Flora and Fungi: Composition and Function

Most land plants constitute obligate symbiosis with soil fungi forming mycorrhizae (= fungal roots) in the case of vascular plants and mycorrhiza-like associations in the case of liverworts and hornworts. The fungi significantly improve nutrient uptake in the mostly nutrient-limited conditions in nature and supply minerals to the plants (Read and Perez-Moreno 2003). Glomeromycota, Hymenomycetes of Basidiomycota, Pezizales, some Leotiales, and other Ascomycota are the most important mycorrhizal fungi forming structurally distinctive associations, as determined by evolution and environmental constraints (Kottke 2002; Brundrett 2004). The tropical mountain rain forest in South Ecuador is not only exceptionally diverse in tree species, but also a hotspot for ericads, orchids, ferns, and liverworts (see Chapters 2 and 10.1 in this volume). Diverse mycorrhizal associations were, therefore, expected. Very restricted information was previously published from similar forests (Alexander and Högberg 1986). We, therefore, started with morphological and ultrastructural investigations of the mycorrhizae of the 220 tree species, the ericads, some abundant and mostly endemic, epiphytic pleurothallid orchids, and some epiphytic ferns, and we also investigated some mycorrhiza-like associations of liverworts. Here we consider the mycorrhizal state and the occurrence of the distinct mycorrhizal associations along the altitudinal and horizontal gradients, and we compile a number of new structural features.