Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations

Quesada, Carlos Alberto, Paz, Claudia, Mendoza, Erick Oblitas, Phillips, Oliver Lawrence, Saiz, Gustavo, and Lloyd, Jon (2020) Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations. Soil, 6 (1). pp. 53-88.

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We investigate the edaphic, mineralogical and climatic controls of soil organic carbon (SOC) concentration utilising data from 147 primary forest soils (0-30 cm depth) sampled in eight different countries across the Amazon Basin. Sampled across 14 different World Reference Base soil groups, our data suggest that stabilisation mechanism varies with pedogenetic level. Specifically, although SOC concentrations in Ferralsols and Acrisols were best explained by simple variations in clay content - this presumably being due to their relatively uniform kaolinitic mineralogy - this was not the case for less weathered soils such as Alisols, Cambisols and Plinthosols for which interactions between Al species, soil pH and litter quality are argued to be much more important. Although for more strongly weathered soils the majority of SOC is located within the aggregate fraction, for the less weathered soils most of the SOC is located within the silt and clay fractions. It thus seems that for highly weathered soils SOC storage is mostly influenced by surface area variations arising from clay content, with physical protection inside aggregates rendering an additional level of protection against decomposition. On the other hand, most of the SOC in less weathered soils is associated with the precipitation of aluminium-carbon complexes within the fine soil fraction, with this mechanism enhanced by the presence of high levels of aromatic, carboxyl-rich organic matter compounds. Also examined as part of this study were a relatively small number of arenic soils (viz. Arenosols and Podzols) for which there was a small but significant influence of clay and silt content variations on SOM storage, with fractionation studies showing that particulate organic matter may account for up to 0.60 of arenic soil SOC. In contrast to what were in all cases strong influences of soil and/or litter quality properties, after accounting for these effects neither wood productivity, above-ground biomass nor precipitation/temperature variations were found to exert any significant influence on SOC stocks. These results have important implications for our understanding of how Amazon forest soils are likely to respond to ongoing and future climate changes.

Item ID: 62496
Item Type: Article (Research - C1)
ISSN: 2199-398X
Copyright Information: © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
Funders: Natural Environment Research Council (NERC), Gordon and Betty Moore Foundation (GBMF), European Research Council (ERC), EU Seventh Framework Programme (EU - SFP)
Projects and Grants: NERC grant no. NE/D005590/1 (“TROBIT”), NERC grant no. NE/B503384/1, NERC grant no. NE/D01025X/1, NERC grant no. NE/I02982X/1, NERC grant no. NE/F005806/1, NERC grant no. NE/I028122/1, GBMF grant no. 1656, ERC advanced grant no. 291585, “T-FORCES”, EU - SFP grant no. GEOCARBON283080, EU - SFP grant no. AMAZALERT-282664
Date Deposited: 11 Mar 2020 07:37
FoR Codes: 41 ENVIRONMENTAL SCIENCES > 4101 Climate change impacts and adaptation > 410101 Carbon sequestration science @ 10%
30 AGRICULTURAL, VETERINARY AND FOOD SCIENCES > 3007 Forestry sciences > 300703 Forest ecosystems @ 20%
41 ENVIRONMENTAL SCIENCES > 4106 Soil sciences > 410604 Soil chemistry and soil carbon sequestration (excl. carbon sequestration science) @ 70%
SEO Codes: 96 ENVIRONMENT > 9614 Soils > 961403 Forest and Woodlands Soils @ 100%
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