Background and Aims Global environmental changes significantly impact nitrogen (N) and phosphorus (P) availability in desert steppes, thereby reshaping plant species interactions and ultimately influencing ecosystem structure and functioning. This study investigated how these nutrients affect the competitive interactions between legumes and grasses by altering their adaptive strategies.Methods Pot experiments were conducted using the dominant grass species Stipa breviflora and the leguminous species Melissitus ruthenicus under different treatments involving control without nutrient inputs, N input alone, P input alone and combined N and P inputs. Plant growth, nutrient uptake and root traits were evaluated in monocultures and mixed plantings.Key Results In the relatively N-enriched desert steppes, P addition increased grass biomass by 76 % in monocultures; however, this effect was not observed when the grass were planted alongside the leguminous species. Legume exhibited a more pronounced response to P supplementation, with biomass increasing by up to 106 %. The relative total biomass (RBT) remained below 1 across all treatments, indicating the presence of interspecific competition. In simultaneous mixed planting, grass species were dominant under N-only treatments, whereas the legume exhibited a competitive advantage under P-only treatment. The concentrations of N and P in shoots of the grass remained unchanged following nutrient inputs and coexistence with the legume. In contrast, the N and P concentrations in legume shoots demonstrated the contrary trends, and were negatively and positively correlated with biomass, respectively. Both the grass and the legume increased total root length and reduced root diameter when coexisting. The priority effect (i.e. first seeding) enhanced the secretion of acid phosphatase and carboxylates by roots of the legume, and coexistence stimulated these root exudates in the grass.Conclusions Nitrogen inputs moderately enhance grass growth, whereas P inputs benefited legumes by modifying rhizosphere processes, thereby mitigating their competitive disadvantage under N enrichment. These findings highlight the potential for global change-induced reduced P availability to shift plant dominance in grasslands.

The capacity of nutrient-limited forests to enhance carbon (C) sequestration under elevated CO2 (eCO2) remains a critical uncertainty in C cycle modeling. While existing evidence suggests that low phosphorus (P) bioavailability may constrain CO2 fertilization effects on plant growth, the extent to which this limitation modulates ecosystem responses to eCO2 in forests adapted to P-deficient soils remains poorly understood. Here, using eight P-enabled models, we simulated the magnitudes and mechanisms through which P bioavailability interacts with eCO2, emulating an ecosystem-scale P enrichment experiment at a P-limited Eucalyptus forest undergoing long-term Free-Air CO2 Enrichment. While models predicted pronounced P effects on tree growth, P enrichment unexpectedly did not increase the CO2 effects on tree growth and ecosystem C sequestration. Models prioritized either CO2-driven or P-driven growth, but rarely both. This tradeoff emerged due to model-specific assumptions on 1) partitioning of the extra P in soil labile versus nonlabile pools; 2) plant photosynthetic acclimation to P deficiency; 3) C and nutrient use strategies regulating plant size and allocation; and 4) microbial-driven soil decomposition processes. By generating divergent yet biologically plausible outcomes, these predictions establish critical testable hypotheses for empirical research and highlight multiple P-related pathways that may influence the future land C sink.

Phosphorus (P) limitation may constrain the capacity of forests to remove CO2 from the atmosphere under elevated CO2 (eCa). One key mechanism is that limited P availability requires plants to invest additional fixed carbon belowground, which then returns to the atmosphere via soil respiration. However, the extent and pathways of this response remain unclear. We quantified total soil respiration and inferred its component fluxes before and after alleviating P limitation via fertilization in an established eCa experiment in mature Eucalyptus woodland. eCa increased soil respiration by 22.5% regardless of P availability. Dependence of the stimulation on soil moisture indicated it was driven primarily by root-derived respiration rather than soil organic matter-derived heterotrophic respiration. Fine-root production was stimulated by eCa only after P addition, suggesting that P fertilization triggered a shift from rhizomicrobial respiration, associated with microbial use of root exudates and residues, to autotrophic respiration from root growth and metabolism. These findings indicate that within 9 months of P addition, EucFACE plants may have shifted P-acquisition strategies under eCa. As the first ecosystem-scale study on the interactive effect of eCa and P limitation, this research improves mechanistic understanding of short-term belowground responses and provides insight to motivate follow-up studies.

The Congo basin is home to the second largest tropical forest in the world Therefore, it plays a crucial role in the global carbon cycle. Yet very few field based data on related processes exist. Gaining knowledge on a species level is also crucial for understanding these ecosystems. Leaf chamber measurements allow to measure photosynthetic capacity on a leaf level and by so, quantify the photosynthetic capacity of individual species. Moreover, they allow to quantify a plant´s reaction to environmental parameters such as light, atmospheric CO2 concentration and temperature. Such data is crucial to improve the calibration and robustness of global vegetation models. These models are key tools to estimate the global carbon budget and ecosystem responses to climate change as a part of the Intergovernmental Panel on Climate Change exercises. To date, no such data exists for the forests of the Congo Basin which prevents us to properly understand forest dynamics and resilience to global changes.In this research, we quantify leaf level carbon uptake and its response to light, CO2 and Temperature for dominant tree species within the footprint of the CongoFlux tower in Yangambi (DR Congo). As such, we deliver the first in-field leaf-level photosynthetic parameters dataset for a lowland tropical forest of the Congo Basin. Doing this, we explore the controls of interspecific variation in photosynthetic capacity including plant guild, species and vertical canopy position. Our study takes place at the research site of CongoFlux, Yangambi (DR Congo).

BACKGROUND AND AIMS:Phosphorus (P)-impoverished soils shape plant adaptation in biodiverse ecosystems worldwide, from Australian heathlands to Amazonian rainforests to southern China's karst regions. While non-mycorrhizal lineages like Proteaceae and Cyperaceae use carboxylate exudation that mobilise P, and are celebrated for such strategies, the mechanisms allowing mycorrhizal Myrtaceae-especially eucalypts-to thrive in these soils without fungal assistance remain unclear. Given Myrtaceae's dominance in P-impoverished Australian ecosystems, a key question arises: How do mycorrhizal plants succeed in P-impoverished environments without relying on fungal symbiosis? We challenge the paradigm that carboxylate-driven P acquisition is exclusive to non-mycorrhizal species. METHODS:Using leaf manganese concentrations ([Mn]) as a proxy for carboxylate exudation, we assessed trait diversification across Myrtaceae genera. We collected leaf and soil samples from 34 species of eucalypt (Angophora, Blakella, Corymbia, Eucalyptus) and other Myrtaceae from 18 sites in south-eastern Australia. KEY RESULTS:Our findings reveal consistently high leaf [Mn] in many Myrtaceae, comparable to that in known carboxylate-releasing species, indicating intensive P mining. This suggests convergent evolution of carboxylate exudation in mycorrhizal Myrtaceae, fundamentally reshaping our understanding of nutrient acquisition in symbiotic plants. Significant interspecific variation was observed, with Angophora showing markedly higher [Mn] than Eucalyptus, suggesting divergent P-acquisition strategies within Myrtaceae. Weak phylogenetic signals for leaf [Mn] and [P] in eucalypts imply repeated evolutionary change in these traits, similar to what is known in other Australian species adapted to P scarcity. CONCLUSIONS:By demonstrating carboxylate-driven P mining in mycorrhizal Myrtaceae, we redefine the mechanisms behind their dominance in low-P environments. Trait diversity-linked to variation in carboxylate-mediated P acquisition and plant-soil feedbacks-likely drives niche differentiation and genus-level distribution across south-eastern Australia. Connecting leaf [Mn] to carboxylate-driven P mining advances our understanding of trait evolution in Myrtaceae and provides a framework for predicting plant-soil interactions in P-impoverished ecosystems globally.

Extreme heat can push plants beyond their thermal safety margin (TSM) if maximum leaf temperature (Tleaf_max) exceeds leaf critical temperature (Tcrit). The TSM is potentially useful for assessing heat vulnerability across species but needs further validation, so we exposed 50 tree/shrub species in controlled glasshouses to a 6-day heatwave (peak air temperature = 41°C). Many species increased their mean Tcrit during the heatwave (42%), with ΔTcrit ranging from +1°C to 4°C, but other species did not acclimate or were impaired by heat stress (58%). Species Tleaf_max explained ~55% of the variation in species Tcrit and was a key correlate of the plasticity of Tcrit among species. Species with high ΔTcrit also had higher ΔTleaf_max, with leaves being 7°‒12°C hotter during the heatwave than under baseline conditions. Both Tleaf_max and TSMs were correlated with heatwave damage across diverse species from contrasting climate zones. Species differences in TSMs were stable across measurement temperatures, correctly identified the most vulnerable species, and were strongly associated with Tleaf_max. Our results suggest that (1) Tleaf_max alone is more informative than Tcrit for ranking species heat tolerance, and (2) species vulnerability to heatwaves is most reliably assessed by using TSMs that integrate Tleaf_max with Tcrit across species.

Accurate aboveground woody biomass (AGB) estimates are crucial for assessing the impact of elevated CO2 (eCO(2)) on net carbon sequestration in trees. Estimating AGB essentially involves developing allometric models using destructively harvested data. Due to the costs and restrictions of harvesting, models from other regions are often used. In the past two decades, terrestrial laser scanning (TLS) has become a widely accepted, non-destructive method for measuring tree structure. We provide new TLS-based allometric AGB models for Eucalyptus tereticornis, the dominant tree species at EucFACE, a replicated, ecosystem-scale mature forest free-air CO2 enrichment (FACE) experiment in Australia. Based on TLS-derived diameter at breast height (DBH), tree height (H), and crown area (CA) of 116 trees, we developed both an AGB:DBH model and an AGB:(CAxH) model. Our TLS-based AGB:DBH model (uncertainty = 19 %, bias <-1 %), shows substantially larger AGB growth compared to the previously-used allometric model at EucFACE. Although this new model does not change previous conclusions about the impact of eCO(2) on tree-level AGB increments at EucFACE, it does indicate a notable increase in AGB increment, particularly for larger trees. This highlights the need to recalculate net primary productivity and carbon partitioning at EucFACE. Additionally, we present a TLS-based AGB:(CAxH) model (uncertainty = 27 %, bias <1 %). These models improve accuracy in assessing carbon storage at EucFACE and offer scalable methods for monitoring AGB in E. tereticornis across broader landscapes. By enabling reliable, landscape-level carbon estimates, this work supports targeted forest management and conservation strategies under rising CO2 conditions.

Trait-based analyses have shown great potential to advance our understanding of terrestrial ecosystem processes and functions. However, challenges remain in adequately synthesising a multidimensional and covarying trait space. Reducing the number of studied traits while identifying the most informative ones is increasingly recognized as a priority in functional ecology. Here, we develop a trait reduction procedure based on network analysis of a global dataset comprising 27 traits in three steps. We first construct all possible reduced networks and identify optimal reduced networks that capture the structure of the full 27-trait network. Then we apply the constraints on trait consistency to identified optimal reduced networks and establish consistent network series across ecoregions. We find the best performing networks that capture the three main dimensions of the full network (hydrological safety, leaf economic strategy, and plant reproduction and competition) and the global variance of network metrics. Finally, we find a parsimonious representation of trait covariation strategies is achieved by a 10-trait network which preserves 60% of all the original information while costing only 20.1% of the full suite of traits. Our results show the network reduction approach can improve our understanding on the main plant strategies and facilitate the future trait-based research.

Most cities are likely to experience hotter summers and less precipitation in dry months by 2050. Urban tree species selected based on historical climates may be vulnerable to future climate extremes, particularly heatwaves during drought. In Sydney, Australia, an extreme summer in 2019-2020 caused extensive canopy dieback in 20 % and the death of 8 % of surveyed trees (n = 150 trees), but it was unclear why certain trees were vulnerable to severe drought stress and hydraulic failure. Here, we measured environmental variables (i.e., volumetric water content of surface soil, percentage of impervious surfaces), tree physiology, and growth of 19 urban tree species from 2019 to 2023, spanning the extreme and subsequent three wet summers. We found that the most drought-stressed trees with low predawn (Psi(pre)) and midday (Psi(mid)) leaf water potentials had small diameters (<10 cm) and were surrounded by a high proportion of impervious surfaces (>75 %). Severe drought stress only affected similar to 7 % of studied trees (n = 118 trees) but was correlated with low tolerance of heat stress and caused long-lasting declines in tree growth. On average, the extreme summer decreased growth by 64 %, with the greatest reductions and slowest recovery for the most heat-stressed trees, drought-stressed trees, and some exotic species. A better understanding of dynamic changes in urban tree water access and water use is needed. Future efforts should include physiological traits related to both drought and heat tolerance, considered at the individual tree and species-level, to understand urban tree vulnerability to future climates and improve the selection of climate-resilient urban species.

Understanding leaf photosynthetic traits and their variation in tropical forests is crucial for improving model predictions of forest productivity, and accurately representing the high functional diversity in these forests remains a challenge. Moreover, leaf photosynthesis data are lacking for the tropical forest of the Congo basin. We observed photosynthetic, chemical and structural leaf traits of 24 woody species in a Congolese tropical forest and studied their variance across functional guilds, within-tree crown positions and overall canopy positions defined by their relative height within the canopy. Guild and crown position jointly influenced leaf traits, with a significant effect observed (marginal R2 > 0.43). The traditional guild classification explained a significant portion of the observed interspecies variation, revealing a clear gradient from shade-tolerant to light-demanding species. Crown position significantly affected intraindividual leaf trait variability, with bottom crown leaves exhibiting trait values at least 19.3% lower than top leaves. Importantly, the linear relationship between relative canopy height and leaf traits emerged as a robust and continuous metric, effectively integrating both inter- and intraspecific variability. We conclude that while guild-based classifications provide a useful framework for identifying plant functional groups, relative canopy height offers a robust and quantitative approach for capturing overall canopy trait variation, valuable for modeling canopy processes.

Global vegetation growth is thought to be limited by nitrogen (N) more than by other nutrients. Here we document a stronger phosphorus (P) limitation on global photosynthesis compared with N over the last four decades. On the basis of more than 80,000 field observations of foliar nutrients and a machine learning method, we generated a long-term global dataset of foliar N and P concentrations for the period 1980-2017. We show a larger declining rate of foliar P concentration (-0.80 ± 0.008% yr-1) than of N concentration (-0.31 ± 0.002% yr-1). This decline has led to an increase in terrestrial areas limited by foliar P and a widespread constraint on vegetation photosynthesis, more than 1.5 times stronger than the constraint by foliar N. The increasing trend in global photosynthesis over the past 4 decades has been reduced by approximately 17.2% and 6.7% as a result of the decline in foliar P and N, respectively. This stronger P limitation on global photosynthesis implies a weakening of terrestrial carbon sinks due to an emerging P constraint and calls for stricter strategies for reducing anthropogenic emissions to mitigate climatic warming.

The capacity for terrestrial ecosystems to sequester additional carbon (C) with rising CO2 concentrations depends on soil nutrient availability1,2. Previous evidence suggested that mature forests growing on phosphorus (P)-deprived soils had limited capacity to sequester extra biomass under elevated CO2 (refs. 3-6), but uncertainty about ecosystem P cycling and its CO2 response represents a crucial bottleneck for mechanistic prediction of the land C sink under climate change7. Here, by compiling the first comprehensive P budget for a P-limited mature forest exposed to elevated CO2, we show a high likelihood that P captured by soil microorganisms constrains ecosystem P recycling and availability for plant uptake. Trees used P efficiently, but microbial pre-emption of mineralized soil P seemed to limit the capacity of trees for increased P uptake and assimilation under elevated CO2 and, therefore, their capacity to sequester extra C. Plant strategies to stimulate microbial P cycling and plant P uptake, such as increasing rhizosphere C release to soil, will probably be necessary for P-limited forests to increase C capture into new biomass. Our results identify the key mechanisms by which P availability limits CO2 fertilization of tree growth and will guide the development of Earth system models to predict future long-term C storage.

Both mistletoes and their hosts are challenged by increasing drought, highlighting the necessity of understanding their comparative hydraulic properties. The high transpiration of mistletoes requires efficient water transport, while high xylem tensions demand strong embolism resistance, representing a hydraulic paradox. This study, conducted across four environments with different aridity indices in Yunnan, China, examined the xylem traits of 119 mistletoe-host species pairs. Mistletoes showed lower water use efficiency, indicating a more aggressive water use. They also showed lower hydraulic efficiency (lower vessel diameter and theoretical hydraulic conductivity) but higher safety (lower vulnerability index and higher conduit wall reinforcement, vessel grouping index, and wood density) compared with their hosts, supporting the trade-off between efficiency and safety. Environmental variation across sites significantly affected xylem trait comparisons between mistletoes and hosts. Additionally, the xylem traits of mistletoes were strongly influenced by host water supply efficiency. The overall xylem trait relationships in mistletoes and hosts were different. These findings stress the impact of host and site on the hydraulic traits of mistletoes, and suggest that mistletoes may achieve high transpiration by maintaining high stomatal conductance under low water potentials. This study illuminates the distinctive adaptation strategies of mistletoes due to their parasitic lifestyle.

Fire-prone landscapes experience frequent fires, disrupting above-ground biomass and altering below-ground soil nutrient availability. Augmentation of leaf nutrients or leaf water balance can both reduce limitations to photosynthesis and facilitate post-fire recovery in plants. These modes of fire responses are often studied separately and hence are rarely compared. We hypothesized that under severe burning, woody plants of a coastal scrub ecosystem would have higher rates of photosynthesis (Anet) than in unburned areas due to a transient release from leaf nutrient and water limitations, facilitating biomass recovery post-burn. To compare these fire recovery mechanisms in regrowing plants, we measured leaf gas exchange, leaf and soil N and P concentrations, and plant stomatal limitations in Australian native coastal scrub species across a burn sequence of sites at 1 year after severe fire, 7 years following a light controlled fire, and decades after any fire at North Head, Sydney, Australia. Recent burning stimulated increases in Anet by 20% over unburned trees and across three tree species. These species showed increases in total leaf N and P as a result of burning of 28% and 50% for these macronutrients, respectively, across the three species. The boost in leaf nutrients and stimulated leaf biochemical capacity for photosynthesis, alongside species-specific stomatal conductance (gs) increases, together contributed to increased photosynthetic rates after burning compared with the long-unburned area. Photosynthetic stimulation after burning occurred due to increases in nutrient concentrations in leaves, particularly N, as well as stomatal opening for some species. The findings suggest that changes in species photosynthesis and growth with increased future fire intensity or frequency may be facilitated by changes in leaf physiology after burning. On this basis, species dominance during regrowth depends on nutrient and water availability during post-fire recovery.

Traits with intuitive names, a clear scope and explicit description are essential for all trait databases. The lack of unified, comprehensive, and machine-readable plant trait definitions limits the utility of trait databases, including reanalysis of data from a single database, or analyses that integrate data across multiple databases. Both can only occur if researchers are confident the trait concepts are consistent within and across sources. Here we describe the AusTraits Plant Dictionary (APD), a new data source of terms that extends the trait definitions included in a recent trait database, AusTraits. The development process of the APD included three steps: review and formalisation of the scope of each trait and the accompanying trait description; addition of trait metadata; and publication in both human and machine-readable forms. Trait definitions include keywords, references, and links to related trait concepts in other databases, enabling integration of AusTraits with other sources. The APD will both improve the usability of AusTraits and foster the integration of trait data across global and regional plant trait databases.

The importance of phosphorus (P) in regulating ecosystem responses to climate change has fostered P-cycle implementation in land surface models, but their CO 2 effects predictions have not been evaluated against measurements. Here, we perform a data-driven model evaluation where simulations of eight widely used P-enabled models were confronted with observations from a long-term free-air CO 2 enrichment experiment in a mature, P-limited Eucalyptus forest. We show that most models predicted the correct sign and magnitude of the CO 2 effect on ecosystem carbon (C) sequestration, but they generally overestimated the effects on plant C uptake and growth. We identify leaf-to-canopy scaling of photosynthesis, plant tissue stoichiometry, plant belowground C allocation, and the subsequent consequences for plant-microbial interaction as key areas in which models of ecosystem C-P interaction can be improved. Together, this data-model intercomparison reveals data-driven insights into the performance and functionality of P-enabled models and adds to the existing evidence that the global CO 2 -driven carbon sink is overestimated by models.

&lt;p&gt;Leaves form the primary interface between plant physiology, CO2 in the atmosphere and energy (light). Plant productivity (i.e. carbon (C) gain) is primarily determined by the amount of leaf area, leaf orientation and distribution in space. Not much attention has been paid to possible changes in leaf orientation and distribution with elevated CO2 (eCO2), but its effect on plant growth could alter the proportions of sunlit and shaded leaf areas and feedback on carbohydrate available for further growth. We report on first measurements of leaf inclination angle distribution, foliage clumping in a native evergreen Eucalyptus woodland - the EucFACE experiment in Western Sydney, New South Wales, Australia - in ambient CO2 and exposed to +150 ppm elevated CO2 (eCO2). We found that a spherical leaf angle distribution, a common assumption in ecosystem modeling, was not an appropriate supposition for present species (&lt;em&gt;Eucalyptus tereticornis &lt;/em&gt;Sm.; &lt;em&gt;Eucalyptus amplifolia &lt;/em&gt;Naudin) at this site. Our measurements of leaf inclination angles from imagery indicated an erectophile, highly skewed unimodal leaf inclination angle distribution function. We conclude that despite the measured steeper angles under eCO2 concentrations, the leaf angle change is not significant and falls within the expected natural variability and uncertainties connected with the measurement method. The lack of a clear response of leaf orientation and foliage clumping to eCO2 concentration indicates that the previously produced datasets of leaf inclination angles and foliage clumping maps with Earth observation data may be suitable while modelling carbon and water cycles under climate change.&lt;/p&gt;

Mistletoes play important roles in biogeochemical cycles. Although many studies have compared nutrient concentrations between mistletoes and their hosts, no general patterns have been found and the nutrient uptake mechanisms in mistletoes have not been fully resolved. To address the water and nutrient relations in mistletoes compared with their hosts, we measured 11 nutrient elements, two isotope ratios and two leaf morphological traits for 11 mistletoe and 104 host species from four sites across a large environmental gradient in southwest China. Mistletoes had significantly higher phosphorus, potassium, and boron concentrations, nitrogen isotope ratio, and lower carbon isotope ratio (δ13 C) indicative of lower water-use efficiency than hosts, but other elements were similar to those in hosts. Sites explained most of the variation in the multidimensional trait space. With increasing host nitrogen concentration, both mistletoe δ13 C and the difference between mistletoe and host δ13 C increased, providing evidence to support the 'nitrogen parasitism hypothesis'. Host nutrient concentrations were the best predictors for that of the mistletoe nutrient elements in most cases. Our results highlight the important roles of environmental conditions and host nutrient status in determining mistletoe nutrient pools, which together explain their trophic interactions with hosts in subtropical and tropical ecosystems.

1. The live fuel moisture content (LFMC) is an important precondition for wildfire activity, yet it remains challenging to predict LFMC due to the dynamic interplay between atmospheric and hydrological conditions that determine the plant's ac-cess to, and loss of water.2. We monitored LFMC and a range of plant water- use traits (predawn and mid-day leaf water potentials [Psi leaf]), leaf traits (specific leaf area [SLA]), hydrological status (soil water content [SWC] in the shallow layer and full profile) and atmos-pheric variables (air temperature, vapour pressure deficit [VPD], CO2 concentra-tions) in a mature eucalypt woodland at the Eucalyptus Free- Air CO2 Enrichment (EucFACE) facility during a drought.3. We combined plant traits, hydrological status and atmospheric variables into a biophysical model to predict LFMC dynamics, and compared these with predic-tions of LFMC based on a satellite model and established relationships between Psi leaf and LFMC from pressure- volume curves.4. Predawn Psi leaf could be well predicted from changes in SWC, but variation in midday Psi leaf and LFMC were more responsive to atmospheric than hydrological variables. The biophysical model explained up to 89% of variability in LFMC and outperformed established approaches to predict LFMC. SLA was the single most important variable to predict LFMC, followed by VPD, which explained 33% of the remaining variability in LFMC.5. Our study demonstrates that the co- variation of plant traits and atmospheric and hydrological conditions affect LFMC during drought, suggesting a new way for-ward for predicting LFMC by combining biophysical and satellite- based models of LFMC with seasonal forecasts of meteorological and hydrological variables.