Abstract
Abstract. Legumes can be considered as pioneer plants during ecosystem development, as they form a symbiosis with different nitrogen fixing rhizobia species, which enable the plants to grow on soils with low available nitrogen content. In this study we compared the abundance and diversity of nitrogen fixing microbes based on the functional marker gene nifH, which codes for a subunit of the Fe-protein of the dinitrogenase reductase, in nodules of different size classes of Trifolium arvense (L.). Additionally, carbon and nitrogen contents of the bulk soil and plant material were measured. Plants were harvested from different sites, reflecting 2 (2a) and 5 (5a) yr of ecosystem development, of an opencast lignite mining area in the south of Cottbus, Lower Lusatia (Germany) where the artificial catchment "Chicken Creek" was constructed to study the development of terrestrial ecosystems. Plants from the 5a site revealed higher amounts of carbon and nitrogen, although nifH gene abundances in the nodules and carbon and nitrogen contents between the two soils did not differ significantly. Analysis of the nifH clone libraries showed a significant effect of the nodule size on the community composition of nitrogen fixing microbes. Medium sized nodules (2–5 mm) contained a uniform community composed of Rhizobium leguminosarum bv. trifolii, whereas the small nodules (<2 mm) consisted of a diverse community including clones with non-Rhizobium nifH gene sequences. Regarding the impact of the soil age on the community composition a clear distinction between the small and the medium nodules can be made. While clone libraries from the medium nodules were pretty similar at both soil ages, soil age had a significant effect on the community compositions of the small nodules, where the proportion of R. leguminosarum bv. trifolii increased with soil age.
Highlights
As a result of global chOancgee, ainntheSlacstiecennctuery an increase in initial ecosystems can be observed worldwide
Samples were taken from two sites directly adjacent to the artificial catchment “Chicken Creek”, which is located in an opencast lignite mining area in the south of Cottbus, Lower Lusatia (51◦36 N, 14◦16 E)
In summary the data indicate that the plants from the 5a site were more effective in nitrogen fixation, as their nitrogen content was significantly higher, the ammonium concentrations in soil did not differ significantly
Summary
As a result of global chOancgee, ainntheSlacstiecennctuery an increase in initial ecosystems can be observed worldwide. Initial ecosystems can evolve naturally for example during the retreat of glaciers or in response to human activities mainly in areas with opencast mining activities. Questions addressing food web formation in initial edcyonsaymstiecmsS,sopalrlaeindnt oeEtsotaanblryltishohfmbeansticaencdolsoogi-l ical interest and of high commercial concern. To address these issues an experimental catchment called “Chicken Creek” was constructed in the opencast lignite mining area in the south of Cottbus, Lower Lusatia (Germany) (Kendzia et al.T, 2h00e8)C, wrhyicohspprohviedersea unique opportunity to study initial ecosystem development. Already after five years of soil development, increasing complexity of food webs and increasing density of woody plants like birch, pine, and black locust was monitored (Elmer et al, 2011; Schaaf et al, 2010), which indicates a very fast progress in ecosystem development
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