Project

resilience; propagule pressure; extreme drought; invasibility; seedling establishment; plant-AMF networks ; soil pathogens; soil moisture; climate change

Lead
Um zu verstehen wie sich Lebensgemeinschaften mit fortschreitendem Klimawandel und zunehmendem Ausbreitungsdruck exotischer Arten verändern, interessieren wir uns für Prozesse, die die Zusammensetzung von Lebensgemeinschaften bestimmen.
Lay summary
Auswirkungen und Spätfolgen von Trockenheit auf die Invasibilität von Grasland Nach heutigem Wissensstand hängt die biotische Widerstandsfähigkeit einer Pflanzengemeinschaft gegen Invasionen wesentlich von der Konkurrenz zwischen den bereits vorhandenen und den neu-eindringenden Pflanzen um Ressourcen ab. Die Empfindlichkeit eines Lebensraumes von neu-eindringenden Arten besetzt zu werden (Invasibilität), kann durch kurzfristige Licht- und Nährstoffpulse erhöht werden. Nach Sommerdürren, die das Wachstum der vorhandenen bremsen, könnte die Invasibilität erhöht sein. Da Trockenperioden in der Schweiz und in weiten Teilen der Erde häufiger oder intensiver werden, könnte dies für Ökosysteme ungeahnte Folgen haben. Unsere bisherigen Feldexperimente mit simulierter Trockenheit deuten darauf hin, dass auch andere biotische Interaktionen als die Konkurrenz die Invasibilität in Grasland-Ökosystemen wesentlich beeinflussen könnten. In der Fortsetzung des Projektes Invasibility of Swiss grasslands planen wir Feld- und Topfexperimente um die unterschiedlichen und verzögerten Auswirkungen der Trockenheit besser zu erfassen. Wir untersuchen, wie der Etablierungserfolg von Pflanzen in Abhängigkeit von Niederschlag, Produktivität und biotischen Interaktionen verändert wird und interessieren uns speziell für Interaktionen zwischen Pflanzen und Bodenmikroben und ihre wechselnden Rollen als Konkurrenten um Licht und Nährstoffe, als Nährstoff-Lieferanten via Pflanzen-Micorrhiza-Netzwerke und als Mutualisten oder Pathogene.

Direct link to Lay Summary

Last update: 14.10.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

The question of what drives community assembly is crucial for an understanding of how communities will behave under global change, including scenarios of climate change or increased propagule pressure of exotic species. In current ecological thinking, competition with resident plants is often assumed to play an important role in biotic resistance to plant invasions. Therefore, opportunities for invasion are supposed to be better when the resident plants are damaged or stressed, for example as a consequence of drought, which in turn results in changed pulses of light and unexploited nutrients. As dry spells tend to increase in length and intensity over large regions of the globe including Switzerland, due to climate change, ecologists are concerned about the possibility that plant communities and ecosystems may become more invasible and shift to new states or loose current functions.Recent field experiments simulating extreme drought events in grasslands have not often found an increase in invasibility. This implies that drought effects are not only mediated by competition but also by other biotic interactions such as those with antagonistic and mutualistic soil microbes. Indeed, ecologists have convincingly argued that soil pathogens and arbuscular mycorrhizal fungi (AMF) are important determinants of plant community composition and functioning. However, the bulk of evidence is based on simplified experimental conditions in the greenhouse and few attempts have been made to simultaneously investigate the role of these ecological mechanisms in the field where biotic interactions are much more complex and environmental fluctuation and heterogeneity may have a paramount influence. This proposal is a continuation of the project Invasibility of Swiss grasslands. Research questions are inspired by surprising results of the extreme-drought experiment of the previous project, i.e. the lack of a relationship between establishment of sown species and productivity of the resident community over a wide gradient of productivity, the predominantly negative drought-legacy effect on establishment success, and the clearly weaker establishment success of non-indigenous vs. indigenous grassland species in the field, but not in the greenhouse. We propose three complementary experiments to investigate mechanisms of drought-legacy effects (Fig. 1). The experiments are linked by the overall questions of whether, and how much, climate change (variable summer precipitation, manipulated by rainout shelters and irrigation) and land-use intensification (productivity) affect the performance of added invader species (invasibility) mediated by biotic interaction. Biotic interactions considered include those with resident plants and soil microbes, and their various roles as competitors for light, competitors for nutrients, providers of nutrients via plant-AMF networks, pathogens, and mutualists will be studied.EXPERIMENT A is a field experiment started in 2014 at twelve grasslands sites across Switzerland, covering an annual productivity gradient in the range of 180-1200 gm-2. EXPERIMENT B will be started in 2015 in two of these sites, in fertilized and unfertilized grassland. The greenhouse-EXPERIMENT C is a follow-up study of EXPERIMENT A using soil samples with stored microbial legacies of ‘precipitation history’. Based on the results of these experiments we wish to enhance our mechanistic understanding of grassland invasibility in Switzerland and make an important step forward in the prediction of global-change effects on herbaceous vegetation.Fig. 1 Three complementary experiments investigate invasibility in response to an integrated set of drivers (summer precipitation, productivity) mediated via biotic filters: EXPERIMENT A aims at quantifying the importance of resident plants, soil fungal pathogens and soil fungal mutualists. EXPERIMENT B quantifies the various roles of resident plants as suppliers of, or competitors for resources. EXPERIMENT C investigates whether the performance of invader species under different moisture conditions is affected by ‘precipitation history’ via soil microbes.