Decision-Making in Plants: Resource Allocation to Mycorrhizal Hyphal Networks

Background

In contrast to animals, plants have no central nervous system with which to integrate decision-making when foraging for resources. Nevertheless, intuitively, integration of information must be important for plants. This is particularly evident in the case of symbioses such as the mycorrhizal symbiosis, where the plant invests photosynthetic products (chiefly carbon) into a fungal partner in order to get access to mineral nutrients foraged for by the fungus. If part A of a plant root system has a connection with an arbuscular mycorrhizal fungus (AMF) that takes more resources than it returns and part B has an AMF connection that takes less than it returns, the plant should favor part B over part A to maximize its fitness. However, can a plant indeed select between the two AMF connections and display an "intelligent" integrated response?

Methods

To answer this question we construct experimental systems with split plant root systems of which one side has a more beneficial AMF connection than the other side. This is done in two ways: (i) the two sides contain two AMF species differing in their ability to supply mineral resources to the plant, (ii) the two sides contain the same beneficial AMF species, but this AMF species is connected on one side to a different plant species known to disproportionately draw mineral resources from the mycorrhizal network while contributing relatively little carbon. The plant response is being assessed via growth analysis and tissue concentrations of C14 fed to the plant and P33 provided to the AMF on the two sides.

Because we expect that plants are more selective when resources are scarce, we use low or high levels of N and P in our experimental systems. Furthermore, we intend to expand the experimental systems to include two plants mutually limited by either N or P to test if resource sharing via a common AMF will occur to a greater extent than if the limitation is not mutual. The results of our research can contribute to the fundamental question of "decision-making" in plants and to the applied question of how interactions between plants and AMF affect plant performance in the wild and in agro-ecosystems.

Participants

Prof. Dr. Bernhard Schmid (Project Leader)
PD Dr. Pascal Niklaus
Dr. Lindsay Turnbull
Alicia Argüello (Ph.D.)

Co-operation partners

Prof. Dr. Andres Wiemken, Institute of Botany, University Basel
Dr. Marcel van der Heijden, Agroscope Reckenholz-Zurich (ART)

Publications

Kiers, E.T., van der Heijden, M.G.A. (2006) Mutualistic stability in the arbuscular mycorrhizal symbiosis: exploring hypotheses of evolutionary cooperation. Ecology 87: 1627-1636.

Oehl, F., Sieverding, E., Ineichen, K., Ris, E.A., Boller, T., Wiemken, A. (2005) Community structure of arbuscular mycorrhizal fungi at different soil depths in extensively and intensively managed agroecosystems. New Phytologist 165: 273-283.

Prati, D., Matthies, D., Schmid, B. (1997) Reciprocal parasitization in Rhinanthus serotinus: a model system of physiological integration in clonal plants. Oikos 78: 221-229.