Plant‐Available Calcium Varies Widely in Soils on Serpentinite Landscapes

Abstract

Serpentinitic landscapes are characterized by unusual plant species composition and vegetation patchiness. We hypothesized that soil extractable Ca content is correlated with vegetation Ca concentration and may contribute to the unusual vegetation characteristics. Eleven pedons from California were sampled within soil survey mapping polygons containing the modal location for a classic “serpentine soil.” Soil NH4OAc‐extractable Ca/Mg ratio varied from 0.1 to 1.5 and total elemental Ca/Mg ratio varied from <0.01 to 1.9. Soil extractable Ca content was influenced by parent material mineralogy: soils with a Ca/Mg ratio of 0.2 or less were derived from serpentinite parent materials with only trace Ca‐bearing minerals; soils with a Ca/Mg ratio >1.0 were derived from non‐serpentinite parent materials, and soils with a Ca/Mg ratio from 0.2 to 1.0 were derived from serpentinite parent material that had minor amounts of accessory Ca‐bearing minerals. Based on greenhouse studies, the Ca concentration of the leaf of the grass Vulpia microstachys (Nutt.) Monro correlated better with soil‐extractable Ca (r2 = 0.69, P < 0.01) than with total elemental analysis Ca (r2 = 0.40, P > 0.05). The shallow soil depths of the pedons, together with the generally high coarse fragment content, limit the soil volume available to roots. Pedons with the highest extractable Ca/Mg (1.34 and 1.89) also had the greatest extractable Ca pool, 1169 and 394 g m−2, respectively. Among the 11 pedons, extractable Ca/Mg ratio, extractable‐Ca pool, and the distribution of the Ca pool within the pedon all varied, and these variables were important determinants of plant performance, as determined by leaf Ca content. Of these variables, soil extractable‐Ca content was the best determinant of plant performance as indicated by leaf Ca concentration.