Global database and model on dissolved carbon in soil solution

Abstract

<p><strong>Abstract.</strong> Abstract. Dissolved carbon leaching in and from soils plays an important role in C transport along the terrestrial-aquatic continuum. However, a global overview and analysis of dissolved carbon in soil solutions, covering a wide range of vegetation types and climates, is lacking. We compiled a global database on annual average dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in soil solutions, including potential governing factors, with 762 entries from 351 different sites covering a range of climate zones, land cover types and soil classes. Using this database we develop regression models to calculate topsoil concentrations, and concentrations vs. depth in the subsoil at the global scale. For DIC, the lack of a proportional globally distributed cover inhibits analysis on a global scale. For DOC, annual average concentrations range from 1.7 to 88.3 (median = 25.27) mg C/L for topsoils and from 0.42 to 372.1 (median = 5.50) mg C/L for subsoils (excluding lab incubations). Highest topsoil values occur in forests of cooler, humid zones. In topsoils, multiple regression showed that precipitation is the most significant factor. Our global topsoil DOC model (R<sup>2</sup> = 0.36) uses precipitation, soil class, climate zone and land cover type as model factors. Our global subsoil model describes DOC concentrations vs. depth for different USDA soil classes (overall R<sup>2</sup> = 0.45). Highest subsoil concentrations are calculated for Histosols.</p>

Soil dissolved organic carbon in terrestrial ecosystems: Global budget, spatial distribution and controls

“…Moreover, in forests, species composition influence the quality of C input, which affects microbial decomposition and thus leads to changes in soil DOC concentration. For example, temperate coniferous forest features a lower DOC concentration than temperate broadleaf forest, which is consistent with previous studies (Camino‐Serrano et al, 2014; Currie, Aber, McDowell, Boone & Magill, 1996; FernandezSanjurjo, Vega, & GarciaRodeja, 1997; Langeveld et al, 2019). This is a result of the mechanism by which higher lignin content lowers the quality of plant litter and thus hinders microbial decomposition, leading to less DOC being released (Wang et al, 2015).…”

“…However, in contrast with this study, Langeveld et al (2019) reported much lower DOC levels in Arctic regions. This difference may be caused by ignoring DOC concentrations in soil solution and in dry or frozen soils in Langeveld et al (2019) The global DOC budget is estimated as 12.97 Pg C for the 0-100 cm soil profile, which accounts for 0.880% of TOC, smaller than the fraction of soil organic C in soil microbial biomass C (Xu et al, 2013). The residence time of soil DOC ranges from a few hours to a few days, with some low molecular compound cycling on a minute timescale (Boddy et al, 2007).…”

“…Soil texture has been reported to affect soil DOC concentration through effects on DOC sorption capacity and soil organic matter (SOM) stabilization potential (Camino‐Serrano et al, 2014; Filep & Rekasi, 2011; Schwendenmann & Veldkamp, 2005). Moreover, soil classes partly account for differences in hydrological flow paths, leading to identified differences in subsoil DOC concentrations between the US Department of Agriculture (USDA) soil classes (Don & Schulze, 2008; Johnson, Lehmann, Couto, Novaes, & Riha, 2006; Langeveld et al, 2019). In this study, DOC concentration is high in sandy‐loam soils and low in sandy clay soils and clay soils (Figure 5), likely due to differences in the water holding capacity and cation exchange capacity among soil types.…”

“…The log‐transformation was used to convert DOC concentrations (mg/g) to ensure normality for robust statistical analyses. This model was built in a combined forward/backward multiple‐linear regression analysis using two‐thirds of the data points, and the ‘best’ model was chosen based on the lowest Akaike information criterion (AIC) value (Langeveld et al, 2019).…”

“…Therefore, all factors contributing to litter formation, root growth and microbial activities affect the DOC concentrations in soils (Neff & Asner, 2001). A large amount of studies have found large variations in DOC concentration among climate zones, vegetation type and soil properties (Christ & David, 1996; Guggenberger & Zech, 1993) across temporal and spatial scales (Langeveld et al, 2019). Numerous studies and experiments have been conducted to examine the controls on DOC concentrations (Filep & Rekasi, 2011), including temperature and moisture (Christ & David, 1996), soil pH (Andersson & Nilsson, 2001; Filep, Kincses, & Nagy, 2003), soil texture/clay (Thomsen, Olesen, Schjønning, Jensen, & Christensen, 2001), organic matter content (Hagedorn, Kaiser, Feyen, & Schleppi, 2000; Michel, Matzner, Dignac, & Kögel‐Knabner, 2006), soil nitrogen (N) content, and microbial activity (Cookson et al, 2005; Nemeth, Bartels, Vogel, & Mengel, 1988).…”