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Increases of soil C, N, and P pools along an acacia tree density gradient and their effects on trees and grasses
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2013 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 16, no 2, 347-357 p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen (N) fixing trees including many species of Acacia are an important though variable component of savanna ecosystems. It is known that these trees enrich the soil with carbon (C) and N, but their effect on the combined C:N:P stoichiometry in soil is less well understood. Theory suggests that they might reduce available phosphorus (P), creating a shift from more N-limited conditions in grass-dominated to more P-limited conditions in tree-dominated sites, which in turn could feed back negatively on the trees' capacity to fix N. We studied the effects of Acacia zanzibarica tree density upon soil and foliar N:P stoichiometry, and the N-2-fixation rates of trees and leguminous herbs in a humid Tanzanian savanna. Foliar N:P ratios and N-2-fixation rates of trees remained constant across the density gradient, whereas soil C, N and organic P pools increased. In contrast, the N:P ratio of grasses increased and N-2-fixation rates of leguminous herbs decreased with increasing tree density, indicating a shift towards more P-limited conditions for the understory vegetation. These contrasting responses suggest that trees and grasses have access to different sources of N and P, with trees being able to access P from deeper soil layers and perhaps also utilizing organic forms more efficiently.

Place, publisher, year, edition, pages
2013. Vol. 16, no 2, 347-357 p.
Keyword [en]
carbon sequestration, legume, nitrogen-fixing trees, nutrient limitation, N:P stoichiometry, plant-soil feedback, phosphorus, savanna, tree-grass interactions, woody encroachment
National Category
Environmental Sciences Ecology
URN: urn:nbn:se:umu:diva-67958DOI: 10.1007/s10021-012-9621-4ISI: 000315580200013OAI: diva2:615924
Available from: 2013-04-12 Created: 2013-04-09 Last updated: 2013-04-12Bibliographically approved

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Sitters, Judith
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