Neoformations (Nodules and Placic Layers) in Surface-Gleyed Loamy Sandy Soils of the Northern Part of the Tambov Plain

Ecological and geochemical assessment of the content of chemical elements and features of their spatial distribution in Fe nodules of soils in the Middle Cis-Urals

“…The FMN accumulate Cd, Pb, Co, and Mo in arable deeply gleyed light gray soils in the southern part of the East European Plain (Tambov Region). The content of Zn and Cu in concretions of light gray soils is significantly lower than in concretions of soddy-podzolic soils of the taiga zone [37].…”

Distribution of Mn Oxidation States in Grassland Soils and Their Relationships with Soil Pores

“…Moreover, many microbial decomposers have the capacity to oxidize Mn­(II) in order to subsequently benefit from the decomposing power of reactive Mn­(III) complexes. , Yet, besides catalyzing decomposition, Mn also enables C protection. Dissolved organic C adsorbs on the surfaces of Mn oxides, − often resulting in Mn nodules with C content several times exceeding that of the bulk soil. , Mn­(III)/Mn­(IV) oxides coat surfaces of soil mineral particles, often trapping or coprecipitating with soil organic compounds. , However, the permanence of SOM protection within Mn nodules is dubious since in anaerobic conditions, Mn­(III)/Mn­(IV) oxides can be reduced and dissolved through a number of abiotic and biotic pathways, often freeing the previously protected SOM …”

“…The strong dependence of Mn oxidation state (OxS) on O 2 availability and microbial activity, as well as differences in Mn­(II), Mn­(III), and Mn­(IV) solubilities, lead to formation of complex spatial patterns in Mn distribution at spatial scales ranging from a few millimeters to entire soil profiles. In anaerobic conditions, soluble Mn­(II) formed during Mn oxide reduction diffuses toward boundaries of oxic/anoxic transition zones, where it is then oxidized, forming MnIII/MnIV nodules. ,, Fluctuating hydromorphic conditions and periodic exposure to oxic environments leads to the formation of sizeable (> few millimeters) Mn­(III)/Mn­(IV) concretions, orthsteins, and nodules. ,− Moreover, the speed in the onset of oxic conditions defines the particular shape of the resultant Mn concretions . At fine (few centimeters) scales, spatial patterns in Mn oxide depositions can reflect the transition zone’s position, the availability of organic materials subject to active microbial decomposition, and locations of hyphae from fungal decomposers. ,, …”