Unveiling the Global Richness of Arbuscular Mycorrhizal Fungi
By Stefanie Lutz & Marcel van der Heijden, University of Zurich and Agroscope
The symbiotic relationship between plant roots and mycorrhizal fungi is an ancient and vital cornerstone of life on land. Originating over 450 million years ago, this partnership has enabled plants to colonise terrestrial environments and shape ecosystems across grasslands, forests and deserts. Among these fungi, arbuscular mycorrhizal fungi (AMF) are particularly well known for their role in plant nutrient acquisition, drought tolerance and disease resistance, all while receiving essential carbon compounds from their plant hosts.
Traditionally, AMF research has focused on the Glomeromycota (G-AMF), a group of fungi extensively studied for their association with most land plants. However, recent discoveries have shown that fungi of the Mucoromycota phylum, in particular the enigmatic Endogonomycetes (E-AMF), also form arbuscule-like structures, broadening our understanding of mycorrhizal diversity. While the evolutionary and ecological nuances of these fungi remain a subject of debate, the broader view underscores their importance in plant-fungal mutualisms.
A Hidden Wealth of Diversity
Figure 1: Diverse AMF structures, from left to right: arbuscules (credits: Ryan Geil), vesicles and hyphae (credits: Marcel van der Heijden), and spore assemblage (credits: Fritz Oehl) (credits soil profile: Gabriela Brändle, Agroscope).
In our recent study published in Fungal Ecology, we aimed to increase knowledge of the global molecular diversity of AMF by analysing existing long-read sequencing data from a combination of global field surveys covering 4,733 sampling sites across all terrestrial biomes and continents. Our study provides the first combined estimate of global G-AMF and putative E-AMF richness, far exceeding previously reported numbers and taxa. Specifically, we detected 8,517 OTUs (Operational Taxonomic Units, roughly corresponding to species) of G-AMF, exceeding previous AMF richness estimates by a factor of five to fifteen. In addition, we identified 600 OTUs for putative E-AMF with many unknown species, providing the first global estimate for this group.
Advances in sequencing technologies, such as the use of long-read sequencing, are paving the way for more accurate assessments of fungal diversity. These tools allow researchers to uncover rare and cryptic species, filling gaps in our understanding and providing a basis for global biodiversity assessments.
Towards a Comprehensive Understanding
Understanding the diversity of AMF is more than an academic pursuit. These fungi are an integral part of ecosystem resilience, particularly in the face of climate change and habitat degradation. Rich and diverse mycorrhizal communities improve soil health, enhance plant productivity and stabilise ecosystems under changing environmental conditions. Grasslands, for example, host the highest AMF richness, highlighting their role as hotspots for conservation efforts.
The ongoing study of AMF is a reminder of the intricate, often invisible networks that sustain life on Earth. As we expand our knowledge of these ancient symbionts, we not only unravel the complexities of their evolution and ecology, but also equip ourselves to better protect the ecosystems they support. By embracing the full spectrum of AMF diversity, from G-AMF to E-AMF, we can foster a more resilient and sustainable future for both natural and managed landscapes.