Association with pedogenic iron and aluminum: effects on soil organic carbon storage and stability in four temperate forest soils

Abstract

Soil organic carbon (SOC) can be stabi-lized via association with iron (Fe) and aluminum (Al) minerals. Fe and Al can be strong predictors of SOC storage and turnover in soils with relatively high extractable metals content and moderately acidic to circumneutral pH. Here we test whether pedogenic Fe and Al influence SOC content and turnover in soils with low Fe and Al content and acidic pH. In soils from four sites spanning three soil orders, we quan-tified the amount of Fe and Al in operationally-defined poorly crystalline and organically-complexed phases using selective chemical dissolution applied to the soil Cbased turnover times. We found that poorly crystalline Fe and Al content predicted SOC turnover times (p \ 0.0001) consistent with findings of previous studies, while organically-complexed Fe and Al content was a better predictor of SOC concentration (p \ 0.0001). Greater site-level MAP (p \ 0.0001) and colder site-level MAT (p \ 0.0001) were corre-lated with longer SOC turnover times but were not correlated with SOC content. Our results suggest that poorly crystalline Fe and Al effectively slow the turnover of SOC in these acidic soils, even when their combined content in the soil is less than 2% by mass. However, in the strongly acidic Spodosol, organo-metal complexes tended to be less stable resulting in a · · more actively cycling mineral-associated SOC pool.

Drivers of postfire soil organic carbon accumulation in the boreal forest

“…In our study, metal oxide content exerted a primary control on illuvial horizon C stocks, indicating that binding of organic matter on the mineral phase is a major direct process of C sequestration (Kramer, Sanderman, Chadwick, Chorover, & Vitousek, ; Mikutta, Kleber, Torn, & Jahn, ; Porras et al., ). Doetterl et al.…”

“…Eastern North America is projected to receive about 10% more precipitation by the end of this century (IPCC, ). According to our results, increasing the water supply through greater amounts of precipitation could increase mineral soil C stocks through enhanced mineral weathering and leaching, releasing metal oxides that can bind to organic matter (Doetterl et al., ; Mikutta et al., ; Porras et al., ; Rumpel & Kögel‐Knabner, ). Otherwise, the projected increase in fire frequency suggested by models (Kloster & Lasslop, ; Wang et al., ; Wotton, Flannigan, & Marshall, ) could weaken the C capture function of boreal forests (Genet et al., ; Pan et al., ).…”

“…In this hypothesis, climate exerts an indirect control only on C stocks (Doetterl et al., ) through its direct effect on mineral weathering and on the amounts of metal oxides leached from the upper horizons (Egli et al., ). Soil pH is hypothesized to have both a direct effect on C stocks through changes brought to the decomposition process and an indirect effect on C stocks through changes occurring in the creation of organometallic complexes (Buurman & Jongmans, ; Porras, Hicks Pries, McFarlane, Hanson, & Torn, ). Time since fire exerts an indirect effect on C stocks by influencing soil pH through the liming effect within the first few years after fire (see FH1), whereas over the long‐term, mineral soil acidifies through a charge imbalance in the nutrient uptake with vegetation growth (Driscoll & Likens, ).…”

“…In this hypothesis, climate exerts an indirect control only on C stocks (Doetterl et al, 2015) through its direct effect on mineral weathering and on the amounts of metal oxides leached from the upper horizons (Egli et al, 2009). Soil pH is hypothesized to have both a direct effect on C stocks through changes brought to the decomposition process and an indirect effect on C stocks through changes occurring in the creation of organometallic complexes (Buurman & Jongmans, 2005;Porras, Hicks Pries, McFarlane, Hanson, & Torn, 2017).…”

“…the mineral phase is a major direct process of C sequestration (Kramer, Sanderman, Chadwick, Chorover, & Vitousek, 2012;Mikutta, Kleber, Torn, & Jahn, 2006;Porras et al, 2017). Doetterl et al (2015) argue that over a wide climatic gradient soil C stocks primarily evolve with climate-driven mineral weathering and release of reactive mineral surfaces.…”