Drought is a major threat to plant growth in many parts of the world. During periods of drought, multiple aspects of plant physiology are negatively affected. For instance, water shortages induce osmotic imbalance, inhibit photosynthesis, decrease nutrient uptake, and increases the production of reactive oxygen species (ROS). In this context, it is necessary to develop sustainable strategies for crops that would help mitigate these conditions. In previous studies, endophytic Zopfiella erostrata strains were found to extensively colonize plant roots, forming a profuse melanized mycelium in the rhizosphere, which could be involved in improving water uptake and nutrient mineralization in plants. The aim of this study is to evaluate the effect of different strains of Z. erostrata on stress mitigation in wheat and tomato plants grown under water deficit conditions. General plant growth variables, as well as physiological and biochemical parameters, related to oxidative status were determined. Our data demonstrate that inoculation with both Zopfiella strains had a very significant effect on plant growth, even under water deficit conditions. However, we observed an even more pronounced impact, depending on the plant and strain involved, suggesting a certain degree of plant/strain compatibility. The biochemical aspects, the accumulation of proline, the oxidative damage to lipids, and the activity of antioxidant enzymes varied considerably depending on the endophyte and the plant evaluated.

Symbiotic associations with arbuscular mycorrhizal fungi (AMF) offer an effective indirect mechanism to reduce heavy metal (HM) stress; however, it is still not clear which AMF species are more efficient as bioremediating agents. We selected different species of AMF: Rhizoglomus custos (Custos); Rhizoglomus sp. (Aznalcollar); and Rhizophagus irregularis (Intraradices), in order to study their inoculation in wheat grown in two soils contaminated with two levels of HMs; we tested the phytoprotection potential of the different AMF symbioses, as well as the physiological responses of the plants to HM stress. Plants inoculated with indigenous Aznalcollar fungus exhibited higher levels of accumulation, mainly in the shoots of most of the HM analyzed in heavily contaminated soil. However, the plants inoculated with the non-indigenous Custos and Intraradices showed depletion of some of the HM. In the less-contaminated soil, the Custos and Intraradices fungi exhibited the greatest bioaccumulation capacity. Interestingly, soil enzymatic activity and the enzymatic antioxidant systems of the plant increased in all AMF treatments tested in the soils with both degrees of contamination. Our results highlight the different AMF strategies with similar effectiveness, whereby Aznalcollar improves phytoremediation, while both Custos and Intraradices enhance the bioprotection of wheat in HM-contaminated environments.

The present work evaluated the influence of eight different soil remediation techniques, based on the use of residual materials (gypsum, marble, vermicompost) on the reduction in metal(loid)s toxicity (Cu, Zn, As, Pb and Cd) in a polluted natural area. Selected remediation treatments were applied in a field exposed to real conditions and they were evaluated one year after the application. More specifically, five ecotoxicological tests were carried out using different organisms on either the solid or the aqueous (leachate) fraction of the amended soils. Likewise, the main soil properties and the total, water-soluble and bioavailable metal fractions were determined to evaluate their influence on soil toxicity. According to the toxicity bioassays performed, the response of organisms to the treatments differed depending on whether the solid or the aqueous fraction was used. Our results highlighted that the use of a single bioassay may not be sufficient as an indicator of toxicity pathways to select soil remediation methods, so that the joint determination of metal availability and ecotoxicological response will be determinant for the correct establishment of any remediation technique carried out under natural conditions. Our results indicated that, of the different treatments used, the best technique for the remediation of metal(loid)s toxicity was the addition of marble sludge with vermicompost.

Polycyclic aromatic hydrocarbons (PAHs) are strong toxic compounds mainly released to the environment during combustion of fossil fuels, and have strong toxic effects on living organisms, with soil being one of their main reservoirs. High PAH levels in soils can interfere with plant growth and biomass production, causing several losses of diversity. In this study, we evaluated the effects of the co-inoculation of Trichoderma viride and Funneliformis mosseae on PAH dissipation and alleviation of oxidative stress in Triticum aestivum L. (wheat) plants growing in a phenanthrene-spiked soil. We determined the effect of single and dual fungal inoculation on phenanthrene dissipation rates, soil enzyme activities, dry biomass, antioxidant enzymes, lipid peroxidation, and organic acid exudation of plants growing in a soil spiked with phenanthrene at 500 and 1000 mg kg⁻¹ soil. The co-inoculation with T. viride and F. mosseae resulted in a high phenanthrene dissipation from the soil. Also, dry biomass, soil enzymes, antioxidant response, organic acid exudation and phenanthrene content in roots were increased by the dual inoculation treatments, whereas lipid peroxidation and phenanthrene content in shoots were reduced. Our results show that the co-inoculation with these two soil fungi significantly promotes phenanthrene dissipation from soil and contributes to alleviating oxidative damage in wheat plants exposed to high levels of phenanthrene.

An integral and affordable strategy for the simultaneous production of lignin-modifying and carbohydrate active enzymes and organic amendment, with the aid of a saprobe fungus was developed by using olive oil and wine extraction by-products. The polyporal fungus Trametes versicolor was cultivated in soy or barley media supplemented with dry olive mill residue (DOR) as well as with grape pomace and stalks (GPS) in solid state fermentation (SSF). This strategy led to a 4-fold increase in the activity of laccase, the principal enzyme produced by SFF, in DOR-soy media as compared to controls. T. versicolor managed to secrete lignin-modifying enzymes in GPS, although no stimulative effect was observed. GPS-barley media turned out to be the appropriate medium to elicit most of the carbohydrate active enzymes. The reuse of exhausted solid by-products as amendments after fermentation was also investigated. The water soluble compound polymerization profile of fermented residues was found to correlate with the effect of phytotoxic depletion. The incubation of DOR and GPS with T. versicolor not only reduced its phytotoxicity but also stimulated the plant growth. This study provides a basis for understanding the stimulation and repression of two groups of enzymes of industrial interest in the presence of different carbon and nitrogen sources from by-products, possible enzyme recovery and the final reuse as soil amendments.