Effets des racines, des vers de terre et du compost sur les propriétés physiques de technosols construits

Les technosols construits sont une alternative au prélèvement de terre végétale en milieu naturel. La gestion durable de ces technosols suppose de comprendre l'évolution de leurs propriétés hydriques. Nous avons analysé les courbes de retrait de technosols dont la teneur en compost varie de 0 à 50%, en présence ou non de plantes et/ou de vers de terre. Les résultats montrent que ces organismes expliquent plus la variance (19%) des propriétés hydriques du sol que la dose de compost (14%). Le compost et les plantes jouent un rôle positif sur l'eau disponible présente à la fois dans la macroporosité et dans la microporosité, les vers de terre jouant un rôle positif uniquement sur cette dernière. L'effet conjoint des organismes et du compost explique davantage la variance ( 40%) que les effets simples de ces facteurs. En règle générale, l'effet simple du compost est inférieur à celui des plantes et des vers

Dynamics of bacterial communities in relation to soil aggregate formation during the decomposition of 13C-labelled rice straw

The addition of fresh organic matter is known to modify both microbial community structure and soil aggregation. The objective of this study was to understand the relationship between the dynamics of the soil microbial community structure in relation to that of their habitats during the decomposition of straw. Soil samples, ground (2000 μm) were measured. Fatty acid methyl ester (FAME) profiling was used to determine total bacterial community structure and FAME based stable isotope probing (FAME-SIP) was used to characterise the straw degrader communities. The mineralisation rate of the native C and the CStraw was high. The formation of macroaggregates (>2000 μm) occurred within 2 days in amended and unamended samples but did so to a greater extent in the amended samples. The CStraw was mainly located in fractions >200 μm, where degraders were the most abundant. The ¹³C-FAME profiles followed the same trends as total FAME profiles through time and within soil fractions, suggesting common dynamics between straw degraders and total bacterial communities: Gram-negative were more important in fraction >200 μm and during the early stages of the incubation while Gram-positive and actinobacteria dominated in fine fractions and at the end of the incubation. Bacterial community structure changed rapidly (within 2 days) in conjunction with the formation of new microbial habitats, suggesting that the relationship between the two is very close

Cascading effects of elevated ozone on wheat rhizosphere microbial communities depend on temperature and cultivar sensitivity

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Influence of organic matter content on hydro-structural properties of constructed technosols

Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emerging from the assembly of artefacts have never been documented. The soil shrinkage curve (SSC) could provide relevant structural information about constructed Technosols, such as the water holding capacity of each pore system (macropores and micropores). The objectives of this study were (i) to evaluate the SSC and water retention curve (WRC) to describe the structure of constructed Technosols and (ii) to understand the influence of organic matter content on soil hydro-structural properties. In this study, Technosols were obtained by mixing green waste compost (GWC) with the material excavated from deep horizons of soil (EDH). The GWC was mixed with EDH in six different volumetric percentages from 0% to 50% (GWC/total). The GWC and EDH exhibited highly divergent hydro-structural properties: the SSC was hyperbolic for GWC and sigmoid for EDH. All six mixture treatments (0%, 10%, 20%, 30%, 40% and 50% GWC) exhibited the classical sigmoid shape, revealing two embedded levels of pore systems. The 20% GWC treatment was hydro-structurally similar to the 30% and 40% GWC treatments; so, a large quantity of expansive GWC is unnecessary. The relation with the GWC percentage was a second-degree equation for volumetric available water in micropores, but was linear for volumetric available water in macropores and total volumetric available water. Total volumetric available water in the 50% GWC treatment was twice as high as that in the 0% GWC treatment. By combining SSCs and WRCs, increasing the GWC percentage increased water holding capacity by decreasing the maximum equivalent size of water-saturated micropores at the shrinkage limit and increasing the maximum equivalent size of water-saturated macropores, resulting in an increased range of pore diameter able to retain available water

Coastal environments shape chemical and microbial properties of forest litters in circum Mediterranean region

International audienceThis study explores how chemical and microbial properties of litters can be affected by coastal environments across the Mediterranean basin. A litterbag experiment including Pinus halepensis Mill. and Pistacia lentiscus L., collected from both inland and coastal areas was set up in France, Greece and Algeria. Control litterbags were left in their sampling sites and a transfer of litterbags from inland to coastal area was performed to test whether the effect of the specific constraints of coastal environments varies according to the country and the litter type. After 10 months, litter chemical composition (CP/MAS 13 C-NMR) and microbial activities (cellulase, respiration, Biolog) and structure (TRFLP) were analysed. Coastal conditions led to various responses: i) litter aromaticity differed in the coastal zones depending on the country (high in Greek coastal area, low in Algerian coastal zone), ii) less functionally-diversified microbial communities were found in Greek coastal area compared to French and Algerian coasts, iii) genetic diversity and richness were strongly impacted after transfer to the coastal zone whatever the country. The type of litter shaped microbial communities: i) at a local scale i.e. in either coastal or inland area, catabolic profiles and cellulase activities varied with the plant species, ii) at a regional scale, the effect of coastal conditions differed with the plant species (basal respiration, Shannon-Weaver index, catabolic diversity H', cellulases and catabolic profiles). Thus, litter microbial properties differed in coastal environments across the Mediterranean basin and plant litter type plays a major role in microbial properties at large spatial scale

Metabolising old soil carbon: Simply a matter of simple organic matter?

International audienceBare fallow soils that have been deprived of fresh carbon inputs for prolonged periods contain mostly old, stable organic carbon. In order to shed light on the nature of this carbon, the functional diversity profiles (MicroResp(TM), Biolog(TM) and enzyme activity spectra) of the microbial communities of long-term bare-fallow soils were analysed and compared with those of the microbial communities from their cultivated counterparts. It was assumed that the catabolic and enzymatic profiles would reflect the type of substrates available to the microbial communities. The catabolic profiles suggested that the microbial communities in the long-term bare-fallow soil were exposed to a less diverse range of substrates and that these substrates tended to be of simpler molecular forms. Both the catabolic and enzyme activity profiles suggested that the microbial communities from the long-term bare-fallow soils were less adapted to using polymers. These results do not fit with the traditional view of old, stable carbon being composed of complex, recalcitrant polymers. Microbial communities from the long-term bare fallow soils tended to preferentially use substrates with higher nominal oxidation states of carbon relative to the substrates used by the microbial communities from the cultivated soils. This suggests that the microbial communities from the long-term bare-fallow soils were better adapted to using readily oxidizable, although energetically less rewarding, substrates. Microbial communities appear to adapt to the deprivation of fresh organic matter by using substrates that require little investment, such as enzyme production