Soil Compartments Research Articles

Woolly beech aphid infestation reduces soil organic carbon availability and alters phyllosphere and rhizosphere bacterial microbiomes

PurposeThe woolly beech aphid thrives on European beech leaves, which has complex direct and indirect impacts on above- and belowground processes. A mechanistic understanding of insect-mediated changes in organic carbon (OC) availability for microbial life and its implications for element cycling is still lacking. This study aims at disentangling aphid-induced effects on phyllosphere and rhizosphere bacterial communities, as well as investigating feedbacks to OC transfer from the canopy to the mineral soil.MethodsFollowing 2.5 months of infestation, we tracked the fate of OC (13CO2 pulse-labelling) in several compartments of beech sapling – soil mesocosms over 5 days. In ecosystem solutions, water extracts and soil/plant compartments we determined OC and N and solid δ13C. Bacterial community structure (16S rRNA gene targeted amplicon sequencing and quantitative PCR) and metabolite profiles (LC-qTOF-MS) were analysed.ResultsWe found significantly higher aphid-mediated inputs of OC within throughfall. Honeydew-derived C on infested leaves was inconsequential for total phyllosphere bacterial abundances, but verifiably affected the community structure. In all soil compartments, cold-water extractable OC pools declined significantly by frequent inputs of readily available OC. This pattern might relate to reductions in rhizodepositions and altered microbial processing by accelerated soil C-mineralization. As a result, the abundance of metabolites changed significantly in different ecosystem solutions.ConclusionsOur findings attest that insect infestations induce distinct direct and indirect effects on plant-insect-microbiome interactions leading to marked alterations in C dynamics. This integrated approach improves our understanding on microbial dynamics and biogeochemistry and evaluates the role of insects for ecosystem processes.

The nitrification inhibitor nitrapyrin has non-target effects on the soil microbial community structure, composition, and functions

Nitrapyrin is a nitrification inhibitor used to retain ammonia-N in soil to improve crop yields and quality. Nitrapyrin targets specifically the ammonia oxidizers, but it is not known if it has non-target effects on the soil microbial communities. Here, we tested the hypothesis that nitrapyrin also leads to large shifts in soil microbial community structure, composition, diversity and functions. To test this hypothesis, we set-up a field experiment where wheat (Triticum aestivum cv. AC Walton) was fertilized with ammonium nitrate (NH4NO3) and supplemented or not with nitrapyrin. Rhizosphere and bulk soils were sampled twice (at grain filling and harvest), the 16S rRNA gene and ITS region were amplified and sequenced to follow the changes in archaeal, bacterial and fungal community structure, composition and diversity. To assess microbial functions, several genes involved in the nitrogen cycle were quantified by real-time qPCR, and volatile organic compounds (VOCs) were trapped in the rhizosphere at the moment of sampling. Sampling dates and soil compartments had overwhelming effects on the microbial communities. However, nitrapyrin still significantly affected the relative abundance of Thaumarchaeota, Proteobacteria, Nitrospirae and Basidiomycota, and several genera. Nitrapyrin also significantly affected bacterial and fungal community structure, and the abundance of all the N-cycle gene tested, but always in interaction with the sampling date. In contrast, nitrapyrin had no significant effect on the emission of VOCs, where only sampling dates significantly influenced the profiles observed. Our results show that nitrapyrin influences non-target soil- and plant-associated microbial communities. In the longer term, these shifts might counteract the positive effect of nitrapyrin on crop nutrition and greenhouse gas emissions.

Modeling multimedia fate and health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the coastal regions of the Bohai and Yellow Seas

Using an improved multimedia fate model, this study simulated the spatial distributions, partitioning behaviors, and mass exchanges of PAH16 (16 species with priority by the USEPA) in multiple environmental compartments in the coastal regions of the Bohai and Yellow Seas, Northern China. The model predictions generally matched well with the measured results, as the deviations of most points were within one order of magnitude in the air, freshwater, and 3 soil compartments. The estimated concentrations of ΣPAH16 in the northern part were higher than those in the southern part, which was consistent with the emissions of each part. Approximately 97.6% of the ΣPAH16 mass was distributed in soils; therefore, soils served as the dominant sink of PAH16. The estimated net flux of ΣPAH16 from air to soil ranged from 0.4 to 10.7 mg/m2/year (an average of 3.2 mg/m2/year), and the estimated flux of deposition from air to soil fell in the range of 0.4–10.8 mg/m2/year (an average of 3.2 mg/m2/year), which served as the dominant process at the air-soil interface. The estimated net flux of ΣPAH16 from air to freshwater ranged from −15.3 to 9.4 mg/m2/year (an average of −0.3 mg/m2/year), and the reversed volatilization flux from freshwater to air ranged from 0.01 to 21.1 mg/m2/year (an average of 3.7 mg/m2/year). This situation indicated notable spatial variations and volatilization as the main process affecting the direction of net flux at the air-freshwater interface. Deterministic risk assessment and probabilistic risk assessment were conducted. The overall health risks of the studied regions were acceptable, while the excess lifetime cancer risk (ELCR) by air inhalation was greater than that by soil ingestion. CapsuleMultimedia fate model-predicted distributions and compositions of PAH16 in different compartments, compartmental exchange fluxes and directions, and deterministic and probabilistic ELCR via different exposure pathways were assessed.

Intercropping Systems Modify Desert Plant-Associated Microbial Communities and Weaken Host Effects in a Hyper-Arid Desert.

Intercropping is an important practice in promoting plant diversity and productivity. Compared to the accumulated understanding of the legume/non-legume crop intercrops, very little is known about the effect of this practice when applied to native species on soil microbial communities in the desert ecosystem. Therefore, in the present study, bulk soil and rhizosphere microbial communities in the 2-year Alhagi sparsifolia (legume)/Karelinia caspica (non-legume) monoculture vs. intercropping systems were characterized under field conditions. Our result revealed that plant species identities caused a significant effect on microbial community composition in monocultures but not in intercropping systems. Monoculture weakened the rhizosphere effect on fungal richness. The composition of bacterial and fungal communities (β-diversity) was significantly modified by intercropping, while bacterial richness (Chao1) was comparable between the two planting patterns. Network analysis revealed that Actinobacteria, α- and γ-proteobacteria dominated bulk soil and rhizosphere microbial co-occurrence networks in each planting pattern. Intercropping systems induced a more complex rhizosphere microbial community and a more modular and stable bulk soil microbial network. Keystone taxa prevailed in intercropping systems and were Actinobacteria-dominated. Overall, planting patterns and soil compartments, not plant identities, differentiated root-associated microbiomes. Intercropping can modify the co-occurrence patterns of bulk soil and rhizosphere microorganisms in desert ecosystems. These findings provided a potential strategy for us to manipulate desert soil microbial communities and optimize desert species allocation in vegetation sustainability.

Release of phthalate esters from a local landfill in the Tibetan Plateau: Importance of soil particle-size specific association

High loads of phthalate esters (PAEs) in background regions can be directly attributed to the local sources, and their association with soil particles may determine the environment behaviors. However, little is known about the particle-size specific distributions of PAEs in soils from point source to the surroundings. In this study, 12 PAE congeners were measured in clay (< 2 μm), silt (2–63 μm) and sand fractions (63–250 μm) from surficial soils and soil profiles (0–200 cm) around the Lhasa landfill. The total concentrations of PAEs in bulk soils varied from 0.44 to 22.3 μg/g, with a dominance of bis(2-ethylhexyl) phthalate (DEHP). The clay-sorbed PAEs exhibited a decreasing trend with the increasing distance from landfill. This distribution pattern was well described by the Gaussian air pollution model, suggesting the airborne particles/gaseous transport of clay-sorbed PAEs. The Boltzmann equation explained the spatial variation of silt-sorbed PAEs, reflecting the atmospheric dispersion of silt-sorbed PAEs. In comparison, the sand-sorbed PAEs in surrounding soils showed downslope accumulation possibly due to the aeolian transport of sand particles. Half-life of the most abundant PAE congener DEHP was assumed based on the soil inventories from observed concentration and the Level III fugacity model simulations, and the results indicated significant longer half-life of DEHP in deeper soils (~24,000 h) than in surficial soils (5500 h). This study elucidates that the distribution and fate of soil PAEs would depend on their association with particles in the source area, and the relative stability of DEHP in deeper soils would further increase PAE inventory in soil compartment.

Oxygen matters: Short- and medium-term effects of aeration on hydrolytic enzymes in a paddy soil

Rapid exposure of anoxic microbial communities to oxygen (O2) can have unpredictable effects, including strong suppression of their enzymatic activity. Nonetheless, most medium- and long-term incubation studies on soil organic matter transformations fail to consider aeration effects during sample post-processing and/or assays. Moreover, it remains unclear whether anoxic enzymatic systems are adapted to quick switch to oxic conditions. We evaluated the effects of short-term (2-h oxic (+O2) vs. anoxic (–O2) assays) and medium-term aeration (after 10-day oxic vs. anoxic pre-incubation) on the kinetic parameters (Vmax, Km) of phosphomonoesterase, β-glucosidase, and leucine aminopeptidase in top bulk, rooted, and bottom bulk paddy soil of flooded rice mesocosms. We hypothesized contrasting short- and medium-term responses of hydrolytic enzyme activities to aeration (i) a negative short-term effect caused by reactive O2 species toxicity and/or other mechanisms, and (ii) adaptation of anoxic microbial communities to medium-term aeration reducing the impact of ongoing O2 exposure.Overall, 2-h aeration suppressed Vmax values by 7–43% and catalytic efficiency Ka (Vmax/Km) by 3–22%, and extended the substrate turnover time Tt (7–33%) of three tested enzymes in all soil compartments pre-incubated without O2. In contrast, no short-term suppressive effect of O2 was observed on three tested enzymes after oxic pre-incubation. Medium-term aeration increased Vmax (by 12–253%) and Ka (by 3–78%) of the enzymes and shortened Tt (4–42%) as compared to the anoxic counterpart. These findings support our hypothesis about anoxic microbial community adaptation over the medium-term aeration. Accordingly, the sensitivity of anoxic hydrolytic enzymes to a short-term O2 exposure and the O2 adaptation mechanisms require strong consideration (i) for enzyme assays of anoxic soils and (ii) for understanding the soil organic matter dynamics in environments with O2 fluctuations.

Short-term dynamic responses of soil properties and soil fauna under contrasting tillage systems

Achieving sustainability is a worldwide current concern in agriculture that brings important challenges but also opportunities for rethinking agroecosystems. While many studies focused on tillage effects upon soil organisms, few of them have considered this into a temporal framework. In a study conducted in actual field conditions, we evaluated at short-term (7 months) the dynamic of several abiotic and biotic soil parameters under contrasting tillage systems. We hypothesised that (1) the reduction and especially the stopping of the soil mechanical perturbation lead overall to an improvement of the soil physical structure and the food resources available for soil fauna. (2) According to their specific ecological requirements, Collembola and Earthworms will show different dynamics of responses following alleviation of soil mechanical perturbation. (3) For a single group (either Collembola or earthworms), differences between tillage systems are dependent on the sampling period. We used a field set-up held on the INRA experimental station of Estrées-Mons (North of France). Three tillage systems were investigated: conventional tillage (with the soil inverted up to 25 cm depth) reduced tillage (limited to the first 7–8 cm depth) and no-tillage. Each treatment was replicated 4 times randomly (3 × 4 = 12 plots in total). Collembola and earthworms were sampled at each plot using standard methods. During the course of the experiment, two tillage operations were performed one in mid-March and one in mid-May. Samplings of soil fauna were performed on a regular basis according to tillage operation: 1 day before, and respectively 1; 7; 30; 49; 56; 104; 210 days after. Abiotic parameters (bulk density, SOC stock, Mean Weight Diameter (MWD) and aggregates size) and microflora (microbial and fungal biomass and their activity) were also monitored and used as explaining factors. Our findings showed that slightly reducing the intensity of soil mechanical perturbation, did not favour soil fauna. But, when stopping tillage, population sizes of earthworm and Collembola increased. This is related to the improvement of the distribution of, and accessibility to, organic matter as a basic food source (SOC stock, microbial and fungal biomass and their potential C mineralisation activity), the physical structure of the soil and the distribution of pore sizes as a space life (bulk density, MWD and aggregates size). Our kinetic study has shown that the different groups of soil fauna respond differently to mechanical soil disturbance. Overall, conservation tillage can foster one of the numerous services provided by the soil compartment, namely the soil biodiversity and therefore improve soil quality and health.

Seawater intrusion: an appraisal of taxa at most risk and safe salinity levels.

Seawater intrusion into low-lying coastal ecosystems carries environmental risks. Salinity levels at these coastal ecosystems may vary substantially, causing ecological effects from mortality to several sublethal endpoints, such as depression of rates of feeding, somatic growth, or reproduction. This review attempts to establish safe salinity levels for both terrestrial and freshwater temperate ecosystems by integrating data available in the literature. We have four specific objectives: (i) to identify the most sensitive ecological taxa to seawater intrusion; (ii) to establish maximum acceptable concentrations-environmental quality standards (MAC-EQSs) for sea water (SW) from species sensitivity distributions (SSDs); (iii) to compile from the literature examples of saline intrusion [to be used as predicted environmental concentrations (PECs)] and to compute risk quotients for the temperate zone; and (iv) to assess whether sodium chloride (NaCl) is an appropriate surrogate for SW in ecological risk assessments by comparing SSD-derived values for NaCl and SW and by comparing these with field data. Zooplankton, early life stages of amphibians and freshwater mussels were the most sensitive ecological receptors for the freshwater compartment, while soil invertebrates were the most sensitive ecological receptors for the terrestrial compartment. Hazard concentration 5% (HC5 ) values, defined as the concentration (herein measured as conductivity) that affects (causes lethal or sublethal effects) 5% of the species in a distribution, computed for SW were over 22 and 40 times lower than the conductivity of natural SW (≈ 52mS/cm) for the freshwater and soil compartment, respectively. This sensitivity of both compartments means that small increments in salinity levels or small SW intrusions might represent severe risks for low-lying coastal ecosystems. Furthermore, the proximity between HC5 values for the soil and freshwater compartments suggests that salinized soils might represent an additional risk for nearby freshwater systems. This sensitivity was corroborated by the derivation of risk quotients using real saline intrusion examples (PECs) collected from the literature: risk was >1 in 34 out of 37 examples. By contrast, comparisons of HC5 values obtained from SSDs in field surveys or mesocosm studies suggest that natural communities are more resilient to salinization than expected. Finally, NaCl was found to be slightly more toxic than SW, at both lethal and sublethal levels, and, thus, is suggested to be an acceptable surrogate for use in risk assessment.

Substrate quality effects on stabilized soil carbon reverse with depth

High-quality plant inputs to the soil with low lignin to nitrogen ratios have been conceptualized to foster the formation of soil organic matter (SOM) and carbon (C) in stabilized soil compartments, such as aggregates and organo-mineral associations (MAOM), in dependence of the soil’s capacity to store additional C (i.e., C saturation deficit). Yet, evidence for these conceptualizations from field experiments is scarce and it is unclear whether factors commonly not included in laboratory experiments (such as soil depth) may modulate the influence of substrate quality on SOM formation. We, thus, tested the effect of substrates with different qualities (from European alder and Scots pine) on C stocks in bulk soil, free particulate and aggregate-occluded organic matter, and MAOM in soils at various ages after reclamation and at different soil depths in a common-garden field experiment.Our results revealed that substrate quality generally acted in the predicted way in the upper investigated soil layer (0–5 cm depth), i.e., high-quality substrates increased C stocks in MAOM. Surprisingly, the effect of substrate quality reversed with depth (5–15 cm; i.e., low-quality litters were associated with higher C stocks in MAOM), potentially due to a higher sensitivity (or “priming”) of native SOM in response to high-quality substrates at depth or a lower probability of such substrates reaching deeper soil layers. These patterns appeared to be largely independent of the soils’ theoretical capacity to stabilize additional C, which was exceeded in all investigated soils. Based on the results of our field experiment, we highlight the need to refine recent conceptualizations by focusing on environmental factors that are commonly not accounted for in laboratory-scale experiments and that may alter the direction in which substrate quality acts to influence the formation of SOM.

Country-Specific Environmental Risks of Fragrance Encapsulates Used in Laundry Care Products.

Fragrance encapsulates (FEs) are designed to deliver fragrance components, notably in laundry care products. They are made of thermoset polymeric shells surrounding the fragrance content. These materials enter the environment mainly during laundry washing, but little is known about their distribution in and impact on the environment. The aim of the present study was to estimate the environmental concentrations of FE shells in freshwater, sediment, and soil compartments for 34 selected countries and to compare them with ecotoxicological effects. Probabilistic material flow analysis was used to estimate worst‐case predicted environmental concentrations (PECs). The lowest freshwater PEC was predicted for Finland (0.00011 µg/L) and the highest for Belgium (0.13 µg/L). Accumulation of FE shells between 2010 and 2019 was considered for sediments and sludge‐treated soils. The PECs in sediments ranged from 3.0 µg/kg (Finland) to 3400 µg/kg (Belgium). For sludge‐treated soil, the concentration was estimated to be between 0 (Malta and Switzerland) and 3600 µg/kg (Vietnam). Ecotoxicological tests showed no effects for FE shells at any tested concentration (up to 2700 µg/L freshwater, 5400 µg/kg sediment, and 9100 µg/kg soil), thus not allowing derivation of a predicted‐no‐effect concentration (PNEC). Therefore, to characterize the environmental risks, the PEC values were compared with highest‐observed‐no‐effect concentrations (HONECs) derived from ecotoxicological tests. The PEC/HONEC ratios were 9.3 × 10–6, 0.13, and 0.04 for surface waters, sediments, and sludge‐treated soils, respectively, which are much below 1, suggesting no environmental risk. Because the PEC values constitute an upper boundary (no fate considered) and the HONEC values represent a lower boundary (actual PNEC values based on NOECs will be higher), the current risk estimation can be considered a precautionary worst‐case assessment. Environ Toxicol Chem 2022;41:905–916. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Modelling the Organic Evolution of a Mediterranean Limestone Soil under Usual Cropping of Durum Wheat and Faba Bean

The modeling of carbon (C) and nitrogen (N) fluxes between microorganisms and plants in pure and associated cultures of durum wheat and faba bean demonstrated a close link between the C and N cycles in agroecosystems. The MOMOS (microorganisms and organic matter of soils) model integrates simplified descriptions of photosynthesis (origin of organic C in soil), N microbial exchange (soil origin for N), N fixation (atmospheric origin for N), and plant growth with an organic matter decomposition core that has the soil microbial community at its center. This work provides estimates of the exchange parameters between plant organs and microbes, which were compared to literature data when available. In a connection with photosynthesized C, the root demand for inorganic N can be adjusted by its microbial production. Our approach is a new methodology for improving plant production, by optimizing the interactions with soil microorganisms. Additionally, the coupling of plant growth and microbial processes enabled determining changes of the organic compartments of soil. In the unfertilized limestone soil of this study, sequestration was found to be located in the labile microbial metabolites for one year, then significantly transferred to stable humus during 6-year intercropping. Thus, we propose the MOMOS mathematical tool, not only for guiding ecological intensification, but also related to the management of agroecosystems for climate change mitigation.

Rhizobium alamii improves water stress tolerance in a non-legume

With the increasing demand for alternative solutions to replace or optimize the use of synthetic fertilizers and pesticides, the inoculation of bacteria that can contribute to the growth and health of plants (PGPR) is essential. The properties classically sought in PGPR are the production of phytohormones and other growth-promoting molecules, and more rarely the production of exopolysaccharides. We compared the effect of two strains of exopolysaccharide-producing Rhizobium alamii on rapeseed grown in a calcareous silty-clay soil under water stress conditions or not. The effect of factors ‘water stress’ and ‘inoculation’ were evaluated on plant growth parameters and the diversity of microbiota associated to root and root-adhering soil compartments. Water stress resulted in a significant decrease in leaf area, shoot biomass and RAS/RT ratio (root-adhering soil/root tissues), as well as overall beta-diversity. Inoculation with R. alamii YAS34 and GBV030 under water-stress conditions produced the same shoot dry biomass compared to uninoculated treatment in absence of water stress, and both strains increased shoot biomass under water-stressed conditions (+7% and +15%, respectively). Only R. alamii GBV030 significantly increased shoot biomass under unstressed or water-stressed conditions compared to the non-inoculated control (+39% and +15%, respectively). Alpha-diversity of the root-associated microbiota after inoculation with R. alamii YAS34 was significantly reduced. Beta-diversity was significantly modified after inoculation with R. alamii GBV030 under unstressed conditions. LEfSe analysis identified characteristic bacterial families, Flavobacteriaceae and Comamonadaceae, in the RT and RAS compartments for the treatment inoculated by R. alamii GBV030 under unstressed conditions, as well as Halomonadaceae (RT) and several species belonging to Actinomycetales (RAS). We showed that R. alamii GBV030 had a PGPR effect on rapeseed growth, increasing its tolerance to water stress, probably involving its capacity to produce exopolysaccharides, and other plant growth-promoting (PGP) traits.

Robustness to import declines of three types of European farming systems assessed with a dynamic nitrogen flow model

CONTEXTAgriculture in Western Europe is predominantly input-intensive (fertilisers, water, fuel, pesticides) and relies on feed imports. As a result, it is dependent on oil, which may start to decline in production in the 2020s, thus exposing the agricultural sector to potential economic stress, including increased input prices and decreased farmer purchase capacities. Therefore, it is necessary to assess the capacity of European farming systems (FS) to maintain production levels despite a decline in oil production (i.e., robustness). OBJECTIVEWe aimed to model and compare the time variations in the animal- and crop-sourced production of three French FS under three scenarios of decreased availability of feed and synthetic fertiliser imports. METHODSWe developed a FS-scale dynamic model that considers nitrogen flows between livestock, plant, and soil compartments. Plant production is a function of soil mineral nitrogen levels, and livestock numbers depend on feed availability. The three FS are characterised by different crop-grassland-livestock balances: (i) field crop (Plateau Picard), (ii) intensive monogastric (Bretagne Centrale), and (iii) extensive ruminant (Bocage Bourbonnais). The three scenarios consist of different combinations of synthetic nitrogen fertilisers and feed import availability declines until 2050: a decrease in synthetic fertilisers only (Synth-), a decrease in feed imports (Feed-), and a decrease in both external inputs (Synth-Feed-). RESULTS AND CONCLUSIONSThe first two scenarios highlight the positive role of livestock effluents and permanent grasslands on the robustness of food production. In the Synth-Feed- scenario, the extensive ruminant FS exhibits robustness (no decline in food production) for 13 years, whereas the field crop FS exhibits robustness for 4 years. In contrast, the intensive monogastric FS shows decreased food production within the first year. The difference between the two crop-livestock FS can be explained by livestock density, herd composition but also plant cover composition. In the long term, all three FS show a decrease in food production between 45 and 60%. SIGNIFICANCEOur modelling work shed some light on the role of ruminants and permanent grasslands in making FS more robust to decreases in synthetic fertiliser and feed import availability, increasing the time without production decline after the beginning of the perturbation. For longer-time resilience, configurational changes are still necessary, however a greater robustness gives more time to implement them, therefore facilitating adaptation and transformation. Our model paves the way to the study of resilience of FS from the point of view of their crop-grassland-livestock configuration and their dependence on external inputs.

Biowaste compost amendment modifies soil biogeochemical cycles and microbial community according to aggregate classes

The use of biowaste compost as soil organic amendment is of great interest for soil recovery. However, there is little knowledge of detailed effects on chemical, microbial, and biochemical properties in different soil compartments (aggregate classes) following long-term amendment with biowaste compost. We studied the distribution of soil organic carbon (SOC), total nitrogen (TN), soil microbial biomass (SMB), microbial community composition and activity in bulk soils and in three water stable aggregate classes (>250, 250–53, and <53 μm), after seven years of different fertilization treatments: biowaste compost (Com), mineral NPK fertilizers (Min), biowaste compost with half-dose N fertilizer (ComN), and no fertilizers as control (Cnt). Microbial biomass was assessed through a double-stranded DNA (dsDNA) based method and enzyme activities were determined using a microplate-based fluorometric assay. Denaturing gradient electrophoresis (DGGE) fingerprinting analysis was used to study the composition of both fungal and bacterial communities. Com and ComN treatments improved significantly SOC, TN and SMB in bulk soils and in all aggregate sizes. Composition of fungal and bacterial communities shifted with biowaste compost, more in soil aggregates than in bulk soils. To this change of microbial community composition in soil aggregates, corresponded a response of enzymes activities to fertilization treatments depending on aggregate size. Com treatment caused the highest enzyme activity in microaggregates (250–53 μm), whereas ComN and Min showed, in general, a higher activity in silt plus clay sized aggregates (<53 μm). The enzymes involved in biogeochemical cycle of P, with the exception of the phytase, displayed the lowest activity in macroaggregates (>250 μm), suggesting that the intensity of this cycle is lower in this soil niche; however, they increased with C accumulation due to both biowaste compost treatments. Furthermore, fungal diversity and richness decreased with fertilization treatments in all fraction except in macroaggregates. Thus, soil aggregates regulated the feedback of chemical, biochemical and microbial properties in response to soil fertilization strategies.

Role of ecosystem-atmosphere exchanges of semi-volatile organic compounds in organic aerosol formation

Deposition of the gas fraction of Semi-Volatile Organic Compounds (SVOC) may be an important removal pathway and may strongly influence concentrations of organic aerosols due to the gas-particle partitioning of SVOC. All the studies on this process are based on the classic Wesely resistance approach that uses Henry's law constants to calculate a deposition rate scaled on the deposition rate of SO2. However, even highly hydrophobic SVOC could be efficiently removed by the vegetation and soils as shown by numerous studies on Persistent Organic Pollutant (POP) modeling. Moreover, the re-volatilization of deposited SVOC is possible and could influence organic aerosol concentrations.An atmosphere-soil-vegetation module was developed and implemented in the 3D air quality model CHIMERE 2017β to represent the accumulation of compounds in the different compartments of the biosphere and the exchanges between them. The soil compartment was represented with a multi-layer approach (the layers corresponding to different in-soil depths) to simulate the multiphase diffusion of compounds inside the soil. Exchanges of SVOC between the air, soil and vegetation compartments were simulated using bi-directional approaches based on Rg (the gas-phase partitioning in the soil compartment) and Kva the vegetation-air partitioning coefficient. Parameters were estimated based on the physical properties of the compounds and their molecular structure.Simulations performed over Europe show that air-vegetation-soil exchanges may be a more efficient removal pathway than dry deposition of particles for SVOC with a gas-phase fraction above 10%. Considering air-vegetation-soil exchanges in the simulations lead to a decrease of organic aerosol concentrations by 15% and primary SVOC (considered as hydrophobic compounds) may be efficiently removed by those pathways (contrary to what is calculated with the Wesely approach). This decrease of concentrations is mainly due to air-vegetation exchanges. During summer, the use of the Wesely approach may lead to a slight overestimation of deposition fluxes (leading to an underestimation of concentration by 1%).Re-volatilization may limit the amount of deposited SVOC. Depending on assumptions, simulations showed that re-emissions (inversion of exchanges toward the emissions) in summer of SVOC accumulated during winter is theoretically possible and may be a minor source of organic aerosol.

Wastewater Management of Wet Scrubbers in Waste-to-energy Facilities: a Life Cycle Analysis

Nowadays, increasing attention is focused on the indirect impacts of emission control technologies and the potential burden shifting. A clear example is the generation of wastewater when wet scrubbing systems are used for flue gas cleaning. The present study takes into consideration a typical wet scrubber for waste-to-energy plants and the available options for wastewater management: physicochemical treatment, evaporation or valorisation. A comparative assessment of the environmental footprint of the alternatives is performed by taking into account the burdens related to the supply of reactants, energy and the disposal of process residues (solid and liquid waste streams). It is thus shown that the recovery of a marketable product from the effluent produces a net environmental benefit, while the choice between wastewater discharge or evaporation represents only a shift of burden between the water and the soil compartments.

Contribution of biological soil crusts to soil organic matter composition and stability in temperate forests

Biological soil crusts (biocrusts) play an important role in the biogeochemical C-, N- and P-cycles but there is limited knowledge about their effect on the composition and stability of organic matter (OM) in soil. In pine and beech dominated temperate forests, the different compartments of biocrust, crust-adhering soil and crust-free soil were analysed by pyrolysis field ionization mass spectrometry (Py-FIMS) and C K-edge X-ray absorption near edge structure (XANES) spectroscopy. Phototrophic biocrust communities had been determined morphologically. Predominant tree species affected OM composition and stability but an overriding effect of biocrust organisms was observed. In biocrusts, the OM mineralization potential was high due to a high carbohydrate/ketone ratio and a high proportion of the fatty acid C22:0. A high proportion of free fatty acids in combination with a high carbohydrate proportion was identified as a relative marker for biocrusts and additional high proportions of lignin dimers were specific for samples under pine. In biocrust under pine, OM in soil compartments was characterized by large proportions of long-chain aliphatics from plant cuticular material. In A-horizon substrate under beech, OM compound classes were not affected by phototrophic species richness, suggesting functional redundancy of these biocrust organisms with regard to OM composition. In contrast to A-horizon substrate, OM in C-horizon substrate was characterized by a higher proportion of easily decomposable material. Under pine, forest management intensity (SMI) affected OM by stand age and density due to effects on phototrophic biocrust species. We conclude that compartment, vegetation, horizon substrate and SMI affected OM composition and stability, and biocrusts hence contributed to soil OM diversity in forest ecosystems.

Microplastic fibers influence Ag toxicity and bioaccumulation in Eisenia andrei but not in Enchytraeus crypticus.

Microplastic fibers (MF) are released from synthetic textiles during washing and end up in the wastewater. Similarly, silver nanoparticles (AgNP), incorporated in textiles as antimicrobial agents, are released in washing machines, also reaching the wastewater treatment plants. Therefore, both MF and AgNP co-exist in the environment and enter the soil compartment mainly via the application of biosolids. Yet, the combined effect of MF and AgNP has not been studied. Here, we assessed the effects of polyester MF on the toxicity of AgNP and AgNO3 to the earthworm Eisenia andrei and the enchytraeid Enchytraeus crypticus. The organisms were exposed to a range of concentration of AgNP (32, 100, 320, 1000, 3200 mg Ag/kg) and AgNO3 (12.8, 32, 80, 200, 500 mg Ag/kg) in LUFA 2.2 soil in the absence or presence of MF (0.01% DW). Reproduction tests were conducted and the toxicity outcomes compared between soils with and without MF. The exposure to MF caused a decrease in the number of juveniles and changed the biochemical composition of earthworms. Moreover, the presence of MF increased the toxicity of AgNP to earthworm reproduction (EC50 = 165 mg Ag/kg) when compared to AgNP exposure alone (EC50 = 450 mg Ag/kg), but did not alter the toxicity of AgNO3 (EC50 = 40 mg Ag/kg). For enchytraeids, no significant difference in Ag toxicity could be detected when MF was added to the soil for both AgNP and AgNO3. Overall, Ag bioaccumulation was not affected by MF, except for a decrease in earthworm body concentration at the highest Ag soil concentration (3200 mg Ag/kg). Our results suggest that the presence of MF in the soil compartment may be a cause of concern, and that the joint exposure to Ag may be deleterious depending on the Ag form, organism, and endpoint. The present work provides the first evidence that a realistic MF concentration in soil lowers AgNP concentration necessary to provoke reproductive impairment in earthworms. The influence of MF on the risk assessment of AgNP should be considered.

Importance of microbial communities at the root-soil interface for extracellular polymeric substances and soil aggregation in semiarid grasslands

In the past years, extracellular polymeric substances (EPS) produced by soil microorganisms received an increasing interest, as they not only protect microbes against environmental stresses, but seem to play a pivotal role in soil structure formation as well. Within soils, root deposits provide an important source of easily accessible energy and nutrients, stimulating microbial growth to produce EPS. Especially under semiarid climates, where a full vegetation cover cannot be sustained, large gradients in living conditions for microbes can be found between the root-soil interface and barren intercanopy spaces.In this study, we aimed to elucidate the plant-specific effects on microbes, EPS production and soil aggregation. At two sites in southern Spain, differing in carbonate and graphite content, legume shrubs of Anthyllis cytisoides and grass tussocks of Macrochloa tenacissima were selected. Soil samples were taken in the adjacent bare interspace, under the canopy and of the rhizosphere. From these samples the microbial community (here bacteria and archaea), EPS(-saccharide) content and soil aggregation (<1 mm) were analysed. DNA extracted from the microbial cells detached from the surface of the sampled roots (rhizoplane), was subjected to 16S rRNA gene amplicon sequencing.The rhizoplane microbial communities differed strongly between plant species and sites, whereby site was the most important factor shaping the communities. The plant species effect on microbial communities diminished strongly with distance to the root surface. At the carbonate-poor Rambla Honda site (site 1), plant species-specific effects were observed in the rhizoplane and rhizosphere, whereas in the carbonate-rich Alboloduy site (site 2) almost no plant species-specific effects were found at the genus level. The larger heterogeneity in microbial communities at site 1 was reflected in EPS-saccharide contents and subsequent soil aggregation, while no difference in soil aggregation was found at site 2. Both parameters increased strongest in the Anthyllis cytisoides rhizosphere at site 1.Despite the lack of a strong gradient with distance from the root at the carbonate-rich site 2, microbial taxa were found by network analysis that positively correlated to EPS-saccharide contents and/or soil aggregation. The relationship between the identified taxa and EPS and/or aggregation relationships were clearest at the root-soil interface, while several other taxa were found to be widely occurring in the other soil compartments too.In conclusion, we found in all compartments potential EPS producers, which could have influenced soil aggregation. Nevertheless, microbes with higher relative abundance in the rhizoplane were linked to higher EPS contents, especially in conjunction with legume shrubs, and subsequently related to soil aggregation. The spatial extent of the root effect was only governed by carbonate contents, as higher carbonate content diminished the observed root effects on the microbial community and subsequent soil aggregation.

Grazing impacts on ecosystem functions exceed those from mowing

Land use change due to the increasing anthropogenic activities is the most important driver leading to alteration of multiple ecosystem functions. Overgrazing is thought to be one of most pervasive and significant degrading processes in grasslands, but direct comparisons with other comparable drivers of land use intensification are lacking. Our results aimed to test how single land use practices (grazing, mowing), and combined land use practices (both grazing and mowing), influence biodiversity, soils and plant function, and the coupling of aboveground and belowground functions and properties in a Eurasian steppe grassland. We examined changes in individual functions associated with aboveground and belowground plant and soil compartments, and multiple combined functions (hereafter ‘multifunctionality’) at 317 sites along an extensive climatic gradient in Northern China. Further, we investigated the correlations (coupling) between aboveground and belowground processes under the three land use scenarios. We found a mixture of effects of grazing, mowing and mowing plus grazing. However, values of many aboveground and belowground attributes were lower when sites were grazed. Although grazed sites had lower values of soil carbon and nutrients, there were no grazing-induced changes in root carbon, nitrogen and phosphorus. More importantly, the most intense land use scenario (grazing combined with mowing) decoupled the correlations between belowground and aboveground functions compared with that of single land uses. Our study demonstrates that mowing is a better long-term management method than grazing for semi-natural grasslands in the Eurasian steppe are heavily grazed. Our results demonstrate that additional land use pressures imposed when mowing and grazing are applied together can decouple the positive associations between plant richness and functions. This knowledge is critical if we are to adopt strategies to maintain diverse grassland ecosystems and the important services and functions that they provide.