than by functional redundancy. Our results indicate that conserving plant diversity is key to strengthening ecosystem resistance and sustaining dryland functioning under intensifying grazing pressure.

Plants are consumed by a variety of organisms, including herbivores and pathogens, which significantly impact plant biomass, diversity, community composition, and ecosystem functioning. While the impacts of vertebrate herbivores are well established, the effects of consumer groups such as insect herbivores, mollusks, and fungal pathogens on plant communities are less clear and remain understudied in many systems. Existing evidence of how they affect plant biomass, diversity, and community composition is mixed, and most studies have focused on individual consumer groups in isolation. However, different consumer groups interact with each other, directly or indirectly, in ways that alter their impacts on plants, and the consequences of these interactions for plant community structure and ecosystem function remain understudied. Further, consumer impacts vary across environmental gradients and likely depend on abiotic conditions such as climate, soil type, or elevation, and biotic conditions such as plant productivity, diversity, or community composition. Existing studies testing the impacts of invertebrate herbivores and fungal pathogens on plant communities differ substantially in methodology, making generalities across large scales difficult. This calls for experimental approaches that implement standardized protocols across many sites. Here, we introduce and report on the methodology of a novel global research network, The Bug-Network (BugNet), that implements standardized consumer-reduction experiments across 5 continents and 18 countries in diverse, herbaceous- or shrub-dominated ecosystems to investigate: (1) the influence of fungal pathogens, insect herbivores, and mollusks on plant diversity and ecosystem functioning, (2) interactions among these consumer groups, and (3) the abiotic and biotic drivers of context-dependent consumer impacts. BugNet aims to advance a predictive understanding of plant-consumer interactions in order to test fundamental ecological hypotheses and improve predictions of global change impacts on biodiversity and ecosystem functioning.

Aim: To evaluate how grazing pressure, a key land-use factor, interacts with climatic, vegetation, and soil variables to shape the fragmentation of perennial vegetation across drylands globally. Location: 171 plots across 25 countries on six continents. Time Period: Field data: 2016-2019. Major Taxa Studied: Perennial grasses, shrubs, and woody plants. Methods: We conducted a standardised field survey across 171 45 m x 45 m plots to assess grazing pressure, vegetation, and soil properties. Vegetation fragmentation was quantified using three patch-based metrics derived from high-resolution satellite images. Linear mixed-effects models were used to relate fragmentation to climatic, vegetation, and soil variables. Predictor importance was assessed through multi-model inference and validated using a random forest approach. Results: Vegetation fragmentation increased with aridity, and this effect was 4.7 times stronger under high grazing pressure than under low pressure. The most influential interactions involved grazing pressure with soil amelioration (49.7% importance) and with vegetation cover (44.6%). Soil amelioration-measured as the enrichment of soil organic carbon beneath vegetation-reduced fragmentation, especially under high grazing pressure. In contrast, the ability of vegetation cover to sustain large patches diminished as grazing intensity increased. Soil amelioration was strongly linked to the proportion of facilitated plant species (p < 0.01), whereas soil organic carbon alone-beneath vegetation (p = 0.37) or in bare areas (p = 0.94)-was not significantly related. Main Conclusions: Grazing pressure and aridity interact to intensify vegetation fragmentation, potentially accelerating land degradation in drylands under future climate and land-use scenarios. Mitigating this fragmentation requires not only enhancing vegetation cover but also promoting plant-soil facilitation processes, especially under high grazing pressure. These findings underscore the critical role of plant-driven soil amelioration in maintaining ecosystem structure and resilience across global drylands.

Aim: Plant functional traits can influence interaction outcomes between nurse and target plants through a "functional trait match", which occurs when the traits of nurse plants ameliorate their environment, and target plants possess traits that allow them to benefit from this ameliorated environment. We investigated how the traits of putative nurse species affect interaction outcomes across global drylands and determined the functional match that promotes facilitation. We also investigated how grazing pressure and global climatic and edaphic gradients affected this trait match. Location: Global drylands. Time Period: 2016-2019. Major Taxa Studied: Vascular plants. Methods: We used a collaborative survey conducted across 29 sites from five continents, where we gathered in situ co-occurrences of dominant species ('nurses') and other vascular plant species, as well as their functional traits [plant height and leaf dry matter content (LDMC)]. Climate, edaphic variables and grazing pressure were measured in situ or extracted from databases. We used a model building approach to determine the effect of dominant plant traits on interaction outcomes, and how the functional trait match between nurse and target species is affected by environmental variables. Results: Tall dominant plants with conservative leaves generally had a greater positive effect on species richness and cover beneath their canopies, but these effects were strongly modulated by grazing pressure and soil pH. Target plants that were significantly associated with dominant plants tended to be shorter, and have more acquisitive leaves than dominant plants, regardless of environmental conditions. However, the difference in height and LDMC between dominant plants and negatively associated target plants was strongly affected by environmental conditions. Main Conclusions: Functional traits play a significant role in determining interaction outcomes between dryland plants. Facilitation in drylands is driven by a conservative-acquisitive trait match, a pattern observed regardless of grazing pressure, climate and soil conditions.

In Gross et al.1 we produced the largest ever standardized dryland plant trait database including 133,769 trait measurements from 301 perennial plant species surveyed across 326 plots and six continents. Our findings indicate that arid and hyper-arid drylands act as a global reservoir of plant phenotypic diversity, challenging the common assumption that harsh environmental conditions reduce plant trait diversity. Tordoni et al.2 speculate that the larger phenotypic diversity in harsh environments found in our study is overestimated and misinterpreted. The re-analyses presented here further confirm that the patterns we originally reported are robust, and thus that the concerns from Tordoni et al. are not well-founded and do not apply to our study. We stand for the main conclusions of our study and maintain that lonely plants in arid land are functionally hyperdiverse. ### Competing Interest Statement The authors have declared no competing interest.

Plants can facilitate their local environment and create a two-phase spatial structure of vegetation and bare soil in drylands, which largely influences ecosystem functioning. Although an increasing number of studies have examined how global change drivers like aridity influence vegetation spatial structure in drylands (e.g., the patch size distribution), it remains unclear how grazing impacts differ from those of climatic gradients, how these effects vary with herbivore feeding habits, and which plant-level traits-such as size and life form-mediate these spatial responses. Here, we coupled spatial vegetation pattern analyses of ecosystem images with field data analyses of the size distribution and dominant life forms of plants from 326 plots sampled across 25 countries and six continents to explore the effects of herbivores on the spatial structure of dryland vegetation. The effects of herbivores on vegetation spatial structure were opposite to the effects of aridity. Specifically, vegetation in grazed areas was clustered into larger patches, with fewer small patches, which skewed the patch-size distribution towards larger patches. These effects differed between browsing and grazing herbivores. Grazing effects were partially explained by the fact that grazing reduced average plant size, increased shrub density, and promoted facilitation among species of contrasting sizes. Similar effects were also confirmed by using model simulations that accounted for positive plant interactions. By linking remotely sensed images, a global field survey, and a mathematical model, our study uncovers the species-level mechanisms by which herbivores shape ecosystem-level spatial patterns and provides insights into the consequence of herbivory pressure on the resilience of drylands.

It is unclear how much land use intensification ecosystems can withstand before undergoing abrupt changes in their structure and dynamics. Here we assess how the functional structure, diversity and temporal stability of 150 agricultural grasslands responded to large variations in land use intensification, namely, different intensities of fertilization, grazing and mowing. Using multi-site time series (2008-2020) of plant trait distributions, we identify two thresholds where the functional structure, diversity and stability of grasslands changed dramatically. The first threshold occurred between unfertilized and fertilized grasslands, with maximization of trait evenness indicating the persistence of plant species with diverse resource-use strategies in extensively managed grasslands. The second threshold occurred when fertilization exceeded 80 kg N ha-1 yr-1 or when grazing exceeded 500 livestock units days ha-1 yr-1, beyond which the most intensively managed grasslands were functionally poor, highly unstable and vulnerable to extreme weather events. These findings allow us to quantify the level of perturbation beyond which grasslands depart from a high biodiversity state and show that highly intensive management pushes the system to a more unstable state. The identified thresholds may provide targets for sustainable management and fertilization practices.

Mineral-associated organic carbon (MAOC) constitutes a major fraction of global soil carbon and is assumed less sensitive to climate than particulate organic carbon (POC) due to protection by minerals. Despite its importance for long-term carbon storage, the response of MAOC to changing climates in drylands, which cover more than 40% of the global land area, remains unexplored. Here we assess topsoil organic carbon fractions across global drylands using a standardized field survey in 326 plots from 25 countries and 6 continents. We find that soil biogeochemistry explained the majority of variation in both MAOC and POC. Both carbon fractions decreased with increases in mean annual temperature and reductions in precipitation, with MAOC responding similarly to POC. Therefore, our results suggest that ongoing climate warming and aridification may result in unforeseen carbon losses across global drylands, and that the protective role of minerals may not dampen these effects..

Biotic interactions are crucial for determining the structure and dynamics of communities; however, direct measurement of these interactions can be challenging in terms of time and resources, especially when numerous species are involved. Inferring species interactions from species co-occurrence patterns is increasingly being used; however, recent studies have highlighted some limitations. To our knowledge, no attempt has been made to test the accuracy of the existing methods for detecting mutualistic interactions in terrestrial ecosystems. In this study, we compiled two literature-based, long-term datasets of interactions between butterflies and herbaceous plant species in two regions of Germany and compared them with observational abundance and presence/absence data collected within a year in the same regions. We tested how well the species associations generated by three different co-occurrence analysis methods matched those of empirically measured mutualistic associations using sensitivity and specificity analyses and compared the strength of associations. We also checked whether flower abundance data (instead of plant abundance data) increased the accuracy of the co-occurrence models and validated our results using empirical flower visitation data. The results revealed that, although all methods exhibited low sensitivity, our implementation of the Relative Interaction Intensity index with pairwise null models performed the best, followed by the probabilistic method and Spearman's rank correlation method. However, empirical data showed a significant number of interactions that were not detected using co-occurrence methods. Incorporating flower abundance data did not improve sensitivity but enhanced specificity in one region. Further analysis demonstrated incongruence between the predicted co-occurrence associations and actual interaction strengths, with many pairs exhibiting high interaction strength but low co-occurrence or vice versa. These findings underscore the complexity of ecological dynamics and highlight the limitations of current co-occurrence methods for accurately capturing species interactions.

Earth harbours an extraordinary plant phenotypic diversity(1) that is at risk from ongoing global changes(2,3). However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change(4-6)-shape the trait covariation that underlies plant phenotypic diversity(1,7). Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity(8-10). They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Perennial plants create productive and biodiverse hotspots, known as fertile islands, beneath their canopies. These hotspots largely determine the structure and functioning of drylands worldwide. Despite their ubiquity, the factors controlling fertile islands under conditions of contrasting grazing by livestock, the most prevalent land use in drylands, remain virtually unknown. Here we evaluated the relative importance of grazing pressure and herbivore type, climate and plant functional traits on 24 soil physical and chemical attributes that represent proxies of key ecosystem services related to decomposition, soil fertility, and soil and water conservation. To do this, we conducted a standardized global survey of 288 plots at 88 sites in 25 countries worldwide. We show that aridity and plant traits are the major factors associated with the magnitude of plant effects on fertile islands in grazed drylands worldwide. Grazing pressure had little influence on the capacity of plants to support fertile islands. Taller and wider shrubs and grasses supported stronger island effects. Stable and functional soils tended to be linked to species-rich sites with taller plants. Together, our findings dispel the notion that grazing pressure or herbivore type are linked to the formation or intensification of fertile islands in drylands. Rather, our study suggests that changes in aridity, and processes that alter island identity and therefore plant traits, will have marked effects on how perennial plants support and maintain the functioning of drylands in a more arid and grazed world. In global drylands, soils tend to be more fertile beneath tree, shrub and grass islands. Soil fertility was greater beneath taller and wider plants but was unaffected by either grazing pressure or the type of herbivore.

Understanding soil microbial populations influencing biogeochemical cycles with potential implications for greenhouse gas (GHG) fluxes emissions is crucial. Methanotrophic, nitrifying and N2O-reducing microorganisms are major drivers of CH4 and N2O fluxes in soils. The metabolism of these organisms relies on enzymes that require as cofactors metal ions scarcely available in the soil, such as copper (Cu) and zinc (Zn). Despite the importance of these ions, how their concentrations relate to the abundance of these microbes at the global scale has not been addressed yet. Here, we used data from a global survey carried out in 47 drylands from 12 countries to evaluate the role of soil Cu and Zn concentrations, and their relationship with aridity, as drivers of the abundance of methanotrophs, archaeal and bacterial nitrifiers, and N2O reducers. To do so, we performed qPCR analyses of the marker genes pmoA, archaeal and bacterial amoA and nosZI. We did not find an association between the abundance of methanotrophs and Cu or Zn availability. However, our results highlight the importance of Cu influencing the abundance of nitrifying bacteria and N2O reducers, two main actors involved in the N2O cycle. Our findings indicate that dryland soils can be prone to reduce the N2O coming from nitrification to innocuous N2, but reductions in soil Cu availability (e.g., by increased aridity conditions due to climate change) could shift this trend.

In the current context of climate changes, which causes strong habitat variation, an understanding of the mechanisms underlying plant community dynamics is crucial to predict species fates. The taking of inter- and intraspecific trait variability into account would aid the identification of these mechanisms. Recently, a method involving the calculation of hypervolumes (n-dimensional spaces of trait values) was developed for the study of plant responses to their environments. Through hypervolume comparison, we examined the effects of interannual variations in abiotic conditions on aquatic plant communities in ponds of the sub-Antarctic Iles Kerguelen. This model system is particularly relevant for the examination of the consequences of climate changes–related habitat variation, as aquatic plant communities are adapted to cold and overall stable habitat conditions and the sub-Antarctic climate is changing rapidly.We conducted field sampling over 4 years at 3 sites. For all aquatic species, we measured five foliar, shoot, and clonal traits characterizing individual growth strategies that are likely to respond to variations in abiotic conditions on 1565 ramets over the four years. We measured 10 abiotic variables to characterize the plants’ habitats every 3 months during the survey period. Hypervolumes were calculated for each site and year to assess variation in aquatic plant strategies at the community level.We demonstrated (i) the importance of spatiotemporal gradients of trophic status, temperature, and pH and dissolved oxygen concentration for the functional structure of aquatic plant communities; (ii) that the shape of the mean response was trait dependent, with traits related to plant metabolism (specific leaf area and specific internode mass) and three-dimensional space exploration (height and internode length) responding to the three spatiotemporal abiotic gradients; (iii) that selection pressures were especially high on aerial traits relative to clonal traits; and (iv) that given the community response to interannual variations of abiotic conditions, environmental changes should impact macrophyte community productivity.Synthesis. We conclude that the examination of interannual abiotic variation over 4 years is sufficient to detect rapid responses of macrophyte communities, with likely reliance on phenotypic plasticity. Our findings may inform the characterization of future functional changes in aquatic plant communities of the sub-Antarctic region, where similar species are found.

Plants interact in complex networks but how their structure depends on resources, natural enemies and species resource-use strategy remains poorly understood. Here, we quantified competition networks among 18 plants varying in fast-slow strategy, by testing how increased nutrient availability and reduced foliar pathogens affected intra- and inter-specific interactions. Our results show that nitrogen and pathogens altered several aspects of network structure, often in unexpected ways due to fast and slow growing species responding differently. Nitrogen addition increased competition asymmetry in slow growing networks, as expected, but decreased it in fast growing networks. Pathogen reduction made networks more even and less skewed because pathogens targeted weaker competitors. Surprisingly, pathogens and nitrogen dampened each other’s effect. Our results show that plant growth strategy is key to understand how competition respond to resources and enemies, a prediction from classic theories which has rarely been tested by linking functional traits to competition networks.

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning.