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ABSTRACT AimThe consistency of patterns in ontogenetic differences in plant traits across the globe has not been thoroughly studied. Environmental conditions affect leaf functional traits, and these effects can differ between adult trees and saplings due to varying environmental conditions in their aerial and soil environments. Our integrative analysis aims to reveal the global universality of woody plants' ontogeny and explores influencing factors. LocationGlobal. Time PeriodStudies published in 1989–2023. Major Taxa StudiedWoody plants. MethodsWe performed a global meta‐analysis of woody plants with different plant functional types at 64 sites around the world, assessed the ontogenetic differences in nine key leaf traits and explored the environmental factors that affected the ontogenetic differences. ResultsWe observed that (1) leaf traits differed significantly between adult trees and saplings, with environmental factors playing varying roles. Photosynthetic capacity per unit area (A_a) and nitrogen content per unit dry mass (N_m) were lower in saplings than in adults under low solar radiation, but this trend reversed with increased solar radiation. Differences in stomatal density (SD) and stable carbon isotope composition (δ¹³C) between adults and saplings were greatest under low solar radiation; (2) ontogenetic differences in leaf thickness (LT), leaf dry mass per area (LMA) and stomatal conductance (g_s) were greater at lower mean annual temperature (MAT); (3) at high mean annual precipitation (MAP), adults had higher nitrogen content per unit area (N_a), while saplings had higherN_mthan adults; (4) soil conditions were strongly correlated with ontogenetic differences in LT and SD, with soil pH as a key driver of variation inA_a, LT, SD,N_aandN_m. Main ConclusionsOur findings indicate that ontogeny strongly modifies leaf functional traits and that multiple environmental factors influence the magnitude of ontogenetic differences in leaf traits. This underscores the importance of considering ontogeny when predicting trait values across plant developmental stages, modelling vegetation composed of individuals of different ages and forecasting vegetation responses to environmental changes. 

ABSTRACT AimGlobal climate change is compressing species' realised niches and further threatening their distributions. Species traits, especially the trait spectra synthesised from traits, are one way in which species can match changes in their environment. Hence, integrating trait spectra and niches will help us understand how species adapt to their environment under global change. LocationGlobal. Time PeriodPresent. Major Taxa StudiedAngiosperms. MethodWe collected root traits from 158 angiosperm species and leaf traits from 512 angiosperm species from a global trait database to construct the leaf and root trait ‘slow‐fast’ spectrum based on resource acquisition strategy, as well as the collaboration spectrum related to root mycorrhizal colonisation. After rebuilding their phylogenetic relationships and defining species' environmental niches based on 213,979 occurrences of these species, we examined the relationship between these trait spectra and environmental niches along global climatic patterns. ResultPlants with ‘slow’ leaf traits were generally associated with narrow niche breadths and marginal niche positions, especially in high precipitation areas. The relationship between the ‘slow‐fast’ spectrum in root traits and ‘marginal‐central’ niche position reversed with decreasing precipitation. However, the relationships between leaf traits and niche variables were significant for woody species but not for herbaceous species. Main ConclusionOur research expands the plant trait spectra in macroecology applications. The root and leaf ‘slow‐fast’ trait spectra of angiosperms are driven by both macroclimate and long‐term evolutionary pressure. Understanding how these traits relate to the niche of species helps to predict how that species is likely to adapt to environmental change, which can enhance the predictive ability of niche theory for plant environmental adaptability. 

Abstract PremiseClimate change poses challenges to grasslands, including those of the North American Great Plains Region, where shifts in species distributions and fire dynamics are expected. Our present analysis focuses on remaining grasslands within this largely developed and agricultural region. The differential responses of C₄and C₃grass species to future climate conditions, particularly in habitat suitability and flammability, are critical for understanding ecosystem changes. MethodsWe used species distribution models to predict shifts in habitat suitability for 37 grass species under future climate scenarios and assessed flammability traits in a free‐air CO₂‐enrichment study, focusing on species' physiological responses to elevated CO₂, warming, and drought. ResultsOur models predicted that C₄species will retain higher habitat suitability, while C₃species will decline. Leaf‐level flammability analysis showed that species with higher water‐use efficiency under elevated CO will have lower flammability than under non‐elevated, potentially decreasing the predicted rate of fire spread when such species dominate. In contrast, species with higher growth rates but lower water‐use efficiency may be more flammable. Species‐specific responses varied within functional types. Anticipated shifts in species distributions suggest C₄species will become more dominant, potentially altering competitive dynamics and reducing C₃diversity. Changes in flammability under future conditions are expected to influence fire regimes, with a predicted decrease in mean community rate of spread due to the dominance of less‐flammable C₄species. ConclusionsThese findings highlight the need for adaptive fire management and conservation strategies to maintain biodiversity and ecosystem function in North American grasslands under climate change. 

Summary Unlike most ectomycorrhizal (EM) fungi,Cenococcum geophilumis a prolific producer of sclerotia, which represent a large and persistent, yet rarely quantified pool of EM fungal biomass and carbon in soils. How biomass of these asexual propagules is impacted by global change factors, such as anthropogenic nitrogen (N) deposition, remains unquantified.This study examined the effects of long‐term experimental N fertilization on the standing biomass, abundance, and size ofC. geophilumsclerotia in an oak (Quercusspp.) savanna ecosystem at Cedar Creek Ecosystem Science Reserve in Minnesota, USA.Standing sclerotia biomass in the control treatment averaged 192 g m⁻²(95% CI = 136–267 g m⁻²) and declined sharply under N enrichment, by 44% (95% CI = −53–79%) and 66% (95% CI = 39–82%) in the low N (5.4 g N m⁻² yr⁻¹) and high N (17 g N m⁻² yr⁻¹) treatments, respectively. Sclerotia abundance also declined under both fertilization levels by 58% (95% CI: 8–81%) and 62% (95% CI: 12–84%), while sclerotia diameter was significantly reduced only under high N.Given their high carbon content, melanization, and long persistence, the observed declines inC. geophilumsclerotia (c.84–127 g m⁻²) represent substantial losses from belowground carbon (C) pools. These findings indicate that chronic N deposition suppresses the formation of a functionally important and recalcitrant fungal structure, likely impacting soil C storage and mycorrhizal functional diversity. 

ABSTRACT QuestionsThe detection and interpretation of ecological processes are strongly influenced by the spatial scale at which studies are conducted. Scale terms (e.g., ‘local’ or ‘regional’) are frequently used to denote study scale and imply that studies using the same scale term should be directly comparable. However, whether the area encompassed by a particular scale term is consistent across studies remains unclear. LocationGlobal. MethodsWe reviewed 385 papers in plant community ecology and analysed 962 spatial scale terms and their reported areas. We tested whether variation in the use of individual scale terms could be explained by habitat, type of study or geographic region, and virtually sampled a simulated plant community to demonstrate the consequences of this variation for calculating common biodiversity metrics. ResultsSingle scale terms covered areas that vary by an average of 4.7 orders of magnitude, with significant overlap between distinct scale terms. Though this variation could be partly explained by habitat type (e.g., scale terms cover larger areas in forests than grasslands), we still found large variability (3.8 orders of magnitude) in the use of single terms within habitats. We also found overall high consistency (but still high variability) in the use of scale terms across geographic regions and study types. Our community simulation showed that Shannon's and Simpson's indices are highly sensitive to this variation, especially at finer spatial scales, suggesting that variation in the use of individual scale terms has major consequences for synthesising biodiversity trends. ConclusionsWhile terminology can make it appear that studies are directly comparable, they may cover vastly different areas and capture different ecological processes. Spatial scales should be reported in a standardised fashion by clearly stating the actual study size in abstracts and methods, and inconsistencies in scale term use should be accounted for when synthesising previous research. 

Abstract Grasslands cover approximately a third of the Earth’s land surface and account for about a third of terrestrial carbon storage. Yet, we lack strong predictive models of grassland plant biomass, the primary source of carbon in grasslands. This lack of predictive ability may arise from the assumption of linear relationships between plant biomass and the environment and an underestimation of interactions of environmental variables. Using data from 116 grasslands on six continents, we show unimodal relationships between plant biomass and ecosystem characteristics, such as mean annual precipitation and soil nitrogen. Further, we found that soil nitrogen and plant diversity interacted in their relationships with plant biomass, such that plant diversity and biomass were positively related at low levels of nitrogen and negatively at elevated levels of nitrogen. Our results show that it is critical to account for the interactive and unimodal relationships between plant biomass and several environmental variables to accurately include plant biomass in global vegetation and carbon models. 

Abstract Global environmental change is causing a decline in biodiversity with profound implications for ecosystem functioning and stability. It remains unclear how global change factors interact to influence the effects of biodiversity on ecosystem functioning and stability. Here, using data from a 24-year experiment, we investigate the impacts of nitrogen (N) addition, enriched CO₂(eCO₂), and their interactions on the biodiversity-ecosystem functioning relationship (complementarity effects and selection effects), the biodiversity-ecosystem stability relationship (species asynchrony and species stability), and their connections. We show that biodiversity remains positively related to both ecosystem productivity (functioning) and its stability under N addition and eCO₂. However, the combination of N addition and eCO₂diminishes the effects of biodiversity on complementarity and selection effects. In contrast, N addition and eCO₂do not alter the relationship between biodiversity and either species asynchrony or species stability. Under ambient conditions, both complementarity and selection effects are negatively related to species asynchrony, but neither are related to species stability; these links persist under N addition and eCO₂. Our study offers insights into the underlying processes that sustain functioning and stability of biodiverse ecosystems in the face of global change. 

Abstract Forbs (“wildflowers”) are important contributors to grassland biodiversity but are vulnerable to environmental changes. In a factorial experiment at 94 sites on 6 continents, we test the global generality of several broad predictions: (1) Forb cover and richness decline under nutrient enrichment, particularly nitrogen enrichment. (2) Forb cover and richness increase under herbivory by large mammals. (3) Forb richness and cover are less affected by nutrient enrichment and herbivory in more arid climates, because water limitation reduces the impacts of competition with grasses. (4) Forb families will respond differently to nutrient enrichment and mammalian herbivory due to differences in nutrient requirements. We find strong evidence for the first, partial support for the second, no support for the third, and support for the fourth prediction. Our results underscore that anthropogenic nitrogen addition is a major threat to grassland forbs, but grazing under high herbivore intensity can offset these nutrient effects. 

ABSTRACT AimsThe community composition of native and alien plant species is influenced by the environment (e.g., nutrient addition and changes in temperature or precipitation). A key objective of our study is to understand how differences in the traits of alien and native species vary across diverse environmental conditions. For example, the study examines how changes in nutrient availability affect community composition and functional traits, such as specific leaf area and plant height. Additionally, it seeks to assess the vulnerability of high‐nutrient environments, such as grasslands, to alien species colonization and the potential for alien species to surpass natives in abundance. Finally, the study explores how climatic factors, including temperature and precipitation, modulate the relationship between traits and environmental conditions, shaping species success. LocationIn our study, we used data from a globally distributed experiment manipulating nutrient supplies in grasslands worldwide (NutNet). MethodsWe investigate how temporal shifts in the abundance of native and alien species are influenced by species‐specific functional traits, including specific leaf area (SLA) and leaf nutrient concentrations, as well as by environmental conditions such as climate and nutrient treatments, across 17 study sites. Mixed‐effects models were used to assess these relationships. ResultsAlien and native species increasing in their abundance did not differ in their leaf traits. We found significantly lower specific leaf area (SLA) with an increase in mean annual temperature and lower leaf Potassium with mean annual precipitation. For trait–environment relationships, when compared to native species, successful aliens exhibited an increase in leaf Phosphorus and a decrease in leaf Potassium with an increase in mean annual precipitation. Finally, aliens' SLA decreased in plots with higher mean annual temperatures. ConclusionsTherefore, studying the relationship between environment and functional traits may portray grasslands' dynamics better than focusing exclusively on traits of successful species, per se. 

Abstract Climate change poses a growing threat to many ecosystems, including grasslands, which are a current priority for conservation due to their vulnerability to interacting threats from human activity.North American grasslands are expected to experience warmer temperatures and more frequent and severe droughts in the coming decades, with potential consequences for native biodiversity.We conducted an experiment at Cedar Creek Ecosystem Science Reserve, Minnesota, USA, to investigate how warming and drought treatments affected grassland plant community structure over 6 years in plots planted with species mixtures.Warming consistently reduced plant species richness with its effects on Shannon diversity (which additionally considers species' relative abundances) and dominance varying across years. These warming‐by‐year interactions were likely driven by temporal variability in environmental conditions and species‐specific responses. Notably, legumes consistently showed positive responses to warming.Drought alone had minimal direct effects on species richness and diversity but reduced variability in diversity responses over time, suggesting greater stability of diversity under drought conditions.Synthesis. This study underscores the important role of warming in reducing species richness, altering diversity and reshaping functional group composition in grassland ecosystems. While temporal variability influenced the magnitude of warming effects on diversity, legumes' positive responses highlight the importance of functional group dynamics in potentially buffering against species loss. Long‐term experiments that allow consideration of interannual variability are essential for improving predictions of ecosystem responses and informing adaptive management strategies aimed at sustaining biodiversity and ecosystem functioning in grasslands.