Impact of Douglas-fir and Scots pine seedlings on plagioclase weathering under acidic conditions

Abstract

The weathering of soil minerals in forest ecosystems increases nutrient availability for the trees. The rate of such weathering and its relative contribution to forest tree nutrition, is a major issue when evaluating present and potential forest stand productivity and sustainability. The current paper examines the weathering rate of plagioclase with and without Douglas-fir or Scots pine seedlings, in a laboratory experiment at pH 3-4 and 25 • C. All nutrients, with the exception of Ca, were supplied in sufficient amounts in a nutrient solution. The objective of the experiment was to evaluate the potential of trees to mobilise Ca from the mineral plagioclase that contained 12% of Ca. Amounts of nutrients supplied in the nutrient solution, amounts accumulated in the living tissue of the seedlings and amounts leached from the experimental vessels, were measured. A weathering balance, accounting for leached + accumulated -supplied amounts, was established. Bio-induced weathering, defined as the weathering increase in the presence of trees, relative to the weathering rate without trees (geochemical weathering; control vessels), under the present experimental conditions, explained on average, 40% of total weathering (biological + geochemical). These conditions appeared more beneficial to Scots pine (higher relative growth rate, higher Ca incorporation) than to Douglas-fir.

Root-Associated Bacteria Contribute to Mineral Weathering and to Mineral Nutrition in Trees: a Budgeting Analysis

“…Our results are in accordance with those of Bormann et al (10), who demonstrated in an experimental forest that red pine (Pinus resinosa) plants improved by factors of 2.4 and 1.8 the quantities of calcium and magnesium released by weathering the primary minerals in a forest soil, respectively. In the same way, our results are in accordance with those of Bakker et al (4), who measured plagioclase weathering in a laboratory experiment at pH 3 to 4 and 25°C and showed that the release of Si, Mg, Ca, and Al was increased by a factor of 1.8 in the presence of Douglas fir and Scots pine under these acidic conditions. This effect of plant roots on mineral weathering may result from physical and/or biochemical processes.…”

KSM Soil Diversity and Mineral Solubilization, in Relation to Crop Production and Molecular Mechanism

“…These workers also noted a significant increase in the number of lateral roots and root hairs and promoted growth of pine. Bakker et al (2004) opined that the following changes could promote the effect of K solubilization from minerals: (i) the fragmentation of the minerals due to root activity with a consequent increase in their reactive surfaces, (ii) the root exudates provide the substrates for the bacteria to produce metabolites, (iii) and the production of growth hormones by the bacteria and organic acids to stimulate root development and more root exudation, to effect weathering of K mineral and removal of nutrients by plant uptake (Gahoonia et al 1997). …”

Biogeochemistry of Metals and Metalloids at the Soil–Root Interface

“…In terms of mineral weathering, the rhizosphere thus ends up being an environment more corrosive to mineral structures than that of the adjacent bulk soil. This action has been demonstrated in various studies (Leyval and Berthelin, 1991;Hinsinger et al, 1992;Arocena and Glowa, 2000;Bakker et al, 2004) for weatherable minerals such as micas, apatite, and amphiboles. Hence, the dissolution of soil solids triggered by acidification of the rhizosphere increases the mobilization of metals and their uptake by plants (Marschner, 1995), as demonstrated by Loosemore et al (2004) for tobacco (Nicotiana tabacum L. cv.…”

“…The rhizosphere has been variously conceptualized as the soil-root interface , the environment of plant roots (Lorenz et al, 1997), the portion of the soil in contact with or adhering to roots (Pierret et al, 1999), the zone where root activity significantly influences soil biological properties , the soil in which the microbial activity is influenced by plant roots (Russell, 1982), and the soil volume surrounding roots and containing high densities of microbionts (Bakker et al, 2004). In this context, the rhizosphere is probably best defined as the volume of soil surrounding living plant roots and that is influenced by root activity (Hinsinger, 1998;Hinsinger et al, 2005).…”