Biology subjects

Kempel, A.

Publications and source records attributed to Kempel, A..

7 recordsLinked to original sources

bioRxiv2026

Exploring nematode diversity in soils: comparison of extraction methods and sequencing protocols

Soil nematodes play key roles in regulating organic matter decomposition, nutrient cycling and trophic interactions in the soil ecosystem, and are very useful bioindicators of soil condition and soil health. But to characterise them, we need reliable measurements of nematode biodiversity in soils. DNA-based techniques such as metabarcoding have recently explored their biodiversity, with successful results. However, there are many methodological steps that can modify the outcome considerably and require informed decisions. In this study, we tested the effect on nematode alpha and beta diversity metrics of three methodological steps, namely i) type of extraction of genetic material from the matrix, either from soil directly with different starting amount of material or extracting nematodes first via the Baermann or Oostenbrink methods, ii) the choice of taxonomically-relevant DNA segment for amplification, with a nematode specific primer (NemF/18Sr2b) and a universal eukaryotic primer (3NDf/1132rmod), both within 18S rDNA, and iii) the selection of appropriate reference library for taxonomic assignment (comparing three nematode specialised databases and three broad taxonomic databases). Observed differences in alpha diversity were more pronounced when comparing the nematode extraction vs soil extractions. In particular, direct soil extractions co-extracted many non-nematode taxa, especially if amplified with a universal primer, which can significantly reduce the number of nematode reads obtained and therefore the accuracy of nematode community indexes and other nematode-based metrics. The choice of the reference database strongly affected the taxonomic identification, which calls for extreme caution when making this selection. Notably, specialised databases tended to over assign reads to nematodes that were detected as non-nematodes by broad taxonomic databases. However, beta diversity metrics were consistent across methods, highlighting these metrics as robust against methodological choices. Our study clearly demonstrates that the choices of methods for nematode biodiversity studies using molecular tools can have a big impact on the results, and decisions should be made consciously and carefully.

ecology↗

bioRxiv2023

Disentangling the mechanisms by which nitrogen enrichment affects consumer damage at different organisational levels

Nitrogen enrichment could affect primary consumers by increasing foliar N content (nitrogen-disease hypothesis), by increasing dominance of palatable, fast-growing plants (growth-defence trade-off) or by reducing plant diversity (resource concentration effect). These mechanisms might operate differently at different organizational levels. We tested this in a grassland experiment (PaNDiv), manipulating nitrogen enrichment, plant species richness, fast-slow functional composition, and foliar pathogens. We assessed herbivory and pathogen damage, on focal plant individuals, species, and communities. Plant community characteristics were more important drivers of consumer damage than nitrogen enrichment. Host concentration effects strongly affected pathogens but mostly at the species level. Growth-defence trade-off effects were widespread but frequently emerged from interactions between species (associational effects) or with resource concentration effects, leading to different patterns at species and community levels. Our findings suggest that key mechanisms may operate differently at different organisational levels calling for better understanding of how consumer effects scale across levels.

ecology↗

bioRxiv2022

Plant attributes interact with fungal pathogens and nitrogen addition to drive soil enzymatic activities and their temporal variation

O_LINitrogen enrichment can alter soil communities and their functioning directly, via changes in nutrient availability and stoichiometry, or indirectly, by changing plant communities or higher trophic levels. In addition, soil biota and their associated functions may show strong temporal changes in their response to environmental changes, yet most current studies have only focused on one of these potential drivers or have measured soil functioning only once during the peak growing season. Therefore, we know little about the relative importance of the different mechanisms by which nitrogen enrichment affects soil communities, functioning and temporal stability. C_LIO_LIIn a large grassland experiment manipulating nitrogen enrichment, plant species richness, functional composition and foliar pathogen presence, we measured activities of two enzymes, {beta}-glucosidase and acid phosphatase, as indicators of soil functioning. We did so across different seasons and years to assess their temporal dynamics and how consistently they responded to multiple drivers. C_LIO_LINitrogen addition was the most important driver of {beta}-glucosidase activity, and it increased {beta}-glucosidase activity over time. However, interactions between plant attributes and fungicide application were the main drivers of acid phosphatase activity. The temporal stability of soil enzyme activity was differently affected by two facets of plant diversity (species richness [+] and functional diversity [-]), with nitrogen and fungicide addition dampening these effects. C_LIO_LISynthesis: Fungicide effects, and their interactions with plant diversity, show the importance of foliar pathogens not only for above-but also for belowground processes, and highlight the possibility that these plant enemies are major modulators in the relationships between plant diversity and ecosystem functioning. We also show the need to consider temporal dynamics in belowground processes to better understand the responses of ecosystem functioning to environmental changes such as nutrient enrichment. C_LI

ecology↗

bioRxiv2022

Plant-invertebrate interactions across a forested retrogressive chronosequence

In the long-term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post-fire forested island-chronosequence across which retrogression occurs, we show that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom-up to top-down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of plant biomass. Our results suggest that effects of nutrient limitation, following ecosystem retrogression, on trophic cascades are modified by independent variation in predator abundance, which requires a more holistic approach to trophic ecology to better understand herbivore effects on plant communities.

ecology↗

bioRxiv2019

Rare species perform worse than common species under changed climate

Predicting how species, particularly rare and endangered ones, will react to climate change is a major current challenge in ecology. Rare species are expected to have a narrower niche width than common species. However, we know little whether they are also less able to cope with new climatic conditions. To simulate climate change, we transplanted 35 plant species varying in rarity to five botanical gardens in Switzerland, differing in altitude. For each species we calculated the difference in climate between their natural habitats and the novel climate of the respective botanical garden. We found that rare species had generally lower survival and biomass production than common species. Moreover, rare plant species survived less when the amount of precipitation differed more from the one in their natural range, indicating a higher susceptibility to climate change. Common species, in contrast, survived equally well under all climates and even increased their biomass under wetter or drier conditions. Our study shows that rarer species are less able to cope with changes in climate compared to more widespread ones, which might even benefit from these changes. This indicates that already rare and endangered plant species might suffer strongly from future climate change.

ecology↗

bioRxiv2019

Sick plants in grassland communities: a growth-defense trade-off is the main driver of fungal pathogen abundance and impact

Aboveground fungal pathogens can substantially reduce biomass production in grasslands. However, we lack a mechanistic understanding of the drivers of fungal infection and impact. Using a global change biodiversity experiment we show that the trade-off between plant growth and defense is the main determinant of fungal infection in grasslands. Nitrogen addition only indirectly increased infection via shifting plant communities towards more fast growing species. Plant diversity did not decrease infection, likely because the spillover of generalist pathogens or dominance of susceptible species counteracted dilution effects. There was also evidence that fungal pathogens reduced biomass more strongly in diverse communities. Further, fungicide altered plant-pathogen interactions beyond just removing pathogens, probably by removing certain fungi more efficiently than others. Our results show that fungal pathogens have large effects on plant functional composition and biomass production and highlight the importance of considering changes in pathogen community composition to understand their effects.

ecology↗

bioRxiv2019

Context dependency of biotic interactions and its relation to plant rarity

AimBiotic interactions can determine rarity and commonness of species, however evidence that rare and common species respond differently to biotic stress is scarce. This is because biotic interactions are notoriously context-dependent and traits leading to success in one habitat might be costly or unimportant in another. We aim to identify plant characteristics that are related to biotic interactions and may drive patterns of rarity and commonness, taking environmental context into account.\n\nLocationSwitzerland\n\nMethodsIn a multi-species experiment, we compared the response to biotic interactions of 19 rare and 21 widespread congeneric plant species in Switzerland, while also accounting for variation in environmental conditions of the species origin.\n\nResultsOur results restrict the long-standing hypothesis that widespread species are superior competitors to rare species to only those species originating from resource rich habitats, in which competition is usually strong. Tolerance to herbivory and ambient herbivore damage on the other hand, did not differ between widespread and rare species. In accordance to the resource-availability hypothesis, widespread species from resource rich habitats where more damaged by herbivores (less defended) than widespread species from resource poor habitats - such a growth-defense tradeoff was lacking in rare species. This indicates that the evolutionary important tradeoff between traits increasing competitive-ability and defence is present in widespread species but may have been lost in rare species.\n\nMain conclusionsOur results indicate that biotic interactions, above all competition, might indeed set range limits, and underlines the importance of including context-dependency in studies comparing traits of common and rare or invasive and non-invasive species.

ecology↗