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Studying intraspecific variation in multistress responses is central for predicting and managing the population dynamics of wild plant species under rapid global change. Yet, it remains a challenging goal in this field to integrate knowledge on the complex biochemical underpinnings for the targeted ‘non-model’ species. Here, we studied divergence in combined drought and heat responses among Northern and Southern European populations of the dune plant Cakile maritima, by combining comprehensive plant phenotyping with metabolic profiling via FT-ICR-MS and UPLC-TQ-MS/MS. We observed pronounced constitutive divergence in growth phenology, leaf functional traits, and defence chemistry (glucosinolates and alkaloids) among population origins. Most importantly, the magnitude of growth reduction under drought was partly weaker in southern plants and associated with divergence in plastic growth responses (leaf abscission) and the modulation of primary and specialized metabolites with known central functions not only in plant abiotic but also in biotic stress responses. Our study indicates that divergent selection has shaped the constitutive and drought-/heat-induced expression of numerous morphological and biochemical functional traits to mediate higher abiotic stress resistance in southern Cakile populations, and highlights that metabolomics can be a powerful tool to explore the underlying mechanisms of local adaptation in ‘non-model’ species.

Studying natural variation in multi-stress resistance is central for predicting and managing the population dynamics of wild plant species under rapid global change. Yet, it remains a challenging goal in this field to integrate knowledge on the complex biochemical underpinnings for the targeted ‘non-model’ species. Here, we studied latitudinal divergence in combined drought and heat stress resistance in European populations of the dune plantCakile maritima, by combining comprehensive plant phenotyping with metabolic profiling via FT-ICR-MS and UPLC-TQ-MS/MS.We observed pronounced constitutive divergence in growth phenology, leaf functional traits and defence chemistry (glucosinolates, alkaloids) among population origins. Most importantly, the magnitude of growth reduction under stress was partly weaker in southern plants and associated with divergence in plastic growth responses (root expansion, leaf abscission) and the stress-induced modulation of primary and specialized metabolites with known central functions not only in plant abiotic but also biotic stress resistance.Our study supports that divergent selection has shaped the constitutive and stress-induced expression of numerous morphological and biochemical functional traits to mediate higher abiotic stress resistance in southernCakilepopulations, and highlights that metabolomics is a powerful tool to explore the mechanistic underpinnings of local stress adaptation in ‘non-model’ species.HighlightPlant defence chemistry and its modulation by abiotic stress exhibits latitudinal clines across natural populations of a coastal plant.

Aims Positive biodiversity–ecosystem functioning relationships have been widely reported, predominately from grassland ecosystems. However, this does not necessarily have to apply accordingly in more complex situations such as in forests across different vertical strata. For instance, overstorey tree species richness has been shown to be associated with a lower understorey productivity. Whether or not tree species richness effects add to understorey productivity by increasing (i.e. due to habitat heterogeneity) or reducing resource availability (i.e. through increasing competition) and whether understorey productivity is indeed being governed more strongly by tree species identity are likely to change over time. Moreover, studies also suggested that richness–productivity relationships change with the environmental context. Using an experimental forest plantation with manipulated tree species richness, this study examined these temporal and environmental dynamics across strata. Methods In the context of the Biodiversity-Ecosystem Functioning project in subtropical China (BEF-China), we made use of understorey biomass samples repeatedly collected over a time period of 3 years along a tree species richness gradient. The effects of tree species richness, tree species identities and time were studied across different environmental treatments for their impact on understorey biomass. Important Findings While we found significant and consistent tree layer identity effects on understorey biomass, no such effect was encountered for tree species richness. Our results also indicate that among structural layers in forests, there might not be a single, generalizable overstorey species richness–understorey productivity relationship, and that the extent as to which overstorey-related environmental factors such as light transmittance contribute to understorey productivity change with time. Overall, we demonstrate that temporal dynamics should be considered when studying relationship among structural layers in forests.

Exotic plant species can evolve adaptations to environmental conditions in the exotic range. Furthermore, soil biota can foster exotic spread in the absence of negative soil pathogen–plant interactions or because of increased positive soil biota–plant feedbacks in the exotic range. Little is known, however, about the evolutionary dimension of plant–soil biota interactions when comparing native and introduced ranges.To assess the role of soil microbes for rapid evolution in plant invasion, we subjected Verbascum thapsus, a species native to Europe, to a reciprocal transplant experiment with soil and seed material originating from Germany (native) and New Zealand (exotic). Soil samples were treated with biocides to distinguish between effects of soil fungi and bacteria. Seedlings from each of five native and exotic populations were transplanted into soil biota communities originating from all populations and subjected to treatments of soil biota reduction: application of (a) fungicide, (b) biocide, (c) a combination of the two, and (d) control.For most of the investigated traits, native populations showed higher performance than exotic populations; there was no effect of soil biota origin. However, plants developed longer leaves and larger rosettes when treated with their respective home soil communities, indicating that native and exotic plant populations differed in their interaction with soil biota origin. The absence of fungi and bacteria resulted in a higher specific root length, suggesting that V. thapsus may compensate the absence of mutualistic microbes by increasing its root–soil surface contact. Synthesis. Introduced plants can evolve adaptations to soil biota in their new distribution range. This demonstrates the importance of biogeographic differences in plant–soil biota relationships and suggests that future studies addressing evolutionary divergence should account for differential effects of soil biota from the home and exotic range on native and exotic populations of successful plant invaders., We tested for differential effects of soil microbes from the native and introduced ranges for the exotic range expansion of Verbascum thapsus in a reciprocal transplant experiment. We found significant interactions between plant range origin and soil biota origin and suggest that V. thapsus may compensate a lack of mutualistic microbes by increasing root surface. Our results emphasize that the evolutionary dimension of plant–soil biota interactions needs to be considered in explaining plant invasions.

Environmental factors change with an increase in elevation, such as increased UV-B radiation and decreased water availability, and thus may pose as barriers in upwards range expansion of plant species. Although evidence has been provided for an increasing number of exotic species reaching high elevations, the mechanisms behind still remain to be resolved, specifically, as to what extent processes of plasticity and adaptation are involved in overcoming these environmental barriers. In order to test for the role of genetic differentiation, specifically attributable to changes in water availability and UV-B radiation along elevational gradients in exotic plant species, we conducted a greenhouse experiment with eleven exotic herbaceous plant species sampled along an elevational gradient from 1500 to 3000 m a.s.l. in Drakensberg, South Africa. Seeds were collected across sections over the entire elevational gradient of Sani Pass. The experiment was run in a greenhouse with individuals grown from seeds of different elevational origins and subjected to combinations of three levels of UV-B radiation and two levels of soil moisture. Measures of performance and functional traits were repeatedly assessed as response measures in a species-wise manner. The results revealed a significant impairment of plant performance by increased levels of UV-B radiation as well as by reduced water availability. This emphasizes the existence of cross-resistance mechanisms that alleviate the negative impacts if plants are subjected to both combined stressors at the same time. Additionally, there seems to be a strong dependency of leaf trait responses on the developmental stage of the individual. We found evidence for adaptive processes related to increasing UV-B radiation levels in high montane areas, suggesting that factors fostering evolutionary responses, such as longer residence time and high genetic diversity could promote additional ascent of exotic species into high elevation areas.

Plant diversity begets diversity at other trophic levels. While species richness is the most commonly used measure for plant diversity, the number of evolutionary lineages (i.e. phylogenetic diversity) could theoretically have a stronger influence on the community structure of co-occurring organisms. However, this prediction has only rarely been tested in complex real-world ecosystems. Using a comprehensive multitrophic dataset of arthropods and fungi from a species-rich subtropical forest, we tested whether tree species richness or tree phylogenetic diversity relates to the diversity and composition of organisms. We show that tree phylogenetic diversity but not tree species richness determines arthropod and fungi community composition across trophic levels and increases the diversity of predatory arthropods but decreases herbivorous arthropod diversity. The effect of tree phylogenetic diversity was not mediated by changed abundances of associated organisms, indicating that evolutionarily more diverse plant communities increase niche opportunities (resource diversity) but not necessarily niche amplitudes (resource amount). Our findings suggest that plant evolutionary relatedness structures multitrophic communities in the studied species-rich forests and possibly other ecosystems at large. As global change non-randomly threatens phylogenetically distinct plant species, far-reaching consequences on associated communities are expected. A free Plain Language Summary can be found within the Supporting Information of this article.

We investigate whether inbreeding has particularly fatal consequences for dioecious plants by diminishing their floral attractiveness and the associated pollinator visitation rates disproportionally in females. We also test whether the magnitude of such effects depends on the evolutionary histories of plant populations. We recorded spatial, olfactory, colour and rewarding flower attractiveness traits as well as pollinator visitation rates in experimentally inbred and outbred, male and femaleSilene latifoliaplants from European and North American populations differing in their evolutionary histories. We found that inbreeding specifically impairs spatial and olfactory attractiveness. Our results support that sex-specific selection and gene expression partially magnified these inbreeding costs for females, and that divergent evolutionary histories altered the genetic architecture underlying inbreeding effects across population origins. Moreover, they highlight that inbreeding effects on olfactory attractiveness have a huge potential to disrupt interactions among plants and specialist moth pollinators, which are mediated by elaborate chemical communication.

A large proportion of temperate forest plant diversity is found in the herb layer.However, for many of its species, little is known about their autecology, whichmakes it difficult to assess potential threats and efficiently safeguard the diversity of understorey herbaceous communities. This also applies to Gageaspathacea (Liliaceae), a globally rare spring geophyte, which mainly occurs indeciduous forests of northern Central Europe. We investigated the causal relationships between population characteristics of G. spathacea and abiotic siteconditions across different forest communities in the center of its distributionalrange. Leaf length (a surrogate of the species' vegetative propagation) was positively related to soil moisture and soil nitrogen. Consequently, mean leaflength was highest in moist forest communities of the alliance Alno-Ulmion.Moreover, mean variability in leaf length was lowest in those forests, indicatinga higher and more stable vegetative propagation via bulbils. We found no support for a significant relationship between leaf length and leaf density orbetween leaf length and flower formation. Population density varied stronglyamong forest sites, but was not related to soil moisture and hardly influenced by soil nitrogen. Our results suggest that soil water and nutrient supply play avital role in determining the species' vegetative propagation, whereas the duration of habitat continuity is most likely an important determinant of population size and density. Conservation strategies therefore require a betterunderstanding of the complex interrelationships between abiotic site conditionsand the historical context-dependency of habitats. A large proportion of temperate forest plant diversity is found in the herb layer. However, for many of its species, little is known about their autecology, which makes it difficult to assess potential threats and efficiently safeguard the diversity of understorey herbaceous communities. This also applies to Gagea spathacea (Liliaceae), a globally rare spring geophyte, which mainly occurs in deciduous forests of northern Central Europe. We investigated the causal relationships between population characteristics of G. spathacea and abiotic site conditions across different forest communities in the center of its distributional range. Leaf length (a surrogate of the species' vegetative propagation) was positively related to soil moisture and soil nitrogen. Consequently, mean leaf length was highest in moist forest communities of the alliance Alno‐Ulmion. Moreover, mean variability in leaf length was lowest in those forests, indicating a higher and more stable vegetative propagation via bulbils. We found no support for a significant relationship between leaf length and leaf density or between leaf length and flower formation. Population density varied strongly among forest sites, but was not related to soil moisture and hardly influenced by soil nitrogen. Our results suggest that soil water and nutrient supply play a vital role in determining the species' vegetative propagation, whereas the duration of habitat continuity is most likely an important determinant of population size and density. Conservation strategies therefore require a better understanding of the complex interrelationships between abiotic site conditions and the historical context‐dependency of habitats.

Spatially explicit data on heterogeneously distributed plant populations are difficult to quantify using either traditional field-based methods or remote sensing techniques alone. Unmanned Aerial Vehicles (UAVs) offer new means and tools for baseline monitoring of such populations. We tested the use of vegetation classification of UAV-acquired photographs as a method to capture heterogeneously distributed plant populations, using Jacobaea vulgaris as a model species. Five sites, each containing 1–4 pastures with varying J. vulgaris abundance, were selected across Schleswig–Holstein, Germany. Surveys were conducted in July 2017 when J. vulgaris was at its flowering peak. We took aerial photographs at a 50 m altitude using three digital cameras (RGB, red-edge and near-infrared). Orthomosaics were created before a pixel-based supervised classification. Classification results were evaluated for accuracy; reliability was assessed with field data collected for ground verification. An ANOVA tested the relationship between field-based abundance estimations and the supervised classifications. Overall accuracy of the classification was very high (90.6%, ± 1.76 s.e.). Kappa coefficients indicated substantial agreement between field data and image classification (≥ 0.65). Field-based estimations were a good predictor of the supervised classifications (F = 7.91, df = 4, P = 0.007), resulting in similar rankings of J. vulgaris abundance. UAV-acquired images demonstrated the potential as an objective method for data collection and species monitoring. However, our method was more time consuming than field-based estimations due to challenges in image processing. Nonetheless, the increasing availability of low-cost consumer-grade UAVs is likely to increase the use of UAVs in plant ecological studies.

Negative relationships between species richness and elevation are common and attributed to changes in single environmental properties associated to elevation, such as temperature and habitat area. However, research has lacked taxonomic breadth and comprehensive elevation studies that consider multiple groups from different trophic levels are rare. We thus analysed 24 groups of plants, arthropods, and microorganisms grouped into six trophic guilds (predators, detritivores, herbivores, plants, bacteria and fungi) along a relatively short elevational gradient (~600 m) in a subtropical forest in south-east China. The total species richness of all organisms was not related to elevation, nor was the richness of plants, herbivores or microorganisms. However, species richness and abundance in two major trophic guilds of arthropods changed with elevation, which was mediated by changes in elevation-associated habitat properties. Specifically, deadwood mass increased with elevation, which increased detritivore richness indirectly via detritivore abundance, thus supporting the ‘more individuals hypothesis’. In contrast, lower predator richness at higher elevations was directly related to lower mean temperatures, which had no effect on abundance. Our study demonstrates that even along relatively short gradients, elevation can have strong direct and abundance-mediated effects on species richness, but with effects varying from positive to negative signs depending on local resource availability and the characteristics of groups or trophic guilds. If elevation positively influences local environmental properties that benefit a given group, richness can increase towards higher elevations. Thus, the effect of global change in mountainous regions should be evaluated within the local environmental context using multi-taxon approaches.

The Janzen-Connell (JC) hypothesis is a major ecological explanation for high species richness, in particular in tropical forest ecosystems. Central components of the JC hypothesis are noncompetitive effects of distance and density dependence, two drivers that contribute independently to species coexistence, but are ultimately linked in the field. However, although numerous studies provide evidence for either distance- or density-dependent effects based on observational data, experimental testing of simultaneous and interactive effects of distance and density has rarely been conducted, especially in a comprehensive multispecies approach. Here, we make use of the forest Biodiversity-Ecosystem Functioning project (BEF) -China to estimate distance- and density-dependent effects in a reciprocal tree seedling transplant experiment of 11 tree species. We deployed 13,490 juveniles of all 11 species in their own (home) and in all foreign monocultures (away), as well as at three different levels of planting density, thereby testing for distance and density effects, respectively. In addition, to quantify the amount to which density effects were brought about by potential additional effects of intraspecific competition, we set up a common garden experiment with different levels of planting density, where an additional "shadow" treatment controlled for effects of canopy shading. Although the "away" and "high-density" treatments significantly impaired the performance and productivity of seedlings, leaf damage and survival was exclusively affected by either the home/away or the density treatment, respectively. Negative density-dependent effects on leaf damage were less pronounced in the "home" treatment, showing that the effects were not additive. In addition, results obtained in the Common Garden Experiment showed that negative effects of high density may be also brought about by intraspecific competition as an alternative density-responsive mechanism and less by true JC effects. Overall, our results provide strong support on a multispecies basis for the influence of host-specific effects already operating in early stages of a forest plantation. However, they also emphasize the need to account appropriately for potential additional density-responsive mechanisms such as intraspecific competition or microenvironmental conditions when addressing the role of JC effects for species coexistence.

Species‐rich grasslands are highly endangered habitats in Central Europe. To halt their ongoing loss, many sites have become subjects of restoration efforts. Traditionally, restoration success is measured using target species or by comparing similarity in species composition. Here, we suggest to additionally use functional community composition to assess restoration success as functional traits might offer mechanistic insights into restoration processes. In a 5‐year restoration experiment, we annually evaluated the responses of (i) floristic composition and species diversity, (ii) number and cover of target species, (iii) functional identity and (iv) functional diversity to four different methods of assisted recolonization through species introduction: hay transfer and application of threshing material from a local provenance, combined with and without addition of regional seed mixtures of target species, as well as to a control treatment. Across all treatments, floristic composition, species diversity, and number and cover of target species approached the values of reference sites. In the last observation year, Shannon diversity was still lower in all treatment plots than in the reference plots, while the number of target forb species had reached or exceeded the reference levels. We demonstrated that the community was also restored functionally in many aspects, but not in all studied traits. Calculated community‐weighted means (CWMs), specific leaf area (SLA) and leaf dry matter content (LDMC) in experimental plots did not differ significantly from the reference plots, thereby indicating that productivity of restored sites had reached target values. In contrast, CWMs of strategy types and pollination modes revealed significant differences, showing that biotic interactions among plant species and with other trophic levels have not yet been fully restored. However, almost all CWMs showed a trajectory towards the reference, thus giving a positive prospect for the future development. With respect to functional diversity (FD), we found steadily increasing FD values for almost all traits analysed. Synthesis and applications. We demonstrated that all applied restoration measures were appropriate to achieve the restoration aim in terms of species composition of a given community and the establishment of target species. With respect to many functional traits, the restored meadows were already as functional as communities from the reference sites. Hence, including functional criteria did not only corroborate traditional criteria of restoration success but also allowed identifying those floodplain meadow's functions that can be quickly and less quickly restored.

Ultraviolet (UV) radiation intensities differ among global regions, with significantly higher levels in the southern hemisphere. UV-B may act as an environmental filter during plant invasions, which might particularly apply to plant species from Europe introduced to New Zealand. Just like for any other abiotic or biotic filter, successful invaders can cope with novel environmental conditions via plastic responses and/or through rapid adaptation by natural selection in the exotic range. We conducted a multi-species experiment with herbaceous plants in two common gardens located in the species' 'native' and exotic ranges, in Germany and New Zealand, respectively. We used plants of German and New Zealand origin of eight species to test for adaptation to higher UV-B radiation in their new range. In each common garden, all plants were exposed to three radiation treatments: (i) ambient sunlight, (ii) exclusion of UV-B while transmitting ambient UV-A, and (iii) combined exclusion of UV-B and UV-A. Linear mixed-effect models revealed significant effects of UV-B on growth and leaf traits and an indication for UV-B-induced biomass reduction in both common gardens pointing to an impact of natural, ambient UV radiation intensities experienced by plants in the northern and in the southern hemisphere. In both common gardens, the respective local plants (i.e. German origins in Germany, New Zealand origins in New Zealand) displayed enhanced productivity and aboveground biomass allocation, thus providing evidence for recent evolutionary processes in the exotic range. Genetic differentiation between different origins in consequence of divergent local selection pressures was found for specific leaf area. This differentiation particularly hints at different selective forces in both ranges while only little evidence was found for an immediate selective effect of high UV-B intensities in the exotic range. However, reaction norm slopes across ranges revealed higher plasticity of exotic individuals in functional leaf traits that might allow for a more sensitive regulation of photoprotection measures in response to UV-B. During the colonization, New Zealand populations might have been selected for the observed higher phenotypic plasticity and a consequently increased ability to successfully spread in the exotic range.

Clonal growth may increase the likelihood for alien plants becoming invasive, as it is an efficient foraging and spatial exploration strategy. Here, we investigated the effect of artificial herbivory on organs of clonal growth and its potential to drive post-introduction evolutionary change. Based on the assumption that tolerance traits are costly and that clonal alien species may benefit from investing freed resources into growth, fecundity or nutrient acquisition, we tested the hypothesis of lower tolerance to herbivory on organs of clonal growth in alien plants. In a common-garden experiment we studied divergence in plants from native German and alien New Zealand populations of six species with different clonal growth forms. A nutrient treatment testing the plant’s acquisition abilities, was combined with artificial herbivory on clonal organs. We investigated origin-dependent differences in sexual reproduction, plant growth and the production of clonal organs. For aboveground and clonal organ biomass, alien plants showed lower tolerance to artificial herbivory on clonal organs than native plants. In the combined herbivory and nutrient treatment, alien plants of four species grew fewer clonal organs when compared to the nutrient treatment alone. Alien plants of the other two species produced more clonal organs, regardless of treatment. All species revealed significant differences in flower production between origins, with five of them producing more flowers on alien than on native plants. The results support the hypothesis that a release of herbivory on clonal organs has lead to subtle evolutionary changes in tolerance of alien plants and to a species-dependent increase in plant vigour, clonal growth and/or sexual reproduction that may enhance their invasive success.

Questions The forest herb layer provides a multitude of ecosystem services as a result of its species-rich character. Herb layer diversity and biomass are both influenced by tree layer composition and species richness through species-specific influences on environmental conditions. The results of observational studies on richness–biomass relationships between tree and herb layer have not been unequivocal. We examined tree species identity and richness effects on herb layer species richness, composition, biomass and nutrient concentrations in young experimental tree plantations. Location BIOTREE tree diversity experiment, Kaltenborn, Germany. Methods Sixteen plots were planted in 2004, using a pool of four tree species (beech, oak, Douglas-fir, Norway spruce) and four richness levels, comprised of all possible species combinations. In this way, complete dilution was avoided, allowing separation of tree species identity and richness effects. Mixed plots consisted of a matrix of monospecific patches. One permanent vegetation quadrat of 1 m2 was established in the centre of four patches per plot. The herb layer was monitored in 2004 and 2010; in 2010 light measurements were performed in each quadrat, and in 2011 above-ground biomass was sampled on 0.25 m2 within the quadrat. Results Community composition shifted markedly between 2004 and 2010. Tree species identity did not yet influence temporal compositional turnover or herb layer species richness in 2004 and 2010. Ellenberg N indicated a temporal shift towards lower soil fertility under all tree species, whereas Ellenberg R indicated decreasing soil acidity under beech and Douglas-fir. Ellenberg L and F showed no shift from 2004 to 2010. Apart from the significantly lower Ellenberg N for beech, none of the Ellenberg indicators indicated interspecific differences. Douglas-fir, and especially Norway spruce, negatively influenced total above-ground herb layer biomass. Douglas-fir also induced lower relative light availability, higher potassium, magnesium and nitrogen concentrations and lower carbon:nitrogen ratios in the total biomass. Higher tree species richness positively affected graminoid and total biomass and also slightly increased plot-level herb layer species richness. Conclusions Despite the young age of the experiment, tree species identity and richness effects on the herb layer could be discerned. We expect these relations to become stronger with time.

Tree diversity improves forest productivity Experimental studies in grasslands have shown that the loss of species has negative consequences for ecosystem functioning. Is the same true for forests? Huang et al. report the first results from a large biodiversity experiment in a subtropical forest in China. The study combines many replicates, realistic tree densities, and large plot sizes with a wide range of species richness levels. After 8 years of the experiment, the findings suggest strong positive effects of tree diversity on forest productivity and carbon accumulation. Thus, changing from monocultures to more mixed forests could benefit both restoration of biodiversity and mitigation of climate change. Science , this issue p. 80

Biodiversity-ecosystem functioning (BEF) research has extended its scope from communities that are short-lived or reshape their structure annually to structurally complex forest ecosystems. The establishment of tree diversity experiments poses specific methodological challenges for assessing the multiple functions provided by forest ecosystems. In particular, methodological inconsistencies and nonstandardized protocols impede the analysis of multifunctionality within, and comparability across the increasing number of tree diversity experiments. By providing an overview on key methods currently applied in one of the largest forest biodiversity experiments, we show how methods differing in scale and simplicity can be combined to retrieve consistent data allowing novel insights into forest ecosystem functioning. Furthermore, we discuss and develop recommendations for the integration and transferability of diverse methodical approaches to present and future forest biodiversity experiments. We identified four principles that should guide basic decisions concerning method selection for tree diversity experiments and forest BEF research: (1) method selection should be directed toward maximizing data density to increase the number of measured variables in each plot. (2) Methods should cover all relevant scales of the experiment to consider scale dependencies of biodiversity effects. (3) The same variable should be evaluated with the same method across space and time for adequate larger-scale and longer-time data analysis and to reduce errors due to changing measurement protocols. (4) Standardized, practical and rapid methods for assessing biodiversity and ecosystem functions should be promoted to increase comparability among forest BEF experiments. We demonstrate that currently available methods provide us with a sophisticated toolbox to improve a synergistic understanding of forest multifunctionality. However, these methods require further adjustment to the specific requirements of structurally complex and long-lived forest ecosystems. By applying methods connecting relevant scales, trophic levels, and above- and belowground ecosystem compartments, knowledge gain from large tree diversity experiments can be optimized. Biodiversity–ecosystem functioning (BEF) research has extended its scope from communities that are short‐lived or reshape their structure annually to structurally complex forest ecosystems. The establishment of tree diversity experiments poses specific methodological challenges for assessing the multiple functions provided by forest ecosystems. In particular, methodological inconsistencies and nonstandardized protocols impede the analysis of multifunctionality within, and comparability across the increasing number of tree diversity experiments. By providing an overview on key methods currently applied in one of the largest forest biodiversity experiments, we show how methods differing in scale and simplicity can be combined to retrieve consistent data allowing novel insights into forest ecosystem functioning. Furthermore, we discuss and develop recommendations for the integration and transferability of diverse methodical approaches to present and future forest biodiversity experiments. We identified four principles that should guide basic decisions concerning method selection for tree diversity experiments and forest BEF research: (1) method selection should be directed toward maximizing data density to increase the number of measured variables in each plot. (2) Methods should cover all relevant scales of the experiment to consider scale dependencies of biodiversity effects. (3) The same variable should be evaluated with the same method across space and time for adequate larger‐scale and longer‐time data analysis and to reduce errors due to changing measurement protocols. (4) Standardized, practical and rapid methods for assessing biodiversity and ecosystem functions should be promoted to increase comparability among forest BEF experiments. We demonstrate that currently available methods provide us with a sophisticated toolbox to improve a synergistic understanding of forest multifunctionality. However, these methods require further adjustment to the specific requirements of structurally complex and long‐lived forest ecosystems. By applying methods connecting relevant scales, trophic levels, and above‐ and belowground ecosystem compartments, knowledge gain from large tree diversity experiments can be optimized.

Forest ecosystems contribute substantially to global terrestrial primary productivity and climate regulation, but, in contrast to grasslands, experimental evidence for a positive biodiversity-productivity relationship in highly diverse forests is still lacking1. Here, we provide such evidence from a large forest biodiversity experiment with a novel design2 in subtropical China. Productivity (stand-level tree basal area, aboveground volume and carbon and their annual increment) increased linearly with the logarithm of tree species richness. Additive partitioning3 showed that increasing positive complementarity effects combined with weakening negative selection effects caused a strengthening of the relationship over time. In 2-species mixed stands, complementary effects increased with functional distance and selection effects with vertical crown dissimilarity between species. Understorey shrubs reduced stand-level tree productivity, but this effect of competition was attenuated by shrub species richness, indicating that a diverse understorey may facilitate overall ecosystem functioning. Identical biodiversity-productivity relationships were found in plots of different size, suggesting that extrapolation to larger scales is possible. Our results highlight the potential of multi-species afforestation strategies to simultaneously contribute to mitigation of climate change and biodiversity restoration.

Exotic plant invasions are widely observed to have strong biogeographic patterns with invasive species occurring at higher abundances in their introduced range when compared with their native range. However, only few field studies have validated this assumption by comparing plant populations of multiple species in their native and introduced ranges and have evaluated to what extent changes in sexual and clonal reproduction potentially have contributed to the success of plant invasions. Here, we present the results of a comparative field study in both the native (Germany) and the introduced (New Zealand, NZ) ranges of six clonal plant species with different invasive status: Achillea millefolium L., Pilosella officinarum Vaill., Hypericum perforatum L., Prunella vulgaris L., Leucanthemum vulgare Lam. and Lotus pedunculatus Cav. We hypothesized that all six species show better performance in introduced NZ than in native German populations and tested if population structures investigated at different scales provide a useful tool to identify differences between native and introduced occurrences. In 10 populations per species and country we assessed plant density and flowering proportion at the population scale and around individual plants, thereby identifying the ‘crowdedness’ of the populations. Furthermore, we collected individual plants and determined the number of attached clonal organs and plant biomass. For all six species crowdedness in NZ populations was higher than in German populations. Additionally, overall population density of four species and the production of clonal organs (expressed as total number or per biomass ratio) of three species were higher in NZ than in Germany. When measured around individual plants, the flowering proportion was higher in native German populations of Pilosella officinarum, Hypericum perforatum and Leucanthemum vulgare. Although the study species differed in their invasive status, our findings show that for all six species performance was better in introduced than in native populations. Furthermore, this study emphasizes that multiple measures of plant performance, different spatial scales and differences among species should be taken into account when trying to identify biogeographic differences in the performance of weed species.

Attempts to find a consensus on traits promoting the invasiveness of exotic species have agreed on the idiosyncrasy of successful invasions. Despite considerable efforts to integrate aspects of context-dependency into theories of invasions, none of them has provided an evolutionary perspective taking consistently into account the direction of environmental changes in terms of ‘constraint’ vs . ‘release’. Applying the filter theory of species sorting, I consider different filters at different scales explaining evolutionary changes during invasions. Within this hierarchical approach, the focus is on the factorial filters climate, abiotic environment and biotic environment, distinguishing trophic interactions and plant-plant interactions. This review summarizes the evidence of adaptive shifts from native to exotic ranges, thereby differentiating the direction of shifts with regard to either constrained or released situations. Following this systematic approach, the present paper identifies further trade-offs within hierarchical levels complementing already existing hypotheses such as those for biotic interactions. In particular, the role of climatic changes should more explicitly be linked with evolutionary responses during invasions. Studying exotic species successfully invading several regions with different environmental conditions will be a promising starting point to enlarge the understanding of context-dependency of invasions.

AimsThe aim of our research was to understand small-scale effects of topography and soil fertility on tree growth in a forest biodiversity and ecosystem functioning (BEF) experiment in subtropical SE China.MethodsGeomorphometric terrain analyses were carried out at a spatial resolution of 5×5 m. Soil samples of different depth increments and data on tree height were collected from a total of 566 plots (667 m2 each). The soils were analyzed for carbon (soil organic carbon [SOC]), nitrogen, acidity, cation exchange capacity (CEC), exchangeable cations and base saturation as soil fertility attributes. All plots were classified into geomorphological units. Analyses of variance and linear regressions were applied to all terrain, soil fertility and tree growth attributes.Important FindingsIn general, young and shallow soils and relatively small differences in stable soil properties suggest that soil erosion has truncated the soils to a large extent over the whole area of the experiment. This explains the concurrently increasing CEC and SOC stocks downslope, in hollows and in valleys. However, colluvial, carbon-rich sediments are missing widely due to the convexity of the footslopes caused by uplift and removal of eroded sediments by adjacent waterways. The results showed that soil fertility is mainly influenced by topography. Monte–Carlo flow accumulation (MCCA), curvature, slope and aspect significantly affected soil fertility. Furthermore, soil fertility was affected by the different geomorphological positions on the experimental sites with ridge and spur positions showing lower exchangeable base cation contents, especially potassium (K), due to leaching. This geomorphological effect of soil fertility is most pronounced in the topsoil and decreases when considering the subsoil down to 50cm depth. Few soil fertility attributes affect tree height after 1–2 years of growth, among which C stocks proved to be most important while pHKCl and CEC only played minor roles. Nevertheless, soil acidity and a high proportion of Al on the exchange complex affected tree height even after only 1–2 years growth. Hence, our study showed that forest nutrition is coupled to a recycling of litter nutrients, and does not only depend on subsequent supply of nutrients from the mineral soil. Besides soil fertility, topography affected tree height. We found that especially MCCA as indicator of water availability affected tree growth at small-scale, as well as aspect. Overall, our synthesis on the interrelation between fertility, topography and tree growth in a subtropical forest ecosystem in SE China showed that topographic heterogeneity lead to ecological gradients across geomorphological positions. In this respect, small-scale soil–plant interactions in a young forest can serve as a driver for the future development of vegetation and biodiversity control on soil fertility. In addition, it shows that terrain attributes should be accounted for in ecological research.

Both phenotypic and genetic variation can affect the establishment success of exotic species. Using the weed Senecio vernalis Waldst. & Kit. with a continuous westward expansion of the native geographic range, we asked to what degree seed traits and germination patterns differ among different habitat disturbance types in the introduced region. We hypothesized that seed traits and germination pattern differ between different disturbance types, with lighter seeds and enhanced germination speed in highly disturbed habitats. Since S. vernalis colonizes successfully various disturbed habitats, we expected to find a high phenotypic genetic variation. Individuals from 19 populations were sampled from one region in Eastern Germany to study seed trait variation and germination success by means of a germination experiment and to assess genetic patterns using amplified fragment length polymorphism (AFLP) markers. Contrary to our expectation, habitat disturbance types did not differ in seed traits, germination characteristics or genetic variation. Instead, we found highest phenotypic and genetic variation within populations. Maximum percentage of germination was positively affected by seed mass. In addition, there was a weak but significant association between AFLP band patterns and population size and seed width, indicating that some variation in seed traits has a genetic component. In conclusion, the absence of a population differentiation at this geographic scale makes it unlikely that adaptation to different disturbance regimes is involved. Instead, a high variation in seed traits, overall high germination and genetic variation within populations under a wide range of habitat disturbance conditions seems to enable the offspring to colonize various habitat disturbance types.

The attempt to identify traits associated with plant invasions has revealed ambiguous results to date. Accounting for environmental and temporal variation in multispecies trait comparisons of native and invasive species might help explain such inconsistency. The relative importance of light and nutrient availability was tested in a greenhouse experiment on trait expression and variation of 15 native and 15 invasive herb species from Southeast China. In addition, N uptake of a subset of these species and its temporal pattern were assessed by means of a 15N tracer experiment. A predominant lack of significant differences between the two status groups indicated strong overall trait similarities, thus supporting the 'join-the-local' hypothesis. However, at high light levels, the invasive species displayed significantly higher trait relative growth rates, whereas the native species had a higher tissue quality as displayed in a higher dry matter content of shoots and leaves. The invasion success of the invasive species could neither be explained by a general higher N uptake nor by a distinction in temporal N uptake strategy between native and invasive species. Despite comparable fundamental niches of the species, increased growth rates under beneficial light conditions may provide a head start advantage for invasive species compared to native ones. The present study confirms the assumption of an opportunistic strategy for invasive species and emphasizes the need to assess trait variation between native and invasive species in different environmental contexts.

We analyzed the influence of above- and belowground factors on the soil microbial community in a Chinese subtropical forest, one of the most diverse biomes in the northern hemisphere. Soil samples were taken at different depths from four replicate comparative study plots in each of three forest age classes (young 10–40 years, medium 40–80 years, old ≥80 years). Microbial biomass and community structure were then determined using phospholipid fatty acid (PLFA) analysis, and basal respiration and microbial biomass carbon (Cmic) were determined by substrate-induced respiration. These data were then related to plant community and soil variables using non-metric multidimensional scaling analysis and post-hoc permutational correlations. We found that microbial lipid composition and abundance were not related to forest age class. Instead, microbial lipid composition and abundance were related to factors reflecting primary production, i.e., percent litter cover, percent dead wood cover, and percent tree layer cover. Specifically, the relative abundance (mol fraction) of indicators for arbuscular mycorrhizal fungi, Gram-positive and Gram-negative bacteria were positively significantly correlated with percent litter cover. We also found that the biomass of all microbial groups and total PLFA were negatively significantly related to percent deadwood cover. In addition, $$ {\text{pH}}_{{{\text{H}}_{ 2} {\text{O}}}} $$ was the only soil parameter that was correlated significantly to microbial biomass. Our results indicate that overarching ecological factors such as plant productivity and soil pH are important factors influencing the soil microbial community, both in terms of biomass and of community composition in this subtropical ecosystem.

Intensity of ultraviolet-B radiation (UV-B) differs between northern and southern hemispheres. Therefore, exotic plants species that originate from the northern hemisphere provide an opportunity to study the effects of UV-B on plant physiology and growth, and their implications for the role of adaptation and phenotypic plasticity during plant invasion on the southern hemisphere. We conducted a growth-chamber experiment with and without UV-B on Hieracium pilosella plants from Germany, where the species occurs natively and New Zealand (NZ), where it is invasive. We tested the hypothesis that: (i) H. pilosella plants respond to UV-B with high phenotypic plasticity, demonstrating the ability to react to changes in UV-B, and (ii) NZ plants are better adapted to UV-B than German plants as a result of directional selection of well adapted phenotypes. Consistent with our first hypothesis H. pilosella plants reacted plastically to UV-B by producing longer foliar hairs and a higher leaf dry matter content (LDMC) when they were treated with UV-B regardless of their origin. Additionally, irrespective of the treatment, plants from NZ displayed a higher LDMC and grew less but longer leaves than German plants. Plants showed typical stress responses and a reduction in growth caused by the UV-B treatment: below-ground biomass and production of ramets were reduced when plants were treated with UV-B. H. pilosella proved to be particularly well predisposed to grow in areas of high UV-B radiation. Our findings hint at the necessity to consider UV-B radiation in future research on mechanisms of invasions in regions with high UV-B irradiation. Species that provide the ability to respond directly to UV-B might have an advantage to invade these areas. As UV-B intensity is likely to change in the future due to ongoing ozone depletion, research addressing the effects of UV-B during plant invasions is of increasing importance.

Hybridization has been repeatedly put forward to explain the invasiveness of Rhododendron ponticum L. in the British Isles. The present study investigates the pattern of ecotypic differentiation and hybridization among native North American R. catawbiense and R. maximum, native R. ponticum from Georgia and Spain, and invasive R. ponticum from Ireland and aims to assess the contribution of hybridization for Rhododendron invasion in the British Isles. Six populations per taxon were analyzed with AFLP markers for genetic dissimilarity, subjected to germination and growth experiments, and tested for frost hardiness. We assessed variation in morphological and ecological characteristics to identify traits displaying evidence of hybridization, thus, promoting invasiveness. Molecular marker analyses revealed a clear distinction between North American R. catawbiense and R. maximum on the one hand, and all R. ponticum populations on the other hand, displaying a complete intermixture of native Spanish and invasive Irish populations. Multivariate analyses of traits revealed leaf length–width ratio, relative growth rates (RGRs) in leaf length, root biomass, and shoot–root ratio to significantly discriminate between the different taxa and unequivocally assigned invasive Irish R. ponticum to the Spanish phenotypes. While the Irish R. ponticum had similar growth traits as conspecific native R. ponticum provenances, germination and biomass allocation were more similar to North American R. catawbiense and R. maximum. Hybridization did not contribute to explaining invasiveness of R. ponticum in Ireland. The similarity in germination and biomass allocation of invasive Irish R. ponticum and North American species has evolved independently and can more probably be attributed to an independent shift within the Ponticum cluster in Ireland.

Question: Knowledge of the interaction between understorey herb and overstorey tree layer diversity is mostly restricted to temperate forests. How do tree layer diversity and environmental variables affect herb layer attributes in subtropical forests and do these relationships change in the course of succession? Do abundance and diversity of woody saplings within the herb layer shift during succession?

Adaptive processes in invasive plant populations may explain exotic range expansions and ecotypic shifts between native and invasive populations of the same species. Sufficient genetic variation in invasive populations occurring within the new range is a precondition for selection. While genetic diversity can be considerably reduced during invasions following founder effects and genetic drift, it can also be maintained via mechanisms of effective gene flow. Rhododendron ponticum L., an aggressive invader in the British Isles, is an appropriate test species for investigating changes in genetic diversity and differentiation. Six native populations in Georgia and Spain each and six invasive populations in Ireland were analyzed with amplified fragment length polymorphism markers to calculate genetic distances, genetic diversity, and differentiation within and among populations. While the highest level of genetic diversity was found within native Georgian populations, thus indicating a refugium, native Spanish...

The germination stage is critical in plant life-history and is also a key process during the expansion of species’ ranges into new environments. In this study we investigated the germination patterns of three plant species (Achillea millefolium, Hieracium pilosella and Hypericum perforatum) that are invasive to New Zealand (NZ) and native to Central Europe. We asked whether the species show differences in germination temperature requirements, germination speed and maximum germination rates, and thus, whether they display evidence of adaptation to different conditions in the invasive range. Seeds from three populations per species and region were subjected to three different temperature regimes to compare germination rates among origins and across temperature conditions. For Achillea millefolium and Hypericum perforatum, germination rates were significantly higher for invasive NZ provenances than for native German ones. Seeds from invasive populations of all three species displayed increased maximum germination at medium temperature conditions when compared to native populations, which indicates altered germination strategies in the invaded range. Changes in temporal development patterns were most conspicuous for invasive Hieracium pilosella and Hypericum perforatum populations. These findings imply that adaptation in germination patterns towards different climatic conditions in invasive populations has occurred. Our study emphasises the importance of the germination stage during plant invasion and its role in explaining range expansion of these species.

During plant species invasions, the role of adaptive processes is particularly of interest in later stages of range expansion when populations start invading habitats that initially have not been disposed to invasions. The dioecious tree Acer negundo, primarily invasive in Europe in wet habitats along riversides and in floodplains, has increased its abundance in dry habitats of industrial wasteland and ruderal sites during the last decades in Eastern Germany. We chose 21 invasive populations from wet and from dry habitats in the region of Halle, Saxony-Anhalt, Germany, to test whether Acer negundo exhibits a shift in life-history strategy during expansion into more stressful habitats. We analyzed variables of habitat quality (pH, soil moisture, exchangeable cations, total C and N content) and determined density, sex ratio and regeneration of the populations. In addition, we conducted germination experiments and greenhouse studies with seedlings in four different soil moisture environments. Local adaptation was studied in a reciprocal transplant experiment. We found habitat type differentiation with lower nutrient and water supply at the dry sites than at the moist sites and significant differences in the number of seedlings in the field. In accordance, seeds from moist habitats responded significantly faster to germination treatments. In the transplant experiment, leaf life span was significantly larger for populations originating from dry habitat types than from moist habitats. This observed shift in life history strategy during secondary invasion of A. negundo from traits of establishment and rapid growth towards traits connected with persistence might be counteracted by high gene flow among populations of the different habitat types. However, prolonged leaf life span at dry sites contributed remarkably to the invasion of less favourable habitats, and, thus, is a first indication of ongoing adaptation.

Forest ecosystems are an integral component of the global carbon cycle as they take up and release large amounts of C over short time periods (C flux) or accumulate it over longer time periods (C stock). However, there remains uncertainty about whether and in which direction C fluxes and in particular C stocks may differ between forests of high versus low species richness. Based on a comprehensive dataset derived from field-based measurements, we tested the effect of species richness (3-20 tree species) and stand age (22-116 years) on six compartments of above- and below-ground C stocks and four components of C fluxes in subtropical forests in southeast China. Across forest stands, total C stock was 149 ± 12 Mg ha

Aim Our aim was to test for changes in growth patterns of three clonally growing plant species (Achillea millefolium, Hieracium pilosella and Hypericum perforatum) between native and invaded regions. We addressed the hypotheses that with differing important life-history traits, invasive populations perform better than native populations, and that this expected better performance is linked to weakened trade-offs between individual growth and sexual and clonal reproduction. Location Germany and New Zealand. Methods We conducted field surveys for the three above-mentioned species in both native German and invasive New Zealand populations, and collected data at both population and individual levels. Results At the population level, the proportion of flowering plants, population size and population density were all higher in invasive populations. Similarly, at the individual level, the number of stolons per plant, stolon–biomass ratio and population crowdedness (local plant density in a specified area around a target plant) were significantly higher in New Zealand. Plant height did not differ between countries, and plant biomass was lower in New Zealand than in Germany for Achillea millefolium and Hypericum perforatum. These two species showed significant trade-offs between individual growth and sexual and clonal reproduction. Achillea millefolium exhibited a weakened trade-off in its invaded range, where the same proportion of flowering plants was sustained at much higher levels of population crowdedness than in its native range. Main conclusions The apparent invasion success of the three study species is generally due to better overall performance in their respective invaded ranges. In respect of both Achillea millefolium and Hypericum perforatum, this is driven primarily by increased vegetative reproduction. In contrast, Hieracium pilosella seems to benefit more from increased sexual reproduction in its invaded range. Shifts in trade-offs as a general trend seem to be of minor importance.

The extent and nature of biological invasions are mainly influenced by either the genotype of the invading species, the suitability of the new habitat or by genotype-habitat interactions expressed in adaptations to the new environment. The relevance of these factors was assessed for the invasive evergreen shrub Rhododendron ponticum. Habitat characteristics of soil, climate and community properties were analysed in six native populations in both Georgia (Caucasus) and Spain and in six invasive ones in Ireland. Growth variables of rhododendron individuals and seedling occurrences in the field served as response variables. We performed a reciprocal transplant experiment with rhododendron cuttings and determined survival of transplants in all countries. Due to low survival rates in Georgia and Spain, vegetative increase was only analysed for Ireland. The Irish sites benefited from significantly higher nutrient supply than the Spanish and Georgian sites. We found both strong positive correlations of nutrient supply and negative correlations of seasonal temperature amplitude with growth variables of shoots and seedling density. Origin, target site and interaction effects were significant in the survival of transplanted rhododendron individuals. The Irish site was more favorable for all genotypes, but the invasive genotypes did not perform better than the native ones. The total increase in shoot length of transplants in Ireland was highest in the Irish genotypes, which might suggest adaptation of the Irish populations to their new area. In conclusion, we found evidence for invasiveness of Irish Rhododendron ponticum populations, but only in the invaded habitat. Nonetheless, habitats in the new range also seem to be well suited to native Spanish populations, supporting the idea that invasibility of these new sites also contributes to rhododendron invasion success.

Subtropical and tropical forests are biodiversity hotspots, and untangling the spatial scaling of their diversity is fundamental for understanding global species richness and conserving biodiversity essential to human well-being. However, scale-dependent diversity distributions among coexisting taxa remain poorly understood for heterogeneous environments in biodiverse regions. We show that diversity relations among 43 taxa—including plants, arthropods and microorganisms—in a mountainous subtropical forest are highly nonlinear across spatial scales. Taxon-specific differences in β-diversity cause under- or overestimation of overall diversity by up to 50% when using surrogate taxa such as plants. Similar relationships may apply to half of all (sub)tropical forests—including major biodiversity hotspots—where high environmental heterogeneity causes high biodiversity and species turnover. Our study highlights that our general understanding of biodiversity patterns has to be improved—and that much larger areas will be required than in better-studied lowland forests—to reliably estimate biodiversity distributions and devise conservation strategies for the world's biodiverse regions., Measurements of biodiversity may differ according to the extent of area sampled, although how this changes across taxa is not well understood. Here, Schuldt et al. find that the diversity of plants, arthropods and microorganisms in a heterogeneous subtropical forest is highly nonlinear across spatial scales.

Previous studies have shown that the invasive spread of Rhododendron ponticum in the British Isles is influenced by the more favourable environmental conditions in the new territory than in the species’ home range. In this study, we asked whether the species’ invasion success might also involve a genotypic background for higher growth and germination rates in invasive populations. We tested the hypotheses that invasive populations have higher absolute germination rates, germinate faster and exhibit higher growth rates. We present data from greenhouse and climate chamber experiments with seed material and Rhododendron cuttings from six populations each of native Georgian, native Spanish and invasive Irish populations subjected to different temperature environments. There were no differences in the maximum germination rate and optimum germination temperature between native and invasive origins. We found significant differences in germination velocity with the Irish seeds responding most rapidly to all germination treatments. Accordingly, in the growth experiment the invasive Irish origins had the highest relative growth rates in all environments tested. Our results provide evidence for a genetic shift in invasive populations towards an increased investment in growth and towards a faster germination rate. Both traits would contribute to explaining this species’ range expansion. The underlying evolutionary mechanisms for this shift are discussed, including the possibility of hybridisation or of an ecological release from hitherto experienced constraints in the native area.

Summary The objective of this paper is to identify the factors that promote the invasiveness of Rhododendron ponticum L. by the means of comparative field observations. Rhododendron ponticum (Ericaceae) is an evergreen shrub with a natural distribution in the Mediterranean and Black Sea area and was introduced to the British Isles in 1763. Thenceforward, the species has been considered as a major threat to natural ecosystems there. We compared native and invasive populations of Rhododendron ponticum with respect to trait patterns that are associated with invasiveness. Six populations each in the natural part of its range, in Georgia (Caucasus) and Spain as well as six invasive ones in Ireland were examined with regard to biometrical, morphological and ecological characteristics. Invasive Irish populations differed from non-invasive ones mainly in growth patterns and showed much higher rates of annual shoot growth in the field and higher rates of seedling recruitment. In contrast, native Spanish populations were discriminated by their shape and age; whereas native Georgian rhododendron, above all, showed distinctive leaf characteristics. In general, the relationship between Irish and Spanish populations was closer than to the Georgian ones. Our results suggest that both genotype and environment account for the trait pattern found in Irish populations. Differences in genetically fixed traits had a greater effect in morphological differences to Georgian provenances. In contrast, the invasive Irish rhododendron were favoured by a more benign environment than the Spanish populations.