Epsilon Open Archive

Abstract

This thesis comprises four studies on the identification and ecology of arbuscular mycorrhizal fungi (AMF) in grasslands and in arable soils. Fungi belonging to the phylum Glomeromycota are obligate symbionts in the roots of land plants where they form arbuscular mycorrhiza. The symbiotic association increases the ability of the host plant to take up nutrients from the soil via the extensive mycelia of the fungal symbionts, which have a larger and better distributed surface area for uptake than the roots alone. In turn, the fungi obtain carbohydrates that the plants produce. Arbuscular mycorrhiza are almost ubiquitous in grasslands, and therefore assumed to play a key role in ecosystem functioning. AMF taxa in the plant roots were identified with the use of different molecular techniques. Their phylogenetic affiliations were investigated and the significance of some relevant ecological factors shaping the AMF community structure was evaluated. In a seminatural grassland, we observed that AMF richness decreased in relation to increasing levels of nitrogen in the soil. The temporal patterns and species composition of the fungal communities colonizing the roots of two co-existing plant species were also shown to be different. We also found that AMF communities colonizing a single plant species varied between different localities within the same region. We used a long-term field experiment to show how different management practices affected the microbial soil biota. We compared the application of different organic and inorganic fertilisers, and their effect upon the AM fungi colonizing maize roots and the bacteria in root-associated soil aggregates. Some amendments induced dramatic changes in the richness and composition of the bacterial and the fungal communities. In conclusion, our experiments revealed evidence of complex ecological patterns in this cryptic but important group of fungi. Human management practices in grasslands and arable fields can shape the communities of both AMF and bacteria in the soil. Improved knowledge of the spatial and temporal niches of different taxa is a prerequisite in order to design manipulative experiments that can establish the link between taxonomical and functional diversity.