Interaktionen zwischen Pflanzen und Bodenlebewelt : Pflanzengesundheit und Ökosystemfunktionen

Die Studie behandelt das Thema anhand von zwei aktuellen Beispielen: (i) der Wirksicherheit induzierter Resistenz in Gerste und (ii) den Auswirkungen atmosphärischer CO2-Anreicherung im Grünland. Die Wirksicherheit induzierter Resistenz ist zur Zeit noch unbefriedigend. Da diese Resistenz über eine Veränderung des pflanzlichen Metabolismus verläuft, hat sie möglicherweise Folgen für die pflanzenbasierenden Nahrungsnetze und wird andererseits von der standortspezifischen Zusammensetzung der Bodenlebewelt und deren Auswirkungen auf die Pflanze beeinflusst. In einem Feldversuch wurde daher untersucht, ob die Anwendung des chemischen Resistenzinduktors Bion® Einfluss auf die Bodenlebewelt hat. In zwei Gewächshausversuchen wurde getestet, ob Veränderungen der Bodenlebewelt die Resistenzinduktion und/oder deren Wirksamkeit beeinflussen. Im Feldversuch kam es zu einer starken Erhöhung des Nematodenbefalls in Bion®-behandelter Gerste aber nicht in Brachpflanzen. Mikrobielle Parameter und freilebende Nematoden wurden durch die Bion®-Anwendung nicht beeinflusst. Die Gewächshausversuche ergaben eine Modifizierung der Bion®-Wirksamkeit sowohl durch Mykorrhiza-Pilze als auch durch pflanzenparasitäre Nematoden. Der Effekt der beiden Organismen war sehr ähnlich und jeweils abhängig vom Grad der Wurzelinfektion. Bei starker Wurzelinfektion entwickelten sich auf Bion®-behandelten Pflanzen mehr Mehltaupusteln als auf unbehandelten Pflanzen. Die Induktion des Resistenz-Signalweges wurde durch die beiden Organismen nicht beeinflusst. Bei einmaliger Anwendung von Bion® sind somit feedback-Effekte über wurzelassoziierte nicht aber über freilebende Bodenorganismen zu erwarten. Das Auftreten dieser Effekte ist abhängig von der behandelten Pflanzenspezies und setzt die Überschreitung bestimmter Schwellenwerte der Wurzelbesiedlung voraus. Die Beeinflussung des Signalweges erfolgt ’downstream’ von der Resistenzinduktion durch den chemischen Induktor. Als Folge kann sich die Bion®-Wirkung von krankheitshemmend zu krankheitsfördernd umkehren. Die feedback-Effekte kommen daher als Ursache für die unbefriedigende Wirksicherheit der induzierten Resistenz in Frage. Die Reaktion der Bodenlebewelt auf die CO2-Anreicherung der Atmosphäre ist von besonderer Bedeutung, da sie die Senken- bzw. Quellen-Eigenschaften des Ökosystems für Kohlenstoff beeinflusst. Vor allem ausgedehnte natürliche und semi-natürliche Systeme wie Wälder und Grünländer tragen zum globalen Kohlenstoffhaushalt bei. Es gibt mittlerweile Hinweise darauf, dass die Effekte steigender CO2-Konzentration auf Bodenprozesse bzw. terrestrische Ökosysteme nicht linear sind, über die Auswirkungen in der nahen Zukunft ist bisher aber nichts bekannt. In einem dreijährigen Freilandversuch wurde daher die atmosphärische CO2-Konzentration über einem extensiv genutzten Grünland der gemäßigten Breiten um 20% erhöht und die Reaktion der Bodenlebewelt untersucht. Die CO2-Anreicherung führte ab dem zweiten Versuchsjahr auf CO2-angereicherten Parzellen zu einer im Vergleich zu den Kontrollflächen erhöhten mikrobiellen und bakteriellen Biomasse sowie zu einer erhöhten mikrobiellen Aktivität. Trotzdem war der metabolische Quotient reduziert, ebenso wie die Abundanz der Nematoden aus der c/p-Gruppe 2 des Maturity-Index, die eine typische r-Strategie verfolgen. Die Veränderungen der mikrobiellen Biomasse waren in allen drei Versuchsjahren auf die Reaktion der Bakterien zurückzuführen, während die pilzliche Biomasse durch die CO2-Anreicherung nicht beeinflusst wurde. Der Vergleich mit Literaturdaten ergab, dass die Auswirkungen einer moderaten CO2-Erhöhung, trotz eines grundlegenden Unterschiedes in der Reaktion der Mikroflorakomponenten, denen einer CO2-Verdopplung ähnlich waren. Die Verminderung des Energie- und Stoffumsatzes innerhalb des Mikronahrungsnetzes ist vermutlich auf eine Veränderung in der Nährstoffverfügbarkeit im Boden aufgrund der Beeinflussung des pflanzlichen Stoffwechsels durch die atmosphärische CO2-Anreicherung zurückzuführen . Es ist anzunehmen, dass es dadurch zu einer Erhöhung der Kohlenstoffspeicherung im Boden kommt. Die Ergebnisse bekräftigen allerdings die Befürchtung, das Speicherpotential terrestrischer Ökosysteme für zusätzliches C sei geringer als ursprünglich angenommen. Zudem könnten CO2-induzierte Veränderungen wesentlich früher auftreten als erwartet.The study include investigations on (i) induced resistance in barley and (ii) effects of the increasing atmospheric CO2 concentration on a temperate grassland. Induced resistance (IR) is a promising new technology for crop protection that relies on the elicitation of nonspecific defense responses in the host plant prior to the arrival of pests. It can be hypothesized that IR may have unintended side effects on composition and performance of the soil community. Aditionally, practical use in agriculture is limited by the low predictability of IR success. One explanation for the high variability of IR effectiveness might be the modulating impact of soil organisms. A field experiment focused on the response of soil biota to the application of BION®, a chemical inducer of resistance, on barley and fallow plots. Two greenhouse experiments investigated the relationship between IR effectiveness and the density of root invading organisms. BION® treatment increased root infection by parasitic nematodes in barley but not in fallow plants. It did not cause measurable changes in microbial parameters or the composition of free-living nematodes. Root infection by mycorrhizal fungi and nematodes both affected IR effectiveness. While Bion® treatment mostly reduced the number of lesions on barley leaves caused by powdery mildew at no/low and medium root infection this effect was reversed at high root infection. However, the onset of IR signaling was not impaired by the two organisms. In the short term, therefore, feedback effects of root associated but not free-living soil organisms on IR effectiveness are to be expected. The effects are plant specific, depend on the level of root infection, and are generated downstream of the chemical induction. As a consequence BION® treatment might enhance disease severity instead of reducing it. Hence, feedback effects of root associated soil organisms help to explain the variability in the effectiveness of IR. The concentration of atmospheric CO2 is predicted to increase rapidly during this century. Marked changes in the structure and function of terrestrial ecosystems have to be expected. Particular attention must be paid to the reaction of the below ground community because soil organisms mediate the effect of rising atmospheric CO2 on the long-term ability of terrestrial ecosystems to sequester carbon. Vast natural and semi-natural ecosystems such as forests and grasslands significantly contribute to the global carbon balance. Experiments are commonly performed at high CO2 concentrations (e.g. twice the preindustrial or current concentration). As there is evidence that the effects of rising atmospheric CO2 on soils are nonlinear extrapolations from those experiments may not allow a sufficient forecast of CO2 effects on terrestrial ecosystems in the near future. To complement these studies the response of belowground biota inhabiting a semi-natural temperate grassland soil to a moderate increase in atmospheric CO2 (+ 20%) was investigated for a period of three consecutive years. Increasing microbial biomass and low metabolic quotient indicate an enhancement of C storage in the soil microfood web in years two and three. This was paralleled by a reduction in the abundance of a nematode group following the r-strategy. According to measurements on the amounts of soil extractable C and N, changes in resource availability seem to be key to the response of the soil microfood web. A strong response of bacteria to elevated CO2 was found, while the fungal biomass remained largely unchanged. This contrasts to findings reported in the literature. It is hypothesized that this may be due to contrasting effects of different levels of CO2 enrichment on the microbial community, i.e. stimulation of bacteria at moderate levels and stimulation of fungi at high levels of CO2 enrichment. However, various CO2 effects observed in this study are in a similar range to those observed in other studies for a much higher level of atmospheric carbon. These include the long-term increase of microbial respiration, the particular sensitivity of predaceous nematodes, and the shift towards less active components of the nematode community. The findings thus confirm that the potential of terrestrial ecosystems to accumulate additional carbon might be lower than previously thought. Furthermore, CO2 induced changes of temperate grassland ecosystems might emerge much earlier than expected

insights for ecological applications from the German Biodiversity Exploratories

Biodiversity, a multidimensional property of natural systems, is difficult to quantify partly because of the multitude of indices proposed for this purpose. Indices aim to describe general properties of communities that allow us to compare different regions, taxa, and trophic levels. Therefore, they are of fundamental importance for environmental monitoring and conservation, although there is no consensus about which indices are more appropriate and informative. We tested several common diversity indices in a range of simple to complex statistical analyses in order to determine whether some were better suited for certain analyses than others. We used data collected around the focal plant Plantago lanceolata on 60 temperate grassland plots embedded in an agricultural landscape to explore relationships between the common diversity indices of species richness (S), Shannon's diversity (H'), Simpson's diversity (D1), Simpson's dominance (D2), Simpson's evenness (E), and Berger–Parker dominance (BP). We calculated each of these indices for herbaceous plants, arbuscular mycorrhizal fungi, aboveground arthropods, belowground insect larvae, and P. lanceolata molecular and chemical diversity. Including these trait-based measures of diversity allowed us to test whether or not they behaved similarly to the better studied species diversity. We used path analysis to determine whether compound indices detected more relationships between diversities of different organisms and traits than more basic indices. In the path models, more paths were significant when using H', even though all models except that with E were equally reliable. This demonstrates that while common diversity indices may appear interchangeable in simple analyses, when considering complex interactions, the choice of index can profoundly alter the interpretation of results. Data mining in order to identify the index producing the most significant results should be avoided, but simultaneously considering analyses using multiple indices can provide greater insight into the interactions in a system

Data from: Community- weighted mean plant traits predict small scale distribution of insect root herbivore abundance

Small scale distribution of insect root herbivores may promote plant species diversity by creating patches of different herbivore pressure. However, determinants of small scale distribution of insect root herbivores, and impact of land use intensity on their small scale distribution are largely unknown. We sampled insect root herbivores and measured vegetation parameters and soil water content along transects in grasslands of different management intensity in three regions in Germany. We calculated community-weighted mean plant traits to test whether the functional plant community composition determines the small scale distribution of insect root herbivores. To analyze spatial patterns in plant species and trait composition and insect root herbivore abundance we computed Mantel correlograms. Insect root herbivores mainly comprised click beetle (Coleoptera, Elateridae) larvae (43%) in the investigated grasslands. Total insect root herbivore numbers were positively related to community-weighted mean traits indicating high plant growth rates and biomass (specific leaf area, reproductive- and vegetative plant height), and negatively related to plant traits indicating poor tissue quality (leaf C/N ratio). Generalist Elaterid larvae, when analyzed independently, were also positively related to high plant growth rates and furthermore to root dry mass, but were not related to tissue quality. Insect root herbivore numbers were not related to plant cover, plant species richness and soil water content. Plant species composition and to a lesser extent plant trait composition displayed spatial autocorrelation, which was not influenced by land use intensity. Insect root herbivore abundance was not spatially autocorrelated. We conclude that in semi-natural grasslands with a high share of generalist insect root herbivores, insect root herbivores affiliate with large, fast growing plants, presumably because of availability of high quantities of food. Affiliation of insect root herbivores with large, fast growing plants may counteract dominance of those species, thus promoting plant diversity

PLOSONEdata

PLOSONEdat

Cinémagazine : hebdomadaire illustré

24 août 19281928/08/24 (A8,N34)-1928/08/24

Root feeding insect s.

<p>Root feeding insect s.</p

List of plant functional traits used as predictors in generalized mixed effects models, with abbreviations, data source and relevance for explaining root herbivore abundance.

<p>o.m. = own (field) measurement</p><p>List of plant functional traits used as predictors in generalized mixed effects models, with abbreviations, data source and relevance for explaining root herbivore abundance.</p

Average mantel correlation coefficients.

<p>over all investigated sites with standard deviation for a) plant communities, b) trait composition and c) insect root herbivore abundance. Mantel correlograms for individual sites are given in the supplementary material.</p

The Root Herbivore History of the Soil Affects the Productivity of a Grassland Plant Community and Determines Plant Response to New Root Herbivore Attack

<div><p>Insect root herbivores can alter plant community structure by affecting the competitive ability of single plants. However, their effects can be modified by the soil environment. Root herbivory itself may induce changes in the soil biota community, and it has recently been shown that these changes can affect plant growth in a subsequent season or plant generation. However, so far it is not known whether these root herbivore history effects (i) are detectable at the plant community level and/or (ii) also determine plant species and plant community responses to new root herbivore attack. The present greenhouse study determined root herbivore history effects of click beetle larvae (Elateridae, Coleoptera, genus <i>Agriotes</i>) in a model grassland plant community consisting of six common species (<i>Achillea millefolium</i>, <i>Plantago lanceolata</i>, <i>Taraxacum officinale</i>, <i>Holcus lanatus</i>, <i>Poa pratensis</i>, <i>Trifolium repens</i>). Root herbivore history effects were generated in a first phase of the experiment by growing the plant community in soil with or without <i>Agriotes</i> larvae, and investigated in a second phase by growing it again in the soils that were either <i>Agriotes</i> trained or not. The root herbivore history of the soil affected plant community productivity (but not composition), with communities growing in root herbivore trained soil producing more biomass than those growing in untrained soil. Additionally, it influenced the response of certain plant species to new root herbivore attack. Effects may partly be explained by herbivore-induced shifts in the community of arbuscular mycorrhizal fungi. The root herbivore history of the soil proved to be a stronger driver of plant growth on the community level than an actual root herbivore attack which did not affect plant community parameters. History effects have to be taken into account when predicting the impact of root herbivores on grasslands.</p> </div

Effects of soil biota community (SB, SEG 33 and SEG 37), <i>Agriotes</i> training (AP1, <i>Agriotes</i> presence in phase 1, untrained and trained) and <i>Agriotes</i> presence (AP2, without and with) on plant and AMF parameters in phase 2.

<p>significance level:</p>*<p>p<0.05,</p>**<p>p<0.01,</p>***<p>p<0.001,</p><p>ns = not significant, LEH: length of extraradical AMF hyphae, AMF: arbuscular mycorrhizal fungi.</p