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Why this research Matters The objective of this study was to understand how genetic variation in a riparian species, Populus angustifolia, affects mass and energy exchange between the land and atmosphere across ~1,700 km of latitude of the western United States. To examine the potential for large‐scale land–atmosphere feedbacks in hydrologic processes driven by geographic differences in plant population traits, we use a physical hydrology model, paired field, and greenhouse observations of plant traits, and stable isotope compositions of soil, stem, and leaf water of P. angustifolia populations. Populations show patterns of local adaptation in traits related to landscape hydrologic functioning—a 47% difference in stomatal density in greenhouse conditions and a 74% difference in stomatal ratio in the field. Trait and stable isotope differences reveal that populations use water differently which is related to historical landscape hydrologic functioning (evapotranspiration and streamflow). Overall, results suggest that populations from landscapes with different hydrologic histories will differ in their ability to maintain favorable water balance with changing atmospheric demands for water, with ecosystem consequences.

© 2020 The Authors., Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives., Support was provided by NSF‐DEB‐1743681 to K.K.M. and A.J.T. We thank Shalin Hai‐Jew for helpful discussion of the survey and qualitative methods.

Plant-microbial-soil interactions are key to understanding plant community succession, invasion success, patterns of biodiversity and aspects of ecosystem function. Yet root and rhizosphere chemistry is highly complex, and little is known about natural variation across environmental gradients. Variation in tree species root chemical phenotypes should alter how rhizosphere microbes respond, showing a plant conditioning effect on the chemical makeup of the soil. Here, we used metabolomics to assess bulk small molecule profiles addressing the hypothesis that genetic variation across a species range would result in varying metabolic profiles in roots and surrounding soil. Using UPLC-HRMS we assessed the small molecule profile of root tissue and surrounding rhizosphere soil from 5-year old plant clones collected from six populations of Populus angustifolia across the western U.S., grown in a common environment. Population-level variation was found in over 12,000 root metabolomes and over 5000 soil organic compounds across the populations. Redundancy analysis of over twelve thousand metabolites suggests that plant population origin can account for up to 36% of the variation in roots and 30% of the variation in rhizosphere soil chemistry. Co-inertia analysis indicates that variation in root metabolite profiles explains 15% of the variation in paired soil samples. Distinct populations have evolved different root tissue metabolomes. The difference in root metabolites across populations altered the rhizosphere soil composition, creating variable soil chemical communities from a homogenous starting condition. This suggests that intra-specific plant conditioning of soil varies by plant population.

Research on the evolutionary ecology of urban areas reveals how human-induced evolutionary changes affect biodiversity and essential ecosystem services. In a rapidly urbanizing world imposing many selective pressures, a time-sensitive goal is to identify the emergent issues and research priorities that affect the ecology and evolution of species within cities. Here, we report the results of a horizon scan of research questions in urban evolutionary ecology submitted by 100 interdisciplinary scholars. We identified 30 top questions organized into six themes that highlight priorities for future research. These research questions will require methodological advances and interdisciplinary collaborations, with continued revision as the field of urban evolutionary ecology expands with the rapid growth of cities.

Our understanding of terrestrial nitrogen (N) cycling is changing as new processes are uncovered, including the sources, turnover and losses of N from ecosystems. We integrate recent insights into an updated N‐cycling framework and discuss how a new understanding integrates eco‐evolutionary dynamics with nutrient cycling. These insights include (a) the significance of rock weathering as a biologically meaningful N source to plants and microbes; (b) the lack of consistent N limitation of organic matter decomposition by soil microbes; (c) species‐specific variation in plant N limitation; and (d) how fire effects on soil N shift with ecosystem properties. Using an eco‐evolutionary framework and revised knowledge of N cycling, we describe how (a) rock N weathering could have contributed more strongly to gradients in soil N availability than previously recognized, (b) evolution and co‐evolution of plant and soil microbial resource‐use traits underlie whether decomposition and production are N‐limited, and (c) the effects of fire on soil N pools are mediated by composition of plant species and time‐scale. Our revised framework of N cycling provides a way forward for improving biogeochemical models to more accurately estimate rates of plant production and decomposition, and total soil N. A free Plain Language Summary can be found within the Supporting Information of this article.

Plant species that occur in different soil nutrient environments often vary in plant functional traits that affect soil nutrient cycling, creating positive feedbacks that reinforce nutrient availability. Variation in such nutrient feedbacks could affect plant fitness, but few studies have explored the eco‐evolutionary dynamics of within‐species nutrient feedbacks, and the role that soil communities may play in mediating plant evolutionary responses. We investigated whether a widespread Populus species regulates soil fertility, resulting in positive nutrient feedbacks that influence population divergence. Here, we combined field observations, a reciprocal transplant experiment, and soil community sequencing to test how nutrient feedbacks might facilitate plant adaptation to soil environments. We find that: (1) Plant populations exist along a soil fertility gradient in the field and display trait variation consistent with positive nutrient feedbacks, (2) populations assemble distinct soil prokaryotic communities that are structured by soil chemistry, (3) populations show inconsistent patterns of local adaptation to their soil communities, however (4) genetic variation in plant–soil interactions reinforces soil nutrient differences. Soil communities may mediate variation in plant adaptation across a soil fertility gradient such that plant–soil interactions reinforce positive nutrient feedbacks. Identifying the eco‐evolutionary links between plant trait variation, soil nutrients and microbial communities demonstrates that plants modify and adapt to soil environments. These results support the hypothesis that eco‐evolutionary feedbacks may result when plant–soil interactions (eco) affect ecosystem‐level processes that sustain population‐level feedbacks and selective gradients (evo). A plain language summary is available for this article.

Identifying the potential for natural soil microbial communities to predictably affect complex plant traits is an important frontier in climate change research. Plant phenology varies with environmental and genetic factors, but few studies have examined whether the soil microbiome interacts with plant population differentiation to affect phenology and ecosystem function. We compared soil microbial variation in a widespread tree species (Populus angustifolia) with different soil inoculum treatments in a common garden environment to test how the soil microbiome affects spring foliar phenology and subsequent biomass growth. We hypothesized and show that soil bacterial and fungal communities vary with tree conditioning from different populations and elevations, that this soil community variation influences patterns of foliar phenology and plant growth across populations and elevation gradients, and that transferring lower elevation plant genotypes to higher elevation soil communities delayed foliar phenology, thereby shortening the growing season and reducing annual biomass production. Our findings show the importance of plant-soil interactions that help shape the timing of tree foliar phenology and productivity. These geographic patterns in plant population × microbiome interactions also broaden our understanding of how soil communities impact plant phenotypic variation across key climate change gradients, with consequences for ecosystem functioning.

Wildfires are increasing in frequency and intensity as drier and warmer climates increase plant detrital fuel loads. At the same time, increases in urbanization position 9% of fire-prone land within the United States at the wildland–urban interface. While rarely studied, the compounded effects of urbanization and wildfires may have unknown synergistically negative effects on ecosystems. Previous studies at the wildland–urban interface often focus on aboveground plant communities, but belowground ecosystems may also be affected by this double disturbance. In particular, it is unclear how much fire and urbanization independently or interactively affect nutritional symbioses such as those between arbuscular mycorrhizal (AM) fungi and the majority of terrestrial plants. In November 2016, extreme drought conditions and long-term fire suppression combined to create a wildfire within the Great Smoky Mountains National Park and the neighboring exurban city of Gatlinburg, TN. To understand how the double disturbance of urbanization and fire affected AM fungal communities, we collected fine roots from the 5 dominant understory species in September 2018 at each of 18 sites spanning 3 burn severities in both exurban and natural sites. Despite large variation in burn severity, plant species identity had the largest influence on AM fungi. AM fungal colonization, richness, and composition all varied most among plant species. Fire and urbanization did influence some AM fungal metrics; colonization was lower in burned sites and composition was more variable among exurban locations. There were no interactions among burn severity and urbanization on AM fungi. Our results point to the large influence of plant species identity structuring this obligate nutritional symbiosis regardless of disturbance regime. Therefore, the majority of AM fungal taxa may be buffered from fire-induced ecosystem changes if plant community composition largely remains intact, plant species life history traits allow for AM fungal persistence after fire disturbance, and/or nearby undisturbed habitat can act as an inoculum source for recolonization following fires. Thus, it is critical to maintain natural, undisturbed habitats interspersed within the wildland–urban interface.

Past research on plant-soil feedbacks (PSF), largely undertaken in highly controlled greenhouse conditions, has established that plant species differentially alter abiotic and biotic soil conditions that in turn affect growth of other conspecific and heterospecific individuals in that soil. Yet, whether feedbacks under controlled greenhouse conditions reflect feedbacks in natural environments where plants are exposed to a range of abiotic and biotic pressures is still unresolved. To address how environmental context affects PSF, we conducted a meta-analysis of previously published studies that examined plant growth responses to multiple forms of competition, stress, and disturbance across various PSF methodology. We asked the following questions: (1) Can competition, stress, and disturbance alter the direction and/or strength of PSF? (2) Do particular types of competition, stress, or disturbance affect the direction and/or strength of PSF more than others? and (3) Do methods of conducting PSF research (i.e., greenhouse vs. field experiments and whether the source of soil inoculum conditioning is from the field vs. greenhouse) affect plant growth responses to PSF or competition, stress, and disturbance, or their interactions? We discovered four patterns that may be predictive of what future PSF studies conducted under more realistic conditions might reveal. First, relatively little is known about how PSF responds to environmental stress and disturbance compared to plant-plant competition. Second, specific types of competition enhanced negative effects of soil microbes on plant growth, and specific environmental stressors enhanced positive effects of soil microbes on plant growth. Third, whether PSF experiments are conducted in the field or greenhouse can change plant growth responses. And, fourth, how the soil conditioning phase is conducted can change plant growth responses. With more detail than previously shown, these results confirm that environmental context writ large can change plant growth responses in PSF experiments. These data should aid theory and predictions for conservation and restoration applications by showing the relative importance of competition, stress, and disturbance in PSF studies over time. Lastly, these data demonstrate how variation in experimental methods can alter interpretation and conclusions of PSF studies.

Soil microbiomes are rapidly becoming known as an important driver of plant phenotypic variation and may mediate plant responses to environmental factors. However, integrating spatial scales relevant to climate change with plant intraspecific genetic variation and soil microbial ecology is difficult, making studies of broad inference rare. Here we hypothesize and show: 1) the degree to which tree genotypes condition their soil microbiomes varies by population across the geographic distribution of a widespread riparian tree, Populus angustifolia; 2) geographic dissimilarity in soil microbiomes among populations is influenced by both abiotic and biotic environmental variation; and 3) soil microbiomes that vary in response to abiotic and biotic factors can change plant foliar phenology. We show soil microbiomes respond to intraspecific variation at the tree genotype and population level, and geographic variation in soil characteristics and climate. Using a fully reciprocal plant population by soil location feedback experiment, we identified a climate-based soil microbiome effect that advanced and delayed bud break phenology by approximately 10 days. These results demonstrate a landscape-level feedback between tree populations and associated soil microbial communities and suggest soil microbes may play important roles in mediating and buffering bud break phenology with climate warming, with whole ecosystem implications., Ian Ware et al. use reciprocal plant population by soil location feedback experiments to show how the soil microbiomes of the narrowleaf cottonwood are influenced by genetic and environmental variation, and how these factors affect foliar phenology. They find a landscape-level feedback between tree populations and their associated soil microbial counterparts. This study contributes to the understanding of the interplay between soil, climate, plant and microbial populations with climate warming.

Genetic variation within a dominant riparian forest tree affects susceptibility to a leaf-galling aphid (Pemphigus betae), which induces phytochemical and structural changes in leaf tissue. Research Highlights: We show here that these changes to tree leaf tissue alter adjacent in-stream leaf litter decomposition rates and the aquatic macroinvertebrate community associated with litter in the stream for some Populus genotypes. Background and Objectives: Naturally occurring hybrid cottonwoods (Populus fremontii &times, Populus angustifolia) are differentially susceptible to aphid attack and vary in induced phytochemistry following attack. When leaves are galled by aphids, foliar tissue is altered structurally (through the formation of pea-sized gall structures) and phytochemically (through an increase in foliar condensed tannin concentrations). Materials and Methods: To examine the effect of aphid-galled leaves on forest stream processes, we collected both galled and un-galled leaves from five clones of three hybrid cottonwood genotypes in an experimental forest. We measured in-stream litter decomposition rates, aquatic fungal biomass and aquatic macroinvertebrate community composition. Results: Decomposition rates differed among genotypes and the galled litter treatments, with a 27% acceleration of decomposition rate for the galled litter of one genotype compared to its own un-galled litter and no differences between galled and un-galled litters for the other two genotypes. Genotype by foliar gall status interactions also occurred for measures of phytochemistry, indicating a prevalence of complex interactions. Similarly, we found variable responses in the macroinvertebrate community, where one genotype demonstrated community differences between galled and un-galled litter. Conclusions: These data suggest that plant genetics and terrestrial forest herbivory may be important in linking aquatic and terrestrial forest processes and suggest that examination of decomposition at finer scales (e.g., within species, hybrids and individuals) reveals important ecosystem patterns.

It has been firmly established that oak regeneration benefits from prescribed burning and reduced competition with fire-intolerant tree species. Despite recommendations for research on the role of the microsite environment for oak regeneration, very little is known about the interacting effects of fire, soil, and surrounding plant community on oak establishment. We collected undisturbed and burned soil in the aftermath of a wildfire in Great Smoky Mountains National Park and used amplicon sequencing to identify differences in composition of bacterial and fungal communities between unburned and burned soils. To assess the effects of plant community, fire-induced shifts in soil microbial communities, and their interaction we conducted a glasshouse experiment and grew Quercus velutina seedlings in factorial treatments of plant neighbor (oak vs. pine seedling) and soil burn status (unburned vs. burned soil). Fire reduced the diversity of plant pathogenic and saprotrophic fungi and reduced the relative abundance of plant pathogenic fungi. Fire did not affect soil bacterial communities. Shifts in soil fungal community composition enhanced oak seedling root growth, but the effect of the soil microbiome was mediated by plant neighbor interactions. Seedling root growth was negatively correlated with diversity of pathogenic fungi. Root growth was enhanced in burned soil relative to unburned soil, but only when growing with a pine seedling neighbor as opposed to an oak seedling neighbor. Results from this study show that interactions between soil microbes and nearby plants can in part mediate oak seedling growth. As such, nuanced decisions that consider the ecological interactions of the microsite environment are needed to achieve desired outcomes for oak regeneration.

Under increasing anthropogenic nitrogen (N) deposition, some plant species will thrive while others will not. Previous work has shown that plant phylogeny can predict these responses, and that interactions with mycorrhizal fungi are a mechanism that drives variation in plant responses to N enrichment. Yet, much of this work has ignored the roles of other root‐associated fungi and whole soil fungal communities in driving these responses. We tested whether soil fungi mediate responses of plant growth and plant–soil feedbacks (between close and distant plant relatives) to N enrichment by implementing a greenhouse experiment in which we applied factorial treatments of N fertilization, host‐specific soil inocula and fungicide to 15 eucalypt tree species that co‐occur on the island state of Tasmania, Australia, and form two phylogenetic lineages within the subgenus Symphyomyrtus. Conspecific‐conditioned soil fungi enhanced growth responses to N enrichment for plants within one lineage (lineage 1) but depressed growth responses to N enrichment for plants within another lineage (lineage 2). Lineage‐specific shifts in ectomycorrhizal (ECM) colonization were consistent with previous evidence that more vs. less successful strategies under N enrichment are those where carbon allocation to mycorrhizal fungi is reduced vs. maintained, respectively. The latter was also accompanied by a stronger reduction in root colonization of non‐filamentous fungi (of unknown function) under N enrichment. Plant–soil feedbacks were neutral for lineage 1 but negative for lineage 2 (i.e. greater growth in soils conditioned by opposite vs. same lineage individuals), but were not altered by N enrichment or fungicide. Lineage‐level differences in root colonization suggest that these feedbacks could be driven by differential plant responsiveness to dark septate endophytes and non‐filamentous fungi, the colonization of which seemed to benefit plant growth. Synthesis: Our results confirm that interactions with soil fungi (ECM fungi, in particular) underlie phylogenetic patterns in tree species' growth responses to N enrichment and may, thus, influence which plants win or lose under future N deposition scenarios. Yet, we provide some of the first evidence (albeit from controlled rather than natural conditions) that N deposition may not play a strong role in shifting plant–soil feedbacks.

Plant–microbial feedbacks are important drivers of plant community structure and dynamics. These feedbacks are driven by the variable modification of soil microbial communities by different plant species. However, other factors besides plant species can influence soil communities and potentially interact with plant–microbial feedbacks. We tested for plant–microbial feedbacks in two Eucalyptus species, E. globulus and E. obliqua, and the influence of forest fire on these feedbacks. We collected soils from beneath mature trees of both species within native forest stands on the Forestier Peninsula, Tasmania, Australia, that had or had not been burnt by a recent forest fire. These soils were subsequently used to inoculate seedlings of both species in a glasshouse experiment. We hypothesized that (i) eucalypt seedlings would respond differently to inoculation with conspecific versus heterospecific soils (i.e., exhibit plant–microbial feedbacks) and (ii) these feedbacks would be removed by forest fire. For each species, linear mixed effects models tested for differences in seedling survival and biomass in response to inoculation with conspecific versus heterospecific soils that had been collected from either unburnt or burnt stands. Eucalyptus globulus displayed a response consistent with a positive plant–microbial feedback, where seedlings performed better when inoculated with conspecific versus heterospecific soils. However, this effect was only present when seedlings were inoculated with unburnt soils, suggesting that fire removed the positive effect of E. globulus inoculum. These findings show that external environmental factors can interact with plant–microbial feedbacks, with possible implications for plant community structure and dynamics.

Summary 1. Contemporary global change, including the widespread mortality of foundation tree species, is altering ecosystems and plant communities at unprecedented rates. Plant-soil interactions drive myriad community dynamics, and we hypothesized such interactions may be an important driver of succession following the loss of foundation tree species. 2. We examined whether plant-soil biota interactions, in the context of a putatively important light gradient associated with foundation tree decline, mediate the expansion of Rhododendron maximum in southeastern US forests where Tsuga canadensis (eastern hemlock), a dominant foundation tree species, is in decline. Using an 11-month, controlled inoculation experiment paired with Illumina sequencing, we tested the following hypotheses: (1) Relative to conspecific (R. maximum-conditioned) soils, R. maximum seedlings have higher performance in soils conditioned by T. canadensis and lower performance in interspace soils (conditioned by neither T. canadensis nor R. maximum) due to variation in soil fungal biota, and (2) seedling performance is greater in high light versus low light environments (matching environments under infested versus uninfested T. canadensis crowns, respectively). 3. In partial support of the first hypothesis, we found that R. maximum seedling performance was highest in T. canadensis-conditioned and R. maximum-conditioned soils and lowest in interspace soils. Mechanistically, soils conditioned by T. canadensis and R. maximum had more ericoid and ectomycorrhizal fungi, less saprotrophic fungi, and were less species-rich than interspace soils, and variation in these community traits predicted substantial variation in R. maximum seedling biomass. However, in support of our second hypothesis, soil effects on plant performance were evident in high light only; in low light, soil inoculation did not affect plant performance and plants performed worse on average. 4. Synthesis. Our findings suggest interactions with soil biota act synergistically with altered abiotic environments to mediate species responses to widespread foundation tree mortality, providing evidence for a novel mechanism of plant response to large-scale disturbance. Examining plant-soil interactions in the context of relevant abiotic gradients can therefore enhance our understanding, predictions, and management of community development processes following forest disturbance. This article is protected by copyright. All rights reserved.

Increasing rates of anthropogenic nitrogen (N) enrichment to soils often lead to the dominance of nitrophilic plant species and reduce plant diversity in natural ecosystems. Yet, we lack a framework to predict which species will be winners or losers in soil N enrichment scenarios, a framework that current literature suggests should integrate plant phylogeny, functional tradeoffs, and nutrient co-limitation. Using a controlled fertilization experiment, we quantified biomass responses to N enrichment for 23 forest tree species within the genus Eucalyptus that are native to Tasmania, Australia. Based on previous work with these species' responses to global change factors and theory on the evolution of plant resource-use strategies, we hypothesized that (1) growth responses to N enrichment are phylogenetically structured, (2) species with more resource-acquisitive functional traits have greater growth responses to N enrichment, and (3) phosphorus (P) limits growth responses to N enrichment differentially across species, wherein P enrichment increases growth responses to N enrichment more in some species than others. We built a hierarchical Bayesian model estimating effects of functional traits (specific leaf area, specific stem density, and specific root length) and P fertilization on species' biomass responses to N, which we then compared between lineages to determine whether phylogeny explains variation in responses to N. In concordance with literature on N limitation, a majority of species responded strongly and positively to N enrichment. Mean responses ranged three-fold, from 6.21 (E. pulchella) to 16.87 (E. delegatensis) percent increases in biomass per g N·m−2·yr−1 added. We identified a strong difference in responses to N between two phylogenetic lineages in the Eucalyptus subgenus Symphyomyrtus, suggesting that shared ancestry explains variation in N limitation. However, our model indicated that after controlling for phylogenetic non-independence, eucalypt responses to N were not associated with functional traits (although post-hoc analyses show a phylogenetic pattern in specific root length similar to that of responses to N), nor were responses differentially limited by P. Overall, our model results suggest that phylogeny is a powerful predictor of winners and losers in anthropogenic N enrichm

Global change is widely altering environmental conditions which makes accurately predicting species range limits across natural landscapes critical for conservation and management decisions. If climate pressures along elevation gradients influence the distribution of phenotypic and genetic variation of plant functional traits, then such trait variation may be informative of the selective mechanisms and adaptations that help define climatic niche limits. Using extensive field surveys along 16 elevation transects and a large common garden experiment, we tested whether functional trait variation could predict the climatic niche of a widespread tree species (Populus angustifolia) with a double quantile regression approach. We show that intraspecific variation in plant size, growth, and leaf morphology corresponds with the species' total climate range and certain climatic limits related to temperature and moisture extremes. Moreover, we find evidence of genetic clines and phenotypic plasticity at environmental boundaries, which we use to create geographic predictions of trait variation and maximum values due to climatic constraints across the western US. Overall, our findings show the utility of double quantile regressions for connecting species distributions and climate gradients through trait‐based mechanisms. We highlight how new approaches like ours that incorporate genetic variation in functional traits and their response to climate gradients will lead to a better understanding of plant distributions as well as identifying populations anticipated to be maladapted to future environments., Accurately forecasting plant species distributions and range limits is a central challenge for understanding climate change effects on the landscape. Here, we extend a recently proposed quantile regression approach using within‐species functional trait variation across elevation gradients to predict a widespread tree species' climate niche. Collectively, these findings point towards the ecological and evolutionary drivers of climate range limits and demonstrate how this approach can improve current niche models by including intraspecific trait‐climate responses.

Theoretical models pertaining to feedbacks between ecological and evolutionary processes are prevalent in multiple biological fields. An integrative overview is currently lacking, due to little crosstalk between the fields and the use of different methodological approaches. Here, we review a wide range of models of eco‐evolutionary feedbacks and highlight their underlying assumptions. We discuss models where feedbacks occur both within and between hierarchical levels of ecosystems, including populations, communities and abiotic environments, and consider feedbacks across spatial scales. Identifying the commonalities among feedback models, and the underlying assumptions, helps us better understand the mechanistic basis of eco‐evolutionary feedbacks. Eco‐evolutionary feedbacks can be readily modelled by coupling demographic and evolutionary formalisms. We provide an overview of these approaches and suggest future integrative modelling avenues. Our overview highlights that eco‐evolutionary feedbacks have been incorporated in theoretical work for nearly a century. Yet, this work does not always include the notion of rapid evolution or concurrent ecological and evolutionary time scales. We show the importance of density‐ and frequency‐dependent selection for feedbacks, as well as the importance of dispersal as a central linking trait between ecology and evolution in a spatial context. A plain language summary is available for this article.

Summary Numerous studies have demonstrated biodiversity–productivity relationships in plant communities, and analogous genetic diversity–productivity studies using genotype mixtures of single species may show similar patterns. Alternatively, competing individuals among genotypes within a species are less likely to exhibit resource-use complementarity, even when they exhibit large differences in their effects on ecosystem function. In this study, we test the impact of genotype diversity and genetic identity on ecosystem function using an ecosystem-scale common garden experiment. Distinct tree genotypes were collected across the entire natural range of the riparian tree Populus fremontii in the USA, and grown in 1–16 genotype combination forest stands. Due to the warm climate and irrigation of the planting location along the Colorado River (AZ, USA), mature forest physiognomy with trees up to 19 m tall was achieved in just five years. Several key patterns emerged: (i) genotype richness did not predict forest productivity, suggesting a lack of net biodiversity effects; (ii) we found differences among genotype monoculture stands comparable to differences in average productivity across all forest biomes on Earth; (iii) productivity was predicted based on genetic marker similarity in trees; (iv) genetic-based differences in leaf phenology (early leaf-on and late leaf-fall timing) were correlated with >80% of the variation in tree and forest productivity irrespective of home-site conditions. Large differences in productivity among genotypes can result in dramatic differences in forest productivity without resulting in diversity–productivity relationships that are present in species-scale biodiversity studies.

Plants are dependent on their root systems for survival, and thus are defended from belowground enemies by a range of strategies, including plant secondary metabolites (PSMs). These compounds vary among species, and an understanding of this variation may provide generality in predicting the susceptibility of forest trees to belowground enemies and the quality of their organic matter input to soil. Here, we investigated phylogenetic patterns in the root chemistry of species within the genus Eucalyptus. Given the known diversity of PSMs in eucalypt foliage, we hypothesized that (i) the range and concentrations of PSMs and carbohydrates in roots vary among Eucalyptus species, and (ii) that phylogenetic relationships explain a significant component of this variation. To test for interspecific variation in root chemistry and the influence of tree phylogeny, we grew 24 Eucalyptus species representing two subgenera (Eucalyptus and Symphyomyrtus) in a common garden for two years. Fine root samples were collected from each species and analyzed for total phenolics, condensed tannins, carbohydrates, terpenes, and formylated phloroglucinol compounds. Compounds displaying significant interspecific variation were mapped onto a molecular phylogeny and tested for phylogenetic signal. Although all targeted groups of compounds were present, we found that phenolics dominated root defenses and that all phenolic traits displayed significant interspecific variation. Further, these compounds displayed a significant phylogenetic signal. Overall, our results suggest that within these representatives of genus Eucalyptus, more closely related species have more similar root chemistry, which may influence their susceptibility to belowground enemies and soil organic matter accrual.

Summary While an appreciation of plant–soil feedbacks (PSF) continues to expand for community and ecosystem ecology, the eco-evolutionary mechanisms and consequences of such feedbacks remain largely unknown or untested. Determining the cause and effect of plant phenotypes is central for understanding these eco-evolutionary dynamics since phenotypes respond to soil selective gradients that are, in turn, modified by plant traits. Genetic variation in plant phenotypes can change soil processes and biotic communities; oppositely, soil gradients and microbial communities can influence the expression and evolution of plant phenotypes. Although these processes represent the two halves of genetic based PSF, research in these areas has developed independently from one another. Greater connectivity between research on ecosystem consequences of plant genetic variation and soil selective gradients that drive plant phenotypic evolution will create novel and important opportunities to link ecology and evolution in natural systems. Papers in this special feature build on the inherent ecological and evolutionary processes involved in PSF, outlining many ways to identify and test mechanisms that connect ecosystem ecology and evolution.

Biodiversity at many scales (functional group, species, genetic) can result in emergent ecological patterns. Here we explore the influence of tree genotypic variation and diversity on in-stream ecosystem processes and aquatic communities. We test whether genetically diverse inputs of leaf litter interact with a keystone organism, anadromous salmon, to influence in-stream ecosystem function. We used reach-level manipulation of salmon carcasses and leaf litter bags to examine how nutrient inputs interact with genetic variation in leaf litter decomposition. Genotypic variation in black cottonwood (Populus balsamifera ssp. trichocarpa) significantly influenced leaf litter chemistry, litter mass loss, and fungal biomass, but these variables were only weakly influenced by salmon carcass presence or a genotype × salmon (G × E) interaction. Mixtures of genotypes tended to demonstrate antagonistic effects (slower than expected decomposition) in the absence of salmon, but synergistic effects (faster than expected decomposition) when salmon were present. Our findings suggest that the influence of plant genotypic variation in linking aquatic and terrestrial ecosystems may be altered and in some cases intensified in the presence of a keystone vertebrate species.

Summary Decades of research show that plants vary in their growth responses to increasing soil nitrogen (N), supporting theory on evolutionary trade-offs between competitive and conservative growth strategies. However, we lack an explicit examination of the evolutionary processes guiding trade-offs in competitive and conservative growth responses to N addition (GRN), processes which should include selection across environmental gradients and constraint within certain plant functional types. To determine current variation in GRN across plants, we collected previously published data on total biomass responses of 125 terrestrial plant species to N fertilization, relative to control soil N conditions. We calculated phylogenetic signal of GRN to assess the influence of shared evolutionary history on variation in N use capacities. To determine whether this variation is consistent with stabilizing selection towards unique N use capacities across environmental gradients and plant functional types, we compared the fit (second-order Akaike Information Criterion) of species’ GRN data to models that approximate evolution according to genetic drift with and without stabilizing selection across plant functional types, biomes, latitude, mean annual temperature and annual precipitation. More than one in four species in our analysis responded negatively or neutrally to increasing soil N and responses ranged from a 60% decrease to an 1800% increase in biomass with added N. We identified a significant phylogenetic signal for GRN, and evolutionary models incorporating stabilizing selection plus genetic drift explained more variation in GRN than models incorporating genetic drift alone. Parameter estimates from selection-based models indicate that plant functional types have experienced selection towards GRN values (i.e. evolutionary optima) that differ more than among biomes or across climatic gradients. Overall, our results suggest that phylogenetic relatedness and stabilizing selection associated with functional constraints are two aspects of past evolution that govern whether species will be winners or losers in global soil N addition scenarios.

Recent work has demonstrated that the presence or abundance of specific genotypes, populations, species and phylogenetic clades may influence community and ecosystem properties such as resilience or productivity. Many ecological studies, however, use simple linear models to test for such relationships, including species identity as the predictor variable and some measured trait or function as the response variable without accounting for the nestedness of genetic variation across levels of organization. This omission may lead to incorrect inference about which source of variation influences community and ecosystem properties. Here, we explicitly compare this common approach to alternative ways of modeling variation in trait data, using simulated trait data and empirical results of common-garden trials using multiple levels of genetic variation within Eucalyptus, Populus and Picea. We show that: 1) when nested variation is ignored, an incorrect conclusion of species effect is drawn in up to 20% of cases; 2) overestimation of the species effect increases – up to 60% in some scenarios – as the nested term explains more of the variation; and 3) the sample sizes needed to overcome these potential problems associated with aggregating nested hierarchical variation may be impractically large. In common-garden trials, incorporating nested models increased explanatory power twofold for mammal browsing rate in Eucalyptus, threefold for leaf area in Populus, and tenfold for branch number in Picea. Thoroughly measuring intraspecific variation and characterizing hierarchical genetic variation beyond the species level has implications for developing more robust theory in community ecology, managing invaded natural systems, and improving inference in biodiversity–ecosystem functioning research. Synthesis Until recently, ecologists acknowledged the ubiquity of within-species trait variation, but paid scant attention to how much it affects communities and ecosystems. Here, the authors used simulated trait data and common-garden studies to demonstrate that we ignore intraspecific trait variation at our peril. In both simulated and experimental systems, in many cases ignoring intraspecific variation led to incorrect statistical inferences and inflated the effect size of species identity. This study shows that ecologists must characterize hierarchically nested genetic and phenotypic variation to fully understand the links between individual traits, community structure and ecosystem functioning.

Plant‐soil feedbacks (PSFs) are important drivers of plant community structure and diversity, with species varying in the way they both condition soils and respond to them. While plant phylogenetic relationships alone can predict this variation in some instances, trait conservatism across phylogenies may provide more reliable predictions. Using integrated common garden and glasshouse inoculation experiments including 13 Eucalyptus species across two subgenera, we specifically investigated soil microbial conditioning and root chemical traits as underlying drivers of phylogenetic differences in PSF. We found that eucalypt species responded variably to soils conditioned by closely related species, depending on their phylogenetic lineage, which was further related to root terpene concentrations and the presence/absence of specific fungal taxa in conditioned soils. Overall, these findings show that trait conservatism in root chemical traits and the subsequent conditioning of soil microbial communities can explain whether or not plants show phylogenetic patterns in PSF.

We examined the hypothesis that climate-driven evolution of plant traits will influence associated soil microbiomes and ecosystem function across the landscape. Using a foundation tree species, Populus angustifolia, observational and common garden approaches, and a base population genetic collection that spans 17 river systems in the western United States, from AZ to MT, we show that (a) as mean annual temperature (MAT) increases, genetic and phenotypic variation for bud break phenology decline; (b) soil microbiomes, soil nitrogen (N), and soil carbon (C) vary in response to MAT and conditioning by trees; and (c) with losses of genetic variation due to warming, population-level regulation of community and ecosystem functions strengthen. These results demonstrate a relationship between the potential evolutionary response of populations and subsequent shifts in ecosystem function along a large temperature gradient.

The interactions among plants, soil biotic communities, and soil are increasingly shown to be important in ecology but are underappreciated in evolutionary biology. Through genetic interactions among co-occurring taxa, plants and the biotic soil community influence the fitness and performance of each over time. At the intraspecific level, variation in plant traits leads to conditioning of soil physical and chemical properties and biotic communities which can have positive, neutral, or negative feedbacks to plants. These feedbacks can have positive fitness effects that lead to divergence of traits in plants. Building on the growing literature showing the genetic basis to plant conditioning of soils and the role of plant–soil feedback in determining plant performance and fitness, we review: (1) evolutionary theory linking plants and soils (which broadly includes soil physical and chemical properties as well as the biotic community); (2) provide examples of genetically based variation in plant–soil feedback (PSF); and (3) identify the evolutionary consequences of PSF. Together, modeling and empirical results show that intraspecific interactions among plants and soils vary across environments that can lead to geographic variation in feedback responses and evolutionary divergence. Both local adaptation and maladaptation are equally likely to occur which can drive divergence in plant traits and ecosystem function in different directions. Overall these results demonstrate that plant–soil interactions are ideal for demonstrating eco-evolutionary feedbacks which has implications for understanding a range of population, community, and ecosystem outcomes in a changing world.

Summary 1. Community genetics studies frequently focus on individual communities associated with individual plant genotypes, but little is known about the genetically based relationships among taxonomically and spatially disparate communities. We integrate studies of a wide range of communities living on the same plant genotypes to understand how the ecological and evolutionary dynamics of one community may be constrained or modulated by its underlying genetic connections to another community. 2. We use pre-existing data sets collected from Populus angustifolia (narrowleaf cottonwood) growing in a common garden to test the hypothesis that the composition of pairs of distinct communities (e.g. endophytes, pathogens, lichens, arthropods, soil microbes) covary across tree genotypes, such that individual plant genotypes that support a unique composition of one community are more likely to support a unique composition of another community. We then evaluate the hypotheses that physical proximity, taxonomic similarity, time between sampling (time attenuation), and interacting foundation species within communities explain the strength of correlations. 3. Three main results emerged. First, Mantel tests between communities revealed moderate to strong (q = 0.25‐0.85) community‐genetic correlations in almost half of the comparisons; correlations among phyllosphere endophyte, pathogen and arthropod communities were the most robust. Secondly, physical proximity determined the strength of community‐genetic correlations, supporting a physical proximity hypothesis. Thirdly, consistent with the interacting foundation species hypothesis, the most abundant species drove many of the stronger correlations. Other hypotheses were not supported. 4. Synthesis. The field of community genetics demonstrates that the structure of communities varies among plant genotypes; our results add to this field by showing that disparate communities covary among plant genotypes. Eco-evolutionary dynamics between plants and their associated organisms may therefore be mediated by the shared connections of different communities to plant genotype, indicating that the organization of biodiversity in this system is genetically based and non-neutral.

Within a species, plant traits may vary substantially along environmental gradients. However, is such variation (1) consistent across locations and (2) genetic or non-genetic (i.e., plastic) in nature? In this study, we combine field observations and a common garden experiment to assess Rhododendron maximum trait variation within and among three elevation gradients. Our findings reveal that trait variation along environmental gradients in this species is (1) highly population-specific and (2) driven primarily by non-genetic factors (i.e., plasticity). Overall, our findings highlight the importance of examining multiple locations and suggest that trait responses to environmental change vary by location., Elevation gradients are frequently used as space-for-time substitutions to infer species’ trait responses to climate change. However, studies rarely investigate whether trait responses to elevation are widespread or population-specific within a species, and the relative genetic and plastic contributions to such trait responses may not be well understood. Here, we examine plant trait variation in the dominant woody shrub, Rhododendron maximum, along elevation gradients in three populations in the South Central Appalachian Mountains, USA, in both field and common garden environments. We ask the following: (i) do plant traits vary along elevation? (ii) do trait responses to elevation differ across populations, and if so, why? and (iii) does genetic differentiation or phenotypic plasticity drive trait variation within and among populations? We found that internode length, shoot length, leaf dry mass, and leaf area varied along elevation, but that these responses were generally unique to one population, suggesting that trait responses to environmental gradients are population-specific. A common garden experiment identified no genetic basis to variation along elevation or among populations in any trait, suggesting that plasticity drives local and regional trait variation and may play a key role in the persistence of plant species such as R. maximum with contemporary climate change. Overall, our findings highlight the importance of examining multiple locations in future elevation studies and indicate that, for a given plant species, the magnitude of trait responses to global climate change may vary by location.

Human activity is causing wild populations to experience rapid trait change and local extirpation. The resulting effects on intraspecific variation could have substantial consequences for ecological processes and ecosystem services. Although researchers have long acknowledged that variation among species influences the surrounding environment, only recently has evidence accumulated for the ecological importance of variation within species. We conducted a meta-analysis comparing the ecological effects of variation within a species (intraspecific effects) with the effects of replacement or removal of that species (species effects). We evaluated direct and indirect ecological responses, including changes in abundance (or biomass), rates of ecological processes and changes in community composition. Our results show that intraspecific effects are often comparable to, and sometimes stronger than, species effects. Species effects tend to be larger for direct ecological responses (for example, through consumption), whereas intraspecific effects and species effects tend to be similar for indirect responses (for example, through trophic cascades). Intraspecific effects are especially strong when indirect interactions alter community composition. Our results summarize data from the first generation of studies examining the relative ecological effects of intraspecific variation. Our conclusions can help inform the design of future experiments and the formulation of strategies to quantify and conserve biodiversity.

When plants colonize new habitats altered by natural or anthropogenic disturbances, those individuals may encounter biotic and abiotic conditions novel to the species, which can cause plant functional trait divergence. Over time, site-driven adaptation can give rise to population-level genetic variation, with consequences for plant community dynamics and ecosystem processes. We used a series of 3000-yr-old, lava-created forest fragments on the Island of Hawai`i to examine whether disturbance and subsequent colonization can lead to genetically differentiated populations, and where differentiation occurs, if there are ecosystem consequences of trait-driven changes. These fragments are dominated by a single tree species, Metrosideros polymorpha (Myrtaceae) or ʻōhiʻa, which have been actively colonizing the surrounding lava flow created in 1858. To test our ideas about differentiation of genetically determined traits, we (1) created rooted cuttings of ʻōhiʻa individuals sampled from fragment interiors and open lava sites, raised these individuals in a greenhouse, and then used these cuttings to create a common garden where plant growth was monitored for three years; and (2) assessed genetic variation and made QST/FST comparisons using microsatellite repeat markers. Results from the greenhouse showed quantitative trait divergence in plant height and pubescence across plants sampled from fragment interior and matrix sites. Results from the subsequent common garden study confirmed that the matrix environment can select for individuals with 9.1% less shoot production and 17.3% higher leaf pubescence. We found no difference in molecular genetic variation indicating gene flow among the populations. The strongest QST level was greater than the FST estimate, indicating sympatric genetic divergence in growth traits. Tree height was correlated with ecosystem properties such as soil carbon and nitrogen storage, soil carbon turnover rates, and soil phosphatase activity, indicating that selection for growth traits will influence structure, function, and dynamics of developing ecosystems. These data show that divergence can occur on centennial timescales of early colonization.

In the face of climate change, shifts in genetic structure and composition of terrestrial plant species are occurring worldwide. Because different genotypes of these plant species support different soil biota and soil processes, shifts in genetics are likely to have cascading effects on ecosystems. We explore plant genetic effects on soil function in the context of climate change, and selection by soils, soil biota and plant-soil feedbacks. We propose categories of genetically-based plant traits that should be prioritized in research on genetic-based effects on soil processes including plant productivity and C allocation, tissue quality, plant water-use, and rhizosphere mutualisms. Additionally, we posit that soil community responses to climate change should be considered in concert with plant genotype because of sensitivity of soil communities to climate. We use two case studies to highlight these points. We argue that the effects of climate change as an agent of selection on plants may cascade to affect soils, and ultimately the structure, composition and function of ecosystems. Understanding the ecological and evolutionary potential of plant-soil linkages may help us understand and mitigate the extended consequences of global change for ecosystems worldwide. Accordingly, we conclude with experimental approaches for examining genetically-based plant-soil interactions across climate change gradients.

Summary 1. Predicting the response of communities and ecosystems to range shifts as a consequence of global climate change is a critical challenge confronting modern evolutionary ecologists. 2. Indirect genetic effects (IGEs) occur when the expression of genes in a conspecific neighbouring species affects the phenotype of a focal species, and the same concept applies for interspecific indirect genetic effects (IIGEs) except that the neighbouring species is then required to be heterospecific. 3. Theory and empirical data indicate that indirect genetic effects and interspecific indirect genetic effects have fundamental roles in understanding the consequences of genotypic diversity, evolutionary feedbacks, the co-evolutionary process and coadaptation and are a primary mechanism for the broad ecological and evolutionary dynamics that are likely to be a consequence of climate change. 4. When indirect genetic effects and interspecific indirect genetic effects occur along environmental gradients, both positive and negative feedbacks can evolve, resulting in regions of strong local adaptation and competition as well as regions of complementarity and facilitation. Such evolutionary dynamics have direct consequences for how individuals interact and evolve in mixture and drive the services ecosystems provide. 5. Integrating indirect genetic effects and interspecific indirect genetic effects, feedbacks and diversity effects along environmental gradients represents a major conceptual, theoretical and empirical frontier that must be considered to understand the whole-system consequences of climate change on biodiversity and the services ecosystems provide.