Plant and Soil

, Volume 328, Issue 1, pp 95–108

Combined effects of soil moisture and nitrogen availability variations on grass productivity in African savannas


    • Department of Environmental SciencesUniversity of Virginia
    • Department of Civil and Environmental EngineeringPrinceton University
  • Paolo D’Odorico
    • Department of Environmental SciencesUniversity of Virginia
  • Lydia Ries O’Halloran
    • Department of ZoologyOregon State University
  • Kelly Caylor
    • Department of Civil and Environmental EngineeringPrinceton University
  • Stephen Macko
    • Department of Environmental SciencesUniversity of Virginia
    • Program in Geobiology and Low Temperature GeochemistryU. S. National Science Foundation
Regular Article

DOI: 10.1007/s11104-009-0085-z

Cite this article as:
Wang, L., D’Odorico, P., O’Halloran, L.R. et al. Plant Soil (2010) 328: 95. doi:10.1007/s11104-009-0085-z


Savannas cover about 20% of the Earth’s land area and 50% of Africa. As an indispensable component of savanna, grasses play an important role in these ecosystems. A better understanding of grass productivity and its controlling factors in savanna ecosystems could therefore be a key to understand the functioning of savannas and predict savanna responses to future climatic changes. In this study, a stable isotope fertilization experiment was conducted to determine how factors limiting grass production in savannas differ across regional climate gradients. The study was conducted on the geomorphically homogenous Kalahari Transect (KT), which offers an ideal setting to study nutrient and vegetation dynamics independently of confounding soil effects. The results show that the grasses assimilated the added fertilizer at all the sites but they did not respond to nitrogen fertilization for both dry and wet years, and at both dry and wet ends of the Transect. Although prior studies have proposed a switch between water and nitrogen limitations between arid and mesic savannas, our results suggest that nitrogen availability may not limit grass productivity across the whole KT. Thus, although the traditional classifications as nutrient poor (broad-leaf) and nutrient rich (fine-leaf) savanna ecosystems may still be useful, it does not necessarily imply the existence of nitrogen limitation in the nutrient poor area; in fact, it is more likely that the herbaceous species found in the more humid sites (nutrient poor sites) are already adapted to lower nitrogen availability.


AridBotswanaFertilizationKalahari Transect15NSavannaSemi-aridStable isotopesTracerWaterZambia

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© Springer Science+Business Media B.V. 2009