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

Abstract

The principal nutrient source for forest trees derives from the weathering of soil minerals which results from water circulation and from plant and microbial activity. The main objectives of this work were to quantify the respective effects of plant-and root-associated bacteria on mineral weathering and their consequences on tree seedling growth and nutrition. That is why we carried out two column experiments with a quartz-biotite substrate. The columns were planted with or without pine seedlings and inoculated or not with three ectomycorrhizosphere bacterial strains to quantify biotite weathering and pine growth and to determine how bacteria improve pine growth. We showed that the pine roots significantly increased biotite weathering by a factor of 1.3 for magnesium and 1.7 for potassium. We also demonstrated that the inoculation of Burkholderia glathei PML1(12) significantly increased biotite weathering by a factor of 1.4 for magnesium and 1.5 for potassium in comparison with the pine alone. In addition, we observed a significant positive effect of B. glathei PMB1(7) and PML1(12) on pine growth and on root morphology (number of lateral roots and root hairs). We demonstrated that PML1(12) improved pine growth when the seedlings were supplied with a nutrient solution which did not contain the nutrients present in the biotite. No improvement of pine growth was observed when the seedlings were supplied with all the nutrients necessary for pine growth. We therefore propose that the growth-promoting effect of B. glathei PML1(12) mainly resulted from the improved plant nutrition via increased mineral weathering.In ecosystems with low inputs and without any fertilization or soil amendment by humans, the nutrients available to plants come from atmospheric inputs and weathering of soil minerals. This is mainly the case with forest ecosystems which, in addition, are frequently located on poor and acidic soils (3). Plants developing on acidic soils are subjected to two major constraints: (i) high concentrations of ions like Al 3ϩ and H ϩ which inhibit root growth and (ii) low mineral nutrient availability as a result of low reserves and impaired uptake due to high H ϩ concentrations (40).In temperate and boreal forest ecosystems, the vast majority of trees live in close association with symbiotic fungi, the ectomycorrhizal fungi, which connect tree roots to the soil environment via a broad network of hyphae. These fungi contribute to plant nutrition by carrying far away from the roots and from very small pores, the water and the nutrients they released by weathering the primary minerals (30, 59). In addition, the ectomycorrhizal symbiosis modifies root exudation qualitatively and quantitatively by changing the metabolic functions of the roots (34, 51, 56). It creates a special environment called mycorrhizosphere, where the bacterial equilibrium is different from that of the bulk soil (soil without any influence of roots) (36). These modifications of the bacterial equilibrium in the mycorrhizosphere are likely to contribut...

Screening of Nitrogen Fixers From Rhizospheric Bacterial Isolates Associated With Important Desert Plants

“…The elemental N is abundant in the earth's atmosphere [12] however; most of the tropical soils are deficient in available N. In ecosystems with low inputs and without any fertilization or soil amendments by humans, the nutrients available to plants come either from atmospheric inputs [3] or from biological fixation [15]. Biological nitrogen fixation (BNF) is one way of converting elemental nitrogen into plant usable form.…”

Linking diversity to function: highlight on the mineral weathering bacteria

“…Very few studies have used such approaches so far. Among them, Calvaruso et al [11] tested the impact of the inoculation of Burkholderia glathei strain PML1(12), previously identified as being mineral weathering efficient in an in vitro assay, using microcosms containing pine seedlings grown in a mixture of biotite and quartz. They reported that this bacterial strain significantly enhanced the release of nutritive cations from biotite compared to non-inoculated plants, and improved the plant growth.…”

“…Interestingly, this growth promoting effect was only observed under nutrient-poor conditions, suggesting a role for this bacterial strain only when nutritive cations were in limit of concentration for the plant nutrition. To go further in the understanding of the mineral weathering process, Calvaruso et al [11] also addressed the question of the effect of combination of bacterial strains. These authors showed that the combination of different efficient mineral weathering bacteria in the same microcosm do not always result in a significant increase of mineral weathering and sometimes even reduces it compared to monoinoculation conditions.…”

Effect of waste mica on transfer factors of134Cs to spinach and lettuce

“…Potassium-solubilizing microorganisms are capable of solubilizing the unavailable forms of potassium in K-bearing minerals such as mica, illite and orthoclase through production and excretion of organic acids such as citric, oxalic and tartaric acids. Organic acids can facilitate the weathering of minerals by releasing K from rocks or through the formation of metal-organic complexes by forming chelate with silicon ions to bring the K into solution (Song and Huang, 1988;Calvaruso et al, 2006;Bakker et al, 2004;van Scholl et al, 2008). Other possible hypotheses/mechanisms to mobilize the soil K reserve are due to biofilm formation on the rhizospheric mineral surfaces by certain bacterial strains (Balogh-Brunstad et al, 2008).…”