Using a Multi-Trait Approach to Manipulate Plant Functional Diversity in a Biodiversity-Ecosystem Function Experiment

A frequent pattern emerging from biodiversity-ecosystem function studies is that functional group richness enhances ecosystem functions such as primary productivity. However, the manipulation of functional group richness goes along with major disadvantages like the transformation of functional trait data into categories or the exclusion of functional differences between organisms in the same group. In a mesocosm study we manipulated plant functional diversity based on the multi-trait Functional Diversity (FD)-approach of Petchey and Gaston by using database data of seven functional traits and information on the origin of the species in terms of being native or exotic. Along a gradient ranging from low to high FD we planted 40 randomly selected eight-species mixtures under controlled conditions. We found a significant positive linear correlation of FD with aboveground productivity and a negative correlation with invasibility of the plant communities. Based on community-weighted mean calculations for each functional trait, we figured out that the traits N-fixation and species origin, i.e. being native or exotic, played the most important role for community productivity. Our results suggest that the identification of the impact of functional trait diversity and the relative contributions of relevant traits is essential for a mechanistic understanding of the role of biodiversity for ecosystem functions such as aboveground biomass production and resistance against invasion

Greenhouse- and Field-Measured Plant-Soil Feedbacks Are Not Correlated

Plant-soil feedbacks (PSFs) have become a commonly invoked mechanism of plant coexistence and abundance. Yet, most PSF experiments have been performed in greenhouse conditions. To test whether or not greenhouse-measured PSF values are of similar magnitude and positively correlated with field-measured PSFs, we compared PSF values from five different studies that measured PSF values in both greenhouse and field conditions. For 36 plant species, greenhouse-measured PSF values were larger than and not positively correlated with field-measured PSF values. Similarly, these 36 species produced 269 soil-specific PSF values, and for each site there was no positive correlation between these greenhouse- and field-measured PSF values. While PSFs were observed in both greenhouse and field conditions, results provided no support at the soil, site or species level that a positive correlation exists between greenhouse- and field-measured PSF. Further, greenhouse-measured PSF appear to overestimate field-measured PSF. Although from five studies, results strongly suggest that field experiments are needed to understand the role of PSFs in plant communities in natural settings

Biodiversity maintains soil multifunctionality and soil organic carbon in novel urban ecosystems

1. Biodiversity in urban ecosystems has the potential to increase ecosystem functions and support a suite of services valued by society, including services provided by soils. Specifically, the sequestration of carbon in soils has often been advocated as a solution to mitigate the steady increase in CO2 concentration in the atmosphere as a key driver of climate change. However, urban ecosystems are also characterized by an often high level of ecological novelty due to profound human‐mediated changes, such as the presence of high numbers of non‐native species, impervious surfaces or other disturbances. Yet it is poorly understood whether and how biodiversity affects ecosystem functioning and services of urban soils under these novel conditions. 2. In this study, we assessed the influence of above‐ and below‐ground diversity, as well as urbanization and plant invasions, on multifunctionality and organic carbon stocks of soils in non‐manipulated grasslands along an urbanization gradient in Berlin, Germany. We focused on plant diversity (measured as species richness and functional trait diversity) and, in addition, on soil organism diversity as a potential mediator for the relationship of plant species diversity and ecosystem functioning. 3. Our results showed positive effects of plant diversity on soil multifunctionality and soil organic carbon stocks along the entire gradient. Structural equation models revealed that plant diversity enhanced soil multifunctionality and soil organic carbon by increasing the diversity of below‐ground organisms. These positive effects of plant diversity on soil multifunctionality and soil fauna were not restricted to native plant species only, but were also exerted by non‐native species, although to a lesser degree. 4. Synthesis. We conclude that enhancing diversity in plants and soil fauna of urban grasslands can increase the multifunctionality of urban soils and also add to their often underestimated but very valuable role in mitigating effects of climate change

A multidimensional framework for measuring biotic novelty: How novel is a community?

Anthropogenic changes in climate, land use, and disturbance regimes, as well as introductions of non‐native species can lead to the transformation of many ecosystems. The resulting novel ecosystems are usually characterized by species assemblages that have not occurred previously in a given area. Quantifying the ecological novelty of communities (i.e., biotic novelty) would enhance the understanding of environmental change. However, quantification remains challenging since current novelty metrics, such as the number and/or proportion of non‐native species in a community, fall short of considering both functional and evolutionary aspects of biotic novelty. Here, we propose the Biotic Novelty Index (BNI), an intuitive and flexible multidimensional measure that combines (a) functional differences between native and non‐native introduced species with (b) temporal dynamics of species introductions. We show that the BNI is an additive partition of Rao's quadratic entropy, capturing the novel interaction component of the community's functional diversity. Simulations show that the index varies predictably with the relative amount of functional novelty added by recently arrived species, and they illustrate the need to provide an additional standardized version of the index. We present a detailed R code and two applications of the BNI by (a) measuring changes of biotic novelty of dry grassland plant communities along an urbanization gradient in a metropolitan region and (b) determining the biotic novelty of plant species assemblages at a national scale. The results illustrate the applicability of the index across scales and its flexibility in the use of data of different quality. Both case studies revealed strong connections between biotic novelty and increasing urbanization, a measure of abiotic novelty. We conclude that the BNI framework may help building a basis for better understanding the ecological and evolutionary consequences of global change

Towards an integrative, eco-evolutionary understanding of ecological novelty: studying and communicating interlinked effects of global change

Global change has complex eco-evolutionary consequences for organisms and ecosystems, but related concepts (e.g., novel ecosystems) do not cover their full range. Here we propose an umbrella concept of “ecological novelty” comprising (1) a site-specific and (2) an organism-centered, eco-evolutionary perspective. Under this umbrella, complementary options for studying and communicating effects of global change on organisms, ecosystems, and landscapes can be included in a toolbox. This allows researchers to address ecological novelty from different perspectives, e.g., by defining it based on (a) categorical or continuous measures, (b) reference conditions related to sites or organisms, and (c) types of human activities. We suggest striving for a descriptive, non-normative usage of the term “ecological novelty” in science. Normative evaluations and decisions about conservation policies or management are important, but require additional societal processes and engagement with multiple stakeholders

Interaktionen mit Bodenorganismen, funktioneller Diversität und globalem Wandel

Human activities are the cause of the spread and establishment of many species around the world. The consequences are of various kinds, but species invasions are generally recognized as a major environmental problem, which can change ecosystem functioning and influence biodiversity on local and global scales. Due to their high proportion of exotic species, urban grasslands have a great potential to study the impacts of species invasions in a plant community context rather than focusing on single species. The main aims of this thesis were to elucidate (1) the ecological impacts of exotic plant species in urban grassland communities and (2) the mechanisms why these species become dominant in communities where they are not native. In a plant-soil feedback experiment (Chapter 2), I investigated whether plant-soil feedback effects facilitate the invasion of an exotic plant (Solidago canadensis) in its new range. I hypothesized that feedback effects from the soil do not only affect plant growth but also plant interactions with organisms at higher trophic levels (i.e. shoot herbivores), which might be an important mechanism affecting plant community composition in the field. Results showed that neither growth of S. canadensis nor its interaction with herbivores was affected by plant-soil feedback effects. However, I found that a native competitor (Tanacetum vulgare) performed better with soil biota conditioned by S. canadensis. This is indicative for an indirect facilitative effect from an exotic plant species on a native plant species and was most likely mediated by a group of root- colonizing fungi, the dark-septate endophytes, whose abundance seems to be suppressed in S. canadensis soils. In the second experiment (Chapter 3), I investigated in a mesocosm study the fundamental question whether the functional trait diversity of a plant community consisting of native and exotic plant species is positively related to ecosystem functions such as community productivity and resistance against invasion. As a novel aspect to the functional trait concept, I treated the species’ attribute of being native or exotic as a functional trait and used it alongside morphological and resource capture related traits to predict ecosystem functions from trait diversity. Additionally, I performed a trait analysis to determine the relative importance of each trait in explaining the relationship between functional trait diversity and productivity. I found a significant positive linear correlation of functional trait diversity with aboveground productivity and a negative correlation with invasibility of the plant communities. Based on community-weighted mean calculations for each functional trait, I figured out that the traits N-fixation and the species origin, i.e. being native or exotic, played the most important role for community productivity. These results suggest that the identification of the impact of functional trait diversity and the relative contributions of relevant traits is essential for a mechanistic understanding of the role of biodiversity for ecosystem functions such as aboveground biomass production and resistance against invasion. The fourth experiment (Chapter 4) was closely connected to the experiment from the previous chapter: Here I investigated whether the plant functional trait diversity affects the abundance and diversity of arthropods living on these plants. In this context the attribute of a plant species being native or exotic was considered as a functional trait as well. First, I found that the abundance of specialist aphids of the focus plant species Cirsium arvense, as well as the abundances of mutualistic aphid-tending ants and predatory ladybird beetles were negatively related to plant functional trait diversity. Second, and in contrast to the first result, I found that the total abundances and species richnesses of herbivores and predators present in the mesocosms were positively related to functional diversity. The diversity effect on abundances of higher trophic levels dampened from herbivores to predators. Based on community-weighted mean calculations for each functional trait, I figured out that traits related to plant quality and the plant species origin, i.e. being native or exotic, played the most important role for predicting arthropod abundance and species richness. In my final experiment (Chapter 5), I focused on abiotic stresses. In a mesocosm experiment, I investigated whether individual elements of global change interact synergistically together on the shaping of plant communities. I altered the abiotic conditions temperature and soil compaction and focused on the differential responses of exotic and native plant species within that community. Furthermore, I investigated impacts of both factors on diversity, evenness, and functional trait diversity of the plant community. The results showed that elevated temperature and soil compaction had a negative and positive effect on community productivity, respectively, while no interactions between the environmental factors were found. The responses were driven by the group of exotic plant species, while the group of native plant species remained unaffected. Species diversity, evenness, and functional trait diversity were positively affected by elevated temperature but not by soil compaction. I suggest that this was likely due to a reduction of competition in the community. These results demonstrate that global change factors can have independent and contrasting impacts on the composition and biodiversity of a grassland community.Menschliche Aktivitäten führen dazu, dass viele Arten sich in Gebieten ausbreiten und etablieren können, wo sie natürlicherweise nicht heimisch sind. Die Auswirkungen dieser biologischen Invasionen sind vielgestaltig; im Allgemeinen werden sie jedoch als ein globales Problem betrachtet, da sie die Funktionsweise von Ökosystemen verändern und eine Gefahr für die Biodiversität darstellen können. Pflanzengemeinschaften in urban-industriellen Lebensräumen zeichnen sich durch einen vergleichsweise sehr hohen Anteil von gebietsfremden Pflanzenarten aus. Dadurch eignen sich diese Gemeinschaften besonders gut, um die Auswirkungen von gebietsfremden Pflanzenarten auf fremde Ökosysteme, sowie die Mechanismen, die zu ihrer Etablierung geführt haben, zu erforschen. In einem sogenannten plant-soil feedback-Experiment (Kapitel 2) wurde untersucht, ob feedback-Effekte zwischen Pflanze und Bodenorganismen das Wachstum einer gebietsfremden Pflanzenart (Solidago canadensis) in ihrem neuen Lebensraum fördert. Es wurde vermutet, dass diese feedback-Mechanismen nicht nur das Wachstum der Pflanze selbst, sondern auch ihre oberirdischen Interaktionen mit Herbivoren beeinflussen. Die Ergebnisse dieses Experiments haben gezeigt, dass weder das Pflanzenwachstum noch die Herbivoren-Interaktion von S. canadensis durch plant-soil feedback-Mechanismen beeinflusst wurden. Es wurde jedoch auch gezeigt, dass eine koexistierende einheimische Pflanzenart (Tanacetum vulgare) durch die von S. canadensis ausgelösten Veränderungen im Boden profitierte. Vermutlich unterdrückt S. canadensis eine Gruppe von wurzelbesiedelnden Endophyten, die sogenannten dunkel septierten Endophyten, was dazu führt, dass die einheimische Pflanzenart T. vulgare besser in Böden wächst, die von S. canadensis beeinflusst wurden als in ihren eigenen Böden. Im zweiten Experiment (Kapitel 3) wurde in einem Mesokosmos-Versuch untersucht, ob die funktionelle Diversität einer Pflanzengemeinschaft bestehend aus einheimischen und gebietsfremden Arten, die Produktivität der Gemeinschaft, sowie deren Resistenz gegenüber weiteren Invasionen gebietsfremder Arten beeinflusst. Der floristische Status einer Pflanzenart, welcher angibt ob sie gebietsfremd oder heimisch ist, wurde neben morphologischen und physiologischen funktionellen Merkmalen benutzt, um den Zusammenhang zwischen funktioneller Merkmalsdiversität und den beiden Ökosystemfunktionen Produktivität und Resistenz gegenüber Invasionen zu erklären. Die Ergebnisse dieses Experiments haben gezeigt, dass die Produktivität dieser Pflanzengemeinschaft positiv mit der funktionellen Merkmalsdiversität und negativ mit der Invasion einer weiteren gebietsfremden Art korreliert. Des Weiteren wurde anhand einer Merkmalsanalyse gezeigt, dass das funktionelle Merkmal Stickstofffixierung und der floristische Status einer Art die beiden ausschlaggebendsten Merkmale innerhalb der Pflanzengemeinschaft waren, um deren Produktivität zu erklären. Die Zielstellung des dritten Experiments (Kapitel 4) war eng mit derjenigen des vorherigen Experiments verknüpft: Es wurde in einem Mesokosmos-Versuch untersucht, ob die funktionelle Merkmalsdiversität einer Pflanzengemeinschaft bestehend aus einheimischen und gebietsfremden Arten, die Abundanz und Diversität von Arthropoden, die in dieser Gemeinschaft leben, beeinflusst. Die Ergebnisse haben gezeigt, dass die steigende funktionelle Merkmalsdiversität der Pflanzengemeinschaft die Abundanz einer spezialistischen Blattlausart, sowie die Abundanzen ihrer Symbiosepartner (Ameisen) und Antagonisten (Marienkäfer) negativ beeinflusst. Im Gegensatz dazu wurde gezeigt, dass die funktionelle Pflanzendiversität sich positiv auf die Artenanzahlen und Abundanzen aller Herbivoren und Prädatoren in der Gesellschaft auswirkte. Das Merkmal Stickstofffixierung und der floristische Status der Pflanzenarten hatten auf diesen Zusammenhang den größten Einfluss. Im letzten Experiment (Kapitel 5) wurde in einem Mesokosmos-Versuch untersucht, inwieweit sich die abiotischen Stressfaktoren Bodenverdichtung und Temperaturerhöhung auf die Produktivität und die Zusammensetzung dieser Pflanzengemeinschaft auswirken. Hinsichtlich der Produktivität hatte die Temperaturerhöhung einen negativen, und die Verdichtung des Bodens einen positiven Effekt auf die Gemeinschaft. Die Effekte wurden größtenteils durch die gebietsfremden Pflanzenarten innerhalb der Gemeinschaft hervorgerufen, da diese am stärksten auf die beiden Stressfaktoren reagierten. Der Rückgang der gebietsfremden Pflanzenarten unter erhöhten Temperaturbedingungen wirkte sich positiv auf die Diversität, Evenness und funktionelle Diversität der Gemeinschaft aus. Wahrscheinlich wurde dies durch einen Rückgang der interspezifischen Konkurrenz zwischen den Pflanzenarten hervorgerufen. Diese Ergebnisse verdeutlichen, dass verschiedene abiotische Stressfaktoren unabhängige und gegensätzliche Auswirkungen auf die Zusammensetzung und Biodiversität einer Gemeinschaft haben können

Bukowski_Data

Raw data (traits, biomass) and calculated feedback for biomass

Data from: The strength of negative plant-soil feedback increases from the intraspecific to the interspecific and the functional group level

1. One of the processes that may play a key role in plant species coexistence and ecosystem functioning is plant-soil feedback, the effect of plants on associated soil communities and the resulting feedback on plant performance. Plant-soil feedback at the interspecific level (comparing growth on own soil with growth on soil from different species) has been studied extensively, while plant-soil feedback at the intraspecific level (comparing growth on own soil with growth on soil from different accessions within a species) has only recently gained attention. Very few studies have investigated the direction and strength of feedback among different taxonomic levels, and initial results have been inconclusive, discussing phylogeny and morphology as possible determinants. 2. To test our hypotheses that the strength of negative feedback on plant performance increases with increasing taxonomic level and that this relationship is explained by morphological similarities, we conducted a greenhouse experiment using species assigned to three taxonomic levels (intraspecific, interspecific and functional group level). We measured certain fitness-related aboveground traits and used them along literature-derived traits to determine the influence of morphological similarities on the strength and direction of the feedback. 3. We found that the average strength of negative feedback increased from the intraspecific over the interspecific to the functional group level. However, individual accessions and species differed in the direction and strength of the feedback. None of our results could be explained by morphological dissimilarities or individual traits. 4. Synthesis. Our results indicate that negative plant-soil feedback is stronger if the involved plants belong to more distantly related species. We conclude that the taxonomic level is an important factor in the maintenance of plant coexistence with plant-soil feedback as a potential stabilizing mechanism and should be addressed explicitly in coexistence research, while the traits considered here seem to play a minor role

Using a Multi-Trait Approach to Manipulate Plant Functional Diversity in a Biodiversity-Ecosystem Function Experiment

<div><p>A frequent pattern emerging from biodiversity-ecosystem function studies is that functional group richness enhances ecosystem functions such as primary productivity. However, the manipulation of functional group richness goes along with major disadvantages like the transformation of functional trait data into categories or the exclusion of functional differences between organisms in the same group. In a mesocosm study we manipulated plant functional diversity based on the multi-trait Functional Diversity (FD)-approach of Petchey and Gaston by using database data of seven functional traits and information on the origin of the species in terms of being native or exotic. Along a gradient ranging from low to high FD we planted 40 randomly selected eight-species mixtures under controlled conditions. We found a significant positive linear correlation of FD with aboveground productivity and a negative correlation with invasibility of the plant communities. Based on community-weighted mean calculations for each functional trait, we figured out that the traits N-fixation and species origin, i.e. being native or exotic, played the most important role for community productivity. Our results suggest that the identification of the impact of functional trait diversity and the relative contributions of relevant traits is essential for a mechanistic understanding of the role of biodiversity for ecosystem functions such as aboveground biomass production and resistance against invasion.</p></div

Standardized principal components analysis (PC1 vs. PC2) of the four most important traits.

<p>Plotted are the community weighted means (CWM) of the trait values of the functional traits N-fixation (NF), floristic status, specific leaf area (SLA) and arbuscular mycorrhizal fungi (AMF). CWMs of trait values were calculated for each of the 40 mixtures (plotted numbers) based on species biomass proportions.</p