Nitrogen fixation in nodules of the conifer Lepidothamnus fonkii (Phil.) in Patagonian peatlands, Chile

Werner Borken1, Regina Anzenhofer2, Nelson Bahamonde3, Marcus A. Horn4, Klaus-Holger Knorr5
1 Bayreuth Center of Ecology, Soil Ecology, University of Bayreuth, Germany
2 Bayreuth Center of Ecology, Hydrology, University of Bayreuth, Germany
3 Instituto de la Patagonia, Universidad de Magellanes, Chile
4 Bayreuth Center of Ecology, Ecological Microbiology, University of Bayreuth, Germany
5 Institute for Landscape Ecology, Hydrology Group, University of Münster, Germany

O 6.4 in Biogeochemistry of wetlands

15.07.2014, 12:00-12:20, H17

Nitrogen fixation is an important fundamental biological process for plant nutrition in pristine ecosystems, but mutualistic nitrogen fixation is restricted to few plant and bacteria species. Here we report for the first time mutualistic nitrogen fixation by Lepidothamnus fonkii (Phil.), a small conifer of the family Podocarpaceae that grows in pristine, nutrient-poor peatlands of Chile and Argentina. Analysis of nifH genes (encoding nitrogenases) suggests symbiosis with bacteria of the family Beijerinckiaceae in small nodules of L. fonkii. The acetylene reduction assay, 15N2-application and nifH mRNA analysis indicate high root-associated activity of Beijerinckiaceae related nitrogenases. Root biomass of 220 g m-2 and high density of nodules exhibit a great potential of nitrogen fixation in patches with L. fonkii. We estimated annual nitrogen fixation rates of up to 1 – 2 g m-2 y-1, which far exceed natural background deposition. However, natural abundance of 15N in roots (- 8 per mil) and leafs (-11 per mil) implies that L. fonkii takes up relatively small amounts of the fixed nitrogen. The presence of fungal hyphae in nodules and roots of L. fonkii suggest that a large portion of fixed nitrogen is used by the fungi. The function of the associated fungi in nitrogen cycling and the fate of fixed nitrogen in these peatlands are still unclear.

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last modified 2014-04-03