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Among the various disposal strategies for sewage sludge (SS), soil application is the most suitable. This study was conducted to evaluate soil amendment with SS (0, 10, 20, 30 and 40 g/kg) and its impact on soil fertility and tomato (Solanum lycopersicum L.) growth. The SS significantly improved the agromorphological attributes, the number of produced fruits, and the fruit biomass of tomato plants. The 30 g/kg application of SS led to the highest growth rate and fruit yield. Considering the fruits, the best safe enrichment of metal nutrients was recorded at 30 g/kg, with a significant increase in the micronutrient metals Mn, Zn, Ni, Cu, and Fe with 624, 193, 125, 70, and 32%, respectively, compared to the control. The SS amendment enhanced soil fertility, and heavy metals were within the permissible ranges for agricultural soils. Bioaccumulation factors (BFs) indicated that SS application induced the accumulation of most of the studied metals in the roots, and the BF values of Zn, Cu, Ni, and Pb were > 1. The current study concluded that recirculating SS nutrient components to agricultural soils could offer a valid solution for the sustainable management of this organic waste and enhance plant-crop productivity.

Abstract The food security in today's world is endangered by several threats, including accelerated increases in the world's population, depletion of the Earth's resources, exaggerated environmental pollution, and foreseen climatic changes. As a strategy to diminish these threats, the wise disposal of the huge amounts of sewage sludge (SS) to agricultural soils as a bio‐fertilizer represents a worthy practice for recirculating valuable nutrients to food chains via crop plants. The current study was designed to scientifically test the feasibility of SS application to agricultural soils without causing environmental or health threats. Different SS amendment doses of 0, 10, 20, 30, 40, and 50 g/kg were supplied for soil‐grown barley (Hordeum vulgare L.) plants. Our results show that all of the SS amendment doses improved the postharvest soil properties and enhanced barley growth, with the best results obtained at the 40 g/kg dose. At this amendment dose, the organic matter (OM) content increased to 6.7% compared with 1.4% in control soil. Analysis of the postharvest soils showed that the concentrations of the investigated heavy metals (HMs) (Co, Cu, Mo, Ni, Zn, Cd, Cr, and Pb) were within the allowable limits for agricultural soils at all of the SS amendment doses, except for Co. All of the SS amendment rates enhanced barley growth and yield parameters, including shoot and root lengths and dry weights, spike weight and number of spikes per plant. Up to the 40 g/kg amendment dose, the concentrations of the investigated HMs in the harvested plant tissues were within safe limits, with most of the absorbed HMs persisting in roots. Taking these results together, the current study suggests that controlled application of SS to agricultural soils represents an eco‐friendly SS disposal procedure, which can recycle macro‐ and micronutrients to food chains and hence provide a promising approach for sustainable food security.

Plants are frequently exposed to simultaneous abiotic and biotic stresses, a condition that induces complex responses, negatively affects crop productivity and is becoming more exacerbated with current climate change. In this study, we investigated the effects of individual and combined heat and osmotic stresses on Arabidopsis susceptibility to the biotrophic pathogen Pseudomonas syringae pv. tomato (Pst) and the necrotrophic pathogen Botrytiscinerea (Bc). Our data showed that combined abiotic and biotic stresses caused an enhanced negative impact on plant disease resistance in comparison with individual Pst and Bc infections. Pretreating plants with individual heat or combined osmotic-heat stress strongly reduced the expression of many defense genes including pathogenesis-related proteins (PR-1 and PR-5) and the TN-13 gene encoding the TIR-NBS protein, which are involved in disease resistance towards Pst. We also found that combined osmotic-heat stress caused high plant susceptibility to Bc infection and reduced expression of a number of defense genes, including PLANT DEFENSIN 1.3 (PDF1.3), BOTRYTIS SUSCEPTIBLE 1 (BOS1) and THIONIN 2.2 (THI2.2) genes, which are important for disease resistance towards Bc. The impaired disease resistance against both Pst and Bc under combined abiotic stress is associated with reduced expression of cell wall-related genes. Taken together, our data emphasize that the combination of global warming-associated abiotic stresses such as heat and osmotic stresses makes plants more susceptible to pathogen infection, thus threatening future global food security.

Reactive oxygen species (ROS) are highly controlled signaling species that are involved in regulating gene expression in response to different environmental cues. The production of heat shock proteins (HSPs) is a key strategy that plants use to defend themselves against diverse stresses, including oxidative stress. In this study, expression patterns of the Arabidopsis HSP17.4CI gene, a cytosolic class I small HSP, were systematically profiled under different abiotic, biotic and oxidative stresses. Our data show that HSP17.4CI was early and highly induced by heat, cold, salt, drought and high-light. HSP17.4CI also showed high expression levels in Arabidopsis plants infected with the biotrophic pathogen Pseudomonas syringae, but not in response to the necrotrophic pathogens Alternaria brassicicola and Fusarium oxysporum. Oxidative stress treatments including H2O2 and the herbicide methyl viologen led to induction of HSP17.4CI. The plant hormones abscisic acid (ABA) and salicylic acid (SA) induced the expression of HSP17.4CI, whereas methyl jasmonate (MJ) did not affect the expression level of this gene. Furthermore, we found enhanced expression of HSP17.4CI in catalase mutant plants, which are deficient in catalase 2 activity and accumulate intracellular H2O2. Taken together, data presented here suggest that HSP17.4CI expression is regulated by various signals that connect biotic and abiotic stresses with ROS and can be used as a molecular marker for oxidative stress.

Reactive oxygen species (ROS) are produced in plant cells in response to diverse biotic and abiotic stresses as well as during normal growth and development. Although a large number of transcription factor (TF) genes are up- or down-regulated by ROS, currently very little is known about the functions of these TFs during oxidative stress. In this work, we examined the role of ERF6 (ETHYLENE RESPONSE FACTOR6), an AP2/ERF domain-containing TF, during oxidative stress responses in Arabidopsis. Mutant analyses showed that NADPH oxidase (RbohD) and calcium signaling are required for ROS-responsive expression of ERF6. erf6 insertion mutant plants showed reduced growth and increased H2O2 and anthocyanin levels. Expression analyses of selected ROS-responsive genes during oxidative stress identified several differentially expressed genes in the erf6 mutant. In particular, a number of ROS responsive genes, such as ZAT12, HSFs, WRKYs, MAPKs, RBOHs, DHAR1, APX4, and CAT1 were more strongly induced by H2O2 in erf6 plants than in wild-type. In contrast, MDAR3, CAT3, VTC2 and EX1 showed reduced expression levels in the erf6 mutant. Taken together, our results indicate that ERF6 plays an important role as a positive antioxidant regulator during plant growth and in response to biotic and abiotic stresses.