DNA sequencing: University of Tartu scientists show that arbuscular mycorrhizal fungi are globally distributed

In a recently published paper in Science, the University of Tartu’s plant ecology group, led by Prof. Martin Zobel, present the first global-scale empirical study of arbuscular mycorrhizal (AM) fungal biogeography. Project fieldwork lasted from 2007 to 2012 and resulted in collection of 1014 environmental samples from six continents. The group’s results showed that many AM fungi are globally distributed but nonetheless require careful conservation.

AM fungi inhabit diverse ecosystems from lush tropical forests to temperate habitats and cold tundra. Examples of sampling sites targeted by this study. Photographs by M. Zobel.

The successful growth of 80% of plant species, including the majority of crop plants, depends on microscopic root symbiotic AM fungi. Indeed, plant productivity and diversity in both natural and anthropogenic habitats is strongly influenced by the presence and diversity of these fungi.

However, the global biogeography of AM fungi and drivers of their distribution are largely unknown. As such information is essential for predicting and mitigating losses of biodiversity and ecosystem services, the University of Tartu’s plant ecology group and their international co-authors conducted a global-scale empirical study of AM fungal biogeography.

Using high-throughput DNA sequencing to identify AM fungi in their samples, they found that many (34%) AM fungal taxa exhibit a global distribution, while almost all (93%) are present on multiple continents. This result was unexpected because AM fungi have been assumed to be poor dispersers.

“We started this line of research over 10 years ago by addressing AM fungal diversity in local habitats. We soon realized, however, that we cannot explain local diversity patterns and processes without looking at the broader picture. Our efforts began to snowball, and we ended up with this first systematic global overview of the diversity and distribution of these important symbiotic microbes,” Professor Martin Zobel, head of the plant ecology lab at University of Tartu and center of excellence ‘Frontiers in biodiversity research’ says.

“It was a major challenge to analyze such a complex and comprehensive data set,“ Dr. John Davison, researcher in the plant ecology lab at University of Tartu, added. “While we started by analyzing taxon distributions and the composition of AM fungal communities, the emerging patterns stimulated us to integrate phylogenetic information as well. Rapidly evolving molecular technologies are demanding parallel advances in data storage, bioinformatics and statistical approaches. We are now able to examine cryptic biodiversity with a depth and detail that would have seemed fanciful even a decade ago.”

Despite the wide distributions of AM fungal taxa, AM fungal communities are shaped by local environmental conditions and landscape configurations. Progressive loss and fragmentation of habitats may therefore lead to a situation where ecosystems lack the symbiotic fungi that are essential for sustainable ecosystem functioning, the research group emphasizes.

The wide distributions of AM fungi revealed by the study also raise several new questions, according to the group. Future studies can help to explain how the fungi achieve such efficient dispersal. Another focus of research will be to understand whether the symbiotic characteristics of widespread taxa remain constant throughout their ranges.

In addition to the core authors Martin Zobel, John A. Davis, UT’s Senior Research Fellow in Plant Ecology Mari Moora and UT’s Senior Research Fellow in Plant Ecology Maarja Öpik, co-authors included eight researchers from the UT Institute of Ecology and Earth Sciences and colleagues from the USA, India and Senegal.

The paper Davison et al. (2015) “Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism” was published in Science at 28 August 2015.

Conducting the study was made possible thanks to an extensive international collaborative network and the financial support of the center of excellence FIBIR.

Additional information: Martin Zobel, Professor of Plant Ecology at the University of Tartu, e-mail: martin.zobel@ut.ee.
John Davison, Research Fellow at the University of Tartu, e-mail: john.davison@ut.ee.