title: Aboveground vs. Belowground Carbon Stocks in African Tropical Lowland Rainforest: Drivers and Implications.
abstract: BACKGROUND
  African tropical rainforests are one of the most important hotspots to look for changes in the upcoming decades when it comes to C storage and release. The focus of studying C dynamics in these systems lies traditionally on living aboveground biomass. Belowground soil organic carbon stocks have received little attention and estimates of the size, controls and distribution of soil organic carbon stocks are highly uncertain. In our study on lowland rainforest in the central Congo basin, we combine both an assessment of the aboveground C stock with an assessment of the belowground C stock and analyze the latter in terms of functional pools and controlling factors.
  
  
  RESULTS
  Our study shows that despite similar vegetation, soil and climatic conditions, soil organic carbon stocks in an area with greater tree height (= larger aboveground carbon stock) were only half compared to an area with lower tree height (= smaller aboveground carbon stock). This suggests that substantial variability in the aboveground vs. belowground C allocation strategy and/or C turnover in two similar tropical forest systems can lead to significant differences in total soil organic C content and C fractions with important consequences for the assessment of the total C stock of the system.
  
  
  CONCLUSIONS
  We suggest nutrient limitation, especially potassium, as the driver for aboveground versus belowground C allocation. However, other drivers such as C turnover, tree functional traits or demographic considerations cannot be excluded. We argue that large and unaccounted variability in C stocks is to be expected in African tropical rain-forests. Currently, these differences in aboveground and belowground C stocks are not adequately verified and implemented mechanistically into Earth System Models. This will, hence, introduce additional uncertainty to models and predictions of the response of C storage of the Congo basin forest to climate change and its contribution to the terrestrial C budget.
authors.affiliation: Ghent University, Isotope Bioscience Laboratory - ISOFYS, Ghent, Belgium.|Augsburg University, Department of Geography, Augsburg, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Doetterl
authors.affiliation: Ghent University, Isotope Bioscience Laboratory - ISOFYS, Ghent, Belgium.|Ghent University, Computational & Applied Vegetation Ecology - CAVElab, Ghent, Belgium.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Kearsley
authors.affiliation: Ghent University, Isotope Bioscience Laboratory - ISOFYS, Ghent, Belgium.|Ghent University, Computational & Applied Vegetation Ecology - CAVElab, Ghent, Belgium.
authors.forename: Marijn
authors.initials: M
authors.lastname: Bauters
authors.affiliation: Harvard University, Department of Organismic and Evolutionary Biology, Cambridge, United States of America.
authors.forename: Koen
authors.initials: K
authors.lastname: Hufkens
authors.affiliation: University of Kisangani, Faculty of Sciences, Kisangani, DR Congo.
authors.forename: Janvier
authors.initials: J
authors.lastname: Lisingo
authors.affiliation: Ghent University, Department of Applied Biosciences, Ghent, Belgium.
authors.forename: Geert
authors.initials: G
authors.lastname: Baert
authors.affiliation: Ghent University, Computational & Applied Vegetation Ecology - CAVElab, Ghent, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Verbeeck
authors.affiliation: Ghent University, Isotope Bioscience Laboratory - ISOFYS, Ghent, Belgium.
authors.forename: Pascal
authors.initials: P
authors.lastname: Boeckx
mesh_terms: D018533:Biomass; D002244:Carbon / Q000032:analysis*; D057486:Carbon Cycle; D002980:Climate; D003223:Congo; D017753:Ecosystem; D065928:Forests; D065947:Rainforest; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D002244:Carbon