Human and climate impact on 15N natural abundance of plants and soils in high-mountain ecosystems : A short review and two examples from the Eastern Pamirs and Mt. Kilimanjaro

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Zech, Michael ; Bimüller, Carolin ; Hemp, Andreas ; Samimi, Cyrus ; Broesike, Christina ; Hörold, Claudia ; Zech, Wolfgang:
Human and climate impact on 15N natural abundance of plants and soils in high-mountain ecosystems : A short review and two examples from the Eastern Pamirs and Mt. Kilimanjaro.
In: Isotopes in Environmental and Health Studies. Bd. 47 (2011) Heft 3 . - S. 286-296.
ISSN 1477-2639
DOI: https://doi.org/10.1080/10256016.2011.596277

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Abstract

Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of 15N. A short review displays that δ 15N of plant-soil systems may often serve as an integrated indicator of N-cycles with more positive δ 15N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs showthat intensively grazed pastures are significantly enriched in 15N compared to the lessexploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ 15N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in 15N, indicating that here the N-cycle is relatively closed. However, significantly higher δ 15N values characterise the upper montane forest zone at the transition to the subalpine zone.We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the 15N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening. © 2011 Taylor & Francis.