Ectomycorrhizal fungal competitive interactions in a changing world

Background/Question/Methods

Ectomycorrhizal fungal (EMF) competitive interactions may play a key role in shaping community structure and diversity. Existing EMF competition studies have focused on interspecific interactions between few EMF species associated to conifers and provide a limited understanding of this process. We hypothesize that competitive interactions also occur in other EMF-plant systems both at intraspecific and interspecific levels. We also hypothesize that the outcomes of competitive interactions may vary under global change scenarios since different EMF may respond differently to climate modifications, either as a direct fungal response to environmental factors or as a response to changes occurring in plant hosts. To test these hypotheses, we studied single vs pairwise interactions between EMF associated with Eucalyptus spp. (several isolates of Pisolithus microcarpus, P. albus and Sordariomycetes sp.) under four different climate conditions. We tested two temperature conditions (ambient and ambient + 3°C) and two CO₂ concentration levels (400 and 650 ppm) in a factorial design. We looked at how fungi interacted both in the absence of a plant (direct mycelial interactions) and in the presence of a Eucalyptus grandis seedling (plant-mediated interactions). We measured mycelium growth, plant mycorrhizal colonization by each isolate, plant growth, and C and N leaf contents.

Results/Conclusions

Preliminary results show differences in mycelium growth and colonization ability among the different EMF isolates. We observed a decrease in percentage of mycorrhizas in the presence of another fungus for all the isolates and regardless of the partner’s colonization ability. This resulted in lower total plant colonization when two fungi were interacting. Neither of the isolates was competitively excluded and there were no changes to colony growth rates whether the fungus was paired with the same or a different isolate. The fungi responded positively to an increase in temperature in the single treatments while no response to modified conditions was observed in the pairwise interactions. We conclude that the evaluated EMF isolates compete for the resources provided by the plant without negatively impacting the growth of the other EMF isolate. Competition affects all isolates in a reciprocal way regardless of their colonization ability and causes a decrease in total plant colonization, which has implications in plant growth. Results suggest differences in resource allocation to competition vs mutualism when another fungus is present. We also conclude that competition modulates individual EMF responses to climate modifications and that this factor should be taken into account when trying to predict climate change consequences.