P (Paula) Harkes MSc

P (Paula) Harkes MSc


Research conducted by the Laboratory of Nematology is part of the research program of the Graduate School Experimental Plant Sciences (EPS) and C.T. de Wit Graduate School for Production Ecology & Resource Conservation (PE&RC).


The BE Basic project Sure/Support Towards a quick decision SUPPORT tool for SUstainable use of harvest REsidues aims to develop a decision support tool that will help to balance the inevitable residue removal and highly needed residue recycling in a primary production soil. One of the main deliverables of this project are rapid and cost effective tests for assessing biological soil quality

Soil is one of the most biodiverse and competitive biological environments on our planet. Due to its extreme biodiversity, it is not possible to monitor soil life in its full complexity. To acquire data on soil processes and soil life in a feasible way, indicator groups are often selected. Nematodes, small worm shaped animals that are represented in multiple trophic levels of the soil food web, are such a group. The phylum Nematoda contains bacterivores, fungivores, omnivores, carnivores, as well as facultative or obligate plant and animal parasites. Next to being trophically diverse, this groups abundance in soil, easy extractability from soil and differential sensitivity to stressors are additional assets for its use as an environmental indicator group.  So far, feeding preferences of nematodes have been inferred from their morphology in combination with observational studies. This approach has left a considerable degree of uncertainty and lack of resolution in the assignment of feeding preference within the phylum. To be able to concretize these nematode feeding preferences by associating shifting nematode communities to changes in other groups of soil organisms, large datasets of soil organisms are needed.

Two major organismal groups harbour the main decomposers of organic matter in soil, bacteria and fungi. A single gram of soil contains up to 100,000 bacterial species and up to 16 km of fungal hyphae. Agricultural land use and, more specifically, bio-based residues will affect the diversity and abundance of these soil microbiota. However, the specific responses of various bacterial and fungal groups to both qualitatively and quantitatively changing nutritional supply is not well understood. In the framework of Sure/Support I would like to link qualitative changes in the primary decomposer community to corresponding shifts in the bacterivorous and fungivorous nematode community.   

In order to better understand the ecological food web in the rhizosphere between plants, nematodes and bacteria, molecular assays are developed in order to quantify shifts in bacterial and fungal community composition at a high taxonomic level phyla. In a following step, next generation sequencing approaches will be developed to pinpoint changes in primary decomposer community in great detail, and link these to specific changes in bacterivorous and fungivorous nematode taxa. First indications for taxon specific food preferences have been described in Vervoort et al. (2012), and Quist et al. (2014). In the framework of Sure-Support, we would like to pinpoint and exploit trophic links between bio-based residue-affected microbial communities and bacterivorous and fungivorous nematode assemblages. In this way we will further exploit to potential of this endogenous reporter group as indicator for the biological condition of soils.