Aluminium Toxicity Risk for Pinus pinaster in Acid Soils (Galicia, NW Spain)

Abstract

The influence of bedrock on aluminium toxicity and aluminium speciation in the soil solution was studied in four Pinus pinaster plots. Growth and biomass parameters in the acidic soils were also evaluated in relation to different Al toxicity indices. The plots were developed over slate, biotitic schist, mica schist and granite. Samples of rhizospheric and non-rhizospheric soil, 1-year-old needles and roots were collected in each study plot. Total Al, reactive Al, acid-soluble Al, non-labile and labile Al and Al species (Al 3+ , Al-OH, Al-F and Al-SO 4 ) were determined in soil solution. Reactive Al dominated over the acid-soluble Al, and the non-labile Al predominated over the labile Al in all soils, but particularly over mica schist. In the biotitic schist soil, the Al forms and total Al were lower, whereas concentrations were always higher over mica schist. The Al forms considered most toxic were Al 3+ and Al-OH, and Al concentrations were highest over slate and mica schist. Al toxicity indices in soil, needle and roots showed a risk of toxicity in mica schist, slate and granite. The stand site indices over slate and mica schist were lower, consistent with the high labile Al and Al 3+ + Al-OH in soil solution. Despite the high stand site index over granite, the growth efficiency was low, in accordance with very low ratios of Ca/Al in needles or fine roots. This confirmed the adaptation of maritime pine to granitic substrates.

Determination of critical pH and Al concentration of acidic Ultisols for wheat and canola crops

“…In acidic soils, Al toxicity to plants and soil infertility are the main limiting factors for crop growth (Adams, 1984;Kochian, 1995;Ulrich and Sumner, 1991;Kidd and Proctor, 2000;Eimil-Fraga et al, 2016;Elisa et al, 2016). Soil acidity directly affects crop growth through acidic reactions and shows indirect effects on crop growth by affecting nutrient availability.…”

Efficacy of two different reclamation strategies to improve chemical properties and to reduce Al toxicity in a lignite mine dump during a 20‐year period

“…In fact, the decrease in pH in some plots can be explained because it was relatively high in the first sampling date (1992), as a result of the amendments applied at the start of the reclamation tasks, but the effect disappeared over time. In any case, after 20 years, plots subjected to selection of the sterile materials maintained pH values higher than the rest of the plots, with values even higher than those of Galician natural soils at both depths (surface and subsurface layers; Álvarez, Monterroso, & Fernández Marcos, ; Eimil Fraga et al, ).…”

“…The SO 4 2− values obtained at the beginning of the study (1992) are in general agreement with S concentrations in the materials used to build the plots, being higher in the control plot (Table ). In 2012, SO 4 2− concentrations decreased to values similar to those in natural soils of Galicia (Álvarez et al, ; Eimil Fraga et al, ). In addition to the leaching process, this decrease in SO 4 2− concentrations over time can be related to the reduction of pyritic mineral stock and then to SO 4 2− contribution by oxidation processes.…”

“…In these plots, the increase in organic matter with time favored that most of the inorganic noncrystalline Al could reacted with humic compounds, giving an increase in organo‐aluminum complexes in 2012 (Figure ). In the case of plots THO2 and THO3, the high Al o values (fundamentally of organic origin) can be related to the topsoil applied on surface, because they are of the order of those obtained in natural soils of Galicia (Álvarez et al, ; Eimil Fraga et al, ).…”

“…In well‐aerated media, these iron sulfides oxidize generating strong acidity, which favors mineral alteration and the solubility of elements such as Al, with a toxicity that strongly limits plant growth (Sena, Barton, Angel, Agouridis, & Warner, ; Nogueirol, Monteiro, Gratão, Borgo, & Azevedo, ). The most toxic Al species are Al 3+ and hydroxylated monomers (Al‐OH; Kinraide, Parker, & Zobel, ), and the presence of these species depends on the pH of the medium, the content and quality of organic matter, and the concentration of soluble sulfate and fluoride, anions for which Al has a high affinity (Eimil Fraga, Fernández‐Sanjurjo, Rodríguez‐Soalleiro, & Álvarez‐Rodríguez, ; Rivas‐Pérez et al, ; Merino, Fontaine, Palma, & Matus, ). Strong acidity and low organic matter content characteristic of pyritic dumps decrease precipitation of organo‐aluminum complexes, as well as the formation of Al‐organic matter soluble complexes, with dominance of inorganic monomers, Al 3+ among them (Rivas‐Pérez et al, ).…”