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Background and aims Cluster roots (CRs) constitute a special root adaptation that enables plants to take up nutrients, especially phosphorus (P), from soils with low nutrient availability, including recent volcanic deposits. It is unclear, however, how CR species interact with non-cluster root-bearing (NCR) species, and how substrates' fertility modulates potential interactions. Methods We experimentally assessed the net interaction between CR and NCR species using two substrates of contrasting fertility: nutrient-rich nursery mix and tephra (low P availability). We planted seedlings of two southern South American (SSA) Proteaceae, CR species and two NCR Nothofagus species in pairs (conspecifics and heterospecifics) and as singles. We analysed the effect of seedling neighbours on survival, growth performance (e.g. total biomass and leaf area) and leaf and substrate nutrient concentrations (including manganese, a proxy for P-acquisition efficiency through CR activity) using the relative interaction index. Key Results After three growing seasons, we found that (1) Proteaceae species had fewer CRs and lower CR biomass and grew less in the tephra than in the nursery substrate; (2) Nothofagus species did not improve their survival and growth in the presence of Proteaceae species in any substrate; (3) contrary to Nothofagus , Proteaceae species improved their growth more when planted with any neighbour (including conspecifics) than when planted alone, which was accompanied by a significant accretion of leaf P; and (4) the presence of a neighbour increased the final nitrogen and P concentrations in the nursery substrate, regardless of species identity. Conclusions CRs provide Proteaceae a competitive advantage over NCR species at the seedling stage, which may have important consequences for species coexistence and community structuring. The investigated SSA Proteaceae, which have not evolved in nutrient-impoverished soils, as have their relatives in south-western Australia and South Africa, improve their growth when cultivated in pairs, especially in nutrient-rich substrates. [ABSTRACT FROM AUTHOR]

Mega‐dams create highly fragmented archipelagos, affecting biodiversity and ecosystem functioning in remnant forest isolates. This study assessed the long‐term impact of dam‐induced fragmentation on insular tropical tree communities, with the aim of generating robust recommendations to mitigate some of the detrimental biodiversity impacts associated with future dam development.We inventoried adult and sapling trees across 89 permanent plots, located on 36 islands and in three mainland continuous forest sites in the Balbina Dam, Brazilian Amazon. We examined differences in recruitment, structure, and composition of sapling and adult tree communities, in relation to plot‐, patch‐ and landscape‐scale attributes including area, isolation, and fire severity.Islands harboured significantly lower sapling (mean ± 95% CI 48.6 ± 3.8) and adult (5 ± 0.2) tree densities per 0.01 ha, than nearby mainland continuous forest (saplings, 65.7 ± 7.5; adults, 5.6 ± 0.3). Insular sapling and adult tree communities were more dissimilar than in mainland sites, and species compositions showed a directional shift away from mainland forests, induced by fire severity, island area, and isolation.Insular sapling recruitment declined with increasing fire severity; tree communities with higher community‐weighted mean wood density showed the greatest recruitment declines. Our results suggest that insular tree communities are unstable, with rare species becoming extinction‐prone due to reduced tree recruitment and density on islands, potentially leading to future losses in biodiversity and ecosystem functioning across Balbina's >3,500 reservoir islands.Policy implications. In Balbina, fire and reduced habitat area and connectivity were drivers of tree community decay after only 28 years of insularization, despite strict protection provided by the ~940,000 ha Uatumã Biological Reserve. Given that many dams are planned for lowland, moderately undulating Amazonia, we recommend that dam development strategy explicitly considers (a) dam location, aiming to minimize creation of small (<10 ha) and isolated islands, (b) maintaining reservoir water levels during droughts to reduce fire risk, and (c) including aggregate island area in environmental impact and offset calculations. Ideally, we recommend that alternatives to hydropower be sought in lowland tropical regions, due to the far‐reaching biodiversity losses and ecosystem disruption caused by river impoundment. [ABSTRACT FROM AUTHOR]

Acute outbreaks of pests and disease are increasingly affecting tree populations around the world, causing widespread ecological effects. In Britain, ash dieback Hymenoscyphus fraxineus (Baral et al.) has severe impacts on common ash (Fraxinus excelsior L.) populations, and the emerald ash borer (Agrilus planipennis Fairmaire) is likely to add to the impact in future. This will cause significant changes to the character and functioning of many ecosystems. However, the nature of these changes and the best approach for conserving ecosystems after ash loss are not clear.We present a method to locate those areas most ecologically vulnerable to loss of a major tree species (common ash) and identify the resultant damage to distinctive ecosystem properties. This method uses the functional traits of species and their distributions to map the potential degree of change in traits across space and recommend management approaches to reduce the change. An analytic hierarchy process is used to score traits according to ecological importance.Our results indicate that in some areas of Britain, provision of ash‐associated traits could be reduced by over 50% if all ash is lost. Certain woodland types, and trees outside woodlands, may be especially vulnerable to ash loss. However, compensatory growth by other species could halve this impact in the longer term.We offer management guidance for reducing ecosystem vulnerability to ash loss, including recommending appropriate alternative tree species to encourage through planting or management in particular areas and woodland types.Synthesis and applications. The method described in this paper allows spatially explicit assessment of species traits to be used in the restoration of ecosystems for the first time. We offer practical recommendations for the ash dieback outbreak in Britain to help conserve functional traits in ecosystems affected by the loss of ash. This technique is widely applicable to a range of restoration and conservation scenarios and represents a step forward in the use of functional traits in conservation. The method described in this paper allows spatially explicit assessment of species traits to be used in the restoration of ecosystems for the first time. We offer practical recommendations for the ash dieback outbreak in Britain to help conserve functional traits in ecosystems affected by the loss of ash. This technique is widely applicable to a range of restoration and conservation scenarios and represents a step forward in the use of functional traits in conservation. Editor's Choice [ABSTRACT FROM AUTHOR]

Premise of the Study: It is unclear to what extent the co‐occurrence of angiosperm and gymnosperm species in some marginal ecosystems is explained by reduced growth in angiosperms due to carbon (C) limitation and by high stress tolerance in gymnosperms associated with lack of vessels and resource conservation. Methods: We examined growth patterns and traits associated with C balance in four evergreen angiosperm species (including one vesselless species, Drimys winteri) and three gymnosperm tree species of a cold‐temperate rainforest in southern Chile. We measured the mean basal area increment for the first 50 (BAI50) and the last 10 years (BAI10), wood density, leaf lifespan, and nonstructural carbohydrate (NSC) concentrations in different organs. Key Results: BAI50 was 6‐fold higher in angiosperms than in gymnosperms and ca. 4‐fold higher in Drimys than in the fastest‐growing gymnosperm. BAI10 and aboveground NSC concentrations were significantly higher and leaf lifespan lower in angiosperms than in gymnosperms; these differences, however, were largely driven by the slow growth and low NSC concentrations of the Cupressaceae species (Pilgerodendron uviferum), while the two Podocarpaceae had BAI10 and NSC concentrations similar to angiosperms. In angiosperms, NSC and starch concentrations were generally higher in species with lower BAI10, indicating no severe C limitation. Conclusions: The co‐occurrence of angiosperms and gymnosperms in cold‐temperate rainforests of southern Chile is not explained by growth disadvantages and C limitation in angiosperms. Long leaf longevity, but not lack of vessels, appeared to favor resource conservation and C balance in some gymnosperms (Podocarpaceae). [ABSTRACT FROM AUTHOR]

Invasive plant impacts vary widely across introduced ranges. We tested the hypothesis that differences in the eco‐evolutionary experience of native communities with the invader correspond with the impacts of invasive species on native vegetation, with impacts increasing with ecological novelty. We compared plant species richness and composition beneath Pinus contorta to that in adjacent vegetation and other P. contorta stands across a network of sites in its native (Canada and USA) and non‐native (Argentina, Chile, Finland, New Zealand, Scotland, Sweden) ranges. At sites in North America and Europe, within the natural distribution of the genus Pinus, P. contorta was not associated with decreases in diversity. In the Southern Hemisphere, where there are no native Pinaceae, plant communities beneath P. contorta were less diverse than in other regions and compared to uninvaded native vegetation. Effects on native vegetation were particularly pronounced where P. contorta was a more novel life form and exhibited higher growth rates. Our results support the hypothesis that the eco‐evolutionary experience of the native vegetation, and thus the novelty of the invader, determines the magnitude of invader impacts on native communities. Understanding the eco‐evolutionary context of invasions will help to better understand and predict where invasion impacts will be greatest and to prioritize invasive species management. [ABSTRACT FROM AUTHOR]

Understanding how plants survive drought and cold is increasingly important as plants worldwide experience dieback with drought in moist places and grow taller with warming in cold ones. Crucial in plant climate adaptation are the diameters of water-transporting conduits. Sampling 537 species across climate zones dominated by angiosperms, we find that plant size is unambiguously the main driver of conduit diameter variation. And because taller plants have wider conduits, and wider conduits within species are more vulnerable to conduction-blocking embolisms, taller conspecifics should be more vulnerable than shorter ones, a prediction we confirm with a plantation experiment. As a result, maximum plant size should be short under drought and cold, which cause embolism, or increase if these pressures relax. That conduit diameter and embolism vulnerability are inseparably related to plant size helps explain why factors that interact with conduit diameter, such as drought or warming, are altering plant heights worldwide. [ABSTRACT FROM AUTHOR]

Carbon (C) storage is considered a key component to plant survival under drought and shade, although the combined effects of these factors on survival remain poorly understood. We investigated how drought and shade alter the C dynamics and survival of tree seedlings, and whether drought limits the access to or usage of stored C. We experimentally applied two levels of soil humidity (wellwatered versus drought, the latter induced by dry-down) and light availability (light versus complete darkness) on 1-year-old seedlings of Acer pseudoplatanus L. for 3 months. We quantified the survival, biomass, growth rate and non-structural carbohydrates (NSC) of seedlings at their time of death or at the end of the experiment for those that survived. We found that the soil dried out faster when drought was combined with light than when it was combined with complete darkness. Seedlings subjected to both drought and light showed reduced growth and reached 100%mortality earlier than any other treatment, with the highest NSC concentrations at the time of death. Seedlings exposed to both drought and complete darkness died significantly earlier than seedlings exposed to complete darkness only, but had similar NSC concentrations at time of their death, suggesting that drought accelerated the use of stored C under complete darkness. Complete darkness significantly reduced seedling growth and whole-plant NSC concentrations regardless of soil humidity, while root NSC concentrations were significantly more reduced when complete darkness was combined with drought conditions. Thus, the C dynamics in A. pseudoplatanus seedlings under complete darkness was not hindered by drought, i.e., the access and use of stored C was not limited by drought. The contrasting growth and C storage responses driven by drought under light versus complete darkness are consistent with a key role of the drought progression in the C dynamics of trees. [ABSTRACT FROM AUTHOR]

403I.403II.405III.410IV.411V.412VI.412VII.413VIII.413413References414 Summary: Models describing the biotic drivers that create and maintain biological diversity within trophic levels have focused primarily on negative interactions (i.e. competition), leaving marginal room for positive interactions (i.e. facilitation). We show facilitation to be a ubiquitous driver of biodiversity by first noting that all species use resources and thus change the local biotic or abiotic conditions, altering the available multidimensional niches. This can cause a shift in local species composition, which can cause an increase in beta, and sometimes alpha, diversity. We show that these increases are ubiquitous across ecosystems. These positive effects on diversity occur via a broad host of disparate direct and indirect mechanisms. We identify and unify several of these facilitative mechanisms and discuss why it has been easy to underappreciate the importance of facilitation. We show that net positive effects have a long history of being considered ecologically or evolutionarily unstable, and we present recent evidence of its potential stability. Facilitation goes well beyond the common case of stress amelioration and it probably gains importance as community complexity increases. While biodiversity is, in part, created by species exploiting many niches, many niches are available to exploit only because species create them. [ABSTRACT FROM AUTHOR]

We developed multiple a priori hypotheses to link the observed spatial patterns with colonisation processes in the high alpine cushion plant, Azorella madreporica. We conducted this study in the Molina River basin (33°20′ S, 70°16′ W, 3600 m a.s.l.), in the Andes of central Chile, approximately 50 km east of Santiago. We mapped and measured size (as a surrogate for age) of individual cushions in two populations and used a standard spatial analytical tool (semivariograms) to test our alternative a priori hypotheses related to colonisation mode of the cushion species. In both populations, the size distribution of A. madreporica reflected a negative exponential or inverse-J pattern, typical of uneven-aged populations, where most of the cushions belonged to relatively smaller size classes, in effect, a regular success in the establishment of seedlings, where all size classes of cushions were represented in the population. The results were site-specific, where best-fit semivariograms for spatial cushion's size distribution suggested a gradual colonisation in one population and an episodic colonisation in the other population. Microsite distribution proved to be homogeneous at both sites. Thus, the study of the spatial explicit size-age population distribution of an alpine species provides valuable information about the frequency, magnitude and site variation of the reproductive pulses in these harsh environments. [ABSTRACT FROM AUTHOR]

Plant life-history variation reflects different outcomes of natural selection given the strictures of resource allocation trade-offs. However, there is limited theory of selection predicting how leaves, stems, roots, and reproductive organs should evolve in concert across environments. Here, we synthesize two optimality theories to offer a general theory of plant carbon economics, named as Gmax theory, that shows how life-history variation is limited to phenotypes that have an approximately similar lifetime net carbon gain per body mass. In consequence, fast–slow economics spectra are the result of trait combinations obtaining similar lifetime net carbon gains from leaves and similar net carbon investment costs in stems, roots, and reproductive organs. Gmax theory also helps explain ecosystem and crop productivity and even helps guide carbon conservation strategies. A key element of functional ecology is understanding why some combinations of organismal traits are observed whereas others are rare or absent. Compelling hypotheses explain why certain traits associate with one another into fast–slow economics spectra. Yet, biologists would also like to have a general theory explaining how these trait combinations connect with individual fitness. Merging existing leaf optimal lifespan theory and metabolic scaling theory yields Gmax theory as an example of formalizing a metabolic definition of fitness that explain how life-history variation and economics trait correlation patterns emerge from natural selection favoring individuals with the highest lifetime net carbon gain per body mass. Gmax theory shows that life-history diversity is the manifestation of a myriad of evolutionary ways to obtain a similar individual lifetime net resource gain per body mass across and within species living in a given environment. [ABSTRACT FROM AUTHOR]

Shaping global water and carbon cycles, plants lift water from roots to leaves through xylem conduits. The importance of xylem water conduction makes it crucial to understand how natural selection deploys conduit diameters within and across plants. Wider conduits transport more water but are likely more vulnerable to conductionblocking gas embolisms and cost more for a plant to build, a tension necessarily shaping xylem conduit diameters along plant stems. We build on this expectation to present the Widened Pipe Model (WPM) of plant hydraulic evolution, testing it against a global dataset. The WPM predicts that xylem conduits should be narrowest at the stem tips, widening quickly before plateauing toward the stem base. This universal profile emerges from Pareto modeling of a tradeoff between just two competing vectors of natural selection: one favoring rapid widening of conduits tip to base, minimizing hydraulic resistance, and another favoring slow widening of conduits, minimizing carbon cost and embolism risk. Our data spanning terrestrial plant orders, life forms, habitats, and sizes conform closely to WPM predictions. The WPM highlights carbon economy as a powerful vector of natural selection shaping plant function. It further implies that factors that cause resistance in plant conductive systems, such as conduit pit membrane resistance, should scale in exact harmony with tip-to-base conduit widening. Furthermore, the WPM implies that alterations in the environments of individual plants should lead to changes in plant height, for example, shedding terminal branches and resprouting at lower height under drier climates, thus achieving narrower and potentially more embolism-resistant conduits. [ABSTRACT FROM AUTHOR]

Flowering plants predominantly conduct water in tubes known as vessels, with vessel diameter playing a crucial role in plant adaptation to climate and reactions to climate change. The importance of vessels makes it essential to understand how and why vessel diameter, plant height, and other ecological factors are interrelated. Although shoot length is by far the main driver of variation in mean vessel diameter across angiosperms, much remains to be understood regarding the factors accounting for the abundant variation around the y‐axis in plots of mean species vessel diameter against shoot length. Here, we explore the potential role of porosity types, wood density, leaf phenology, background imperforate tracheary element type, vasicentric tracheids, vascular tracheids, perforation plate type, and successive cambia in causing variation in the y‐intercept or slope of the mean species vessel‐diameter– and vessel‐density–shoot‐length associations at the shoot tip and base. We detected numerous cases of ecologically significant variation. For example, latewood vessels of ring porous species scale with a lower slope than earlywood, i.e., latewood vessels are relatively narrow in taller plants. This pattern is likely the result of selection favoring freezing‐induced embolism resistance via narrow vessels. Wood density was negatively associated with vessel diameter, with low wood density plants having wider vessels for a given height. Species with scalariform perforation plates scale with a lower shoot base vessel‐diameter–shoot‐length slope, likely reflecting selection against scalariform plates in wide vessels. In other cases, functional groups scaled similarly. For example, species with successive cambia did not differ from those with conventional single cambia in their mean vessel‐diameter–shoot‐length scaling, rejecting our prediction that species with successive cambia should have narrower vessels for a given shoot length. They did, however, have fewer vessels per unit shoot cross‐sectional area than plants of similar heights, likely because vessels have longer functional lifespans (and therefore are fewer) in species with successive cambia. Our methods illustrate how vessel diameter can be studied taking shoot length into account to detect ecologically important variation and construct theory regarding plant adaptation via the hydraulic system that includes plant size as a vital element. [ABSTRACT FROM AUTHOR]

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., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

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., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)