Ms. J.D. Zijlstra: "Organic nitrogen uptake and endophytic mutualistic fungi in Dutch heathland ecosystems"

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22 Dec 2006 13:30
Unit: Wageningen UR
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. F. Berendse (Nature Conservation and Plant Ecology)

 In this thesis I tested the hypothesis that tannin-rich plant species e.g. Erica tetralix and Calluna vulgaris are able to monopolize the nutrient cycle by increasing the amounts of organic nitrogen forms relative to inorganic nitrogen forms. In addition, those species are expected to be favored which absorb organic nitrogen compounds through their associations with ericoid or ectomycorrhizal fungi. The results of an incubation experiment with shrub and grass litter showed that litters with C:N ratios above 30 and high tannin concentrations (as found in C. vulgaris) decrease the ratio inorganic nitrogen: dissolved organic nitrogen in soils. Results of a field inventory and of related experiments showed that nitrogen addition and shading both negatively affect the concentration of tannins in Calluna plants. While studying the fungal endophytes of ericaceous roots, a new fungal species was discovered, which is described as Cryptosporiopsis rhizophila Verkley & Zijlstra. Furthermore, isolated grass endophytes are found to be genetically closely related to endophytes, which were isolated from ericaceous hosts. The results of a competition experiment showed that in none of the litter treatments with varying tannin levels, C. vulgaris plants were able to outcompete Deschampsia flexuosa. Grass plants were able to benefit more efficiently from the available soil nitrogen released from the types of litter added. In conclusion, this thesis shows that heathland plants are able to monopolize the nutrient cycle with tannin-rich litter, but this competition advantage can be reduced if competitors have adopted the same strategy to use nutrients.
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