Spatially explicit sampling of AM fungal biomass reveals links to community characteristics and landscape context

A. Y. Ayesh Piyara Wipulasena, Alar Astover, John Davison, Koit Herodes, Inga Hiiesalu, Kadri Koorem, Siqiao Liu, Oscar Zárate-Martínez, Maarja Öpik, Meelis Pärtel, Siim-Kaarel Sepp, Martti Vasar, Martin Zobel, Tanel Vahter

Arbuscular mycorrhizal (AM) fungi are important contributors to soil functioning, yet their biomass and diversity may respond differently to environmental characteristics and historical legacies. Understanding these relationships is necessary for evaluating AM fungi as indicators of soil health. We investigated relationships among AM fungal biomass, community properties and natural habitat availability in contemporary and historical agricultural landscapes. AM fungal biomass in the soil was quantified using the fatty-acid biomarker 16:1ω5 in phospholipid (PLFA) and neutral lipid (NLFA) fractions. These fractions represent predominantly metabolically active and storage-associated biomass, respectively. Biomass estimates were compared with SSU metabarcoding-derived read count, Shannon diversity, community-weighted niche volume, and culturability. NLFA-based biomass estimates were positively associated with DNA read count and taxon richness but showed weak associations with Shannon diversity, whereas PLFA-based estimates were weakly associated with all three metrics. AM fungal biomass was negatively associated with community-weighted culturability but positively associated with community-weighted niche volume. Neither contemporary nor historical natural habitat availability predicted AM fungal biomass at the spatial scales examined, despite previously identified landscape effects on richness and community composition. Thus, landscape legacies were more evident in AM fungal taxonomic structure than in the amount of fungal biomass maintained in agricultural soils. Our findings demonstrate that biomass, diversity and community ecological characteristics capture distinct dimensions of AM fungal communities and can respond differently to environmental drivers across temporal scales.Integrating lipid-based biomass measurements with molecular assessments of diversity and ecological strategy should therefore provide a more comprehensive basis for evaluating AM fungal community condition and their potential as indicators of soil health in agricultural landscapes.