Tectonic Inclusions in Serpentinite Landscapes Contribute Plant Nutrient Calcium

Soil Science Society of America Journal (Impact Factor: 1.72). 05/2008; 72(3). DOI: 10.2136/sssaj2007.0159


Serpentinite-derived soils give rise to botanically distinct systems primarily because of inadequate parent material Ca content. We hypothesized that Ca content varies widely in what have been mapped as soils derived from serpentinite. An exchangeable Ca/Mg ratio <0.7 is often used to relate the imbalance of these nutrient elements in serpentinite-derived soils. We sampled six parent materials and soils from the Coast Ranges of California in Henneke soil series (clayey-skeletal, magnesic, thermic Lithic Argixerolls) modal location map unit polygons. Parent material total CaO content varied from 1.0 to 230 mg kg(-1), and CaO/MgO varied from <0.1 to 4. A combination of x-ray diffraction (XRD), polarized light microscopy (PLM), and electron microscopy was used to identify the Ca-bearing accessory minerals diopside, grossularite, andradite, and tremolite. Accessory mineral content was often too low to be detected by XRD or minerals were too finely disseminated and difficult to detect in thin section by PLM. Electron microscopy, in concert with XRD and PLM, was needed to fully characterize the mineral assemblage. Two sites, Napa and Tehama, contained no serpentine minerals, were not serpentinites, and were tectonic inclusions in the serpentinite landscape. Napa rocks contained almost no Ca-bearing minerals and would be identified as a serpentinite if relying on elemental analysis CaO/MgO ratio alone. Tectonic inclusions and Ca-bearing accessory minerals affect Ca distribution and presumably its availability for plants. Careful mineralogical analysis may be required to identify Ca-bearing accessory minerals.

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Available from: Donald G. McGahan, Dec 14, 2014
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    • "Some soil horizons contained abundant Fe oxyhydroxides (i.e., Bv horizon , Table S2). Such properties are typically found in the soils developed on the serpentine bedrock (Cheng et al., 2011; McGahan et al., 2008). The C content gradually decreased from the surface to subsurface soils, which resulted in a progressively increasing pH in the soil profile (Table S2). "
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    ABSTRACT: Few studies have been conducted to understand phosphorus (P) dynamics in serpentinitic landscapes where soil P availability is often limited due to immobilization by abundant Fe minerals. The objective of this study was to determine soil-solid P speciation and hosting phases in the soil formed on serpentinitic landscapes using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy and solution 31P nuclear magnetic resonance (NMR) spectroscopy in combination with a chemical fractionation technique. Soils formed on a mafic lithology in a temperate forest range of Mt. Asama, Mie, Japan were used. The largest P pool was found in the NaOH extractable fractions, accounting for 52–76% of total P in the soils. Both H2O and HCl fractions were a minor P pool with the average of 3.3% and 10% of total P in the soils, respectively. The NaOH–EDTA extraction for 31P-NMR recovered 31–59% of the total soil P. Orthophosphate monoesters were the major P group in soils enriched with humus, constituting 55–58% P. Inorganic orthophosphate accounted for 63% of P in the soil with abundant Fe minerals. Pyrophosphate was a minor P species accounting for 0–12% of extracted P. P K-edge XANES spectroscopy determined P adsorbed on ferrihydrite as one of the major P species in the soils. The XANES confirmed the low HCl–P concentrations determined in the chemical fractionation by unequivocal absence of apatite-like P phases in the serpentinite-derived soil. Based on the P speciation determined by the combined applications of these techniques indicate that soil P availability is severely low, and P subcycles in this serpentinitic landscape rely on orthophosphate monoesters and P associated with Fe minerals.
    Full-text · Article · Oct 2014 · Geoderma
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    • "Topographic differences create variation at a local scale (Rajakaruna and Bohm 1999; Alexander et al. 2007). At multiple scales, differences in parent material (e.g., degree of serpentinization, mineral composition, presence of accessory minerals) influence soil chemistry, erosion resistance, and weathering rates (Alexander et al. 2007; McGahan et al. 2008, 2009). The New Idria serpentine mass (San Benito and Fresno Counties, California, USA) shows striking within-site variation, with dense chaparral giving way to barrens that are nearly devoid of vegetation except for scattered shrub and tree islands. "
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    ABSTRACT: Where serpentine soils exist, variation in soil properties affects plant species distribution at both coarse and fine spatial scales. The New Idria (California, USA) serpentine mass has barren areas, supporting only sparse shrub and tree islands, adjacent to areas of densely-vegetated serpentine chaparral. To identify factors limiting growth on barren relative to vegetated serpentine soils, we analyzed soils from barren, shrub-island within barren, and vegetated areas and foliage from shrub-island and vegetated areas. We also grew Ceanothus cuneatus (native evergreen shrub), Achillea millefolium (native perennial forb), and Bromus madritensis ssp. rubens (invasive annual grass) in soils from barren and vegetated areas amended factorially with N, K, and Ca in a pot study. In well-watered pots, biomass was greater by 5-, 14-, and 33-fold for Ceanothus, Achillea, and Bromus, respectively, on vegetated-area-collected soils than on barren-collected soils, indicating a strong soil chemistry effect. Although field soil data suggested nutrient deficiency and not heavy metal toxicity, pot study plant data indicated otherwise for two of the three species. On barren-collected soils, only Ceanothus responded positively to added N and Ca and did not show greater foliar Mg or heavy metal (Fe, Ni, Cr, Co, Zn) concentrations than on vegetated-area-collected soils. Ceanothus maintained lower root Mg and heavy metal (Fe, Ni, Cr, Co) concentrations on barren soils and translocated less heavy metal (Fe, Ni, Cr, Co, Mn, Cu) from roots to foliage than Achillea and Bromus. Achillea and Bromus showed significant log-log biomass relationships with foliar Ca:Mg (+), Mg (-), and heavy metals (Fe, Ni, Cr, Co, Mn, Cu, Zn) (-), while Ceanothus showed relationships only with Ca:Mg (+) and Mg (-). The New Idria barren-vegetated pattern appears to be maintained by different factors for different species or functional types— low Ca:Mg ratios on barrens for all species tested, high heavy metal concentrations for Achillea and Bromus, and low macronutrient (N) concentrations for Ceanothus. Combined data from this and other studies suggest high heavy metal concentrations more strongly affect herbaceous than woody species, contributing to variation in species distribution on serpentine soils. KeywordsUltramafic soils–Low nutrient adaptation–Calcium:magnesium ratio–Metal toxicity–Nickel
    Full-text · Article · May 2011 · Plant and Soil
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    • "soils are numerous and have been studied across the globe: in Europe (Chardot et al., 2007; Kierczak et al., 2007, 2008; Quantin et al., 2008; Caillaud et al., 2009), North America (Rabenhorst and Foss, 1981; Rabenhorst et al., 1982; Lee et al., 2004; Oze et al., 2004a, 2004b; Alexander et al., 2007a, 2007b; McGahan et al., 2008, 2009), South America (Garnier et al., 2006, 2008), and the South Pacifi c Ocean particularly on New Caledonia's complex (Becquer et al., 2003, 2006). Pedogenesis diff ers from location to location due to the wide distribution and occurrence of serpentine soils with varying climatic conditions as well as the nature of the parent material and other factors including topography, biota, and time (Lee et al. 2004; Chardot et al., 2007; Hseu et al., 2007). "
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    ABSTRACT: To elucidate the properties of pedogenic Cr and Ni in serpentine soils in terms of mobilization, three pedons on the shoulder (Entisol), backslope (Inceptisol), and footslope (Alfisol) along a toposequence in eastern Taiwan were examined for metal partitioning and their geochemical origins. The analysis combined bulk soil analysis by selective sequential extraction (SSE) with mineralogical methods, including x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) analyses. Experimental results showed that Cr and Ni were mainly concentrated in chromites and silicates, respectively, and were gradually exposed by weathering of the parent materials. The SEM/EDX analysis indicated that chemical modification of the chromites was more prevalent near the soil surface and that the chemical modification increased as available Cr content increased from the shoulder to the footslope. Landscape position was the most important factor in controlling the trends in Ni and Cr fractions. The footslope accumulated more total Cr and Ni than the shoulder and backslope. Additionally, the soil on the footslope received more effective precipitation as run-on water from upslope and was potentially more leached than the soils on the other landscape positions. The accumulation of clay and dithionite-citrate-bicarbonate (DCB) extractable Fe (Fe(d)) and the increase of exchangeable Ca/Mg ratio correlated with the increased total labile pools of Cr and Ni in the soil from the shoulder and backslope to the footslope. However, the concentrations of acid soluble, reducible, and oxidizable fractions (total labile pool) of Ni were higher than those of Cr, indicating that Ni was more available than Cr in all soils tested by the SSE procedures.
    Full-text · Article · Mar 2011 · Soil Science Society of America Journal
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