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Please use this identifier to cite or link to this item: http://hdl.handle.net/10204/1961

Title: Nitrogen cycling in the soil-plant system along a precipitation gradient in the Kalahari sands
Authors: Aranibar, JN
Otter, L
Macko, SA
Feral, CJW
Epstein, HE
Dowty, PR
Eckardt, F
Shugart, HH
Swap, RJ
Keywords: Nitrogen fixation
Nitric oxide emissions
Soil nitrogen pools
Plant nitrogen pools
Kalahari region - Southern Africa
Biodiversity conservation
Environmental sciences
Issue Date: Mar-2004
Publisher: Blackwell Publishing Ltd
Citation: Aranibar, JN, et al. 2004. Nitrogen cycling in the soil-plant system along a precipitation gradient in the Kalahari sands. Global Change Biology, vol. 10(3), pp 359-373
Abstract: Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, N-15 natural abundance (delta(15)N), and soil NO (Nitric oxide) emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N-2 fixation associated with vascular plants was estimated with foliar delta(15)N and the basal area of leguminous plants. Soil and plant N was more N-15 enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N-2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (N-15 enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N-2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in delta(15)N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil-plant system.
URI: http://hdl.handle.net/10204/1961
ISSN: 1354-1013
Appears in Collections:Climate change
Ecosystems processes & dynamics
General science, engineering & technology

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