Similar importance of edaphic and climatic factors for controlling soil organic carbon stocks of the world

Abstract

Abstract. Soil organic carbon (SOC) accounts for two-thirds of terrestrial carbon. Yet, the role of soil physicochemical properties in regulating SOC stocks is unclear, inhibiting reliable SOC predictions under land use and climatic changes. Using legacy observations from 141 584 soil profiles worldwide, we disentangle the effects of biotic, climatic and edaphic factors (a total of 31 variables) on the global spatial distribution of SOC stocks in four sequential soil layers down to 2 m. The results indicate that the 31 variables can explain 60 %–70 % of the global variance of SOC in the four layers, to which climatic variables and edaphic properties each contribute ∼35 % except in the top 20 cm soil. In the top 0–20 cm soil, climate contributes much more than soil properties (43 % vs. 31 %), while climate and soil properties show the similar importance in the 20–50, 50–100 and 100–200 cm soil layers. However, the most important individual controls are consistently soil-related and include soil texture, hydraulic properties (e.g. field capacity) and pH. Overall, soil properties and climate are the two dominant controls. Apparent carbon inputs represented by net primary production, biome type and agricultural cultivation are secondary, and their relative contributions were ∼10 % in all soil depths. This dominant effect of individual soil properties challenges the current climate-driven framework of SOC dynamics and needs to be considered to reliably project SOC changes for effective carbon management and climate change mitigation.

Continental-scale controls on soil organic carbon across sub-Saharan Africa

“…Climate and geochemical variables are similarly important for explaining SOC variations across sub-Saharan Africa (Fig. 3), which is in line with findings from a global study (Luo et al, 2021). However, the explanatory power of climate and geochemical variables are not independent of each other, reflecting the overall strong interaction between climate and geochemistry (Doetterl et al, 2015).…”

“…6i). Similar findings were recently encountered in a global study (Luo et al, 2021). One possibility may be that the relatively large 0-20 cm depth interval might dilute differences that could be more marked in the top few centimeters.…”

“…We adopted an approach introduced by McLennan (1993), which assumes that Ca is typically lost more rapidly than Na during weathering. If a soil sample contained inorganic C (C total -C org ; used as a proxy for carbonates and apatite) and the CaO content was greater than that of Na 2 O in the same sample (n = 476), then the CaO concentration was set to that of Na 2 O from the same sample (Malick and Ishiga, 2016). After applying the correction, no obvious correlation remained between CIA and inorganic C (Fig.…”

Temperature effects on carbon storage are controlled by soil stabilisation capacities

“…Furthermore, cation exchange capacity (CEXC) varies with the type of clay minerals present and the binding efficiencies of the mineral surfaces 42 . In global analyses, texture, pH and CEXC tend to be the three edaphic factors that correlate most strongly with soil C storage 18,20 . For these reasons, we also accounted for variation in both pH and CEXC, and evaluated whether the relationship between soil texture and the effect of temperature on C storage was retained.…”

“…1a) offering a major opportunity for improving understanding of how stabilisation mechanisms control the effects of climate on soil C storage. This is because soil texture, in particular clay content, has been shown to be a strong predictor of a soil's C stabilisation capacity 3,[18][19][20] , directly determining the potential for chemical stabilisation through the formation of organo-mineral complexes, and indirectly affecting physical protection through its influence on aggregate dynamics 21 . Thus, it is now possible to empirically determine whether the effect of temperature on soil C storage is related to SOM stabilisation capacities.…”