Coastal sand dunes, environments that may appear arid and hostile, conceal an extraordinary biological complexity beneath the surface. A new study published in Environmental Microbiome by Arianna Grassi, Irene Pagliarani, Giorgia Cantini, Luciano Avio, Manuela Giovannetti, Monica Agnolucci and Alessandra Turrini of the Department of Agricultural, Food and Agro-Environmental Sciences at the University of Pisa sheds light on a still largely unexplored phenomenon: the bacterial communities living inside and around the spores of mycorrhizal fungi found in the rhizosphere of Ammophila arenaria, the common marram grass of Mediterranean dunes.
Mycorrhizal fungi are beneficial microorganisms that establish symbiotic relationships with the roots of most plants, supporting their nutrition and health, particularly in nutrient-poor and challenging environments such as coastal dunes. Their spores, however, are not isolated structures: they host bacterial communities whose distribution among different fungal taxa has so far remained poorly understood. The study focused on two fungal species particularly abundant in the rhizosphere of Ammophila arenaria in the marine sand dunes of the Park: Racocetra fulgida and Racocetra persica. These revealed a highly heterogeneous composition of bacterial communities associated with their respective spores. The real surprise emerged from the DNA analysis of the bacteria present in the samples, which revealed a very rich and diverse microbial community, with 69 genera associated with R. persica and 34 genera associated with R. fulgida.
These are not just any bacteria: the regular detection of Actinobacteria confirmed a relatively stable relationship with the fungal spores, and most of the identified bacteria belonged to cultivable genera and species with documented key beneficial functions.
The study’s most important conclusion concerns the role of fungal genotype: different fungi recruit highly diversified bacterial communities. In other words, each fungal species selectively “chooses” its own bacterial partners.
These findings also open interesting perspectives for practical applications. Understanding these interactions in fragile dune ecosystems — crucial environments for combating coastal erosion and climate change — could in the future make it possible to develop targeted microbial inoculants for dune restoration and to improve plant resistance to drought.
