Specialist nectar-yeasts decline with urbanization in Berlin

Nectar yeasts are common inhabitants of insect-pollinated flowers but factors determining their distribution are not well understood. We studied the influence of host identity, environmental factors related to pollution/urbanization, and the distance to a target beehive on local distribution of nectar yeasts within Robinia pseudoacacia L. and Tilia tomentosa Moench in Berlin, Germany. Nectar samples of six individuals per species were collected at seven sites in a 2 km radius from each target beehive and plated on YM-Agar to visualise the different morphotypes, which were then identified by sequencing a section of the 26S rDNA gene. Multivariate linear models were used to analyze the effects of all investigated factors on yeast occurrence per tree. Yeast distribution was mainly driven by host identity. The influence of the environmental factors (NO2, height of construction, soil sealing) strongly depended on the radius around the tree, similar to the distance of the sampled beehive. Incidence of specialist nectar-borne yeast species decreased with increasing pollution/urbanization index. Given that specialist yeast species gave way to generalist yeasts that have a reduced dependency on pollinators for between- flower dispersal, our results indicate that increased urbanization may restrict the movement of nectar-specialized yeasts, via limitations of pollinator foraging behavior

Indigenous Arbuscular Mycorrhizal Fungal Assemblages Protect Grassland Host Plants from Pathogens

Plant roots can establish associations with neutral, beneficial and pathogenic groups of soil organisms. Although it has been recognized from the study of individual isolates that these associations are individually important for plant growth, little is known about interactions of whole assemblages of beneficial and pathogenic microorganisms associating with plants

Interaktionen zwischen Wurzelpilzen und ihren Wirtspflanzen in einem Trockenrasen

This doctoral thesis presents the study of potential determinants for coexistence of root associated fungi in a dry grassland habitat. In Chapter 2 we used 454 pyrosequencing of the fungal specific ITS region to study root- associated fungi in 25 plant species within the family of Asteraceae and tested the influence of three main predictors; host plant phylogeny, spatial effects and a gradient in soil type on community composition of root associated fungi. Fungal diversity in the investigated roots was high with 156,816 sequences clustered in 1100 operational taxonomic units (OTUs). In variance partitioning we found all three predictors explaining fungal community composition to a certain percentage. Host plant phylogeny was the most important predictor, explaining 20 % variance, followed by space with 9 % and soil type with only 1 % of explained variance. Null model analysis suggested that fungal taxa co-occurred less often than expected by chance, which demonstrates spatial segregation and indicates negative interactions within fungal communities. With this study, we demonstrated, for the first time in a natural setting, that biotic interactions among fungi and with their plant hosts can be more important than the present edaphic properties and that host plant phylogeny can constrain these interactions. In Chapter 3 and 4 we analyzed the importance of AM fungal diversity for protecting host plants against pathogen attack by reviewing the different mechanism how pathogen protection could arise when considering a divers community of AM fungi. Furthermore, we directly tested the effects of an local AM fungal and a local community of saprobic/pathogenic fungi on two different host plants growing in sterile soil, all from the “Oderhänge Mallnow” in greenhouse experiment. In a literature study we found evidence that considering AM diversity might be important in terms of the different mechanism how pathogen protection could arise. In the greenhouse experiment in Chapter 4, the AM fungal community compensated the negative influence of the community of saprobic/pathogenic fungi on the growth of their host plant. We could further show, that root colonization of non-AM fungi was significantly reduced in the AM fungal treatment compared to the non-AM fungal treatment. These results indicate that interactions between assemblages of beneficial and pathogenic microorganisms can influence the growth of host plants, but that the magnitude of these effects might be plant species-specific.Im Rahmen dieser Doktorarbeit wurden zum Einen verschiedene Faktoren untersucht, die die Zusammensetzung von Pilzgemeinschaften im Wurzelraum beeinflussen und somit auch deren Koexistenz ermöglichen. In Kapitel 2 pyrosequenzierten wir die pilzspezifische ITS-Region von Pilzen aus dem Wurzelraum von 25 verschiedenen Arten aus der Familie der Asteraceae und testeten den Einfluss von drei Hauptfaktoren; Pflanzenphylogenie, räumlicher Effekt und einem Gradient im Bodentyp auf die Zusammensetzung der Pilzgemeinschaften. In den untersuchten Wurzel fanden wir eine sehr hohe Pilzdiversität, 156,816 Sequenzen konnten 1100 sogenannten operational taxonomic units (OTUs) zugeordnet werden. Durch Partitionierung der Varianz zwischen den verschiedenen Prädiktoren konnte gezeigt werden, dass alle drei einen wichtigen Beitrag zur Erklärung der Zusammensetzung der Pilzgemeinschaften in den verschiedenen Pflanzenarten leisten. Die Pflanzenphylogenie stellte dabei mit 20 % den wichtigsten erklärenden Faktor dar, gefolgt von räumlichen Effekten mit 9 % und Bodentyp mit 1 % erklärter Varianz. Die Ergebnisse einer durchgeführten Null model Analyse zeigten, dass die Pilze weniger oft miteinander assoziert waren als durch Zufall erwartet werden würde. Das gefundene Muster gibt Hinweise auf eine räumliche Trennung der verschiedenen Pilzarten und deutet somit auf negative Interaktionen innerhalb der Pilzgemeinschaften hin. Mit dieser Studie konnten wir zum ersten Mal in einer Freilandstudie zeigen, dass die biotischen Interaktionen zwischen Pilzen und ihren Wirtspflanzen wichtiger sein können als edaphische Eigenschaften des Untersuchungsgebietes. Vorallem die Phylogenie der Wirtspflanzen spielt eine zentrale Rolle für die Zusammensetzung der Pilzgemeinschaften. In Kapitel 3 und 4 wurde analysiert, wie wichtig die Diversität von arbuskulären Mykorrhizapilzen (im folgenden nur Mykorrhizapilze genannt) ist, um ihre Wirtspflanzen vor Pathogenen zu schützen. Dafür wurde zunächst eine Literaturstudie durchgeführt. In dieser wurde kritisch hinterfragt, was passieren würde, wenn man anstelle von einem Mykorrhizapilz, eine ganze Gemeinschaft hinsichtlich der unterschiedlichen Mechanismen des Mykorrhizapilz induzierten Pathogenschutzes betrachten würde. In einem Gewächshausexperiment testen wir den direkten Einfluss einer lokalen Mykorrhizapilzgemeinschaft und einer saprobisch/pathogenen Pilzgemeinschaft auf das Wachstum von zwei verschiedenen Wirtspflanzen aus dem selben Herkunftsgebiet, “Oderhänge Mallnow” in sterilem Boden. Durch die Literaturstudie fanden wir Hinweise, dass die Diversität von Mykorrhizapilzen eine wichtige Rolle für die unterschiedlichen Mechanismen des Mykorrhizapilz induzierten Schutz vor Pathogenen spielt und das man sie daher zukünftig mit betrachten sollte. In unserem Gewächshausexperiment konnten die negativen Effekte der saprobisch/pathogenen Pilzgemeinschaft auf das Wachstum der Wirtspflanzen durch die Anwesenheit von Mykorrhizapilzen kompensiert werden. Die Wurzelkolonisation mit nicht-Mykorrhizapilzen war in Anwesenheit von Mykorrhizapilzen signifikant reduziert im Vergleich zu der Behandlung ohne Mykorrhizapilzen. Die gefundenen Ergebnisse deuten daraufhin, dass Interaktionen zwischen Gemeinschaften aus nützlichen und pathogenen Mikroorganismen das Pflanzenwachstum beeinflussen können. Die Größe dieses Effekts wird aber stark von der jeweiligen Pflanzenart abhängen

Plant pathogen protection by arbuscular mycorrhizas : a role for fungal diversity?

Arbuscular mycorrhizal (AM) fungi can confer protection to host plants against some root pathogens, and several mechanisms for these phenomena have been proposed. If AM fungal taxa vary in the ways that they limit the negative effects of pathogens on host plants, additive and/or synergistic interactions among members of diverse AM fungal assemblages and communities may result in a greater pathogen protection than is currently predicted. However, in a review of the literature on interactions between AM and pathogenic fungi, we found few examples that compared the effectiveness of single- and multi-species AM fungal assemblages. Here, we briefly recount the generally recognized mechanisms of pathogen protection by AM fungi and present evidence, where appropriate, for functional diversity among AM fungal taxa with regard to these mechanisms. We propose that functional complementarity of AM fungal taxa in interactions with pathogens could mimic, or even be the cause of, previously observed relationships between AM fungal diversity and plant productivity

Sebacinales, but not total root associated fungal communities, are affected by land-use intensity

There is great scientific and societal interest in the ecology and functioning of the immense diversity of microorganisms associated with plant roots (Mendes et al., 2011; Porras-Alfaro & Bayman, 2011). In particular, research into plant–soil interactions has unveiled a pivotal role of root-associated fungi in influencing plant growth and community structure (van der Heijden et al., 2008; Schnitzer et al., 2011; Wagg et al., 2014). So far, knowledge on the identity of fungi associated with plant roots, and forces structuring the communities they form, is still scarce. This extends to agricultural systems, where communities of belowground fungi are a largely unknown but potentially important driver of plant productivity akin to natural systems, and display a considerably high diversity (Orgiazzi et al., 2012). So far, most research has focused on plant pathogens (e.g.Xu et al., 2012) and on arbuscularmycorrhizal fungi (AMF). AMF are an important group of plant symbionts, and we know that these generally increase in diversity in response to reduced agricultural management intensity (Oehl et al., 2004; Verbruggen et al., 2012). For other groups of root endophytes little is known about responses to agricultural management, even though they may be of high ecological significance (Rodriguez et al., 2009). Apart from potential effects on plants, there is great interest in identifying taxa that may serve as bio-markers for sustainable agricultural practices, as has recently been explored for AMF by Jansa et al. (2014). So far this has not been attempted for other root inhabiting fungi, likely because it is unknown whether root-colonizing fungi are sensitive to changes in land-use intensity. In this study we have sampled wheat roots in agricultural fields that were either managed conventionally (seven sites) or had been converted to organic farming recently (2–4 yr; eight sites), moderately long ago (10– 14 yr; six sites), or had been subjected to long-term organic farming (16–33 yr; eight sites). We analyzed the fungal community in roots using next generation sequencing of fungi and ask how different biotic and abiotic aspects drive fungal communities inhabiting wheat roots

Determinants of root-associated fungal communities within Asteraceae in a semi-arid grassland

While plant-fungal interactions are important determinants of plant community assembly and ecosystem functioning, the processes underlying fungal community composition are poorly understood. Here, we studied for the first time the root-associated eumycotan communities in a set of co-occurring plant species of varying relatedness in a species-rich, semi-arid grassland in Germany. The study system provides an opportunity to evaluate the importance of host plants and gradients in soil type and landscape structure as drivers of fungal community structure on a relevant spatial scale. We used 454 pyrosequencing of the fungal internal transcribed spacer region to analyse root-associated eumycotan communities of 25 species within the Asteraceae, which were sampled at different locations within a soil type gradient. We partitioned the variance accounted for by three predictors (host plant phylogeny, spatial distribution and soil type) to quantify their relative roles in determining fungal community composition and used null model analyses to determine whether community composition was influenced by biotic interactions among the fungi. We found a high fungal diversity (156 816 sequences clustered in 1100 operational taxonomic units (OTUs)). Most OTUs belonged to the phylum Ascomycota (35.8%); the most abundant phylotype best-matched Phialophora mustea. Basidiomycota were represented by 18.3%, with Sebacina as most abundant genus. The three predictors explained 30% of variation in the community structure of root-associated fungi, with host plant phylogeny being the most important variance component. Null model analysis suggested that many fungal taxa co-occurred less often than expected by chance, which demonstrates spatial segregation and indicates that negative interactions may prevail in the assembly of fungal communities. Synthesis. The results show that the phylogenetic relationship of host plants is the most important predictor of root-associated fungal community assembly, indicating that fungal colonization of host plants might be facilitated by certain plant traits that may be shared among closely related plant species

Results from the Multivariate analysis of variance for <i>Galium verum</i> for the response variables total biomass, fine root length, coarse root length and root diameter.

<p>(* = p<0.05; ** p<0.001; *** = p<0.0001, myco = AM fungal treatment, patho = Pathogen treatment, myco∶patho = Interaction of AM fungal and pathogen treatment).</p

Percent root colonisation by AM fungal hyphae and non AM fungal hyphae in the roots of <i>Galium verum</i> and <i>Hieracium umbellatum</i> in the four treatments (Co = Control, Pa = Pathogen community, AMF = AM fungal community, AMF + Pa).

<p>Error bars represent the standard error of the mean.</p

Results from analyses of variance on different response variables for <i>Galium verum</i>.

<p>(* = p<0.05; ** p<0.001; *** = p<0.0001, myco = AM fungal treatment, patho = Pathogen treatment, myco∶patho = Interaction of AM fungal and pathogen treatment).</p

Effect of indigenous soil microbial treatment on the total biomass of <i>Galium verum</i> and <i>Hieracium umbellatum</i> in the four treatments (Co = Control, Pa = Pathogen community, AMF = AM fungal community, AMF + Pa).

<p>Error bars represent the standard error of the mean.</p