The responses of NO2- and N2O-reducing bacteria to maize inoculation by the PGPR Azospirillum lipoferum CRT1 depend on carbon availability and determine soil gross and net N2O production

Seed inoculation by plant growth promoting rhizobacteria (PGPRs) is an agronomic practice that stimulates root carbon (C) exudation and nitrogen (N) uptake. Inoculation thus increases and decreases C and N availabilities to denitrifiers in the rhizosphere, respectively. Hence, denitrification rates in the rhizosphere can be positively or negatively influenced by root activity depending on the balance between these two processes. We assumed that inoculation effect on denitrifiers could strongly differ according to soil conditions. Would denitrifiers be mostly limited by C, inoculation would increase denitrifier abundance and activity through increased labile C availability. Would denitrifiers be limited by N rather than C, inoculation would decrease denitrifier abundance and activity through increased competition for N. Here we manipulated denitrification limitation by C and N (i) in a field trial through the use of different fertilization levels, and (ii) in a growth chamber experiment by mimicking root exudate inputs. We analyzed how the effects of maize inoculation by the PGPR Azospirillum lipoferum CRT1 on potential gross and net N2O production rates and NO2- and N2O-reducer abundances were related to C and N limitation levels. An increase in potential gross (up to +113%) and to a lesser extent net (+37%) N2O production was observed for soils where denitrification was highly limited by C. This was explained by strong and moderate increases in the abundances of NO2- and N2O-reducers, respectively. In contrast, when denitrification was weakly limited by C, gross and net N2O productions were negatively affected by inoculation (-15 and -40%, respectively). Our results show that the inoculation practice should be evaluated in term of possible increased crop yield but also possible modified N2O emission, paying much attention to cropland soils where denitrifiers are highly limited by C

Bulletin de veille du réseau d'écotoxicologie terrestre et aquatique N°49

Bulletin de veille du réseau ECOTO

Bulletin de veille du réseau d'écotoxicologie terrestre et aquatique N°56

Bulletin de Veille ECOTOXBulletin de veille du réseau d'écotoxicologie terrestre et aquatique N°56, Avril 2022 Réalisé par l'équipe de veille sur la période du 1 er mars au 30 avril 2022. Colette Bertrand, Christian Mougin (UMR 1402 EcoSys), Annette Berard (UMR 1114 EMMAH), Soizic Morin (UR 1454 EABX), Olivier Crouzet (UPFS-OFB), Sonia Grimbuhler (UMR 1463 ITAP) et Pascale Karmasyn-Veyrines (DipSO

La méthode PICT (Pollution-Induced Community Tolerance), un outil complémentaire pour l’évaluation du risque et le biomonitoring des pesticides ?

Fiche thématique N°35 du réseau d’écotoxicologie terrestre et aquatiqu

Exopolysaccharides in the rhizosphere: A comparative study of extraction methods. Application to their quantification in Mediterranean soils

International audienceQuantifying and characterizing Extracellular Polymeric Substances (EPS) and especially exopolysaccharides (EPSac) is an issue for understanding the hydro-physical and biological functioning of the rhizosphere. However, few comparative studies of extraction techniques have been carried out on soils and none on calcareous Mediterranean soils. Three soil-bound EPS extraction techniques, i.e. Cation Exchange Resin (CER), EDTA and NaOH + Formaldhyde (NaOH + F) were compared on three contrasted Mediterranean soils. CER presented the lowest extraction efficiency of EPSac, but also the lowest contamination of EPS by extractants and extracellular compounds. Contamination with intracellular compounds was low and similar with the three methods. Mid-Infrared (MIR) spectra enabled the best discrimination of the EPS extracts when they were prepared with CER. CER is then identified to be the suitable extraction technique of EPS (including EPSac) from soils, including calcareous soils. This technique was applied on rhizospheric and bulk soils harvested in an experimental field of tomato cultivation. A rhizospheric effect was highlighted during the growth of plants of two cultivars with both the soilbound EPSac amounts (total sugar equivalent of extracted EPS) and the MIR spectra of extracted EPS. Extraction of soil-bound EPS and their further analysis by spectral and chemometric approaches is a promising way for relating EPS chemical characteristics to their biological and hydric impacts within the plant rhizosphere in a context of agro-ecological transition and climatic change

Soil health in temperate agroforestry systems: What effects of tree rows and tree species?

International audienceIntroducing tree rows within temperate crop fields is considered as a lever to intensify ecosystems services; such systems are defined as alley cropping agroforestry. The potential benefit of these systems for enhancing soil’s functions is rarely studied. Here, we investigate soil health heterogeneity in temperate alley cropping agroforestry systems according to two factors: the position relative to the tree row (at the tree row; at 0.5 m from the tree row in the crop alley; at 6.5m from the tree row in the middle of the crop alley), and tree species with contrasted functional traits that might influence local microclimate (Pyrus communis, Fraxinus sp. and Acer monspessulanum). The study was performed in one of the few mature and species-diverse agroforestry systems in Europe (Domaine de Restinclières, Southern France; 25-year-old trees). Soil health was assessed using two integrative methods: Biofunctool®, that evaluates the three essential soil functions (i) structure maintenance (ii) carbon transformation and (iii) nutrient cycling; and MicroRespTM, that enables to analyse the activity of soil’s microbial catabolic profiles. The position relative to the tree row explained most of the soil health differences. The highest soil health scores were found in the tree row, whilst both positions in the crop alley had similar soil health scores. Tree species impacted soil carbon dynamics and microbial catabolic profiles only. This study confirmed the clear effect of the position relative to the trees observed in other recent studies while it highlighted the role of trees in helping to engineer ecosystems. Higher impact is even expected when considering other specific species as nitrogen fixing trees. Thus, this study underlines the importance of considering spatial organization and tree species choice to optimize soil ecosystem services within temperate agroforestry plots

Soil health in temperate agroforestry systems: What effects of tree rows and tree species?

International audienceIntroducing tree rows within temperate crop fields is considered as a lever to intensify ecosystems services; such systems are defined as alley cropping agroforestry. The potential benefit of these systems for enhancing soil’s functions is rarely studied. Here, we investigate soil health heterogeneity in temperate alley cropping agroforestry systems according to two factors: the position relative to the tree row (at the tree row; at 0.5 m from the tree row in the crop alley; at 6.5m from the tree row in the middle of the crop alley), and tree species with contrasted functional traits that might influence local microclimate (Pyrus communis, Fraxinus sp. and Acer monspessulanum). The study was performed in one of the few mature and species-diverse agroforestry systems in Europe (Domaine de Restinclières, Southern France; 25-year-old trees). Soil health was assessed using two integrative methods: Biofunctool®, that evaluates the three essential soil functions (i) structure maintenance (ii) carbon transformation and (iii) nutrient cycling; and MicroRespTM, that enables to analyse the activity of soil’s microbial catabolic profiles. The position relative to the tree row explained most of the soil health differences. The highest soil health scores were found in the tree row, whilst both positions in the crop alley had similar soil health scores. Tree species impacted soil carbon dynamics and microbial catabolic profiles only. This study confirmed the clear effect of the position relative to the trees observed in other recent studies while it highlighted the role of trees in helping to engineer ecosystems. Higher impact is even expected when considering other specific species as nitrogen fixing trees. Thus, this study underlines the importance of considering spatial organization and tree species choice to optimize soil ecosystem services within temperate agroforestry plots

Soil health in temperate agroforestry: influence of tree species and position in the field

International audienceAlley cropping agroforestry - whereby tree rows are integrated in crop plots - is considered as a lever for the agroecological transition. Its benefit for enhancing soil functioning is rarely studied. We studied soil health in a 25 years temperate agroforestry plot cultivated with barley (Hordeum vulgare) according to two factors: i. the position to the tree row; and ii. the tree species. Soil health was assessed in three positions (in the tree row; in the crop alley next to the tree row and at 6.5 m from the tree row), for three contrasted tree species (Acer monspessulanum, Fraxinus sp., Pyrus communis) using two integrative methods based on soil biological activity (Biofunctool (R), MicroRespTM). The position factor explained soil health differences the best: mean indexes were found 1.6 times higher in the tree row than in both positions in the crop alley, especially the structure maintenance function was impacted (indexes in the tree row = 0.21 to 0.26; indexes in the crop alley = 0.11 to 0.17). Tree species had less impact on soil health and impacted only carbon dynamics and microbial catabolic profiles. Our study invites to consider spatial organization and tree species to optimize soil ecosystem services in agroforestry systems

The Water Cycle, a Potential Source of the Bacterial Pathogen Bacillus cereus

The behaviour of the sporulating soil-dwelling Bacillus cereus sensu lato (B. cereus sl) which includes foodborne pathogenic strains has been extensively studied in relation to its various animal hosts. The aim of this environmental study was to investigate the water compartments (rain and soil water, as well as groundwater) closely linked to the primary B. cereus sl reservoir, for which available data are limited. B. cereus sl was present, primarily as spores, in all of the tested compartments of an agricultural site, including water from rain to groundwater through soil. During rain events, leachates collected after transfer through the soil eventually reached the groundwater and were loaded with B. cereus sl. In groundwater samples, newly introduced spores of a B. cereus model strain were able to germinate, and vegetative cells arising from this event were detected for up to 50 days. This first B. cereus sl investigation in the various types of interrelated environments suggests that the consideration of the aquatic compartment linked to soil and to climatic events should provide a better understanding of B. cereus sl ecology and thus be relevant for a more accurate risk assessment of food poisoning caused by B. cereus sl pathogenic strains

Linking ecotoxicological effects on biodiversity and ecosystem functions to impairment of ecosystem services is a challenge: an illustration with the case of plant protection products

There is growing interest in using the ecosystem services framework for environmental risk assessments of chemicals, including plant protection products (PPPs). Although this topic is increasingly discussed in the recent scientific literature, there is still a substantial gap between most ecotoxicological studies and a solid evaluation of potential ecotoxicological consequences on ecosystem services. This was recently highlighted by a collective scientific assessment (CSA) performed by 46 scientific experts who analyzed the international science on the impacts of PPPs on biodiversity, ecosystem functions, and ecosystem services. Here, we first point out the main obstacles to better linking knowledge on the ecotoxicological effects of PPPs on biodiversity and ecological processes with ecosystem functions and services. Then, we go on to propose and discuss possible pathways for related improvements. We describe the main processes governing the relationships between biodiversity, ecological processes, and ecosystem functions in response to effects of PPP, and we define categories of ecosystem functions that could be directly linked with the ecological processes used as functional endpoints in investigations on the ecotoxicology of PPPs. We then explore perceptions on the possible links between these categories of ecosystem functions and ecosystem services among a sub-panel of the scientific experts from various fields of environmental science. We find that these direct and indirect linkages still need clarification. This paper, which reflects the difficulties faced by the multidisciplinary group of researchers involved in the CSA, suggests that the current gap between most ecotoxicological studies and a solid potential evaluation of ecotoxicological consequences on ecosystem services could be partially addressed if concepts and definitions related to ecological processes, ecosystem functions, and ecosystem services were more widely accepted and shared within the ecotoxicology community. Narrowing this gap would help harmonize and extend the science that informs decision-making and policy-making, and ultimately help to better address the trade-off between social benefits and environmental losses caused by the use of PPPs