Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism
A number of ecosystem services necessary for human wellbeing depend on high levels of plant diversity and performance. The successful growth of 80% of plant species, including the majority of crop plants, depends on microscopic root symbiotic arbuscular mycorrhizal (AM) fungi. Therefore, plant production and diversity in both natural and anthropogenic habitats is strongly influenced by the presence and diversity of these fungal symbionts. However, due to the cryptic lifestyle of AM fungi, the global biogeography of the group and drivers of their distribution are largely unknown. Such information is essential if we want to predict and mitigate losses of biodiversity and ecosystem services.
In a recently published paper in Science, the University of Tartu’s plant ecology group (led by Prof. Martin Zobel) and their international co-authors present the first global-scale empirical study of AM fungal biogeography. Project field work lasted from 2007 to 2012 and resulted in collection of 1014 environmental samples from six continents. The team used high-throughput DNA sequencing to identify AM fungi in their samples.
They found that many (33%) 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. However, as phylogenetic analysis showed that most current AM fungal taxa evolved after the large-scale tectonic reconfigurations, the wide distribution of AM fungi is apparently the result of efficient recent dispersal.
At the same time, local environmental conditions and landscape configurations determine the composition of local fungal communities. This bears a warning message, because progressive habitat loss and fragmentation of landscapes may result in a situation where human-induced dispersal barriers inhibit the arrival of symbiotic fungi which are necessary for ecosystem functioning and service provision. These findings have global ramifications for the management and conservation of biodiversity.
Professor Martin Zobel, head of the plant ecology lab, University of Tartu and center of excellence ‘Frontiers in biodiversity research’ says:
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. Fulfilling such an immense task would not have been possible without an extensive international collaborative network and the financial support of the center of excellence FIBIR.
Dr. Mari Moora, senior researcher in the plant ecology lab, states:
It was a vast effort to obtain a globally-balanced dataset so that the major climatic zones, natural biomes and ecosystem types were represented in a reasonable way using standardized field protocols. Hence, we are most grateful to the colleagues who offered local support and contributed to field work in 20 different countries worldwide.
Dr. Maarja Öpik, senior researcher in the plant ecology lab says:
Understanding the molecular diversity of cryptic organisms requires global sequence and ecological information databases for identification and comparative analyses. The advance and accessibility of molecular technologies have brought about massive growth of DNA-based data concerning the occurrence of AM fungi worldwide. Together with our new, systematically-collected data set, information from numerous case studies collated in a database maintained by our team is starting to illuminate the global diversity patterns of AM fungi on Earth. These are truly exciting times in AM fungal biodiversity and biogeography research.
Dr. John Davison, researcher in the plant ecology lab states:
It was a major challenge to analyze such a complex and comprehensive data set. 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. The result is that we are now able to examine cryptic biodiversity with a depth and detail that would have seemed fanciful even a decade ago.
Take home messages
*Many AM fungi are globally distributed, suggesting that they exhibit unexpectedly efficient dispersal, probably via both abiotic and biotic vectors, including humans.
*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.
AM fungi inhabit diverse ecosystems from lush tropical forests to temperate habitats and cold tundra. Examples of sampling sites targeted by this study. Photos M. Zobel.
Davison, J., Moora, M., Öpik, M., Adholeya, A., Ainsaar, L., Bâ, A., Burla, S., Diedhiou, A.G., Hiiesalu, I., Jairus, T., Johnson, N.C., Kane,A., Koorem, K., Kochar, M., Ndiaye, C., Pärtel, M., Reier, Ü., Saks, Ü., Singh, R., Vasar, M., Zobel M. Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism. Science 349: 970-973.
