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Role of organic matter and soil biota on first steps of soil structuring. The case of alluvial soils from alpine to plain level (FLOODSTRUBIO)
Titre du projet
Role of organic matter and soil biota on first steps of soil structuring. The case of alluvial soils from alpine to plain level (FLOODSTRUBIO)
Description
Floodplains are known to be areas of extraordinary biodiversity with a mosaic of shifting habitats with high interdependency. Nowadays, these ecosystems are subject to conservation and protection. Regarding pedology, floodplains contain a wide pattern of all steps of soil evolution, i.e. from a new sediment deposition to stable soils after several hundred years. However, less attention has been paid in this context to pedogenesis, especially the very first steps of soil structuring in the youngest and the least developed soils. In the present project, we aim to understand the processes and the mechanisms of soil structuring, in particular the role of organic matter and soil fauna.
Then, two types of questions are raised, concerning at the same time basic mechanisms and external regulation:
1- In soils, how is organic matter involved in soil structure? Internal mechanisms in relation to soil biota are needed to better understand physical and biochemical processes implied in organic matter decomposition, incorporation and its further role in soil stabilization processes.
2- Which external constraints may regulate soil structuring? Fluvial dynamics and particularly punctual floods have to be taken into consideration. A detailed knowledge of the historical context and the use of flood simulations could be useful to understand the resilience of soils consecutive to erosion and/or supply of materials. In addition, vegetation (reflecting mesoclimate), humus forms and soil types appear to be relevant.
Within the framework of a functional approach, two main hypothesis could be stated:
1- at the alpine level, pedogenesis processes are assumed to be slower than at the plain level. So, the pioneer stages would be clearly visible as intermediate steps near the headwaters at the opposite from the plains where the soil structural stability is more strongly established.
2- the vegetation and the soil diversity as well as biological activities, are supposed to differ in relation to climatic constraints ; separated effects at the alpine level could be combined at the plain level and the same tendency could be observed at a lateral distance from the river.
To assess these assumptions, we propose to study physico-chemical and biological variables :
1- along the river, from the headwaters to the plains liable to flooding.
2- perpendicular to the river, from the river itself to far away from it, until reaching the climax stage of the vegetation.
We choose to combine manipulated laboratory and field studies, the first ones giving information about key processes, the second ones allowing the understanding of the whole ecosystem and its regulation factors.
For our purpose, we need to use descriptors which are able to highlight, in a very detailed way, the first steps of soil aggregates formation. Thus, the main variables chosen in our project are, according to a gradient of size:
i) organic matter, both autochtonous and allochtonous, which influences the biotic community of the stream as well as the nutrients dynamics of the system,
ii) soil biota, that is a strong functional link between vegetation, organic matter and nutrients dynamics, humus forms and soil types. Soil fauna will be studied, in particular Collembola, Enchytreids and earthworms that are three of the main groups involved in organic matter decomposition, nutrient cycles and soil structuring. In addition, focus will be made at a smaller scale on soil microorganisms (bacteria and fungi). For an exhaustive study, research on soil biota will be carry out by the PhD student and at least two master students.
iii) Humiferous episolum (humus forms), the “energy distribution central point” of the ecosystem, with special hot spots of activities. The episolum is therefore the place for essential steps of pedogenesis combining a two-speed temporal scale: one linked to the vegetation (season or decade) and one related to the soil evolution in its wholeness (decade to century).
iv) soil types, usually weakly developed in the alluvial zone because of the age of the surface, and because of periodic disturbance by inundation, erosion, and/or deposition, and,
v) vegetation, especially riparian vegetation types according to the intra-ecosystem levels (phytocoenoses and synusiae) and taking into account temporal variations.
Chosen as the key process in our research project, the formation of the soil structure gathers and integrates all of these five themes.
Then, two types of questions are raised, concerning at the same time basic mechanisms and external regulation:
1- In soils, how is organic matter involved in soil structure? Internal mechanisms in relation to soil biota are needed to better understand physical and biochemical processes implied in organic matter decomposition, incorporation and its further role in soil stabilization processes.
2- Which external constraints may regulate soil structuring? Fluvial dynamics and particularly punctual floods have to be taken into consideration. A detailed knowledge of the historical context and the use of flood simulations could be useful to understand the resilience of soils consecutive to erosion and/or supply of materials. In addition, vegetation (reflecting mesoclimate), humus forms and soil types appear to be relevant.
Within the framework of a functional approach, two main hypothesis could be stated:
1- at the alpine level, pedogenesis processes are assumed to be slower than at the plain level. So, the pioneer stages would be clearly visible as intermediate steps near the headwaters at the opposite from the plains where the soil structural stability is more strongly established.
2- the vegetation and the soil diversity as well as biological activities, are supposed to differ in relation to climatic constraints ; separated effects at the alpine level could be combined at the plain level and the same tendency could be observed at a lateral distance from the river.
To assess these assumptions, we propose to study physico-chemical and biological variables :
1- along the river, from the headwaters to the plains liable to flooding.
2- perpendicular to the river, from the river itself to far away from it, until reaching the climax stage of the vegetation.
We choose to combine manipulated laboratory and field studies, the first ones giving information about key processes, the second ones allowing the understanding of the whole ecosystem and its regulation factors.
For our purpose, we need to use descriptors which are able to highlight, in a very detailed way, the first steps of soil aggregates formation. Thus, the main variables chosen in our project are, according to a gradient of size:
i) organic matter, both autochtonous and allochtonous, which influences the biotic community of the stream as well as the nutrients dynamics of the system,
ii) soil biota, that is a strong functional link between vegetation, organic matter and nutrients dynamics, humus forms and soil types. Soil fauna will be studied, in particular Collembola, Enchytreids and earthworms that are three of the main groups involved in organic matter decomposition, nutrient cycles and soil structuring. In addition, focus will be made at a smaller scale on soil microorganisms (bacteria and fungi). For an exhaustive study, research on soil biota will be carry out by the PhD student and at least two master students.
iii) Humiferous episolum (humus forms), the “energy distribution central point” of the ecosystem, with special hot spots of activities. The episolum is therefore the place for essential steps of pedogenesis combining a two-speed temporal scale: one linked to the vegetation (season or decade) and one related to the soil evolution in its wholeness (decade to century).
iv) soil types, usually weakly developed in the alluvial zone because of the age of the surface, and because of periodic disturbance by inundation, erosion, and/or deposition, and,
v) vegetation, especially riparian vegetation types according to the intra-ecosystem levels (phytocoenoses and synusiae) and taking into account temporal variations.
Chosen as the key process in our research project, the formation of the soil structure gathers and integrates all of these five themes.
Chercheur principal
Statut
Completed
Date de début
1 Octobre 2007
Date de fin
31 Mai 2011
Chercheurs
Guenat, Claire
Identifiant interne
29460
identifiant
7 Résultats
Voici les éléments 1 - 7 sur 7
- PublicationAccès libreEarthworm communities in alluvial forests: influence of altitude, vegetation stages and soil parameters(2011)
; ; - PublicationAccès libreFunctional responses of multi-taxa communities to disturbance and stress gradients in a restored floodplain(2015-1-1)
; ; ; ; Moretti, Marco1. Trait-based approaches can reveal the mechanisms through which disturbances or stress impact communities, allowing comparisons of the role of different mechanisms in shaping communities among taxonomic groups. Such information can lead to higher comparability, transferability and predictability of the outcome of restoration projects. However, multitaxa trait-based approaches were rarely used in the context of ecosystem restoration. 2. We investigated the responses to environmental gradients of seven taxa (vascular plants, staphylinid and carabid beetles, spiders, isopods, diplopods and earthworms) in a restored floodplain using a species traits approach. We assessed the impact of flood disturbances and soil hydric stress on the functional diversity (FD) and community-weighted mean (CWM) response of traits for each taxon. 3. Ordination of hydrological variables revealed two main gradients. The first was related to the spatiotemporal dynamics of flood disturbances and the second to the average changes in soil hydric conditions. 4. The analysis of CWM revealed that larger, poorly mobile species with narrow ecological tolerances were filtered by regular floods and/or changes in soil hydric conditions. 5. Functional diversity patterns differed between the two gradients: decreasing with increasing flood disturbance, but increasing along the soil hydric stress gradient. This suggests that the mechanisms shaping community composition differ between the two gradients with environmental filtering being dominant with increasing flood disturbances and competition decreasing with more soil hydric stress. 6. Synthesis and applications. Our study shows that the impact of restored flood disturbances and soil hydric stress on plant and invertebrate functional diversity and community- weighted mean can be positive, negative or more complex depending on the taxonomic group and environmental gradient considered. The patterns can to some extent be explained by the specific characteristics of each group. Larger, poorly mobile species with narrow ecological tolerances were particularly vulnerable to changes in disturbance and stress regime following floodplain restoration. These species may therefore be lost in the initial phases of restoration projects, but other more characteristic species of dynamic floodplains will be favoured. Understanding the consequences of these contrasted responses for biodiversity conservation and ecosystem functioning constitutes the next challenge for ecosystem restoration. - PublicationAccès libreCarbon storage and soil organic matter stabilisation in near-natural, restored and embanked Swiss floodplains(2014-2-4)
; ; - PublicationAccès librePatterns of earthworm communities and species traits in relation to the perturbation gradient of a restored floodplain(2012-3-29)
; ; ; Little is known about the diversity and ecology of earthworms in floodplains, as well as their response to natural and anthropic perturbations (e.g. floods, river channelisation, floodplain restoration). We characterised the patterns of earthworm communities and species traits in the different habitats of a lowland restored floodplain in Switzerland. In addition to classical species-based metrics, such as species richness and Shannon diversity, species traits were used to calculate the community weighted means (CWMs) of traits and functional dispersion (FDis). We hypothesised that trait-based metrics would reveal clearer patterns than classical approaches. The distribution of earthworm traits varied among habitats in relation to changes in flooding frequency: poorly developed gravel bar soils most exposed to flooding were characterised by high abundance of small epigeic species and low abundance of large anecic species. Differences in anecic and endogeic earthworm community structure matched flood frequency. In agreement with our hypothesis, CWMs were more strongly correlated to environmental variables than species composition, diversity, or functional diversity. Based on these results, the ratio of the relative abundances of epigeic and anecic species, and the differences in species composition within anecic and endogeic ecological types of earthworms were identified as indicators of soil development in floodplains. - PublicationAccès libreEarthworm communities as indicators for evaluating floodplain restoration success(New York: NOVA Science Publisher, 2013)
; ; ; Guenat, C - PublicationAccès libreImpact of flood deposits on earthworm communities in alder forests from a subalpine floodplain (Kandersteg, Switzerland)(2012)
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