|dc.description.abstracteng||Mycorrhizal fungi are forming EcM on beech (Fagus sylvatica L.) and AM on ash (Fraxinus excelsior L.) and are an important component of several ecosystem processes in forests. One main functional role is nutrient acquisition, storage and subsequently transfer to the host plant in exchange for carbon from the plant.
We analyzed if several mycorrhizal fungal species in an old-growth deciduous forest in Germany differ in their functional roles for nutrient uptake and storage. For this purpose, experiments were conducted to investigate whether field-grown mycorrhizal fungi differ in their nutrient assimilation and storage of elements; and analyzed factors which might influence community composition of mycorrhizal fungi and functional abilities of mycorrhizal species.
The first experiment used plastic columns inserted 5 cm deep in the soil which were filled with seven different mixtures of 13C- / 15N – labelled or unlabeled leaf litter of ash and beech trees (Chapter 2 and 3).
EcM fungal species colonizing beech roots were exposed to different mixtures of ash and beech leaf litter (Chapter 2). Community composition of EcM changed after application of leaf litter and season, while number of EcM species was not affected. Hyphal biomass was higher on second harvest in October than on first harvest in May, but did not differ between leaf litter treatments.
Different EcM fungal species on root tips assimilated 15N from labelled leaf litter (Chapter 3). There were species-specific differences in 15N accumulation and in N concentration of mycorrhizal species and fine roots. Roots accumulated 15N from labelled leaf litter. 15N assimilation in mycorrhizal species increased between the two harvest dates in May and October. Whether different functional traits of EcM species might influence the observed differences for nutrient assimilation (for example nitrogen concentration or fungal exploration types) is discussed.
In the second experiment (Chapter 4 and 5), electron-dispersive X-ray microanalysis (EDX) equipped to a transmission electron microscope (TEM) was used to determine the subcellular element distribution (Mg, P, K, S, Ca) in roots of beech and ash and their associated mycorrhizas.
For this purpose, three EcM species on beech (Clavulina cristata, Cenococcum geophilum and Lactarius subdulcis) and one AM fungal species on ash (Glomus sp.) were analyzed via TEM-EDX (Chapter 4). Subcellular element concentrations were not evenly distributed throughout the cell compartments. Plant root tissues and fungal tissues differed in element concentrations. Glomus sp. on ash showed higher element concentration than the three EcM fungal species on beech. Differences in subcellular element concentrations were found between the three EcM fungi; Cenococcum geophilum showed high sulphur concentrations and Clavulina cristata showed high calcium concentrations than the other EcM species.Furthermore it was tested via TEM-EDX measurements whether subcellular element concentration (Mg, P, K, S, Ca) in tree root tissues of ash and beech and fungal tissues of AM and EcM were affected by the presence of a conspecific or heterospecific neighbouring tree species (Chapter 5). Beech root tissues showed higher P and K concentrations in mixture with ash than in pure beech plots, while ash root tissues showed lower Mg, P, K, and Ca levels than in pure ash plots. AM fungal tissues showed higher element concentrations of Mg, P, K and Ca in pure ash plots, while element concentrations in EcM fungal tissues were not affected.
The findings of this study support that mycorrhizal species on beech and ash trees in an old-growth deciduous forest in Central Europe differ in their functional roles regarding nutrient uptake, transfer and storage.||de