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Responses of ecosystem carbon dioxide fluxes to soil moisture fluctuations in a moist Kenyan savanna

Published online by Cambridge University Press:  11 October 2010

D. O. Otieno ,
G. O. K'Otuto ,
J. N. Maina ,
Y. Kuzyakov  and
J. C. Onyango
D. O. Otieno*
Affiliation:
Department of Plant Ecology, University of Bayreuth, 95440 Bayreuth, Germany
G. O. K'Otuto
Affiliation:
Department of Botany & Horticulture, Maseno University, Private Bag Maseno, Kenya
J. N. Maina
Affiliation:
Department of Botany & Horticulture, Maseno University, Private Bag Maseno, Kenya
Y. Kuzyakov
Affiliation:
Department of Agroecosystem Research, BayCEER, University of Bayreuth, 95440 Bayreuth, Germany
J. C. Onyango
Affiliation:
Department of Botany & Horticulture, Maseno University, Private Bag Maseno, Kenya
*
1Corresponding author. Email: [email protected]
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Abstract:

Measurements were conducted within a fence-exclosure between February 2008 and July 2009 to investigate the influence of soil moisture on ecosystem CO2 fluxes in a Themeda triandra-dominated grassland of a humid Kenyan savanna. Rainout shelters were constructed to reduce ambient rainfall by 0%, 10% and 20% respectively to attain variable soil water content (SWC) during plant growth. SWC within the top 30 cm layer, above-ground biomass, soil and plant nitrogen (N) concentrations were assessed monthly alongside CO2 fluxes. Net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) were measured with closed chambers while carbon (C) partitioning during the wet and dry seasons were assessed through pulse 13C labelling. There were significant seasonal and between plot differences in SWC, above-ground biomass, canopy light utilization efficiency (α), CO2 fluxes and C allocation pattern resulting from differences in SWC. The ecosystem was a net C sink during the wet and C neutral during the dry seasons. The study showed strong seasonal fluctuations in ecosystem CO2 fluxes and underscores the significant role of the savanna grasslands in regional C balance due to its expansive nature. The savanna grassland is however vulnerable to low soil moisture, with significant reduction in CO2 uptake during drought.

Keywords

δ13CAfricabiomassCO2 chambersecosystem respirationgross primary productionhumid savannanet ecosystem exchangenitrogensoil moistureThemeda triandra
Type
Research Article
Information
Journal of Tropical Ecology , Volume 26 , Issue 6 , November 2010 , pp. 605 - 618
Copyright
Copyright © Cambridge University Press 2010

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