Variable selection in near infrared spectra for the biological characterization of soil and earthworm casts

International audienceNear infrared reflectance spectroscopy (NIRS) was used to predict six biological properties of soil and earthworm casts including extracellular soil enzymes, microbial carbon, potential nitrification and denitrification. Partial least squares regression (PLSR) models were developed with a selection of the most important near infrared wavelengths. They reached coefficients of determination ranging from 0.81 to 0.91 and ratios of performance-to-deviation above 2.3. Variable selection with the variable importance in the projection (VIP) method increased dramatically the prediction performance of all models with an important contribution from the 1750–2500 nm region. We discuss whether selected wavelengths can be attributed to macronutrient availability or to microbial biomass. Wavelength selection in NIR spectra is recommended for improving PLSR models in soil research

Metal and metalloid foliar uptake by various plant species exposed to atmospheric industrial fallout: Mechanisms involved for lead

Fine and ultrafine metallic particulatematters (PMs) are emitted frommetallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer ofmetals andmetalloids and their fate in plant leaves remain unclear, although this way of penetration may be a major contributor to the transfer of metals into plants. This study focused on the foliar uptake of various metals and metalloids from enriched PM(Cu, Zn, Cd, Sn, Sb, As, and especially lead (Pb)) resulting fromthe emissions of a battery-recycling factory.Metal and metalloid foliar uptake by various vegetable species, exhibiting different morphologies, use (food or fodder) and life-cycle (lettuce, parsley and rye-grass) were studied. The mechanisms involved in foliar metal transfer from atmospheric particulate matter fallout, using lead (Pb) as a model element was also investigated. Several complementary techniques (micro-X-ray fluorescence, scanning electron microscopy coupled with energy dispersive X-ray microanalysis and time-of-flight secondary ion mass spectrometry) were used to investigate the localization and the speciation of lead in their edible parts, i.e. leaves. The results showed lead-enriched PM on the surface of plant leaves. Biogeochemical transformations occurred on the leaf surfaces with the formation of lead secondary species (PbCO3 and organic Pb). Some compounds were internalized in their primary form (PbSO4) underneath an organic layer. Internalization through the cuticle or penetration through stomata openings are proposed as two major mechanisms involved in foliar uptake of particulate matter

Climate change effects on the stability and chemistry of soil organic carbon pools in a subalpine grassland

Mountain soils stock large quantities of carbon as particulate organic matter that may be highly vulnerable to climate change. To explore potential shifts in soil organic matter (SOM) form and stability under climate change (warming and reduced precipitations), we studied the dynamics of SOM pools of a mountain grassland in the Swiss Jura as part of a climate manipulation experiment. The climate manipulation (elevational soil transplantation) was set up in October 2009 and simulated two realistic climate change scenarios. After 4 years of manipulation, we performed SOM physical fractionation to extract SOM fractions corresponding to specific turnover rates, in winter and in summer. Soil organic matter fraction chemistry was studied with ultraviolet, 3D fluorescence, and mid-infrared spectroscopies. The most labile SOM fractions showed high intra-annual dynamics (amounts and chemistry) mediated via the seasonal changes of fresh plant debris inputs and confirming their high contribution to the microbial loop. Our climate change manipulation modified the chemical differences between free and intra-aggregate organic matter, suggesting a modification of soil macro-aggregates dynamics. Interestingly, the 4-year climate manipulation affected directly the SOM dynamics, with a decrease in organic C bulk soil content, resulting from significant C-losses in the mineral-associated SOM fraction (MAOM), the most stable form of SOM. This SOC decrease was associated with a decrease in clay content, above- and belowground plants biomass, soil microbial biomass and activity. The combination of these climate changes effects on the plant–soil system could have led to increase C-losses from the MAOM fraction through clay-SOM washing out and DOC leaching in this subalpine grassland

Soil organic carbon models need independent time-series validation for reliable prediction

Numerical models are crucial to understand and/or predict past and future soil organic carbon dynamics. For those models aiming at prediction, validation is a critical step to gain confidence in projections. With a comprehensive review of ~250 models, we assess how models are validated depending on their objectives and features, discuss how validation of predictive models can be improved. We find a critical lack of independent validation using observed time series. Conducting such validations should be a priority to improve the model reliability. Approximately 60% of the models we analysed are not designed for predictions, but rather for conceptual understanding of soil processes. These models provide important insights by identifying key processes and alternative formalisms that can be relevant for predictive models. We argue that combining independent validation based on observed time series and improved information flow between predictive and conceptual models will increase reliability in predictions

Quels indicateurs pour évaluer la qualité de sols forestiers soumis à des contraintes environnementales fortes ?

Mountain soils are facing strong changes in land-use and climate, which expose them to three main threats: erosion, loss of biodiversity and organic matter decline. This thesis focuses on mountain soil quality, through key ecosystem processes (decomposition and aggregation of soil organic matter) occurring in topsoils. These key processes control the provision of several soil ecosystem services such as carbon sequestration, nutrient supply, and biological activity. We have tested both simple and composite soil quality indices under environmental constraints in two study sites. Both sites are characterized by a strong vegetation gradient generated by natural constraints (sporadic permafrost in Dévoluy mountains, Isère, France), or human constraints (wildfire chronosequence in the Maures mountains, Var, France). Our results demonstrate that both soil microclimate and wildfire constraints affect soil attributes linked to decomposition and aggregation processes in topsoils. Soil biota (microflora and microfauna) is markedly affected, indicating modifications in soil processes controlled by soil foodweb (main decomposition and aggregation pathways, potential nitrification and denitrification). Near infrared reflectance spectroscopy (NIRS) is found to be a powerful tool for assessing the modifications of physico-chemical and biological quality of soils under environmental constraints.Les sols des régions de montagne sont confrontés à de fortes modifications climatiques et d'usages qui les rendent particulièrement sensibles à trois menaces : l'érosion, la perte de matière organique et de biodiversité. Cette thèse aborde la question de la qualité des sols sous l'angle de processus clés (décomposition et agrégation de la matière organique) au sein de différents compartiments de la partie superficielle du sol vivant (épipédon). Ces processus clés interviennent dans l'intensité des services rendus par les sols comme la séquestration de carbone, la fertilité des sols et le maintien de leur activité biologique. Parmi les indicateurs utilisés dans l'évaluation de la qualité des sols, nous avons choisi de tester des indicateurs simples et composites reliés aux processus clés de deux types d'écosystèmes subissant de fortes contraintes environnementales. Deux sites d'étude situés dans les massifs du Dévoluy (Isère) et des Maures (Var) ont été utilisés. Tous deux sont marqués par un fort gradient de végétation induit par des contraintes naturelles (sols à permafrost pour le site du Dévoluy) ou anthropiques (incendies pour le site des Maures). Dans ce travail, nous formulons trois hypothèses : (i) il existe au niveau des sols une signature originale des modifications environnementales influençant le fonctionnement des écosystèmes forestiers ; (ii) cette signature est liée à la qualité des sols et recouvre une partie biologique largement sous estimée ; (iii) la réflectance du sol résume cette signature et permet sa caractérisation dans des conditions contrastées. Les résultats de la thèse démontrent que les contraintes liées au pédoclimat et aux incendies induisent de fortes modifications des variables décrivant les processus de décomposition et d'agrégation dans les sols. Le compartiment biologique du sol (microflore ou microfaune) est particulièrement affecté par ces contraintes, révélant des modifications dans les processus liés aux chaînes trophiques des sols (voies préférentielles de décomposition et d'agrégation biologique, nitrification et dénitrification potentielles). La spectroscopie proche infrarouge se révèle être un outil pertinent pour rendre compte des modifications de qualité physico-chimiques mais aussi biologiques des sols soumis à de fortes contraintes

Chapitre 41. Évolution des propriétés des sols de lits de ravines marneuses au cours de leur restauration écologique (Draix, France)

L’importance du transfert sédimentaire fin de l’amont vers l’aval du bassin de la Durance est aujourd’hui essentiellement due à la présence de ravines érodées. Le colmatage des retenues hydro-électriques et d’autres conséquences négatives de ce transfert stimulent et justifient la restauration de ces terrains ravinés. Une stratégie d’ingénierie écologique, développée par l’Irstea, consiste à mettre en place des barrières végétales dans le lit des ravines pour favoriser la sédimentation, puis à terme, le développement d’un système sol-plante stable et fertile. Une expérience grandeur nature, menée depuis l’an 2000 dans les Alpes du Sud, a permis de montrer que des barrières de saules implantées en amont de seuils en bois retiennent efficacement les sédiments. Par ailleurs, les atterrissements sédimentaires ainsi formés en amont des barrières sont des zones privilégiées de colonisation végétale. Afin de prédire l’évolution possible sur le long terme du système sol-plante dans ces lits de ravines, un gradient de végétation se développant spontanément dans des lits de ravines a été étudié. Ceci a permis de montrer que, dans le cas où l’activité érosive des ravines ne perturbe pas significativement la dynamique végétale spontanée via des crues trop intenses ou trop régulières, celle-ci est caractérisée par une diversification des strates végétales et favorise la stabilité des agrégats, ainsi que la fertilité du sol. Cette stratégie d’ingénierie écologique semble donc pouvoir faire basculer l’écosystème d’un cycle de dégradation vers un cycle de restauration.In the Durance catchment, gullies activity is responsible for the majority of fine sediment transfer, causing downstream negative consequences. Silting of hydroelectric dams is one of these consequences which lead to the development of various strategies for gullies restoration. An ecological engineering approach, developed by Irstea, consists in using vegetative barriers in gully beds to first promote sediment retention, and then to establish a real soil-plant system, with suitable soil stability and fertility in gully beds to sustain plant biomass production. A real-size experiment, launched ten years ago, showed that Salix cuttings barriers are efficient to retain sediment. In addition, phytogenic mounds, formed upslope plant barriers, are suitable areas for plant colonization. So as to assess the evolution of these gully beds in the next century, a vegetative gradient, meant to reproduce the vegetative succession which may occur in the future, has been studied. It unveiled that in the case of such a dynamics, vegetative cover becomes pluri-stratified and influences soil properties, with a significant increase in aggregate stability and soil fertility along the gradient. This ecological engineering approach thus seems to enable the shift of this ecosystem from a degradation cycle toward a restoration cycle

Effects of five earthworm species on soil structure and organic matter in Luvisols

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Predicting soil quality indices with near infrared analysis in a wildfire chronosequence

International audienceWe investigated the power of near infrared (NIR) analysis for the quantitative assessment of soil quality in a wildfire chronosequence. The effect of wildfire disturbance and soil engineering activity of earthworms on soil organic matter quality was first assessed with principal component analysis of NIR spectra. Three soil quality indices were further calculated using an adaptation of the method proposed by Velasquez et al. [Velasquez, E., Lavelle, P., Andrade, M. GISQ, a multifunctional indicator of soil quality. Soil Biol Biochem 2007; 39: 3066–3080.], each one addressing an ecosystem service provided by soils: organic matter storage, nutrient supply and biological activity. Partial least squares regression models were developed to test the predicting ability of NIR analysis for these soil quality indices. All models reached coefficients of determination above 0.90 and ratios of performance to deviation above 2.8. This finding provides new opportunities for the monitoring of soil quality, using NIR scanning of soil samples

Integrating ecological engineering and ecological intensification from management practices to ecosystem services into a generic framework: a review

International audienceThere are many management approaches proposed to link practices and ecosystem services. Their common aim is to improve the levels of specific ecosystem services by driving key ecosystem functions. However, an operational common grid of analysis is needed. Among these approaches, scientists have recently put forward ecological engineering and ecological intensification which provide relevant examples for building and testing a common grid. Here, we propose to integrate ecological engineering and ecological intensification into a generic framework from management practices to ecosystem services. The novelty of this framework is to consider management practices as gradients of inputs to ecosystems. Specifically , management actions are defined according to the type and level of inputs, characterized along a gradient from endogenous to exogenous inputs, and from biological to artificial inputs. Our framework highlights the importance of the interactions between management practices and natural capital properties. These interactions determine the ecosystem functions that will sustain target ecosystem services. We then show how ecological engineering and ecological intensifica-tion can be distinguished and unified within our framework. To illustrate this, we use four ecological engineering and ecological intensification case studies representing different types and levels of inputs. Our proposed framework should thus help (1) researchers to make improved assessments of the links between practices, ecosystem structure and functions, and ultimately services, and to foster improved meta-, cost-benefit-and life-cycle analyses and evaluations of ecosystem management approaches; (2) project designers by improving the adequacy of their action to the specified target; and (3) managers to establish the specifications of the ecosystem management adapted to their objective