Tectonic Inclusions in Serpentinite Landscapes Contribute Plant Nutrient Calcium

Abstract

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.

Species specific plant-soil interactions influence plant distribution on serpentine soils

“…8). Our study leaves only two possible initial causes-either the explanation for the difference between the two soil types lies with 1) lack of soil development on barrens (perhaps due to instability caused by steeper slopes and/or softer, more erodible parent material, as hypothesized by Coleman 1996 andKruckeberg 1999) or 2) there are differences in parent material that influence soil chemical properties (e.g., Ca-bearing accessory minerals on vegetated soils -see McGahan et al 2008) (upper panel Fig. 8).…”

“…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 2008McGahan et al , 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.…”

Soil mineralogy trends in California landscapes

“…Laboratory analyses show that these soils have atypically high exchangeable Ca:Mg ratios and contain Ca-rich primary minerals. Soils such as these have at least some contribution from a non-ultramafic source, such as colluvium (Lee et al, 2001) or lithologic inclusions McGahan et al, 2008).…”

Karakteristike I Ekološko – Proizvodni Potencijal Zemljišta Na Serpentinitima U Pj ,,Donja Velika Usora“

“…Produktivnost peridotitsko-serpentinitskih zemljišta je uglavnom niska i u velikoj mjeri zavisi od karaktera klime i reljefa (Walker, 1954;Whittaker, 1954). Takođe, stepen serpentinizacije stijene, sadržaj pojedinih minerala i prisustvo akcesornih minerala utiče na hemizam zemljišta, rezistentnost prema eroziji i brzinu razlaganja (McGahan et al, 2008(McGahan et al, , 2009. Dakle, uticaj jednog pedogenetičkog faktora se treba posmatrati kroz prizmu uticaja ostalih faktora, a ne posebno.…”