Text by Kadri Koorem
Recent years have been ground-breaking in describing the diversity patterns of arbuscular mycorrhizal (AM) fungi. These microscopic fungi live in plant roots and receive carbon compounds from the plant in exchange of nutrients. In natural conditions, one plant individual can harbour more than ten taxa of AM fungi. Interestingly, AM fungal communities in the roots of plants in same habitat can be remarkably different. However, we have little information what determines the composition of AM fungi in plant roots and with this study we aimed to contribute to filling this gap.
In the presence of forest canopy, shade-avoidant plant species have been shown to harbour less diverse AM fungal community in their roots than shade-tolerant plant species. We hypothesized that this due to carbon deficiency and in the absence of forest canopy, shade-avoidant plant species can increase their photosynthetic capacity and become associated to more diverse AM fungal community, similarly to shade-tolerant plants. We sampled shade-tolerant and shade-avoidant plant species in the presence and absence of forest canopy. In all plant individuals, we recorded photosynthetic capacity and the composition of AM fungal communities in their roots.
Results of this study indicated that all, but especially shade-avoidant plants have higher photosynthetic capacity in the absence of forest canopy. AM fungal communities, associated to shade-avoidant and shade-tolerant species remained distinctive under the canopy and indeed become more similar in the absence of forest canopy. Interestingly the change in the AM fungal communities was bigger in the roots of shade-tolerant plants, which experienced smaller increase in photosynthetic capacity. Thus it seems that host plant characteristics as well as environment influence AM fungal communities in plant roots but the mechanisms need to be examined further.
Citation: Koorem, K., Tulva, I., Davison, J., Jairus, T., Öpik, M., Vasar, M., Zobel, M, & Moora, M. (2017). Arbuscular mycorrhizal fungal communities in forest plant roots are simultaneously shaped by host characteristics and canopy-mediated light availability. Plant and Soil, 410(1-2), 259-271. (link to full text)
Background and Aims The majority of terrestrial plant species associate with arbuscular mycorrhizal (AM) fungi, to exchange carbon compounds with nutrients. However, the factors that determine the composition of AM fungal communities in individual plant roots remain poorly understood. We hypothesized that AM fungal communities are simultaneously influenced by environmental conditions, such as light availability, and the photosynthetic capacity of host plant species.
Methods We sampled individuals of shade-tolerant and shade-avoidant plant species, growing in the presence and absence of forest canopy, representing conditions of low and high light availability. We recorded photosynthetic parameters, shoot biomass and root AM fungal colonisation of these plant individuals and used 454-sequencing to characterise AM fungal communities in the roots of these plants.
Results Shade-avoidant plant species increased their photosynthetic capacity more than shade-tolerant plant species as a response to increased light availability due to canopy removal. Root AM fungal colonisation of all plants was higher when the forest canopy was absent, but canopy status had little influence on AM fungal richness in plant roots. The composition of AM fungal communities associating with shade-tolerant plants was significantly influenced by canopy status, while a less pronounced difference was observed among shade-avoidant plants.
Conclusions We suggest that both environmental conditions and the ability of plant species to exploit available resources determine the dynamics of mutualistic associations between host plant species and AM fungal taxa.