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The present study examined the biosynthesis and characterization of selenium nanoparticles (SeNPs) using two contrasting endophytic selenobacteria, one Gram-positive (Bacillus sp. E5 identified as Bacillus paranthracis) and one Gram-negative (Enterobacter sp. EC5.2 identified as Enterobacter ludwigi), for further use as biofortifying agents and/or for other biotechnological purposes. We demonstrated that, upon regulating culture conditions and selenite exposure time, both strains were suitable “cell factories” for producing SeNPs (B-SeNPs from B. paranthracis and E-SeNPs from E. ludwigii) with different properties. Briefly, dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) studies revealed that intracellular E-SeNPs (56.23 ± 4.85 nm) were smaller in diameter than B-SeNPs (83.44 ± 2.90 nm) and that both formulations were located in the surrounding medium or bound to the cell wall. AFM images indicated the absence of relevant variations in bacterial volume and shape and revealed the existence of layers of peptidoglycan surrounding the bacterial cell wall under the conditions of biosynthesis, particularly in the case of B. paranthracis. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed that SeNPs were surrounded by the proteins, lipids, and polysaccharides of bacterial cells and that the numbers of the functional groups present in B-SeNPs were higher than in E-SeNPs. Thus, considering that these findings support the suitability of these two endophytic stains as potential biocatalysts to produce high-quality Se-based nanoparticles, our future efforts must be focused on the evaluation of their bioactivity, as well as on the determination of how the different features of each SeNP modulate their biological action and their stability.

Despite the large contribution of macropores made by soil engineers to the soil macroporosity and water infiltration, few studies have addressed the specific contribution of soil engineer groups, dynamics of biopores and their efficiency in conducting water. Thus, we aimed to investigate the link between soil macrofauna, soil biopores and water infiltration under different pedoclimatic conditions. To do so, we conducted an experimentation in twelve study sites with a large longitudinal gradient from France to Vietnam. The experiment consisted in the field incubation of repacked soil in cores (15 cm in height and 15 cm in diameter) and controlling the activity of soil engineers in the manner of litter bag. For each site, soil columns were: (i) covered with a mesh (200µm) or not and (ii) with or without addition of organic residues to the soil surface. After 12 months, we measured (i) the 3D organization of biopores by X-ray computed tomography and (ii) the saturated hydraulic conductivity by Beerkan method. In addition, soil macrofauna communities and the 3D organization of biopores was measured in each study field. Addition of organic residues increased up to 2-fold the volume percentage of biopores which reached similar values than those observed for each study field. The co-inertia analysis between the data matrix characterizing the shape of biopores and the data matrix of the macrofauna communities showed no statistically significant correlation. Saturated hydraulic conductivity increased with the presence of biopores by 2 to 50-fold with the lowest increased in soils presenting largest saturated hydraulic conductivity. In conclusion, these results demonstrated that biopores are rapidly regenerated regardless the pedoclimatic conditions while the efficiency of biopores in conducting water is related to soil properties.

In Mediterranean areas, agricultural systems have to adapt to an environment presenting few water resources with severe drought events, which are expected to increase in frequency and intensity due to global warming. Therefore, these regions are particularly exposed to climate change and need to implement solutions in order to maintain food production. Our objective is to assess the benefits of innovative cropping systems capable to face these constraints. Evolutionary population are mixtures of plants of the same species presenting a high degree of crop genetic diversity needing lower inputs while allowing higher buffering capacities to adapt environmental stress like water shortage. In this study, we investigated the influence that these plants can have on organic matter quality and dynamics and hypothesised that the abilities of the crop to face drought can participate at increasing soil carbon storage in soil. We conducted a field experiment with five different evolutionary populations of wheat, i.e. a bread wheat (Monnalisa), an einkorn wheat (Norberto) and 2 evolutionary populations (Furat-Li Rosi, Furat-Floriddia and BIO2), cultivated following four other plants species (Wheat, Pea, Cickpea or Clover) on two different sites in Italy presenting contrasted conditions (hot-summer Mediterranean climate in Roma and humid subtropical climate in Parma). Bulk soil and rhizosphere soils were sampled and C, N contents as well as organic matter functional groups using Mid Infrared Spectroscopy (MIRS) were assessed. We observed that the infrared signatures differed between our two sites and depending on the previous cropping species. Evolutionary population of wheat showed different signatures than durum and bread wheat. Our results demonstrate that evolutionary population in particular pedoclimatic conditions can influence the fate of soil organic matter.

There is little doubt that anthropogenic activities have led to profound changes in environmental conditions, which impact biogeochemical cycling and soil functioning. Increasing atmospheric carbon dioxide (CO2) concentrations, global temperature increases, changes in precipitation regimes and more frequent occurrence of extreme events in addition to intensive agricultural practices have adverse effects on soil physical and (micro-)biological properties determining their biogeochemical functioning. In this presentation, I will present the global impacts a and their influence on soil functioning, biogeochemical cycling and ecosystem services in different environments. Feedbacks between the effects of climate change and soil will be presented and soil-based strategies for their mitigation and adaptation to their consequences will be discussed.

Salt marshes are carbon rich ecosystems, but they are threatened by sea-level rise. Root litter dynamics have been little studied, despite contributing three times more to carbon burial than leaves litters and being important for salt marsh resilience to sea level rise. Root litter is defined as one single pool in salt marshes, yet this approach might fail to accurately assess root litter decay, as shown in terrestrial ecosystems where a root functional framework proved to be more accurate. We investigated if root functional types (fine absorptive roots, fine transportive roots and rhizomes) and inundation duration affected OM decay rate in a temperate salt marsh. We used a marsh organ and litterbags.We found that the decay rate strongly varied between root functional types, with fine absorptive roots decaying 30% slower than fine transportive roots and 14% slower than rhizomes.The decay rate was poorly explained by C:N ratio, N and C contents, while better correlated with root lignin composition. The duration of inundation had little effect on the belowground OM decay and did not interact with the decay of root functional types. Therefore, a shift toward experimental methods separating roots by function seems necessary to accurately assess the contribution of root litter to carbon burial in salt marshes. Overall, our results suggest that the current global carbon decay of salt marshes may have been overestimated and that fine absorptive roots could be a larger source for carbon burial than previously thought in salt marshes.

Biochar is increasingly considered an efficient amendment to improve soil fertility and store carbon in soils for climate change mitigation. However, few field studies have evaluated biochar impacts on soil fauna and especially earthworms in temperate areas despite their importance for soil structure and laboratory-based evidence of potential adverse effects. We investigated the effects of three biochars (from rapeseed, miscanthus and compost reject) in mixture with a green waste compost on the abundance and composition of earthworm communities during a three-year field experiment in northern France. Compost alone or biochar-compost mixtures were applied at 11.7 t dry matter ha−1 and compared to equivalent mineral fertilization. Biochar-compost mixtures did not affect total earthworm density and biomass, while contrasting effects concerning specific ecological groups were observed. Compost addition increased juvenile endogeic earthworm density roughly one month after amendment while no adverse short-term effects of biochar-compost mixtures were observed. Two years after amendment application, anecic earthworm density was higher for the mixture with compost and biochar from compost rejects, which also resulted in the highest soil organic carbon concentrations. We conclude that biochar-compost mixtures at low but more economically viable biochar application rates could be used as an increasingly understood beneficial soil amendment under temperate climate conditions without adverse effects on earthworm communities.

International audience; Evidence on the contribution of root regions with varied maturity levels in iron plaque (IP) formation and root exudation of metabolites and their consequences for uptake and bioavailability of chromium (Cr) remains unknown. Therefore, we applied combined nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based techniques, micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption near-edge structure (µ-XANES) to examine the speciation and localisation of Cr and the distribution of (micro-) nutrients in rice root tip and mature region. µ-XRF mapping revealed that the distribution of Cr and (micro-) nutrients varied between root regions. Cr K-edge XANES analysis at Cr hotspots attributed the dominant speciation of Cr in outer (epidermal and sub-epidermal) cell layers of the root tips and mature root to Cr(III)-FA (fulvic acid-like anions) (58–64%) and Cr(III)-Fh (amorphous ferrihydrite) (83–87%) complexes, respectively. The co-occurrence of a high proportion of Cr(III)-FA species and strong co-location signals of 52Cr16O and 13C14N in the mature root epidermis relative to the sub-epidermis indicated an association of Cr with active root surfaces, where the dissolution of IP and release of their associated Cr are likely subject to the mediation of organic anions. The results of NanoSIMS (poor 52Cr16O and 13C14N signals), dissolution (no IP dissolution) and µ-XANES (64% in sub-epidermis >58% in the epidermis for Cr(III)-FA species) analyses of root tips may be indicative of the possible re-uptake of Cr by this region. The results of this research work highlight the significance of IP and organic anions in rice root systems on the bioavailability and dynamics of heavy metals (e.g. Cr).

Biochar and compost are increasingly considered sustainable amendments to improve soil fertility, while reducing agrochemical use. However, the efficiency of biochar, compost, and especially their mixtures under field conditions in temperate regions is still poorly studied. The objective of this study was to evaluate the effects of biochar/compost mixtures on crop yield and soil properties in French temperate cropping systems and to compare the amendment effects to soils receiving mineral potassium and phosphorus fertilization. To this end, green waste compost alone (8 t.ha−1) or in mixture with three contrasted biochars (8 t.ha−1 compost and 4 t.ha−1 biochar) were applied to maize-wheat cropping systems located in three major agricultural territories in France. Results showed that maize and wheat yields were predominantly site specific. Within each site, compost and biochar application led to similar yields and nutrient uptakes as compared to the mineral fertilization, suggesting that compost-biochar mixtures might be as efficient as mineral fertilizers to supply potassium and phosphorus, while biochar did not improve compost benefits to plant yield. Moreover, the effects of compost-biochar mixtures on soil organic carbon concentrations were site specific and led to no effect or increase by up to 53%. We conclude that compost-biochar mixtures may increase carbon content in soil and substitute phosphorus and potassium mineral fertilizers for crop production in temperate cropping systems, even though their effects are site specific.

The role of earthworms on biogeochemical carbon cycling is a major knowledge gap resulting from the difficulty of isolating and exploring the effects provided by the diversity of organisms. In this study, we investigated the effect of six earthworm species belonging to three ecological categories on soil organic carbon (SOC) mineralisation. To this end, we produced casts with the six species using subsoil material with low SOC content and miscanthus litter. Cast were subjected to laboratory ageing for 140 days. During this process, we monitored physicochemical parameters, CO2 emissions and determined the micro-scale organisation of the casts’ particulate organic matter and pores using X-ray tomography.Our results showed contrasting properties of fresh casts from the 3 main ecological categories, in accordance with the earthworm species’ morphological or behavioral strategies, indicating that those were maintained in artificial environments. However, species-specific changes in cast properties throughout ageing increased intragroup variability among ecological categories. As a result we observed earthworm species-specific evolution of CO2 mineralisation rates during casts ageing. We found that at least half of the variability in CO2 emissions was explained by cast microstructural changes, related to the spatial arrangement between particulate organic matter, porosity, and mineral particles. We conclude that earthworm species-specific traits may play a role in organic carbon protection through their impact on microstructural cast properties.

International audience

The effect of mineral properties on soil organic carbon (SOC) destabilization processes is poorly known. Andisols developed under temperate old-growth rain forest store important amounts of SOC due to strong mineral adsorption capacity. We evaluated the effect of mineral soil properties on microbial activity and native SOC mineralization in an incubation experiment with and without the addition of labile organic carbon (C) and nutrients. Top- and subsoil horizons of two Andisols with contrasting age from temperate old-growth rain forest were sampled. We used the selective dissolution methods to determine the metals complexed with SOC and allophane content. Radiocarbon analysis activity was performed to determine the 14C activity and 14C ages of all soils as a proxy for SOC persistence. Additionally, we carried out a laboratory incubation under controlled conditions with and without 13C labeled cellulose and nutrient solution (NH4NO3, KH2PO4) addition. A lower microbial activity in the subsoils of both Andisols compared to topsoils in accordance with the lower 14C activity at depth was recorded. After cellulose and nutrient additions, both subsoils horizons showed native SOC mineralization after 80 days of incubation. In contrast, these amendments did not induce native SOC mineralization in topsoils showing differences on C turnover rates between top- and subsoil horizons. In both soils, the native SOC mineralization after labile C and nutrient additions was negatively related to Na-pyrophosphate extractable C and may therefore be controlled by the formation of organo-mineral complexes with increasing soil C age. We conclude that the physicochemical soil characteristics evolving during pedogenesis control the SOC stabilization and also destabilization processes in Andisols developed under temperate old-growth rain forests.

Due to increased drought frequency following climate change, practices improving water use efficiency and reducing water-stress are needed. The efficiency of organic amendments to improve plant growth conditions under drought is poorly known. Our aim was to investigate if organic amendments can attenuate plant water-stress due to their effect on the plant-soil system and if this effect may increase upon ageing. To this end we determined plant and soil responses to water shortage and organic amendments added to soil. We compared fresh biochar/compost mixtures to similar amendments after ageing in soil. Results indicated that amendment application induced few plant physiological responses under water-stress. The reduction of leaf gas exchange under watershortage was alleviated when plants were grown with biochar and compost amendments: stomatal conductance was least reduced with aged mixture aged mixture (-79 % compared to -87 % in control), similarly to transpiration (-69 % in control and not affected with aged mixture). Belowground biomass production (0.25 times) and nodules formation (6.5 times) were enhanced under water-stress by amendment addition. This effect was improved when grown on soil containing the aged as compared to fresh amendments. Plants grown with aged mixtures also showed reduced leaf proline concentrations (two to five times) compared to fresh mixtures indicating stress reduction. Soil enzyme activities were less affected by water-stress in soil with aged amendments. We conclude that the application of biochar-compost mixtures may be a solution to reduce the effect of water-stress to plants. Our findings revealed that this beneficial effect is expected to increase with aged mixtures, leading to a better water-stress resistance over time. However, while being beneficial for plant growth under water-stress, the use of amendments may not be suited to increase water use efficiency.

International audience

International audience; The efficiency of soil organic carbon (SOC) sequestration as a suitable negative emission technology depends mainly on plant-derived organic carbon input and its allocation to stabilised SOC pools. These processes may be affected by fertiliser use and soil type. The purpose of this study was to investigate the effect of the organic fertiliser (poultry manure compost), the mineral fertiliser (rock phosphate) and their mixture on organic carbon (OC) transfer from plant to soil. We studied OC allocation to protected SOC pools of a Luvisol and a Neoluvisol. We carried out a growth chamber experiment with C-13-enriched atmosphere, where ryegrass plants were grown for 7 wk in the two soil types which were amended with the three different fertiliser sources. We quantified root-derived OC input in three SOC density fractions and soil microbial biomass after 7 wk . We found that the addition of poultry manure compost and its mixture with rock phosphate led to more root biomass and more root-derived OC transfer to active pools compared to rock phosphate alone. Soil amended with poultry manure compost had higher microbial biomass contents than soil with mineral fertilisation due to higher available organic phosphorus. We also noticed variations in the dynamics of the stabilised OC pools amongst soils, which could be attributed to the impact of phosphorus fertiliser sources on SOC stabilisation processes. We concluded that organic and mineral phosphorus fertilisers may have a contrasting impact on OC flow from plant to soil and in particular on the allocation of root-derived OC to labile or stable SOC fractions.

International audience; Background and aims Grassland management practices alter plant litter input into soil in terms of quantity and quality via defoliation, nutrient input and trampling. These alterations may impact litter decomposition and soil organic matter (SOM) quality and quantity. Here, we aimed to investigate the effect of four grassland management practices (unmanaged, low and high intensity grazing, and mowing) on organic matter (OM) input quality and its relation with SOM composition. Methods We considered three types of OM input: aboveground and belowground material from living plants and partly degraded aboveground litter. We assessed their quality based on their elemental (C and N) contents, their stable carbon isotope (C-13) and their lignin composition. Results The results showed that C/N ratios differed among plant-derived OM input types but did not vary among treatments. In contrast, lignin biogeochemistry and lignin/N ratios of plant tissues were differentiated according to input type and treatment. High grazing intensity resulted in the lowest lignin/N ratios of aboveground litter. Lignin chemistry of all plant OM input types under grazing treatments indicated low maturity stage. Despite the similar lignin contribution to soil carbon under all grassland management practices, soil lignin was more degraded under mowing than under the other practices. Conclusions We conclude that grassland management may have an impact on SOM composition by altering plant OM input composition rather than its stoichiometry.

Microplastic (MP) input into agroecosystems is of particular concern as their sources are diverse (mulching films, biosolid application, wastewater irrigation, flooding, atmospheric input, road runoff). Compost application, which is needed to sustain soil ecosystem services in the context of a circular economy, may be a source of microplastics. The aim of this study was to evaluate how different composts derived from urban wastes impact the nature and quantity of coarse (2-5 mm) microplastics (CMP) in soils, using a long-term field experiment in France. Composts resulting from different levels of urban waste sorting were investigated. Our approach included the isolation of microplastics from composts and amended soils followed by their characterization using pyrolysis GC/MS spectrometry. We found that coarse microplastic concentrations varied from 26.9 to 417 kg per hectare depending on the compost type, after 22 years of bi-annual application. These values may be higher than for conventional agricultural practices, as application rate was twice as high as for normal practices. Composts made from municipal solid waste were by far the organic amendments leading to the highest quantity of plastic particles in soils, emphasizing the urgent need for limiting plastic use in packaging and for improving household biowaste sorting. Our results strongly suggest that standards regulating organic matter amendment application should take microplastics into account in order to prevent contamination of (agricultural) soils. Moreover, although no impacts on the soil bio-physico-chemical parameters has been noted so far. However, given the huge microplastic inputs, there is an urgent need to better evaluate their effect on soil functioning.

International audience; Alley cropping agroforestry systems are complex agroecosystems highlighted for their positive effects on soil quality. However, the potential spatial heterogeneity of soil quality created by tree rows at the plot scale has seldom been studied. The aim of this study was to evaluate soil quality at the plot scale, under tree rows and along transects perpendicular to the tree row and to compare alley cropping systems with monocropping systems. This study was performed on an alley cropping system that combined hybrid walnut trees (21 years old) and peas. Topsoil was sampled at tree rows between 1 and 2, 2 and 4 and 4 and 6.5 m from the tree row in the alley cropping system, as well as in a neighbouring monocropping plot. Physical, chemical and microbiological indicators of soil quality were measured. Tree row implantation induced spatial heterogeneity in the chemical indicators, microbial biomass, activities and community structure at the alley cropping plot scale. Alley cropping not only improved microbiological soil quality indicators within the tree rows but also in the interrows when compared to a monocropping system. These indicators were then integrated into one soil quality index (SQI) built through a statistical approach. The soil quality index was calculated for the monocropping plot and for each position within the alley cropping plot. After 21 years of agroforestry practice, tree rows and permanent grass cover improved the SQI until 2 m in the interrow. Weighted SQIs were calculated relative to the surface area of each location for the entire alley cropping plot (i.e., tree row + interrow positions) and for the entire alley cropping interrow (i.e., removing the tree row surface area). The weighted SQI of the entire alley cropping plot significantly increased compared with that of the monocropping plot.

International audience; In modern agriculture large amounts of harvesting residues are produced each year due to the increase of agricultural activities in order to maintain food production for the growing population. The development of innovative fertilizers, able to satisfy nutrient needs without adverse effects on the environment. In order to allow for effective production of a carrier material for smart fertilizers, the objective of this study is to propose a statistical method to optimize the water holding capacity (WHC) and organic matter stability properties of co-composted wheat straw (WS) by using a multi response method. We varied WS size (2 cm), charge of Trichoderma harzianum (0, 7 and 14 discs), and nitrogen addition (0, 0.95 and 1.95 g kg(-1)). Optimized carrier material was characterized by a higher porosity (WHC 91.7%) than raw WS, associated to structural changes and slightly increased stability as indicated by C:N ratio of the 59.5, slightly alkaline (pH similar to 8.0), with high OM structural complexity (E-4:E-6 similar to 7,9) and enhanced sorption properties (total acidity similar to 11.6). We conclude that the optimal treatment included co-composting of WS with fine particle size (

Soil microorganisms are an important indicator of soil fertility and health. However, our state of knowledge about soil microbial activities, community compositions and carbon use patterns under metal contaminations is still poor. This study aimed to evaluate the influences of heavy metals (Cd and Pb) on soil microorganisms by investigating the microbial community composition and carbon use preferences. Metal pollution was approached both singly and jointly with low (25 and 2500 mg kg−1) and high (50 and 5000 mg kg−1) concentrations of Cd and Pb, respectively, in an artificially contaminated soil. In a laboratory incubation experiment, bio-available and potentially bio-available metal concentrations, selected soil properties (pH, electrical conductivity, total organic carbon and total nitrogen), and microbial parameters (microbial activity as basal respiration, microbial biomass carbon (MBC) and microbial functional groups) were determined at two sampling occasions (7 and 49 days). Metal contamination had no effect on the selected soil properties, while it significantly inhibited both microbial activity and MBC formation. Contaminated soils had higher microbial quotient (qCO2), suggesting there was higher energy demand with less microbially immobilized carbon as MBC. Notably, the efficiency of microbial carbon use was repressed as the metal concentration increased, yet no difference was observed between metal types (p > 0.05). Based on the microbial phospholipid fatty acids (PLFA) analysis, total PLFAs decreased significantly under metal stress at the end of incubation. Heavy metals had a greater negative influence on the fungal population than bacteria with respective 5–35 and 8–32% fall in abundances. The contaminant-driven (metal concentrations and types) variation of soil PLFA biomarkers demonstrated that the heavy metals led to the alteration of soil microbial community compositions and their activities, which consequently had an adverse impact on soil microbial carbon immobilization. Keywords: Heavy metals, Soil organic carbon, Microbial carbon decomposition, Microbial activity, Microbial community composition, PLFAs

Expansion of farmland with food production as a major service has been largely associated with conversion of natural ecosystems like the Amazon and Savanna into new agricultural land [...]

Carbon sequestration in soils became a major issue that governments have to face under their sustainable development objectives and the international 4p1000 program. Although, earthworms are recognized to play a key role in the structure and dynamics of organic matter (OM) in soils, their contribution to soil OM cycling is not taken into account in biogeochemical models nor well understood. In particular, the fate of OM protected in earthworm casts is unknown. In this study, we investigated the effects of ageing under field conditions on the OM dynamics contained in casts produced by the anecic earthworm Amynthas adexilis in North Vietnam. To this end we investigated (1) the microscale organisation of particulate organic matter and pores during the exposure of casts and control aggregates during 12 months and (2) compared it to the potential OM mineralisation during a laboratory incubation.Our results indicated that fresh casts contained significantly more particulate organic matter (POM) than control soil aggregates and field aged earthworm casts. Conversely, the porosity was higher in soil control aggregates than in casts and the porosity of casts tended to increase with their ageing. The analyses of micro-CT images also revealed that POM and Pores contents between casts samples presented strong variabilities even in the youngest casts category. We found, on average, higher mineralisation rates for casts than for controls and a reduction of the OM mineralisation with the ageing of casts. Our results also highlighted a strong positive correlation (r2 = 0.89) between POM contents determined by the segmentation of micro CT images and CO2 emissions from the incubation experiment. We conclude that earthworms impact the microscale organisation of POM and pores in their casts and thereby influence soil OM dynamics.