How important is arbuscular mycorrhizal colonization in wetland and aquatic habitats?

Plants that live in aquatic habitats are frequently subjected to oxygen limitation and many of them modify their anatomy and physiology to counteract hypoxia. In these habitats, the role of plant associations with arbuscular mycorrhizal fungi (AMF), which are widespread in terrestrial environments and frequently confer benefits to the associated plant, is still debated. Starting from data taken from 34 selected papers, this study focuses on the occurrence of AMF in the roots of wetland and aquatic plants, taking into account the hydrological conditions of the sites, the plant wetland indicators and life forms, plant taxonomy and colonization by dark septate endophytes. The results have demonstrated the importance of hydrology in controlling the frequency and intensity of AMF root colonization, which tends to be low in obligate wetland plants. Moreover, colonization is generally lower and, possibly, less functional in monocots than in dicots. We suggest that the hydrological conditions, by filtering species according to their water tolerance, shape plant community composition, and that although AMF colonization is one of the traits that may increase plant fitness, it is not the most important one. In fact, a range of nutritional and growth strategies, which are more variegated than in terrestrial habitats, exists in wetland/aquatic habitats, and these strategies may rely, or not, on AMF colonization, as a consequence of the habitat and species.