Résultat de la recherche
Indicateurs biologiques et services écosystémiques des sols urbains : propositions de gestion
Effects of endogeic earthworms on the soil organic matter dynamics and the soil structure in urban and alluvial soil materials
Earthworms are considered as key actors of soil processes at different spatial and temporal scales and provide essential ecosystem services linked to climate regulation or primary production. However, little is known about their basic functional roles (e.g. organic matter decomposition, soil structuring processes) in perturbed systems such as urban or alluvial soils. Alluvial soils are characterized by regular physical perturbation through flooding and associated erosion/sedimentation processes which are rather similar to perturbations (e.g. temporal instability, spatial heterogeneity) affecting urban soils. Due to their close soil characteristics, we hypothesized that in both cases, soil functioning is similarwith respect to soil fauna activity. Under controlled conditions, our objective was to investigate the effects of two endogeic earthworm species, Allolobophora chlorotica (pink morph) and Aporrectodea rosea (the two most abundant species found in the studied urban site), on soil organic matter (SOM) dynamics and soil structure (network of earthworm burrows) comparing an urban and an alluvial soil. We investigated the growth of individuals (weight gain and reproduction success) and assessed their effects on SOMdecomposition (cumulative C–CO2 emission, nitrogen and phosphorus mineralization) and soil structure (macroporosity, total length and connectivity of segments) after one and three months of incubation. Our results showed higher growth of A. rosea in the alluvial soil compared to the urban soil. However, the total length of burrows, carbon and nitrogen mineralization were often higher in the urban soil especially when the two species were combined. This trend can be mainly explained by lower organic matter content found in the urban soil whichmay influence positively the burrowing activity and negatively the growth of earthworms. Endogeic earthworms appear a key feature of the soil functioning in the urban context through their roles on organic matter transformation, the formation and maintenance of the soil structure.
Mille ans d’extension urbaine à Neuchâtel: évolution des paysages et des sols
Effects of endogeic earthworms on the soil organic matter dynamics and the soil structure in urban and alluvial soil materials
Earthworms are considered as key actors of soil processes at different spatial and temporal scales and provide essential ecosystem services linked to climate regulation or primary production. However, little is known about their basic functional roles (e.g. organic matter decomposition, soil structuring processes) in perturbed systems such as urban or alluvial soils. Alluvial soils are characterized by regular physical perturbation through flooding and associated erosion/sedimentation processes which are rather similar to perturbations (e.g. temporal instability, spatial heterogeneity) affecting urban soils. Due to their close soil characteristics, we hypothesized that in both cases, soil functioning is similar with respect to soil fauna activity. Under controlled conditions, our objective was to investigate the effects of two endogeic earthworm species, Allolobophora chlorotica (pink morph) and Aporrectodea rosea (the two most abundant species found in the studied urban site), on soil organic matter (SOM) dynamics and soil structure (network of earthworm burrows) comparing an urban and an alluvial soil. We investigated the growth of individuals (weight gain and reproduction success) and assessed their effects on SOM decomposition (cumulative C–CO2 emission, nitrogen and phosphorus mineralization) and soil structure (macroporosity, total length and connectivity of segments) after one and three months of incubation. Our results showed higher growth of A. rosea in the alluvial soil compared to the urban soil. However, the total length of burrows, carbon and nitrogen mineralization were often higher in the urban soil especially when the two species were combined. This trend can be mainly explained by lower organic matter content found in the urban soil which may influence positively the burrowing activity and negatively the growth of earthworms. Endogeic earthworms appear a key feature of the soil functioning in the urban context through their roles on organic matter transformation, the formation and maintenance of the soil structure.
Patterns of earthworm, enchytraeid and nematode diversity and community structure in urban soils of different ages
Annelids (Lumbricidae and Enchytraeidae) and nematodes are common soil organisms and play important roles in organic matter decomposition, nutrient cycling and creation of soil structure and porosity. However, these three groups have rarely been studied together and only few studies exist for urban soils. We studied the diversity and community composition of annelids and nematodes in soils spanning more than two centuries of urban soil development in Neuch^atel (Switzerland) and assessed the relationships 1) among these three groups and 2) between each group and environmental (physical, chemical and functional) characteristics of soils and soil age. While the groups of environmental variables were correlated (Mantel tests) no correlation was found between pairs of soil fauna groups and between each soil fauna group and environmental variables. More specifically, redundancy analyses showed that earthworm assemblages were best correlated with soil bulk density and with soil depth, the latter being positively correlated with soil age. Enchytraeid assemblages and the proportion of enchytraeid r-strategists were respectively best correlated with soil carbonate content and negatively correlated with soil age. Nematodes assemblages were best correlated with soil water content. Moreover, relationships between pairs of soil biota groups, and between each group and environmental (physical, chemical and functional) variables, varied along the soil age gradient (moving window analysis). This study provides new knowledge on urban soil biodiversity and how environmental conditions can influence soil diversity and community patterns in the urban context. The contrasted community patterns of earthworms, enchytraeids and nematodes in urban soils of different ages and their different ecological roles suggest that they represent potential complementary indicators of soil quality and functioning such as soil formation and organic matter dynamics.
Mille ans d'extension urbaine à Neuchâtel : évolution des paysages et des sols
Are urban soils similar to natural soils of river valleys?
Purpose Urban soils and soils of river valleys are constituted of heterogeneous materials that have been manipulated, disturbed or transported at different spatial and temporal scales. Despite these similarities, little is known about soil evolution in urban soils and their comparison with natural soils remains therefore highly useful. We hypothesized that, according to their degree of perturbation, urban soils and natural soils of river valleys have similar soil processes related to their structure, physical and chemical characteristics.
Materials and methods Using a synchronic approach, we compared two soil gradients, one located in the natural reserve of the Allondon River (canton of Geneva, Switzerland) and the other in and around the city of Neuchâtel, Switzerland. A total of five alluvial and 18 urban soil profiles were described according to vegetation type and alluvial terraces formed at different distances from the river for the river valley ecosystem and to soil age for the urban ecosystem. Correlations between soil gradients and classical physical (soil depth, particle-size distribution, coarse fraction) and chemical (Corg, pHH2O, Ptot, Ntot, CaCO3, CEC and C/N ratio) parameters of soils were first tested in order to identify similarities and differences among soil gradients. Data of soil properties were then clustered hierarchically in order to identify soil group classification.
Results and discussion Our results showed similarities and differences between soil gradients. In the urban context, soil thickness was positively correlated to soil age, while the coarse fraction, sand content and C/N were negatively correlated to soil age gradient. In soils of the river valley, most of the chemical variables were either negatively (pHH2O and CaCO3) or positively (CEC, Corg and Ntot) correlated to soil distance from the river. These differences between gradients can be mainly explained by parent material, depositional conditions and land use which can influence soil processes. However, alluvial soils were well clustered with two identified urban soil groups according to soil maturity. Evolved alluvial soils far from the river were grouped with natural and near natural urban soils. Conversely, “young” perturbed alluvial soils were most clustered with human-made soils.
Conclusions From the two selected soil gradients, soils on alluvial sediments are similar to urban soils in some characteristics. However, parent material, depositional conditions and soil and vegetation interactions on soil processes (e.g. matter cycle, energy flux) still need more investigation. This study contributes to the development of a natural soil reference for urban soils.
Are urban soils similar to natural soils of river valleys?
Purpose Urban soils and soils of river valleys are constituted of heterogeneous materials that have been manipulated, disturbed or transported at different spatial and temporal scales. Despite these similarities, little is known about soil evolution in urban soils and their comparison with natural soils remains therefore highly useful. We hypothesized that, according to their degree of perturbation, urban soils and natural soils of river valleys have similar soil processes related to their structure, physical and chemical characteristics. Materials and methods Using a synchronic approach, we compared two soil gradients, one located in the natural reserve of the Allondon River (canton of Geneva, Switzerland) and the other in and around the city of Neuchâtel, Switzerland. A total of five alluvial and 18 urban soil profiles were described according to vegetation type and alluvial terraces formed at different distances from the river for the river valley ecosystem and to soil age for the urban ecosystem. Correlations between soil gradients and classical physical (soil depth, particle-size distribution, coarse fraction) and chemical (Corg, pHH2O, Ptot, Ntot, CaCO3, CEC and C/N ratio) parameters of soils were first tested in order to identify similarities and differences among soil gradients. Data of soil properties were then clustered hierarchically in order to identify soil group classification. Results and discussion Our results showed similarities and differences between soil gradients. In the urban context, soil thickness was positively correlated to soil age, while the coarse fraction, sand content and C/N were negatively correlated to soil age gradient. In soils of the river valley, most of the chemical variables were either negatively (pHH2O and CaCO3) or positively (CEC, Corg and Ntot) correlated to soil distance from the river. These differences between gradients can be mainly explained by parent material, depositional conditions and land use which can influence soil processes. However, alluvial soils were well clustered with two identified urban soil groups according to soil maturity. Evolved alluvial soils far from the river were grouped with natural and near natural urban soils. Conversely, “young” perturbed alluvial soils were most clustered with human-made soils. Conclusions From the two selected soil gradients, soils on alluvial sediments are similar to urban soils in some characteristics. However, parent material, depositional conditions and soil and vegetation interactions on soil processes (e.g. matter cycle, energy flux) still need more investigation. This study contributes to the development of a natural soil reference for urban soils.
La faune du sol comme indicateur de la qualité des sols urbains: étude des communautés de vers de terre, d'enchytréides et de nématodes et de leurs relations avec des sols d'âges différents
Les sols sont l’une des composantes essentielles de l’écosystème urbain. Ils y jouent un rôle majeur dans la régulation du climat, le cycle de la matière organique et des éléments nutritifs. Tous ces processus sont, à des degrés divers et comme dans les sols non urbains, contrôlés par les organismes vivants du sol pour lesquels le sol remplit une fonction d’habitat. La faune du sol - précieux révélateur des activités humaines sur les changements d'état ou de fonctionnement des sols - reste jusqu’ici très peu étudiée en contexte urbain. Comparativement aux écosystèmes naturels ou agricoles, il n’est pas certain que les bioindicateurs usuels soient utilisables et performants dans le cas des sols urbains. Ainsi, l’objectif principal a donc été d’évaluer l’applicabilité des bioindicateurs retenus dans les sols naturels et agricoles dans le contexte urbain.
Dans une approche synchronique, dix-huit sols de différents âges – datant d’avant le XIème jusqu’au début du XXIème siècle - ont été choisis en ville de Neuchâtel et comparés à des sols au comportement jugés proches, les sols alluviaux; dans cette étude, ceux de la réserve naturelle de l’Allondon (canton de Genève) ont été sélectionnés. L’étude des sols et de la faune du sol s’est organisée autour de cinq parties: i) description classique de profils de sols in situ, ii) analyses de descripteurs physico‐chimiques, biotiques et fonctionnels: teneur en eau, pourcentage de squelette, perte au feu (PAF), texture, pHH2O, pHKCl, capacité d’échange cationique (CEC), Corg, Ntot, Polsen, Ptot, Catot, activité enzymatique globale (FDA, Fluoresceine DiAcétate), respiration du sol, abondance bactérienne et teneur en ergostérol, iii) extraction et identification de la faune du sol avec les méthodes appropriées pour chaque groupe (vers de terre, enchytréides et nématodes), iv) étude des communautés (densité, diversité et groupes fonctionnels) entre elles et de leurs relations avec l’âge, les caractéristiques physico-chimiques et fonctionnelles des sols urbains et, enfin, iv) étude comparative en microcosmes d’un sol urbain et alluvial visant à mieux situer le fonctionnement des sols urbains, notamment à travers les processus de structuration du sol et de dynamique de la matière organique suite à l’activité de la faune du sol (vers de terre endogés).
Nos résultats montrent que, selon le niveau de perturbation des sols, les sols urbains ont des caractéristiques physico-chimiques (teneur en argile élevée en fonction de la maturité des sols), pédologiques (processus de décarbonatation) et fonctionnelles (formation d’horizons organo-minéral A et structuré S) proches de celles des sols alluviaux naturels. Dans le cadre de l’étude expérimentale et pour les processus étudiés (structuration du sol, transformation de la matière organique), les sols urbains semblent aussi fonctionner de manière très similaire aux sols alluviaux, ce qui leur permet d’assurer, en ville, des services écosystémiques identiques (ex : régulation du climat, production primaire). À différents niveaux trophiques, les communautés faunistiques étudiées ne sont pas corrélées entre elles et informent sur des particularités différentes des sols urbains : (i) les conditions de leur mise en place (épaisseur du sol) influençant la proportion des catégories écologiques des vers de terre et notamment des anéciques; (ii) leur stabilité (âge des sols) à travers la proportion de stratèges r chez les enchytréides et l’indice de structure (indice fondé sur la complexité des réseaux trophiques) pour les nématodes; et, (iii) leur mode de gestion (arrosage, apports de matériaux carbonatés) corrélé aux structures des communautés de nématodes et d’enchytréides.
De par leur répartition ubiquiste, leur abondance, leur facilité d’extraction et d’identification au niveau de l’espèce/genre et d’un groupe fonctionnel, les vers de terre, les enchytréides et les nématodes peuvent être considérés comme de potentiels indicateurs reflétant les particularités fonctionnelles des sols urbains d’un point de vue physique (structuration du sol par les vers de terre favorisant le régime hydrique du sol et la décomposition de la matière organique par les enchytréides) et chimique (cycle des élément nutritifs assurés par les nématodes). Ces groupes bioindicateurs – définis comme une priorité pour le gouvernement et pour la gestion des territoires urbains en Suisse – permettent de contribuer au développement de méthodes fiables d’évaluation de la qualité des sols urbains.
Patterns of earthworm, enchytraeid and nematode diversity and community structure in urban soils of different ages
Annelids (Lumbricidae and Enchytraeidae) and nematodes are common soil organisms and play important roles in organic matter decomposition, nutrient cycling and creation of soil structure and porosity. However, these three groups have rarely been studied together and only few studies exist for urban soils. We studied the diversity and community composition of annelids and nematodes in soils spanning more than two centuries of urban soil development in Neuchâtel (Switzerland) and assessed the relationships 1) among these three groups and 2) between each group and environmental (physical, chemical and functional) characteristics of soils and soil age.
While the groups of environmental variables were correlated (Mantel tests) no correlation was found between pairs of soil fauna groups and between each soil fauna group and environmental variables. More specifically, redundancy analyses showed that earthworm assemblages were best correlated with soil bulk density and with soil depth, the latter being positively correlated with soil age. Enchytraeid assemblages and the proportion of enchytraeid r-strategists were respectively best correlated with soil carbonate content and negatively correlated with soil age. Nematodes assemblages were best correlated with soil water content. Moreover, relationships between pairs of soil biota groups, and between each group and environmental (physical, chemical and functional) variables, varied along the soil age gradient (moving window analysis).
This study provides new knowledge on urban soil biodiversity and how environmental conditions can influence soil diversity and community patterns in the urban context. The contrasted community patterns of earthworms, enchytraeids and nematodes in urban soils of different ages and their different ecological roles suggest that they represent potential complementary indicators of soil quality and functioning such as soil formation and organic matter dynamics.