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Poster communications

Release of organic carbon, silica, major and trace elements from degrading plant litter under microbial activity in laboratory experiments

Abstract : Working Papers of the Finnish Forest Research Institute 128 Quantification of major and trace elements recycling by plants is hampered by the lack of physico-chemical data on chemical elements release from degrading plant litter in soil and model laboratory environments. In this study, we applied a laboratory experimental approach for determining the organic carbon and approx. 30 chemical elements release rates from litter of typical temperate and boreal plants: larch (Larix gmelinii), elm (Ulmus laevis Pall.), tree fern (Dicksonia squarrosa), in 0.01 M NaCl solutions, circumneutral pH and temperature equals to 25°C. Open system, mixed-flow reactors equipped with dialysis compartment (1 kDa, or approximately 1 nm pore size) and batch reactors were used. Comparative measurements were performed under sterile and non-sterile conditions with evaluation of the number of active heterotrophic bacteria via counting the number of colony-forming units (CFU) on the agar plates. Litter degradation results suggest that chemical elements release rate is independent on dissolved organic carbon release (cellulose hydrolysis). In the opensystem mixed flow experiments, most elements are released at the very first stage of litter dissolution. In the closed-system (batch) experiments over 1 month observation time, the sterile biomass of larch needles liberates similar amount of organic carbon and trace metals (Al, Ti, Fe, Mn, Cu, Sr, Y, Zr, Mo, Pb) as in biotic experiment with the presence of soil bacteria. At the same time, Si release rate in sterile condition (0.74 μmol/g/day) is an order of magnitude lower than in the presence of bacteria (6.2 μmol/g/day). The abiotic release rate of TE in experiments with dialysis compartment (< 1 nm) is at least an order of magnitude lower than that in conventional batch experiments (< 0.22 μm) for many trace elements (Al, Fe, Cu, Ni, Zn, Pb…) likely due to colloidal organic matter control onto speciation of these litter-borne trace metals in solution. Elements that are present in the form of free ions or inorganic complexes (Li, B, Na, Mg, Ca, Si, Rb, Sr, Mo, As, Cs…) exhibit similar, by the order of magnitude, release rates in flow-through dialysis compartment and in the batch dialysis-free experiments. The presence of bacteria (100 to 107 colony forming units per L) in the course of biotic plant litter degradation experiment does not significantly modify the release of organic carbon and major (Ca, Mg) and trace elements (Al, Ti, Mn, fe, Cu, Sr, Pb) both for larch tree and fern biomass. The dry-weight normalized dissolution release rates of at circumneutral pH range (approx. 1–10 nmol/g/day) of most trace elements is several orders of magnitude higher than the rates of element release from common soil minerals (kaolinite, smectite, illite) as well as from primary silicates. We demonstrate, from the viewpoint of the mass balance and the rates of abiotic and microbially-controlled reactions, that the plant litter reservoir is able to provide the dominant contribution of major petrogenic and most trace elements elements (Si, Ca) to the riverine chemical erosion flux.
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Submitted on : Wednesday, March 17, 2021 - 4:00:05 PM
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Fabrice Fraysse1, Liudmila Shirokova1, Oleg Pokrovsky1, Jean-Dominique Meunier3. Release of organic carbon, silica, major and trace elements from degrading plant litter under microbial activity in laboratory experiments. BIOGEOMON 2009, Jun 2009, Helsinki, Finland. ⟨hal-03170268⟩

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