Purpose Copper (Cu) contamination has been increasing in land ecosystems. Biochars (BCs) and arbuscular mycorrhizal fungi (AMF) are known to bind metals, and metallophyte can remove metals from soils. Will BC in combination with AMF contain the Cu uptake by a metallophyte growing in a metalcontaminated soil? The objective of this study was to investigate the effects of BCs on the Cu immobilization and over soil microbial communities in a metal-contaminated soil in the presence of AMF and metallophyte. Materials and methods Two BCs were produced from chicken manure (CMB) and oat hull (OHB). A Cucontaminated sandy soil (338 mg kg −1 ) was incubated with CMB and OHB (0, 1, and 5 % w/w) for 2 weeks. Metallophyte Oenothera picensis was grown in pots (500 mL) containing the incubated soils in a controlled greenhouse for 6 months. A number of analyses were conducted after the harvest. These include plant biomass weight, microbial basal respiration, and dehydrogenase activity (DHA), AMF root colonization, spore number, and glomalin production; changes in fungal and bacterial communities, Cu fractions in soil phases, and Cu uptake in plant tissues. Results and discussion The BCs increased the soil pH, decreased easily exchangeable fraction of Cu, and increased organic matter and residual fraction of Cu. The BCs provided favorable habitat for microorganisms, thereby increasing basal respiration. The CMB increased DHA by ∼62 and ∼574 %, respectively, for the low and high doses. Similarly, the OHB increased soil microbial activity by ∼68 and ∼72 %, respectively, for the low and high doses. AMF root colonization, spore number, and total glomalinrelated soil protein (GRSP) production increased by ∼3, ∼2, and ∼3 times, respectively, in soils treated with 1 % OHB. Despite being a metalophyte, O. picensis could not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments.Conclusions The results show that the BCs decreased bioavailable Cu, decreased Cu uptake by O. picensis, improved habitat for microorganisms, and enhanced plant growth in Cucontaminated soil. This suggests that biochars may be utilized to remediate Cu-contaminated soils.
This work examined the capability of Imperata cylindrica to respond, tolerate and accumulate Cu when growing at high Cu concentration (300 mg kg−1 of substrate) at different times of exposure (2, 14 and 21 days). The Cu accumulation in plants was examined by atomic absorption spectroscopy (AAS) and Cu localized by Scanning Electron Microscopy-Energy Dispersive X-Ray spectroscopy. Additionally, the phenolic compound identifications and concentrations were determined using liquid chromatography coupled to mass spectrometry. Our results showed that root biomass decreased significantly at high Cu levels, with a greater decrease at 21 days (39.8% less biomass in comparison to control). The root showed 328 mg Cu kg−1 dry weight at 21 days of exposure to Cu, being the tissue that accumulates most of the Cu. Lipid peroxidation was a clear indicator of Cu stress, principally in shoots. The exposure to Cu significantly increased the synthesis of phenolic compounds in shoots of plants exposed 21 days to Cu, where 5-caffeoylquinic acid reached the highest concentrations. Our results support that I. cylindrica is a Cu accumulator plant in root organs with a medium level of accumulation (between 200–600 mg Cu kg−1 biomass), which can tolerate the exposure to high Cu levels by means of increasing the synthesis of phenolic compound in shoots, suggesting a potential use as phytoremediation tool in Cu polluted environments.
The application of different techniques of positive stress (eustress), such as mild and moderate saline stress, could enhance the nutritional and functional attributes of food vegetables. The present study aimed to evaluate the positive effect of salinity as a eustressor on the functional quality of red lettuce growing under hydroponic conditions and subjected to increasing salinity. Red lettuce plants were grown for 60 days and, 45 days after sowing, were subjected to different levels of salinity (0, 50, 100, 150, and 200 mM NaCl). The phenolic compound concentration and antioxidant activity were measured at 7 and 15 days after the application of salinity treatment. Moreover, at harvest, the root and shoot biomass and efficiency of photosystem II were evaluated. Our results showed that the highest phenolic concentration and antioxidant activity were obtained through moderate salt stress (50 mM NaCl) applied for 15 days without affecting the photosynthetic activity and biomass production of lettuce plants. By contrast, when severe salt stress levels (150–200 mM NaCl) were applied, an increase in phenolic compounds was also obtained, but concomitantly with a significant reduction in antioxidant activity and biomass production. The application of moderate stress in red lettuce suggests its potential use as a tool to increase the biosynthesis and accumulation of bioactive secondary metabolites, improving the nutritional characteristics of red lettuce.
Drought generates a complex scenario worldwide in which agriculture should urgently be reframed from an integrative point of view. It includes the search for new water resources and the use of tolerant crops and genotypes, improved irrigation systems, and other less explored alternatives that are very important, such as biotechnological tools that may increase the water use efficiency. Currently, a large body of evidence highlights the role of specific strains in the main microbial rhizosphere groups (arbuscular mycorrhizal fungi, yeasts, and bacteria) on increasing the drought tolerance of their host plants through diverse plant growth-promoting (PGP) characteristics. With this background, it is possible to suggest that the joint use of distinct PGP microbes could produce positive interactions or additive beneficial effects on their host plants if their co-inoculation does not generate antagonistic responses. To date, such effects have only been partially analyzed by using single omics tools, such as genomics, metabolomics, or proteomics. However, there is a gap of information in the use of multi-omics approaches to detect interactions between PGP and host plants. This approach must be the next scale-jump in the study of the interaction of soil–plant–microorganism. In this review, we analyzed the constraints posed by drought in the framework of an increasing global demand for plant production, integrating the important role played by the rhizosphere biota as a PGP agent. Using multi-omics approaches to understand in depth the processes that occur in plants in the presence of microorganisms can allow us to modulate their combined use and drive it to increase crop yields, improving production processes to attend the growing global demand for food.
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