Interacting effects of land use type, soil microbes and plant traits on aggregate stability

Soil aggregates are critical to soil functionality, but there remain many uncertainties with respect to the role of biotic factors in forming aggregates. Understanding the interacting effects of soil, land use type, vegetation and microbial communities is a major challenge that needs assessment in both field and controlled laboratory conditions, as well as in bulk and rhizosphere soils. To address these effects and their feedbacks, we first examined the influence of soil, root and litter characteristics along a land use gradient (ancient woodland, secondary woodland, grassland, pasture and arable land) on microbial community structure (in both bulk and rhizosphere soil), as well as on aggregate stability. Then, we performed an inoculation experiment where we extracted soil columns from the arable and secondary woodland and used a third unstructured loamy soil as a control. We sterilized these three soils to remove microbial communities, and then either inoculated the tops of sterilized soil columns with soil from the secondary woodland or the arable field sites. Control columns of all soil types were not inoculated. In a fully-crossed design, we planted two species possessing distinct root system morphological traits: Brachypodium sylvaticum (fibrous system with many thin and fine roots) and Urtica dioica (taproot system with few fine roots). After four months, microbial communities (in bulk and rhizospheric soil) and aggregate stability were measured, along with root traits. In both the field and laboratory experiments, bacterial (16S) and fungal (ITS) biodiversity was determined using high throughput sequencing. In the field study we found that: i) there were strong relationships between aggregate stability and microbial community composition that were driven by land use, ii) the relationship between aggregate stability along the land use gradient and the trophic nature of bacterial communities was not significant, but that certain soil, root and litter parameters shaped bacterial phyla, with oligotrophic bacteria conditioned by the rhizosphere niche, and copiotrophic phyla more dependent on bulk soil conditions, iii) land use gradient (from woodland to arable), reduced the relative abundance of saprotrophic and ectomycorrhizal fungi with an increase in the relative abundance of Ascomycota and a reduction in the relative abundance of Basidiomycota. In the laboratory experiment we found that: i) the inoculation of sterilized soils with soils from the field significantly increased aggregate stability in control soil that was initially poorly structured, ii) the effects of inoculation on aggregate stability were similar when either secondary woodland or arable soils were used as inoculums and iii) these effects were affected significantly by root length density. Our results show that microbial communities influence soil structure and that bacterial communities are intimately associated to rhizospheric conditions and root traits (of which root length density was the most pertinent)

Towards meaningful quantification of glomalin-related soil protein (GRSP) taking account of interference in the Coomassie Blue (Bradford) assay

International audienceGlomalin-related soil protein (GRSP), an operationally defined fraction of soil organic matter containing protein and various other components, is usually quantified using the colorimetric non-specific Bradford method. This method is limited by a short working range, a non-linear response and interference from co‐extracted compounds. These limitations hinder the exact quantification of the protein component. The aim of this study was to investigate the source of interference in the Bradford quantification of GRSP and propose several methodological improvements based on identified interferences. The easily extractable and total GRSP in five topsoils with contrasting texture, organic carbon content and land use were compared. Results showed that: (i) the extent of interference varied between different soils, (ii) the standard addition method overestimated the extent of inhibition, (iii) absorbance should be corrected for colour, (iv) use of the ratio of absorbances at 595 and 465 nm, A595/A465, is not recommended because it is sensitive to pH and dilution‐dependent absorbance at 465 nm, (v) although a quadratic fit to the protein calibration curve was better than the linear fit, it was not possible for the dilution method and (vi) estimation of protein content from the dilution curve of the soil extract appeared to be suitable as it integrates the often observed, and hitherto unexplained, effect of dilution on the calculated protein content of soil extracts and avoids artefacts because of the choice of protein spike and dilution

Assessment of methodologies for the quantification of Glomalin Related Soil Proteins (GRSP): Identification of interferences and methodological improvements

Community level physiological profiles (CLPP) performed by the MicroResp method are reliable ecological indicators to assess soil microbial functional diversity. Functional diversity provides a great insight to microbial roles in ecosystems, and it is regulated among others, by soil physicochemical properties. The application of biochar or wood ash to forest soils is often employed to improve soil structure and soil hydraulic properties, increase soil organic matter stocks, neutralise acidity and restore nutrients. We hypothesized that addition of new carbon sources (biochar and wood ashes) may induce a change in the microbial functional diversity. Two experimental sites were established on acidic soils: one on a loamy soil (SOC% 3.9; pH: 4.8) and another on a sandy loam soil (SOC% 10.8; pH: 3.8). CLPP were performed using MicroResp system in surface (0-5 cm) soil samples. The carbon sources used were selected on the basis of their ecological relevance to the soil microbial community. CLLP data of each experimental site was ordinated by principal component analysis. The first two ordination axes (explaining more than 70% of the variance) were selected and their relation with soil hydraulic and nutritional properties, soil structure and microbial biomass carbon was analysed. The major findings of this study may be summarised as follows: a) In the short term, a shift in the microbial substrate use profile for wood ash and biochar additions was not observed, b) the soil microbial community responded most strongly to the addition of carboxylic acids and carbohydrates in both experimental sites, and c) in the loamy soil the first axis of the PCA was related with pH and the second one to the mean weight diameter of soil aggregates, and in the sandy-loam site, the first axis was related to the available water content and the second one to the mean pore diamete

Wood ash and biochar addition to forests do not shift soil microbial functional diversity in the short term

Community level physiological profiles (CLPP) performed by the MicroResp method are reliable ecological indicators to assess soil microbial functional diversity. Functional diversity provides a great insight to microbial roles in ecosystems, and it is regulated among others, by soil physicochemical properties. The application of biochar or wood ash to forest soils is often employed to improve soil structure and soil hydraulic properties, increase soil organic matter stocks, neutralise acidity and restore nutrients. We hypothesized that addition of new carbon sources (biochar and wood ashes) may induce a change in the microbial functional diversity. Two experimental sites were established on acidic soils: one on a loamy soil (SOC% 3.9; pH: 4.8) and another on a sandy loam soil (SOC% 10.8; pH: 3.8). CLPP were performed using MicroResp system in surface (0-5 cm) soil samples. The carbon sources used were selected on the basis of their ecological relevance to the soil microbial community. CLLP data of each experimental site was ordinated by principal component analysis. The first two ordination axes (explaining more than 70% of the variance) were selected and their relation with soil hydraulic and nutritional properties, soil structure and microbial biomass carbon was analysed. The major findings of this study may be summarised as follows: a) In the short term, a shift in the microbial substrate use profile for wood ash and biochar additions was not observed, b) the soil microbial community responded most strongly to the addition of carboxylic acids and carbohydrates in both experimental sites, and c) in the loamy soil the first axis of the PCA was related with pH and the second one to the mean weight diameter of soil aggregates, and in the sandy-loam site, the first axis was related to the available water content and the second one to the mean pore diameter

Red para la innovación en la selvicultura y los sistemas de integración de riesgos en la gestión forestal

La forêt, en plus de ses fonctions économiques reconnues par tous les acteurs du milieu rural tels que le développement de l'emploi rural et le marché local du bois pour la transformation ou pour l'énergie, rend de nombreux autres services. Cependant, de multiples risques sont identifiables et doivent être gérés dans et pourront éventuellement être aggravés par les changements climatiques: futures sécheresses favorables aux pathogènes et ravageurs ainsi qu'à la propagation des incendies, et le risque de la modification du vent. Le projet FORRISK se focalisera ainsi sur les risques en forêt dont l'intensité est modulée par le changement climatique. L'histoire des forêts du sud de l'Europe nous rappelle que pour de nombreux problèmes, une approche seulement nationale n'a pas de sens. C'est-à-dire, les risques concernés, les réponses à apporter peuvent être soit au niveau technique soit au niveau de l'organisation des institutions. Pour cette raison, FORRISK vise à coordonner et mettre en réseau trois communautés différentes que sont les acteurs politiques, les gestionnaires et les scientifiques, dans le but d'obtenir que la gestion des risques soit partie intégrante des décisions prises à tous les niveaux du secteur forestier. Cela permettra d'initier une plateforme européenne sur les risques forestiers en facilitant des recommandations et des informations pertinentes à tous les niveaux. Pour y parvenir, le projet analysera et comparera les outils institutionnels, les systèmes et organisations liés à la gestion de risques dans les régions étudiées. Ensuite, FORRISK développera sur le terrain des techniques de lutte écologique, génétique et sylvicole, dont les résultats feront l'objet de guides de bonne pratique. Les outils produits consisteront à des cartes de risques à l'échelle régionale ou subrégionale, ainsi que à des modèles informatiques permettant de faire des diagnostics sur le terrain et de modéliser la propagation du fomès dans les peuplements de pin maritime. Ainsi, décideurs politiques, gestionnaires et scientifiques auront entre leurs mains des outils adaptés à la gestion de nombreux risques menaçant la forêt dans leurs régions

FORRISK. Réseau pour l’innovation dans les sylvicultures et les systèmes de gestion intégrée des risques de forêt

La forêt, en plus de ses fonctions économiques reconnues par tous les acteurs du milieu rural tels que le développement de l'emploi rural et le marché local du bois pour la transformation ou pour l'énergie, rend de nombreux autres services. Cependant, de multiples risques sont identifiables et doivent être gérés dans et pourront éventuellement être aggravés par les changements climatiques: futures sécheresses favorables aux pathogènes et ravageurs ainsi qu'à la propagation des incendies, et le risque de la modification du vent. Le projet FORRISK se focalisera ainsi sur les risques en forêt dont l'intensité est modulée par le changement climatique. L'histoire des forêts du sud de l'Europe nous rappelle que pour de nombreux problèmes, une approche seulement nationale n'a pas de sens. C'est-à-dire, les risques concernés, les réponses à apporter peuvent être soit au niveau technique soit au niveau de l'organisation des institutions. Pour cette raison, FORRISK vise à coordonner et mettre en réseau trois communautés différentes que sont les acteurs politiques, les gestionnaires et les scientifiques, dans le but d'obtenir que la gestion des risques soit partie intégrante des décisions prises à tous les niveaux du secteur forestier. Cela permettra d'initier une plateforme européenne sur les risques forestiers en facilitant des recommandations et des informations pertinentes à tous les niveaux. Pour y parvenir, le projet analysera et comparera les outils institutionnels, les systèmes et organisations liés à la gestion de risques dans les régions étudiées. Ensuite, FORRISK développera sur le terrain des techniques de lutte écologique, génétique et sylvicole, dont les résultats feront l'objet de guides de bonne pratique. Les outils produits consisteront à des cartes de risques à l'échelle régionale ou subrégionale, ainsi que à des modèles informatiques permettant de faire des diagnostics sur le terrain et de modéliser la propagation du fomès dans les peuplements de pin maritime. Ainsi, décideurs politiques, gestionnaires et scientifiques auront entre leurs mains des outils adaptés à la gestion de nombreux risques menaçant la forêt dans leurs régions