Arbuscular mycorrhizal and dark septate fungi colonization in an invasive plant from Patagonian wetlands

Arbuscular mycorrhizal and dark septate fungi are common plant symbionts, but their role in promoting host plant fitness depends on environmental variables. Particularly in wetland plants, these associations are less understood. We analysed the role of arbuscular mycorrhizal fungi (AMF) and dark septate fungi (DSF) in the roots of Potentilla anserina (Rosaceae), an invasive species of Patagonia, widely distributed in wetlands. We tested three hypotheses: that fungi colonization varies according to soil moisture and nutrient content (nitrogen and phosphorus), that they enhance P. anserina nutrient content, and benefit plant growth. We measured the percentage of colonization in plants from five wetlands across a moisture gradient with different nutrient content, and performed a growth experiment with soil from these wetlands to evaluate changes in mycorrhizal and endophytic fungal colonization, aerial nutrient content and biomass production. In the field, root colonization by AMF was high in all sites (similar to 90%), whereas DSF was less abundant (similar to 20%), positively related to soil organic matter, and negatively related to soil phosphorus. In the experiment, DSF colonization was inversely related to increasing tissue N and P content. Potentilla anserina grew similarly in all the treatments, but biomass was positively related to DSF colonization. Our results provide evidence that DSF, rather than AMF, confer to this invasive species the ability to grow in soils with different water and nutrient content and may help to explain the wide distribution of this alien species in Patagonian wetlands.