NDLI: Response of CO$_{2}$ fluxes and productivity to water availability in two contrasting ecosystems in northern Benin (West Africa)

Content Provider	Springer Nature Link
Author	Ago, Expedit Evariste Agbossou, Euloge Kossi Cohard, Jean Martial Galle, Sylvie Aubinet, Marc
Copyright Year	2016
Abstract	CO $_{ 2 }$ fluxes were measured during 18 months in a forest and a savannah in northern Benin. Higher values of carbon fluxes were found during the wet season at each site. A strong dependency of carbon fluxes on water relations was found in two contrasting sites. The forest sequestered 640 ± 50 and the savannah 190 ± 40 g C m $^{ −2 }$ year $^{ −1 }$ . In West Africa, the main mechanisms or factors governing the dynamics of ecosystems, especially the dynamics of the carbon fluxes and productivity, still remain less known. This study reports the carbon fluxes over two contrasting ecosystems, notably a protected forest (lat 9.79°N, long 1.72°E, alt 414 m) and a cultivated savannah (lat 9.74°N, long 1.60°E, alt 449 m) in northern Benin. The two sites were among those equipped by the AMMA-CATCH observatory and Ouémé 2025 project.Flux data were analyzed at the daily and seasonal scales in order to understand their controlling variables. We discussed the patterns of CO$_{2}$ fluxes and the characteristics of the two ecosystems. The study also focused on the different water usage strategies developed by the two ecosystems since the alternation between dry and wet seasons highly influenced the seasonal dynamics. Finally, the annual carbon sequestration was estimated together with its uncertainty.The carbon fluxes were measured during 18 months (July 2008–December 2009) by an eddy-covariance system over two contrasting sites in northern Benin. Fluxes data were computed following the standard procedure. The responses of CO$_{2}$ fluxes to the principal climatic and edaphic factors, and the canopy conductance were studied.A clear CO$_{2}$ fluxes response to main environmental factors was observed, however with difference according to the seasons and vegetation types. The ecosystem respiration showed the highest values during the wet season and a progressive decrease from wet to dry periods. Also, the carbon uptake values were high during the wet period, but low during the dry period. However, the CO$_{2}$ fluxes for the protected forest were always higher than that for the cultivated savannah within each defined period. This was due to the seasonal changes not only in phenology and physiology but also to the acclimation to environmental conditions, especially to the soil water availability. The water use efficiency was influenced by VPD during the day conditions for two ecosystems. However, the VPD response curve of water usage was relatively constant for the protected forest during the transitional and wet seasons. In contrary, for the cultivated savannah the VPD response decreased about 46 % from transitional dry-wet to wet seasons and remained relatively constant until transitional wet-dry season. The close relationships between the net CO$_{2}$ assimilation and the canopy conductance were found for the two ecosystems. This suggests a regulation of the stomata by a partial stomatal closure besides the radiation control. Finally, the forest sequestered at the annual scale 640 ± 50 and the savannah 190 ± 40 g C m$^{−2}$ year$^{−1}$.We conclude with a strong relation between the carbon fluxes and water in the two investigated ecosystems. Apart from the radiation control, the stomata also play an important role in the regulation of the CO$_{2}$ assimilation in the two ecosystems.
Starting Page	483
Ending Page	500
Page Count	18
File Format	PDF
ISSN	12864560
Journal	Annals of Forest Science
Volume Number	73
Issue Number	2
e-ISSN	1297966X
Language	English
Publisher	Springer Paris
Publisher Date	2016-03-09
Publisher Institution	Institut National de la Recherche Agronomique (INRA)
Publisher Place	Paris
Access Restriction	Subscribed
Subject Keyword	Eddy covariance CO$_{2}$ fluxes Productivity Ecosystem respiration Forest Savannah Water usage Benin West Africa Forestry Wood Science & Technology Forestry Management Tree Biology Environment
Content Type	Text
Resource Type	Article
Subject	Ecology Forestry

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