PARENT SESSION
Oral Session # 48: Mutualism - Parasitism I: Plants; Modeling.
Presiding: K Jayachandran
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.

The economics of partner selection in ectomycorrhizal mutualism.

Kummel, Miroslav^*,1, Salant, Stephen¹, ¹ University of Michigan, Ann Arbor, MI

ABSTRACT- The objective of this paper is to determine whether mutualistic partner choice in the context of the C for N trading between plants and fungi can be the mechanism causing both co-occurrence of fungal partners of differing effectiveness on a single host and changes in composition of fungal partners along light or carbon availability gradients. We investigated the question both as plants-choose-fungi and as fungi-choose-plants. We constructed a model where growth of the choosing organism is dependent on the exchange rate of C and N it receives from its trading partners. In the model, the trading partners are characterized by their C for N exchange functions. The choosing mutualist selects the composition of its trading partners that maximize its growth. The results of the model are dependent on the shape of C for N exchange functions of the trading partners. In the plants-choose-fungi system both co-occurrence of several ectomycorrhizal fungal (ECM) species on single host plants and changes in ECM composition along light gradients are possible when fungi have accelerating C for N exchange functions. In the fungi-choose-plants system changes in ECM composition on plants along light gradient arise from equivalent non-linearity in the plants' C for N exchange function. Comparison of the plants-choose-fungi and fungi-choose-plants systems reveals conflicts of interest among the mutualists. The model is discussed in light of available empirical evidence.

Key words: mycorrhizae, biological markets, mutualism, model