This research uses conceptual approaches towards the unraveling of the relation between above and below ground multitrophic interactions (Fig. 1). Direct and indirect plant defense strategies, succession and biodiversity are important concepts herein.
Between Heaven and Earth: Multitrophic Interactions
One of the most important reserach questions is "How are below and above ground multitrophic interactions connected en related to genetic, species and spatial diversity."
For example, plants can defend themselves against above and below ground parasites. Some defense mechanisms are always active, i.e. thorns of a plant, we refer to this as constitutive defense. In addition, the defense may be triggered: (secundary) chemical plant compounds (ref.1). Volatile compounds, released by plants when attacked by caterpillars, are used to attract natural enemies of the caterpillars. We have indications that these kind of interaction take place in soil as well (ref.3).
How is the defense system within a plant organized over below and above ground parts? A general plant response is transport of defense compounds to the tips of fresh leaves when attacked by above ground enemies. What happens to the leaves if the root is attacked? The response appears related to the combination of plant species and root grazer. For example, defense compounds were in certain circumstances equally divided over all leaves when attacked by parasites (ref.4). The reason is still unclear. It is possible that compounds that are used to regenerate the root system are produced in old leaves. In addition, it seems that the direction of transport of nutrients is dependent on the kind of root grazer (ref.5). In case of nematode infestations, the defense compounds head a different direction then compared to a carrot fly (Psila rosae (F.) Fig. 2). The plant defense compounds seem to be taken up by caterpillars, wasps and their natural enemies (hyperparasitoids (ref.6). These insects can be literally regarded as "are what they eat". By focus on multitrophic model systems we try to infer general patterns from the diversity of systems.
- Dicke, M., & L.E.M. Vet. 1999. Plant-carnivore interactions: evolutionary and ecological consequences for plant, herbivore and carnivore. Pages 483-520 in H. Olff, V.K. Brown, and R.H. Drent, editors. Herbivores between plants and predators. Blackwell Science, Oxford, UK.
- Wäckers, F.L. 2000. Do oligosaccharides reduce the suitability of honeydew for predators and parasitoids? A further facet to the function of insect-synthesized honeydew sugars. Oikos 90: 197-201.
- Van Tol, R., A. T. C. van der Sommen, M. I. C. Boff, J. van Bezooijen, M. W. Sabelis, & P. H. Smits. 2001. Plants protect their roots by alerting the enemies of grubs. Ecology Letters 4: 292-294.
- Bezemer, T.M., Wagenaar, R., Van Dam, N.M., & Wäckers, F.L. 2003. Interactions between above- and belowground insect herbivores as mediated by the plant defence system. Oikos 101: 555-562.
- Van Dam, N.M. and Raaijmakers, C.E. In voorbereiding.
- Harvey, J. A., N. M. Van Dam, & R. Gols. 2003. Interactions over four trophic levels: foodplant quality affects development of a hyperparasitoid as mediated through a herbivore and its primary parasitoid. Journal of Animal Ecology 72: 520-531