BACKGROUND: Bacterivores, mostly represented by protists and nematodes, are a key component of soil biodiversity involved in soil fertility and plant productivity. In the current context of global ...change and soil biodiversity erosion, it becomes urgent to suitably recognize and quantify their ecological importance in ecosystem functioning. SCOPE: Using meta-analysis tools, we aimed at providing a quantitative synthesis of the ecological importance of soil bacterivores on ecosystem functions. We also intended to produce an overview of the ecological factors that are expected to drive the magnitude of bacterivore effects on ecosystem functions. CONCLUSIONS: Bacterivores in soil contributed significantly to numerous key ecosystem functions. We propose a new theoretical framework based on ecological stoichiometry stressing the role of C:N:P ratios in soil, microbial and plant biomass as important parameters driving bacterivore-effects on soil N and P availability for plants, immobilization of N and P in the bacterial biomass, and plant responses in nutrition and growth.
•Earthworms and termites are key organisms in soil functioning.•They play a significant role in the regulation of ecosystem services.•Their utilization for ecosystem restoration is neglected in ...comparison to plants.•Direct methods to promote soil engineer activity are field inoculations.•Indirect methods are the application of organic matter and vermicompost.•More research is needed on the interactions between the functions and services influenced by soil engineers.
Soil engineers, such as earthworms and termites, are key organisms in soil functioning. They are involved in many ecological processes and play a central role in numerous ecosystem services. This review discusses the management of earthworm and termite activity for the restoration of ecosystems. We review methods to promote soil engineer activity either directly through field inoculation or stimulation or indirectly through the utilization of vermicompost. Examples of their use for the restoration of acid, compacted or crusted, polluted, and eroded soils are also discussed. Finally, we summarize the major obstacles hampering the utilization of soil engineer activity for the restoration of ecosystems, consider new research topics that need further development and highlight the need to consider the interactions between the functions and services influenced by soil engineers.
The priming effect in soil is proposed to be generated by two distinct mechanisms: 'stoichiometric decomposition' and/or 'nutrient mining' theories. Each mechanism has its own dynamics, involves its ...own microbial actors, and targets different soil organic matter (SOM) pools. The present study aims to evaluate how climatic parameters drive the intensity of each priming effect generation mechanism via the modification of soil microbial and physicochemical properties. Soils were sampled in the center of Madagascar, along climatic gradients designed to distinguish temperature from rainfall effects. Abiotic and biotic soil descriptors were characterized including bacterial and fungal phylogenetic composition. Potential organic matter mineralization and PE were assessed 7 and 42 days after the beginning of incubation with
C-enriched wheat straw. Both priming mechanisms were mainly driven by the mean annual temperature but in opposite directions. The priming effect generated by stoichiometric decomposition was fostered under colder climates, because of soil enrichment in less developed organic matter, as well as in fast-growing populations. Conversely, the priming effect generated by nutrient mining was enhanced under warmer climates, probably because of the lack of competition between slow-growing populations mining SOM and fast-growing populations for the energy-rich residue entering the soil. Our study leads to hypotheses about the consequences of climate change on both PE generation mechanisms and associated consequences on soil carbon sequestration.
Soils are now recognized as key components in the design of sustainable agricultural practices within the agroecological framework. They are the place of many ecological functions achieved by living ...organisms interacting with each other and which support the sustainable provision of agrosystem services. In the context of the transformation of agriculture and to improve the sustainability and resilience of family farming, it becomes urgent to promote soil ecological functions, to intensify them by appropriate practices considering the socio-economic constraints, and finally, to be able to monitor them. Here, to improve our consideration of the soil functions for a sustainable agriculture, we first rely on the ecological theories of terrestrial ecosystem functioning to better establish the concept of sustainable functions in agroecosystems. We then propose a methodological framework, called SE-CURE (for “Soil Ecology Cure”), that aims to optimize the ecological functions of the soil for a sustainable supply of ecosystem services. This framework relies on the involvement of stakeholders and is illustrated by a case study in Madagascar where the different steps of the SE-CURE approach have been applied.
Despite the outstanding potential of Andosols for soil organic carbon (SOC) sequestration, the importance of the different mechanisms involved in protecting SOC against mineralization is still ...unclear. Previous studies have described allophane particles as having a fractal structure. One hypothesis is that SOC is adsorbed or trapped in this fractal structure and could be less available to microbes and enzymes. This paper aims to determine the fractal structure of allophanic soils, especially in mesopores (2–50
nm), and to establish a correlation between the SOC bioavailability and the fractal features of the allophane aggregates. The present study confirms the fractal structure of allophane aggregates. The structural features of the pores, measured using N
2 adsorption–desorption curves and SAXS for the nano-scale range, showed correlation with SOC bioavailability. SOC bioavailability decreased with the extent of the fractal structure.
►Allophane aggregates have large mesoporous volumes (scale 2–50
nm). ►Allophane aggregates have a fractal structure (2–50
nm). ►SOC bioavailability decreases with the extent of this fractal structure. ►This peculiar mesopore structure can explain the high SOC stocks in Andosols.
Priming effect (PE) is defined as a stimulation of the mineralization of soil organic matter (SOM) following a supply of fresh organic matter. This process can have important consequences on the fate ...of SOM and on the management of residues in agricultural soils, especially in tropical regions where soil fertility is essentially based on the management of organic matter. Earthworms are ecosystem engineers known to affect the dynamics of SOM. Endogeic earthworms ingest large amounts of soil and assimilate a part of organic matter it contains. During gut transit, microorganisms are transported to new substrates and their activity is stimulated by (i) the production of readily assimilable organic matter (mucus) and (ii) the possible presence of fresh organic residues in the ingested soil. The objective of our study was to see (i) whether earthworms impact the PE intensity when a fresh residue is added to a tropical soil and (ii) whether this impact is linked to a stimulation/inhibition of bacterial taxa, and which taxa are affected. A tropical soil from Madagascar was incubated in the laboratory, with a (13)C wheat straw residue, in the presence or absence of a peregrine endogeic tropical earthworm, Pontoscolex corethrurus. Emissions of (12)CO(2) and (13)CO(2) were followed during 16 days. The coupling between DNA-SIP (stable isotope probing) and pyrosequencing showed that stimulation of both the mineralization of wheat residues and the PE can be linked to the stimulation of several groups especially belonging to the Bacteroidetes phylum.
•Soil quality indicators respond to any duration of cover crop.•Non-carbonated soils are the most vulnerable to vineyard management practices.•Fine-tuned adaptation of practices according to soil ...groups can improve soil quality.
Land management aiming to sustain ecosystem services is an important issue, especially in biodiversity hot spots such as found in Mediterranean areas. In Mediterranean areas, viticulture is an important land use. Vineyards are frequently found on inherently poor soils and are submitted to intensive management practices, which threaten soil functioning and associated ecosystem services. To encourage winegrowers and stakeholders to be reflective and adapt their vineyard practices, we evaluated the effects of three soil management practices (inter row plant cover duration, weeding and fertilization strategies) on soil functioning in 146 commercial plots distributed in Southern France, by a complementary set of biological and physico-chemical indicators. We used the concept of soil dynamic quality to evaluate some soil management practices on soil functioning. The influence of inherent soil properties derived from pedogenesis on soil dynamic indicator response was accounted for by considering the response of soil indicators for three soil groups differing in their stoniness and Ca carbonate content. The three soil management practices systematically influenced some nematode-based indicators, whereas other indicators were ascribable to a specific soil type or practice. We demonstrated that the potential of soil management practices to enhance soil functioning is restricted by soil type. In particular for calcareous soils, the soil functioning is very stable limiting effects of soil management practices. The presence of a cover crop, even temporary, in the inter row, is the only practice which benefits soil functioning whatever the soil type whereas organic fertilization and chemical weeding exhibit contrasting results on soil functioning.
A basic understanding of the fertilization resources (FR) characteristics is required to drive soil functions following the FR application, and to improve crop productivity. The datasets presented ...include the FR characteristics, i.e. their nutrient contents and biochemical quality, and their effects on soil in carbon (C) and nitrogen (N) mineralization. We selected nineteen FR from local farmers, from laboratory institution and from commercial producers. The soil used in experiment was sampled in Imerintsiatosika locality, located in the Central Highlands of Madagascar. Nutrient contents of FR were evaluated by measuring total carbon, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur contents. Biochemical quality of the products was assayed by fractioning organic matter of organic resources in soluble compartments, hemicelluloses, celluloses and lignin equivalent. Laboratory incubations in microcosm experiments were conducted with the mixture of soil and fertilization resources to determine C and N mineralization rates. Carbon mineralization rate was measured using microgas chromatography, and nitrogen mineralization rates were analyzed by colorimetry on a continuous flow analyzer.
The effects of earthworm inoculation and cropping systems on upland rice systems were examined over a four-year period in the Highlands of Madagascar. Each year, endogeic earthworms Pontoscolex ...corethrurus (Rhinodrilidae) were inoculated (EW+) at a density of 75 ind m−2 or were not inoculated (EW0). Inoculation was tested in three cropping systems: conservation agriculture (CA) and traditional tillage with or without residues restitution. Soil and plant properties were measured during the first three years while soil biological properties were assessed at the fourth year. At the end of the experiment, earthworm density was three-fold higher in EW+ than in EW0, demonstrating the success of the inoculation. Earthworm density was more important in CA than in tillage systems. Earthworm inoculation had higher significant effects on soil and plant properties than cropping systems. Earthworm inoculation had positive effects on soil macroaggregation (+43%), aboveground biomass (+27%), rice grain yield (+45%), and N grain amount (+43%). Intensifying earthworm activity in field conditions to meet the challenge of ecological transition is supported by our study.
Carbon sequestration in agricultural soils, through the accumulation of high-quality organic matter, represents great potential to mitigate climate change and simultaneously improve soil fertility. ...Such a challenge is particularly important and relevant in developing tropical countries like Madagascar, where soil carbon storage is vulnerable to climatic variations and where fertilization is generally applied through amendments in organic matter of various origins. The priming effect (PE) is considered here as the stimulation of the mineralization of soil organic matter (SOM) by a supply of fresh organic matter (FOM). PE results from different microbial processes driven by specific biotic and abiotic parameters. Depending on the processes involved, it has been suggested that PE could either counteract SOM accumulation or promote it. The objective of the present study was to explore the relationships between certain agricultural practices (type of crop, quality of fertilization, association with trees), the potential intensity of PE, as well as several abiotic (texture, quantity and quality SOM, nutrient enrichment) a1nd biotic (biomass and phylogenetic composition of microbial communities) factors which have been proposed in the literature as specific determinants of the different PE generation mechanisms. The soils for this study come from a network of farms in a commune in the Highlands of Madagascar. The PE, generated by a supply of 13C-enriched wheat straw, could not directly correlate with agricultural treatments. However, several indirect correlations could be found via several specific abiotic and microbial determinants that are discussed in terms of soil fertility restoration.
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