Prof. dr. Martijn Bezemer

 

In our group at the NIOO we work Plant-Soil-Insect interactions. Since 2016 I am also affiliated as professor " Ecology of plant-microbe-insect interactions" at the Instiute of Biology in Leiden,

Soils are a medium in which plants root, but also house an overwhelming abundance and diversity of living organisms. The local composition and abundance of these organisms depends greatly on the identity of the plant that is growing in the soil. The performance of plants, in turn, is determined by interactions with soil organisms. Hence, via their specific effects on soil organisms, plants can influence the growth of other plants that grow later in the same soil.

Plant soil feedback effects on insects

Plant-soil legacies can cause changes in the composition of plant communities and can change the aboveground chemistry of individual plants. Via these two mechanisms, soil organisms can influence aboveground organisms such as insects that directly or indirectly depend on the plants. We are examining the impact of soil ‘legacy effects’ of plants on other plants and aboveground insects. We study how we can use these aboveground-belowground interactions to restore natural grasslands and to improve resistance of crops to pests in commercial greenhouses.

Running projects:

Restoration of natural grasslands: the “Living legacies” project: Influence of plant-mediated changes in soil communities on aboveground plant-insect interactions (2015-2020)

In this project that is funded by the NWO Talent Scheme (VICI), we examine how soil-derived legacy effects of plants structure natural ecosystems, determine its aboveground biodiversity, and how we can use soil legacy effects to restore degraded ecosystems. We study interactions between plants, soil organisms, and aboveground insects and examine when, how, and at what temporal and spatial scales plant-soil legacy effects influence aboveground plant-insect interactions in natural grasslands. The soil legacy framework will be used to manage soil legacies to restore biodiversity in degraded grassland ecosystems, and in collaboration with restoration practitioners, this will be field-tested in restoration sites.

Field experiments

There are two ongoing field experiments where we test soil-legacy effects on aboveground plant and insect communities.

In the “soil inoculation field experiment” that was initiated in 2016 at a common field site, we inoculated soil (0.5 cm)  collected from different grasslands. In each grassland we collected soil from forb, grass and shrub (heather) dominated patches. All experimental plots were sown with a species rich seed mixture and we examine the development of the plant, soil and insect community in the inoculated plots.

 

 

 

In the “plant-soil feedback field experiment” that was initiated in 2015, we examine the soil legacy of plant communities that consist of fast and slow growing grass and forb species. Specific plant communities were sown and allowed to condition the soil for one or two years in experimental field plots. Hereafter we removed all plants from the plots and sowed a species rich community in each plot. We are studying how soil conditioning with fast or slow growing grasses or forbs and the duration of conditioning influences plant, soil and insect communities.

 

Greenhouse experiments

In greenhouses we carry out microcosm studies to disentangle the legacy effects of particular plant species, groups of soil organisms, plant communities, and insects, to construct a general framework to predicts the impact of soil-legacy effects on plants and aboveground insects.

 

 

Linking aboveground-belowground interactions and plant-soil feedback to improve pest control and sustainability in greenhouse cut-flowers (2013-2019) 

In this project Funded by NWO Groen, we examine how we can reduce the severity of above and belowground pests of the cutflower Chrysanthemum via inoculation of soil microbial communities. Soil microorganisms can influence plant growth and defense and can reduce the damage that aboveground herbivores inflict on a plant. A major challenge is to apply this knowledge to improve sustainable crop production. We examine how soil microbial communities added to sterile soil influence aboveground plant chemistry, the severity of aboveground pests, and the efficiency of predators of these pests. We focus on the Chrysanthemum  and the major above and belowground pests of this crop. Chysanthemum is a major cut-flower crop in greenhouses in the Netherlands that is grown in soil and an important export product. To control soil-borne diseases, the soil is disinfected frequently by steaming. Disinfected soils can be easily colonized by soil pathogens but disease suppressiveness of these soils can be improved by inoculation with microbial communities.

We examine how soil inoculation influences pests and diseases (i) directly, and indirectly via (ii) its effects on plant chemistry or volatile emission, or via (iii) mediating the effects of belowground pathogens on aboveground organisms via the shared plant.

Other projects

Biodiversity and Ecosystem function:

Biodiversity is declining worldwide but the consequences of this loss are still not well understood. We study how changes in plant diversity affect the functioning of grassland ecosystems and how this influences aboveground and belowground multitrophic communities. We study these interactions in two field experiments, a series of old fields, and under controlled conditions in climate chambers and greenhouses. 

Long-term successional biodiversity experiment:

In the field different seed mixtures (15 species, 4 species, 0 species) were sown in a recently abandoned field in 1996. The plots have not been weeded since, but this single sowing event has resulted in long-term differences in plant and soil communities. Since 1996 we have been collecting data on plant and nematode community composition and we now have a unique long-term dataset on how initial seed diversity affects the temporal dynamics of plant and soil communities during secondary succession. We also study ecosystem functioning, invasibility and community and ecosystem stability in the plots. Since the plots are not weeded and colonization is allowed this is a unique biodiversity experiment and the results show that biodiversity-ecosystem function relationships in unweeded, natural plant communities differ remarkably from those observed in controlled biodiversity experiments (see publications for details).

Classical biodiversity experiment:

In 2008 we initiated a classical biodiversity grassland experiment with 70 plots with 1 to 9 plant species and where species diversity and composition are maintained by hand weeding. Here we also study biodiversity – ecosystem function relationships and this enables us to compare it to the successional biodiversity experiment. In the classical biodiversity experiment, we focus particularly on how plant community identity and diversity affects the aboveground and belowground interactions that occur on phytometer plants (tansy ragwort: Senecio jacobaea) that have been planted into these plots, to test for associative resistance and susceptibility, and to test to what extent plant-antagonist interactions are driven by host plant quality and by the surrounding community.

Chronosequence of old fields:

We use a series of old fields that differ in time since cessation of agriculture (1 to 40 years) to study how plant, soil, and aboveground communities develop and how ecosystem stability changes over time during secondary succession. We study how nature restoration can be improved, but also study population dynamics of the plant tansy ragwort in this chronosequence. After an initial period of five to ten years during which this plant species dominates the vegatation, its abundance starts to declline. We examine whether this decline is due to a negative plant soil feedback that develops in these old fields or due to increased competition with other plant species or changes in soil chemical properties.

 Aboveground belowground interactions:

Plants grow aboveground and in the soil, but ecologists frequently study aboveground or belowground processes in isolation. We are interested in question by which mechanisms belowground herbivores, pathogens or decomposers can influence the interactions between plants, herbivores and parasitoids aboveground, and vice versa. We introduce aboveground and belowground organisms on plants in microcosm studies in the greenhouse and study how these organisms interact via induced plant defense responses and whether feeding in one compartment can affect the behaviour of organisms in the other compartment. We also study these interactions in the field. For example, we study ature restoration on ex arable fields and how soil diversity can influence the diversity of plants and herbivores aboveground.

Studying aboveground belowground interactions

Effects of host plant quality and neighbouring plant community composition on aboveground and belowground food webs:

In the field, we study how resource quality and the identity of the neighbouring plant community affect above and belowground food webs on individual plants. Belowground, we construct entire foodwebs underneath individual plants belonging to different species (including Plantago lanceolata and Lotus corniculatus) that grow in the plots of the successional biodiversity epxeriment. Although the food webs are entirely open, and plants grow internmingled with other plants of the same and different species, we are detecting considerable differences in the composition of the soil food webs. Surprisingly, these differences occur in particular in the decomposer part of the foodweb rather than in the root associated organisms. Aboveground we have reared out all herbivores and parasitoids from seed pods of Lotus corniculatus. So far the food web consists of two herbivore species and 20 parasitoid and hyper parasitoid species. We analyze the food webs for complexity, stability, link density etc, and have data on the body size of the emerging adults. We also have detailed information about the size of the pods, the number of seeds, and the origin of the pods (from which plant community were they colleted and from which plant within the community). For these aboveground and belowground food webs we examine the hypothesis that aboveground food webs are influenced most stronly by resource quality while belowground food webs are determined most strongly by neighbouring and legacy effects.

Soil transplantation for ecosystem restoration

Agricultural intensification has resulted in a strong reduction of species-rich grasslands in The Netherlands and great efforts are made to restore diverse grasslands on former arable land. For long, the standing view has been that the diversity and functioning of ecosystems is largely determined by abiotic conditions such as soil fertility and the focus in restoration in the Netherlands has been traditionally on reducing soil fertility, e.g. by removal of the entire topsoil. With topsoil removal the "agricultural"soil microbial community that was present in the soil is also remvoed. Soil microbes o play an important role in plant community development and hence in restoration: a target plant community requires a target soil community. We study how inoculation of areas where top soil has been removed with soil communities collected from well developed nature areas can improve establishment of later-successional (target) plant species. In the “NWO-ALW Biodiversity Works” programme, together with the organization Natuurmonumenten we are evaluating a large soil transplantation trial carried out in the Netherlands in a restoration area where the topsoil has been removed. (See also links to the soil transplantation website, and broadcasts on Dutch radio and TV) 

Ecology of the biobased economy: Biochar amendment in a natural ecosystem:

Together with colleagues from Wageningen University (Jan Willem van Groenigen and Liesje Mommer) and two appointed post docs (Tess van de Voorde and Simon Jeffery) recently started a four year project in which we examine possibilities for  biofuel production from biomass of old fields. We will study the effects of biochar amendment in a nature restoration area on plant communities and soil food webs and ecosystem functions. Biochar (similar properties as active coal), is a left over product from oil production after pyrolisation of biomass. We also organized two workshops on biofuels and biochar. More information on: www.base-project.org.