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International audience; The impact of microplastics on soil physical properties is not well studied. This study was carried out to assess if (micro)plastics incorporated into the soil can act as heat retainers and if they can subsequently have adverse impacts on soil microbial activity. Three types of plastic films were used for this study in a field-experiment carried out during six months in an agricultural soil: 1) a white/transparent greenhouse plastic, 2) black plastic from mulch and 3) a grey oxo-biodegradable plastic from rubbish bags. Both greenhouse film and plastic mulch were collected from the soil surface in the study area, and thus aged in the environment. The oxo-biodegradable plastic was obtained from a local supermarket. For each treatment, three replicates consisting ofsoil surface plots of 50x50 cm were prepared in the field. The spontaneous vegetation was manually removed from the soil surface of each soil plot at the beginning and biweekly over the experimental period. All plastics were manually cut to obtain a mix of micro- and macroplastics (from 4 mm to 50 mm), as plastics debris in agricultural soils can have several sizes and shapes. For each replicate, 100 plastic items were buried in the first five centimetres of the topsoil. No plastic items were added to the control plots. At the beginning and at the end of the experimental time (August and December 2019), soil samples from each replicate were collected to assess their physicochemical properties (e.g. pH, organic matter, electrical conductivity, soil density, soil aggregates), biochemical parameters (arylsulfatase, cellulase dehydrogenase, acid phosphatase, urease, nitrogen mineralization and potentially nitrification) and microbial community colonizing the plastics. Besides, infrared thermography was applied to the soil squares to assess the thermal patterns in each plot. Despite the differences in surface temperatures achieved for the different treatments, it was not possible to find a trend in the results, since the surface temperatures were on average very similar to the control without plastics, although with different thermal patterns. These differences on thermal patterns can be related to soil surface roughness, the sun’s shift on the horizon during the experimental measurements or the aleatory position of plastics buried in soils. Thus, any impact on soil microbial parameters can be related to changes in soil temperature.

International audience; As a result of anthropic pressures, soil contamination is increasing and, consequently, compromising soil functions and impacting crop yields worldwide. Among all contaminants, potentially toxic elements (PTEs) are some of the most common and important, being able to negatively affect the growth and development of plants. Nanotechnology, an emerging field in technological sciences, offers multiple tools that can be used for this purpose. In this way, this work aimed to evaluate the potential of Fe2O3 nanomaterials (nano-Fe2O3) to alleviate metalinduced stress in barley plants (Hordeum vulgare L.), focusing on bioaccumulation patterns and on the redox homeostasis. To achieve this goal, plants grew under two agricultural soils, contaminated with different levels of PTEs, collected from an industrial area, and previously treated or not, with 1% (w/w) nano-Fe2O3. After 14 days of growth, biometric parameters, PTE bioaccumulation and biochemical endpoints, especially those related to the induction of redox disorders, were evaluated. The effectiveness of nano-Fe2O3 to reduce available PTEs in soil solution was also assessed. After exposure to contaminated soils, plant development was greatly affected, as evidenced by significant decreases in root length and fresh weight of roots and leaves. However, upon co-treatment with nano-Fe2O3 this phytotoxicity was partially recovered, with less inhibitory effects on biometric parameters, especially on the less contaminated soil. This pattern was also noticed for levels of total chlorophylls and carotenoids. Regarding the oxidative damage, both soils led to increases in Lipid Peroxidation (LP), though H2O2 levels were only increased in the most contaminated soil. In response to the co-treatment with nano- Fe2O3, barley plants exhibited less oxidative damage, which is evidenced by the decrease of H2O2 and LP in both soils. The present study revealed that nano-Fe2O3 can enhance the tolerance of barley plants to contaminated soils, possibly by limiting the occurrence of oxidative stress, through a set of modifications in the PTE (bio)availability.

International audience; As a result of anthropic pressures, such as industry, deforestation and waste disposal, soil contamination is increasing and, consequently, compromising soil functions and fertility. Among all contaminants, metals are one of the most common and important, being able to negatively affect the growth and development of plants. Thus, new and innovative ways to counteract the adverse effects of metals on plants are urgently needed. Nanotechnology, an emerging field in technological sciences, offers multiple tools that can be used for this purpose. In this way, this work aimed to evaluate the potential of Fe2O3 nanoparticles (NPs) to alleviate metal-induced stress in Hordeum vulgare L. (barley plants). For this goal, plants grew under two metal-contaminated soils (S1 and S2) of Estarreja (Aveiro, Portugal) treated and non-treated with 1% (w/w) Fe2O3 NPs. After 14 days of growth, biometric parameters (root length and fresh biomass) were evaluated, along with the analysis of several biochemical endpoints [photosynthetic pigments, lipid peroxidation (LP) and hydrogen peroxide (H2O2)]. After exposure to S1 and S2 contaminated soils, plant development was greatly affected, as evidenced by significantdecreases in root length and fresh weight of roots and leaves. However, upon cotreatment with Fe2O3 NPs, this phytotoxicity was partially recovered, with less inhibitory effects on biometric parameters, especially in S1. This pattern was also noticed for levels of total chlorophylls and carotenoids. Regarding the oxidative damage, both S1 and S2 led to increases in LP, though H2O2 levels were only increased in S2. In response to the co-treatment with Fe2O3 NPs, barley plants exhibited less oxidative damage, which is evidenced by the decrease of H2O2 and LP in both soils. Altogether, the present study revealed that Fe2O3 NPs are able to enhance the tolerance of barley plants to contaminated soils, possibly by limiting the occurrence of oxidative stress.