Organic matter cycling along geochemical, geomorphic, and disturbance gradients in forest and cropland of the African Tropics – project TropSOC database version 1.0

Abstract

Abstract. The African Tropics are hotspots of modern-day land use change and are, at the same time, of great relevance for the cycling of carbon (C) and nutrients between plants, soils, and the atmosphere. However, the consequences of land conversion on biogeochemical cycles are still largely unknown as they are not studied in a landscape context that defines the geomorphic, geochemical, and pedological framework in which biological processes take place. Thus, the response of tropical soils to disturbance by erosion and land conversion is one of the great uncertainties in assessing the carrying capacity of tropical landscapes to grow food for future generations and in predicting greenhouse gas fluxes from soils to the atmosphere and, hence, future earth system dynamics. Here we describe version 1.0 of an open-access database created as part of the project “Tropical soil organic carbon dynamics along erosional disturbance gradients in relation to variability in soil geochemistry and land use” (TropSOC). TropSOC v1.0 (Doetterl et al., 2021, https://doi.org/10.5880/fidgeo.2021.009) contains spatially and temporally explicit data on soil, vegetation, environmental properties, and land management collected from 136 pristine tropical forest and cropland plots between 2017 and 2020 as part of monitoring and sampling campaigns in the eastern Congo Basin and the East African Rift Valley system. The results of several laboratory experiments focusing on soil microbial activity, C cycling, and C stabilization in soils complement the dataset to deliver one of the first landscape-scale datasets to study the linkages and feedbacks between geology, geomorphology, and pedogenesis as controls on biogeochemical cycles in a variety of natural and managed systems in the African Tropics. The hierarchical and interdisciplinary structure of the TropSOC database allows linking of a wide range of parameters and observations on soil and vegetation dynamics along with other supporting information that may also be measured at one or more levels of the hierarchy. TropSOC's data mark a significant contribution to improve our understanding of the fate of biogeochemical cycles in dynamic and diverse tropical African (agro-)ecosystems. TropSOC v1.0 can be accessed through the Supplement provided as part of this paper or as a separate download via the websites of the Congo Biogeochemistry Observatory and GFZ Data Services where version updates to the database will be provided as the project develops.

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

“…3; Table 3). Additionally, available nutrients (dissolved N and bioavailable P) reported by Doetterl et al (2021b) for the same soils as investigated, were positively correlated to SPR and 14 C of respired CO 2 (Fig. A1) in the mafic and felsic regions.…”

“…Multiple linear regression was used to assess the explanatory power of soil properties to predict SPR and the difference between the soil and respired CO 2 14 C signature ( − 14 C). Before running regression models, we extracted a wide range of physico-chemical soil properties and an SOC quality indicator (C : N) for our investigated soils, where, in parallel studies, soil C stabilization mechanisms were assessed by Reichenbach et al (2021) and microbial activity parameters (C, N and P enzymes and microbial biomass) assessed during our incubation experiment (Table B1) by Doetterl et al (2021b). Overall, our data set consisted of 37 independent variables and 112 aggregated observations for each of our target variables (for CO 2 , results were aggregated from 1350 individual observations of SPR over the course of the experiment).…”

“…In a final step, we used partial correlation analysis, following Doetterl et al (2015b), to interpret the explanatory power of independent variables in our model, while controlling for soil depth. We contextualize our findings with respect to microbial (extracellular enzyme activity; Doetterl et al, 2021b), mineralogical (pedogenic oxides; Reichenbach et al, 2021) and soil fertility parameters (available nutrients and exchangeable base cations; Doetterl et al, 2021a). For all statistical tests, due to the relatively small sample size and to avoid type II statistical errors, a threshold of p < 0.1 was used to indicate significant difference.…”

“…Values reported are averages plus standard deviations (n = 85). Source: Project TropSOC Database Version 1.0 (Doetterl et al, 2021b).…”

The central African soil spectral library: a new soil infrared repository and a geographical prediction analysis

“…In particular, the humid tropics are a front line for these anthropogenic impacts. For example, increasing temperatures and accelerating deforestation in the humid tropics are estimated to enhance greenhouse gas emissions (Don et al, 2011;Cox et al, 2013) but also to significantly reduce soil functions and ecosystem services such as plant nutrient supply, water storage and filtration capabilities, and erosion protection (Veldkamp et al, 2020). Despite the expected severity of these impacts, our understanding of the effects on soils in the humid tropics of Africa is limited by sparse data and uneven distribution of low-latitude research.…”