Analysis of complex trophic networks reveals the signature of land-use intensification on soil communities in agroecosystems

Increasing evidence suggests that agricultural intensification is a threat to many groups of soil biota, but how the impacts of land-use intensity on soil organisms translate into changes in comprehensive soil interaction networks remains unclear. Here for the first time, we use environmental DNA to examine total soil multi-trophic diversity and food web structure for temperate agroecosystems along a gradient of land-use intensity. We tested for response patterns in key properties of the soil food webs in sixteen fields ranging from arable crops to grazed permanent grasslands as part of a long-term management experiment. We found that agricultural intensification drives reductions in trophic group diversity, although taxa richness remained unchanged. Intensification generally reduced the complexity and connectance of soil interaction networks and induced consistent changes in energy pathways, but the magnitude of management-induced changes depended on the variable considered. Average path length (an indicator of food web redundancy and resilience) did not respond to our management intensity gradient. Moreover, turnover of network structure showed little response to increasing management intensity. Our data demonstrates the importance of considering different facets of trophic networks for a clearer understanding of agriculture-biodiversity relationships, with implications for nature-based solutions and sustainable agriculture

Nutritive value and physical and chemical deterrents of forage grass litter explain feeding performances of two soil macrodetritivores

Millipedes (Diplopoda) and terrestrial isopods (Isopoda) may play a significant role in soil decomposition. The present study aimed to contribute to the general understanding of feeding performances of macrodetritivores consuming grass litter by answering two questions. Q1: Are grass litter traits indicating nutritive value (i.e. chemical) and traits indicating feeding deterrents (i.e. mainly physical but not necessarily) both necessary to explain individual feeding performances of soil invertebrates consuming grass litter? Q2: Do grass physical traits indicating physical deterrents (e.g. WHC for mechanical aspects) provide more than, less than or the same amount of information about invertebrate individual performances as grass chemical traits indicating mainly chemical but also physical deterrents (e.g. lignin content directly for digestibility and indirectly for mechanical aspects)? We thus designed a laboratory experiment to assess individual feeding performances of two common macrodetritivores (Armadillidium vulgare (Latreille, 1804) and Glomeris marginata (Villiers, 1789)) in four monospecific treatments of litter from perennial forage grasses (Brachypodium pinnatum P. Beauv., Bromus erectus Huds., Festuca rubra L. and Holcus lanatus L.). A. vulgare feeding performances were correlated with nutritive values (litter N and P contents) and plant mechanical aspects (LDMC: leaf dry matter content). G. marginata performances were correlated with chemical deterrents (cellulose and lignin contents). Thus, (Q1) for grass litters, both traits indicating nutritive value (e.g. N, P) and feeding deterrents (e.g. LDMC, lignin content) are necessary to explain macroinvertebrates feeding performances. We also demonstrated the results depend on the invertebrate species considered. Also, (Q2) chemical deterrents may influence feeding performances of G. marginata the most, while physical deterrents related to mechanical aspects may influence those of A. vulgare the most. Our study shows that using grass chemical and physical traits that indicate both nutritive value and feeding deterrents can help explain feeding performances of macrodetritivores

Responses of earthworm communities to crop residue management after inoculation of the earthworm Lumbricus terrestris (Linnaeus, 1758)

Earthworms are important for soil functioning in arable cropping systems and earthworm species differ in their response to soil tillage and crop residue management. Lumbricus terrestris (Linnaeus, 1758) are rare in intensively tilled arable fields. In two parallel field trials with either non-inversion (NIT) or conventional tillage (CT), we investigated the feasibility of inoculating L. terrestris under different crop residue management (amounts and placement). Simultaneously, we monitored the response of the existing earthworm communities to L. terrestris inoculation and to crop residue treatments in terms of earthworm density, species diversity and composition, ecological groups and functional diversity. L. terrestris densities were not affected by residue management. We were not able to infer effects of the inoculation on the existing earthworm communities since L. terrestris also colonized non-inoculated plots. In NIT and two years after trial establishment, the overall native earthworm density was 1.4 and 1.6 times higher, and the epigeic density 2.5 times higher, in treatments with highest residue application (S100) compared to 25% (S25) or no (S0) crop residues, respectively. Residue management did not affect earthworm species composition, nor the functional trait diversity and composition, except for an increase of the community weighted means of bifide typhlosolis in S0 compared to S100. In CT, however, crop residues did have a strong effect on species composition, ecological groups and functional traits. Without crop residues (S0), epigeic density was respectively 20 and 30% lower than with crop residues placed on the soil surface (S100) or incorporated (I100). Community composition was clearly affected by crop residues. Trait diversity was 2.6 to 3 times larger when crop residues were provided, irrespective of placement. Crop residues in CT also resulted in heavier earthworms and in a shift in the community towards species with a thicker epidermis and cuticle, a feather typhlosolis shape, and a higher average cocoon production rate. We conclude that earthworm communities under conventional tillage respond more strongly to the amount of crop residue than to its placement. Under non-inversion tillage, crop residue amounts affected earthworm communities, but to a smaller degree than under conventional tillage

Approches théoriques, inférence des réseaux et exemple appliqué aux sols de grande culture. L’union fait-elle la force

Approches théoriques, inférence des réseaux et exemple appliqué aux sols de grande culture. L’union fait-elle la force. Séminaire du thème 1 Sols, Activités & Réseaux Biologique

Réponse des détritivores aux pratiques agricoles et sylvicoles

Réponse des détritivores aux pratiques agricoles et sylvicoles. Journée Thématique sur la Faune du Sol, CEF

BETSI, a database for soil ecologists

BETSI, a database for soil ecologists. Workshop 'Towards a global soil biodiversity data platform

Ecologie des sols agricoles

Ecologie des sols agricoles. Journée technique sur le semis direct sous couvert du GIEE Magella

Etude de la relation entre la diversité des macro-invertébrés et la dynamique de la matière organique des sols limoneux de Haute-Normandie

Dans le cadre des sols limoneux des plateaux de Haute-Normandie, ce travail vise à répondre à deux hypothèses : (H1) la biodiversité et les MO du sol sont influencées par les modifications environnementales induites par les gestions agricole et forestière et (H2) les assemblages de macro-détritivores influencent la dynamique de la MO du sol. La relation a été étudiée à l échelle de la parcelle ainsi que dans des microcosmes réalisés au laboratoire. Dans les sols forestiers, les résultats empiriques ne permettent pas d établir un lien entre diversité des macro-détritivores et stocks de C, une relation apparaît toutefois avec certaines fractions des horizons holorganiques. Les résultats expérimentaux permettent de classer les macro-détritivores en groupes distincts à partir de leur effets spécifiques sur la biodégradation des feuilles. De plus, la biodégradation est davantage liée à la diversité fonctionnelle qu à la diversité spécifique. Dans les sols agricoles, les études au champ ne permettent pas de mettre en évidence un lien net entre la diversité spécifique des lombriciens et les stocks de C ou la stabilité structurale. En conditions contrôlées, les effets des vers de terre sur le dégagement de C-CO2, la teneur en MO et la stabilité structurale des macro-agrégats dépendent de l espèce impliquée et du taux de MO du sol. De plus, dans un sol pauvre en MO, l augmentation du nombre d espèces lombriciennes stabilise la minéralisation du C et augmente la stabilité structurale et la teneur en MO des agrégats. D une façon générale, les résultats empiriques montrent que la richesse spécifique des macro-détritivores est plus influencée par le type d occupation du sol que par la dynamique des systèmes, réfutant ainsi en partie l hypothèse H1. D autre part, les stocks de C dans les sols ne varient pas avec l âge du peuplement de l hêtre alors qu ils augmentent avec l âge des prairies, réfutant ainsi en partie l hypothèse H1. De plus, les résultats des expérimentations en microcosmes permettent de classer les espèces en fonction de leurs effets sur la dynamique de la MO. En outre, la dynamique de la MO est modifiée lorsque la diversité des macro-détritivores change, confirmant donc l hypothèse H2.Two hypothesis were tested in loamy soils located in Haute-Normandie (France) : firstly (H1) macro-detritivore diversity and soil OM are influenced by agricultural and silvicultural managements and secondly (H2) macro-detritivore assemblages influence soil OM dynamics. Relationships were investigated at stand scale and in laboratory microcosms. In forest soils, no relationship between macro-detritivore diversity and C stocks appeared from these empirical results, it arose that macro-detritivore diversity and some holorganic fractions are linked. Results from experimental manipulations show that macro-detritivore effects on beech leaf biodegradation can be split into distinct effects groups. Furthermore, functional diversity, assessed through morphological dissimilarity, rather than species diversity better explains assemblage performances. In agricultural soils, no link clearly appears between these parameters. Regarding laboratory experiments results, eathworm effects on C-CO2 release and soil aggregate OM content and stability depend on species identity and initial soil OM. Furthermore, in low OM soil, increasing species diversity stabilizes C mineralisation and but led to an increase of both aggregate OM content and stability. In conclusion, field results show that macro-detritivore species diversity is driven by soil occupancy rather by system dynamics, thus refuting (H1) hypothesis. Furthermore, soil C stock do not vary during forest rotation while it increase with pasture age, refuting and validating the (H1) hypothesis, respectively. On the other hand, microcosm experiments show that macro-detritivores diversity influences soil OM dynamics, validating (H2) hypothesis.ROUEN-BU Sciences (764512102) / SudocBRUNOY-Bib. d'ecologie generale (911145101) / SudocSudocFranceF

Mécanismes liés au vivant : la macrofaune

Mécanismes liés au vivant : la macrofaune. Journée du réseau CarboSM

Relationships between metal compartmentalization and biomarkers in earthworms exposed to field-contaminated soils

Partitioning tissue metal concentration into subcellular compartments relecting 'toxicologically available' pools may provide good descriptors of the toxicological efects of metals on organisms. Here we investigated the relationships between internal compartmentalization of Cd, Pb and Zn and biomarker responses in a model soil organism: the earthworm. The aim of this study was to identify metal fractions reflecting the toxic pressure in an endogeic, naturally occurring earthworm species (Aporrectodea caliginosa) exposed to realistic field-contaminated soils. After a 21 days exposure experiment to 31 field contaminated soils, Cd, Pb and Zn concentrations in earthworms and in three subcellular fractions (cytosol, debris and granules) were quantified. Different biomarkers were measured: the expression of a metallothionein gene (mt), the activity of catalase (CAT) and of glutathione-s-transferase (GST), and the protein, lipid and glycogen reserves. Biomarkers were further combined in an integrated biomarker index (IBR). The subcellular fractionation provided better predictors of biomarkers than the total internal contents hence supporting its use when assessing toxicological bioavailability of metals to earthworms. The most soluble internal pools of metals were not always the best predictors of biomarker responses. metallothionein expression responded to increasing concentrations of Cd in the insoluble fraction (debris + granules). Protein and glycogen contents were also mainly related to Cd and Pb in the insoluble fraction. On the other hand, GST activity was better explained by Pb in the cytosolic fraction. CAT activity and lipid contents variations were not related to metal subcellular distribution. The IBR was best explained by both soluble and insoluble fractions of Cd and Pb. This study further extends the scope of mt expression as a robust and specific biomarker in an ecologically representative earthworm species exposed to field-contaminated soils. The genetic lineage of the individuals, assessed by DNA barcoding with cytochrome c oxidase subunit I, did not inuence mt expression