Calcium-mediated stabilisation of soil organic carbon

Abstract

Soils play an essential role in the global cycling of carbon and understanding the stabilisation mechanisms behind the preservation of soil organic carbon (SOC) pools is of globally recognised significance. Until recently, research into SOC stabilisation has predominantly focused on acidic soil environments and the interactions between SOC and aluminium (Al) or iron (Fe). The interactions between SOC and calcium (Ca) have typically received less attention, with fewer studies conducted in alkaline soils. Although it has widely been established that exchangeable Ca (Ca Exch ) positively correlates with SOC concentration and its resistance to oxidation, the exact mechanisms behind this relationship remain largely unidentified. This synthesis paper critically assesses available evidence on the potential role of Ca in the stabilisation of SOC and identifies research topics that warrant further investigation. Contrary to the common view of the chemistry of base cations in soils, chemical modelling indicates that Ca 2? can readily exchange its hydration shell and create inner sphere complexes with organic functional groups. This review therefore argues that both inner-and outer-sphere bridging by Ca 2? can play an active role in the stabilisation of SOC. Calcium carbonate (CaCO 3 ) can influence occluded SOC stability through its role in the stabilisation of aggregates; however, it could also play an unaccounted role in the direct sorption and inclusion of SOC. Finally, this review highlights the importance of pH as a potential predictor of SOC stabilisation mechanisms mediated by Al-or Fe-to Ca, and their respective effects on SOC dynamics.

Nitrogen fertilization raises CO2 efflux from inorganic carbon: A global assessment

“…Improving N-fertilization management to decrease CO 2 efflux from CaCO 3 and prohibiting soil acidification are effective strategies for decision makers to reduce long-term greenhouse gases emissions not only for N 2 Oas previously accepted (Dalal, Wang, Robertson, & Parton, 2003;Meng, Ding, & Cai, 2005;Shcherbak, Millar, & Robertson, 2014;Stehfest & Bouwman, 2006)but also for CO 2 from CaCO 3 dissolution. Furthermore, decalcification of soils by N fertilization also decreases SOM stability, because binding of organic matter on Ca 2+ is one of the most important mechanisms of C stabilization and sequestration in soils containing CaCO 3 (Rowley, Grand, & Verrecchia, 2018). Therefore, N fertilization will affect CO 2 efflux not only directlyby acidification and release of CO 2 from CaCO 3but also indirectly by decreasing SOM stability (and consequently its faster microbial decomposition) by removing Ca 2+ .…”

Arctic Soil Governs Whether Climate Change Drives Global Losses or Gains in Soil Carbon

“…Models in our testbed all use clay content as a proxy for mineralogical controls on potential physicochemical protection of soil C. This common assumption (Bailey et al, ; Rasmussen et al, ) produces latitudinal gradients in protected soil C in all three of the soil models evaluated here (Figure ), but recent work highlights shortcomings of this assumption, with pH and weathering thresholds that allow either calcium or iron‐ and aluminum‐oxides to stabilize organic matter in soils. (Kramer & Chadwick, ; Rasmussen et al, ; Rowley et al, ). Both the use of clay and chemical extractions simplify the diversity of chemical and physical mechanisms by which soil C may be stabilized (Chadwick & Chorover, ).…”

“…Despite these differences, models in our testbed all use clay content as a proxy to determine the capacity of soils to physicochemically protect soil C (Bailey et al, ). Although generalizability of this assumption is being questioned (Rasmussen et al, ; Rowley et al, ), the protected soil C simulated here broadly corresponds to mineral associated organic matter (MAOM) that could be isolated by particle size or density fractionation (Sohi et al, ). This MAOM typically has older radiocarbon ages, consistent with longer turnover times and greater persistence of mineral‐associated organic C (Trumbore, ), which corresponds to the passive, physicochemically protected, and protected soil C pools simulated by CASA, MIMICS, and CORPSE, respectively (Text S1).…”

Temperature sensitivity of decomposition of soil organic matter fractions increases with their turnover time

“…The total content of clay and silt in soil samples generally reached 25% (Table ), and thus, it suggests that a large amount of clay minerals exist in the soils and the protection by organomineral interactions is strong (Tonan et al, ). Consequently, the OC in both HydrolysF and RecalcitF should be protected by organomineral complexes (Rowley, Grand, & Verrecchia, ), which resulted in slow decomposition rates in HydrolysF and RecalcitF (Figure and Table ). However, HydrolysF decomposed faster than RecalcitF.…”