ween crop and soil biodiversity are still not well predictable, but the idea that changing aboveground diversity will change soil biota is increasingly recognized. Specific soil organisms called nematodes have an important function in soil food webs. This research focuses on the effect of diverse grass-clover mixtures on the occurrence of nematodes in the soil. Total nematodes and two functional groups of nematodes are taken into account. The two groups are entomopathogenic nematodes (EPN’s) of genera Heterorhabditis and Steinernema, and fungal feeding nematodes of the genera Diphtherophora, Aphelenchoididae and Filenchus. Nematodes in general can be used as bioindicator for soil ecological health; EPN’s parasitize on insects larvae and can have a function as biocontrol agents in agricultural fields; fungivorous nematodes are even more frequent than EPN’s and represent abundance of fungi. By taking soil samples and carrying out Q-PCR’s, nematodes in the soil were determined. All studied grass-clover plots are situated in the same field, yet have different treatments considering diversity in species composition and time since tilling. A higher total nematode abundance was found in the older grass-clover plots. Higher aboveground species diversity in grass-clover plots did not result in higher nematode abundances. The genera Steinernema, Diphtherophora and Filenchus were found to occur patchy. This study tries to contribute to the understanding of aboveground-belowground biodiversity interactions and the possibility of managing the soil life underneath our crops.

Introduction

Soil biodiversity is known to play a key role in crop productivity by providing ecosystem services as decomposition and nutrient cycling [1,2,3]. Current studies try to reveal and explain feedbacks between aboveground and belowground diversity. To date, the effect of interactions between crop and soil biodiversity is not well understood. However, the idea that changing aboveground diversity changes soil biota is increasingly recognized [4].

In the soil food web, nematodes play a crucial role [5]. They occur ubiquitous in all habitats. In agriculture nematodes are mostly known as plant parasites, while nematodes encompass a much larger variety which feed on e.g. bacteria, arthropods, other nematodes or fungi. For the reason that nematodes are divided in a broad range of trophic groups, they could be used as bioindicator of soil ecological health. The presence of nematodes from a speci