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Chromium (Cr) is a heavy metal of commercial importance; thus, significant amounts are released in wastewaters. The mobility and distribution of metals in the environment is related not only to their concentration but also to their availability in the environment. Most chromium (Cr) exists in oxidation states ranging from 0 to VI in soils but the most stable and common forms are Cr(0), Cr(III), and Cr(VI) species. Cr can have positive and negative effects on health, according to the dose, exposure time, and its oxidation state. Its behavior in soil, its soil-plant transfer and accumulation in different plant parts vary with its chemical form, plant type and soil physicochemical properties. Soil microbial community plays a key role in governing Cr speciation and behavior in soil. A number of factors have been identified to influence Cr toxicity on activated sludge, such as, pH, biomass concentration, presence of organic substances or other heavy metals, acclimation process, exposure time, etc. Inside plants, Cr provokes numerous deleterious effects to several physiological, morphological, and biochemical processes. Cr induces phytotoxicity by interfering plant growth, nutrient uptake and photosynthesis, inducing enhanced generation of reactive oxygen species, causing lipid peroxidation and altering the antioxidant activities. The present review describes the consequences of Cr toxicity on plants, including morphological, physiological and ultrastructural changes. This review also provides the basic concepts of Cr translocation and interaction with other essential macro- and microelements. Moreover, based on the available literature and current research scenario, this review suggests some possible management and remediation strategies to alleviate Cr toxicity and contamination in soil. It also provides valuable knowledge for further studies towards enhancement of soil phytoremediation and crops improvement. Therefore, there is a dire need to monitor biogeochemical behavior of Cr in soil-plant system. [ABSTRACT FROM AUTHOR]

The impact of heavy metal, i.e., cadmium (Cd), on the growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, and antioxidants machinery (enzymatic and non-enzymatic antioxidants), ions uptake, organic acids exudation, and ultra-structure of membranous bounded organelles of two rice (Oryza sativa L.) genotypes (Shan 63 and Lu 9803) were investigated with and without the exogenous application of ferrous sulfate (FeSO4). Two O. sativa genotypes were grown under different levels of CdCl2 [0 (no Cd), 50 and 100 µM] and then treated with exogenously supplemented ferrous sulfate (FeSO4) [0 (no Fe), 50 and 100 µM] for 21 days. The results revealed that Cd stress significantly (p < 0.05) affected plant growth and biomass, photosynthetic pigments, gas exchange characteristics, affected antioxidant machinery, sugar contents, and ions uptake/accumulation, and destroy the ultra-structure of many membranous bounded organelles. The findings also showed that Cd toxicity induces oxidative stress biomarkers, i.e., malondialdehyde (MDA) contents, hydrogen peroxide (H2O2) initiation, and electrolyte leakage (%), which was also manifested by increasing the enzymatic antioxidants, i.e., superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidant compounds (phenolics, flavonoids, ascorbic acid, and anthocyanin) and organic acids exudation pattern in both O. sativa genotypes. At the same time, the results also elucidated that the O. sativa genotypes Lu 9803 are more tolerant to Cd stress than Shan 63. Although, results also illustrated that the exogenous application of ferrous sulfate (FeSO4) also decreased Cd toxicity in both O. sativa genotypes by increasing antioxidant capacity and thus improved the plant growth and biomass, photosynthetic pigments, gas exchange characteristics, and decrease oxidative stress in the roots and shoots of O. sativa genotypes. Here, we conclude that the exogenous supplementation of FeSO4 under short-term exposure of Cd stress significantly improved plant growth and biomass, photosynthetic pigments, gas exchange characteristics, regulate antioxidant defense system, and essential nutrients uptake and maintained the ultra-structure of membranous bounded organelles in O. sativa genotypes. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) occurs in pools of lower availability due to soil P fixation and therefore, it is a key constrain to crop production. Long term molybdenum-induced effects in wheat and rhizosphere/non-rhizosphere soil P dynamics have not yet been investigated. Here, a long term field experiment was conducted to explore these effects in wheat consisting of two treatments i.e. with molybdenum (+Mo) and without molybdenum (-Mo). The results revealed that molybdenum (Mo) supply increased plant biomass, grain yield, P uptake, preserved the configuration of chloroplast, stomata, and mesophyll tissue cells, suggesting the complementary effects of Mo on wheat yield and P accumulation. During the periods of vegetative growth, soil organic carbon, organic matter, and microbial biomass P were higher and tended to decrease in rhizosphere soil at maturity stage. In +Mo treatment, the most available P fractions [H 2 O-Pi (16.2–22.9 mg/kg and 4.24–7.57 mg/kg) and NaHCO 3 -Pi (130–149 mg/kg and 77.2–88 mg/kg)] were significantly increased in rhizosphere and non-rhizosphere soils, respectively. In addition, the +Mo treatment significantly increased the acid phosphatase activity and the expression of phoN/phoC, aphA, olpA/lppC gene transcripts in rhizosphere soil compared to -Mo. Our research findings suggested that Mo application has increased P availability not only through biochemical and chemical changes in rhizosphere but also through P assimilation and induced effects in the leaf ultra-structures. So, it might be a strategy of long term Mo fertilizer supply to overcome the P scarcity in plants and rhizosphere soil. • Mo supply preserved the leaf ultrastructure through improved P assimilation. • The activity of P enzyme increased in rhizosphere soil in response to Mo application. • Mo application increased the soil P availability through biochemical changes. [ABSTRACT FROM AUTHOR]

Nitrogen management is a major challenge in the environment due toNO3-leaching and volatilization. To address this problem, a lysimeter experiment was conducted for rice-wheat with two lower N rates (15 and 30%) and three higher rates (15, 30 and 45%) than recommended rate (N100%). Higher leaching of NO3 - was noted with N145% up to86.84 mg/leachate in rice while wheat crop showed maximum leaching 48.62 mg/leachate in same treatment. This revealed that during the rice-wheat rotation, NO3-leaching losses were the highest during rice growth than that of wheat. The uppermost rice-wheat grain yield was obtained with 15% higher N. The highest rice-wheat NUE was 31.26 g/g and 45.52 g/g with treatment N115%, respectively. It is concluded that treatment of N115%proved to be efficient than other treatments due to enhanced NUE and yield by reducing NO3-leaching losses. The findings of current study can be helpful to develop proper N fertilizer management strategies for rice-wheat rotation. [ABSTRACT FROM AUTHOR]

Very limited information is available about heavy metal-polycyclic aromatic hydrocarbons (PAHs) depollution involving the modified natural material in soil. Using phenanthrene and cadmium (Cd) as model, this study investigated the effect(s) of modified rice straw by a NaOH solution and on PAHs, heavy metal availability, and their interactions. Treatment included chemical contaminant with/without modified/unmodified rice straw. Fourier Transform Infrared (FTIR) analysis revealed that certain functional groups including anionic matters groups, which can a complex with Cd2+, were exposed on the modified rice straw surfaces. Therefore, Cd concentration was significantly reduced by about 60%, 57%, 62.5 %, and, 64% in the root, shoot, CaCl2, diethylenetriaminepentaacetic acid (DTPA), and extractable Cd, respectively. Subsequently, the prediction of the functional profile of the soil metagenome using Clusters Orthologous Groups (COGs) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed that the significantly changed individual COGs belonged to the carbohydrate metabolism, ion transports, and signaling (including cytochrome P450s) categories. This indicated that ion transports might be involved in Cd management, while carbohydrate metabolism, including bisphenol, benzoate, ethylbenzene degradation, and cytochrome P450s, were rather involved in phenanthrene metabolism. The exposed functional group might serve as an external substrate, and P450s might serve as a catalyst to activate and initiate phenanthrene metabolism process. These finding offer confirmation that modified straw could promote the reduction of heavy metal and the degradation of PAHs in soil. [ABSTRACT FROM AUTHOR]

Different nitrogen (N) sources have been reported to significantly affect the photosynthesis (P n) and its attributes. However, molybdenum (Mo) induced effects on photosynthetic efficacy of winter wheat under different N sources have not been investigated. A hydroponic study was carried out comprising of two winter wheat cultivars '97003' and '97014' as Mo-efficient and Mo-inefficient, respectively to underpin the effects of Mo supply (0 and 1 μM) on photosynthetic efficacy of winter wheat under different N sources (NO 3 ̶, NH 4 NO 3 or NH 4 +). The results revealed that Mo-induced increases in dry weight, gas exchange parameters, chlorophyll contents, NR activities, NO 3 ̶ assimilation, total N contents and transcripts of TaNR and TaNRT1.1 genes under different N sources followed the trend of NH 4 NO 3 > NO 3 ̶ > NH 4 +, suggesting that Mo has more complementary effects to nitrate nutrition than sole ammonium. Interestingly, under Mo-deprivation environments, cultivar '97003' recorded more pronounced alterations in Mo-dependent parameters than '97014' cultivar. Moreover, Mo application significantly improved the chlorophyll contents and chloroplast configuration in all N sources showing that Mo has a key role in chlorophyll biosynthesis and chloroplast integrity. The results also highlighted that Mo-induced enhancements in total N contents and photosynthetic characteristics followed the same order as NH 4 NO 3 > NO 3 − > NH 4 +, suggesting that Mo might affect P n through N metabolism. In crux, our study findings imply that Mo supply increased P n not only through chlorophyll synthesis and chloroplast configuration but also by N uptake and assimilation which may represent a strategy of Mo fertilizer to strengthen the photosynthetic machinery. • Molybdenum improved photosynthetic apparatus through efficient N assimilation. • Molybdenum shows more complementary effects to nitrate nutrition than sole ammonium. • Differential responses to photosynthesis of two wheat cultivars under Mo deficiency. [ABSTRACT FROM AUTHOR]

Nitrogen management is the major challenge due to narrow understanding of yield and N uptake relationship on salt-affected soils. To address this problem, a lysimeter experiment for rice and wheat was conducted on salt-affected soil with two lower (15 and 30 %) and three higher N rates (15, 30 and 45 %) with 50 and 100 % SGR. NO3 - leaching was greater with higher N rates (up to 188 mg Leachate-1) in rice as compared to wheat. After the harvesting of rice and wheat, maximum decrease in soil pHs (7.75 %), ECe (41.50 %), SAR (63.64 %) was with N130 G100 which indicated that applied gypsum 100 % SGR with higher N rate ameliorated the soil more efficiently as compared to 50 % SGR. The highest yields recorded with N130 + 100 % SGR. The highest NUE (15.88 g/g) was with treatment G100 N130 in rice but in wheat (NUE, 44.76 g/g) G100 N70 proved to be the best. It was concluded that G100 N130 proved to be the best and reduced the environmental risks. [ABSTRACT FROM AUTHOR]

Use of Plantago ovata Forsk leaf (also known as blond plantain or isabgol) extract is a novel approach for ameliorating water stress in various agronomic crops such as maize (Zea mays L.). To examine the potential roles of P. ovata extract (0, 20 and 40%) in increasing seed germination, plant growth, photosynthetic measurements, stomatal properties, oxidative stress and antioxidant response, ions uptake and the relationship between studied parameters, we investigated the impacts of its short-term seed priming on Z. mays L. elite cultivar "Cimmyt-Pak" under a control environment and a water deficit stress environment (induced by PEG). It was evident that water deficit stress conditions induced a negative impact on plant growth, stomatal properties and ion uptake in different organs of Z. mays. The decrease in growth-related attributes might be due to overproduction of oxidative stress biomarkers, i.e., malondialdehyde (MDA) contents, hydrogen peroxide (H2O2) initiation, and electrolyte leakage (%), which was also overcome by the enzymatic antioxidants, i.e., superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants, which increased under the water stress environment. However, seed priming with P. ovata extract positively increased germination rate and growth profile, and protected photosynthetic apparatus and stomatal properties by decreasing oxidative stress indicators and increasing activities of antioxidant compounds. Our results also depicted that the optimum concentration of P. ovata extract for Z. mays seedlings under water stress conditions was 20%, while a further increase in P. ovata extract (40%) induced a non-significant negative impact on growth and biomass of Z. mays seedling. In addition, the effect was more promising on Z. mays seedlings when grown under controlled conditions. Here, we concluded that the understanding of the role of seed priming with P. ovata extract in the increment of growth-related attributes, photosynthetic apparatus (Pn, Gs, Ts and Ci) and nutrient uptake (Ca2+, Fe2+, P and Mg2+) introduces new possibilities for their effective use in water deficit stress environments and shows a promising foundation for Z. mays tolerance against water deficit stress conditions. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the most restrictive essential elements to crop growth and development due to less availability in the soil system. Previous studies have reported the synergistic effects between molybdenum (Mo) and P fertilizer on P uptake in various crops. However, an induced long term effect of Mo on soil P dynamics in the rhizosphere and non-rhizosphere has not been reported yet in leguminous crops. In this study, a long term field experiment was conducted to explore the P transformation characteristics and bioavailability in Mo-deficient (-Mo) and Mo-enriched (+Mo) soil under leguminous (broad bean-soybean) cropping system. The results indicated that long-term Mo application increased the plant dry matter accumulation (14.23%–35.27%, for broad bean; 24.40%–37.46%, for soybean) from March–September. In rhizosphere soil, the percent decrease in pH (8.10%) under +Mo treatment of the soybean crop was recorded more during September as compared to broad bean crop. Under Mo supply, H 2 O-Pi fraction increased up to 28.53% and 43.67% while for NaHCO 3 -Pi this increase was up to 5.61% and 11.98%, respectively in the rhizosphere soil of broad bean and soybean, whereas, residual-P exhibited the highest proportion of P fractions. Moreover, compared with -Mo, +Mo treatments significantly increased the soil acid phosphatase (broad bean = 17.43 μmol/d/g; soybean = 28.60 μmol/d/g), alkaline phosphatase (broad bean = 3.34 μmol/d/g; soybean 6.35 μmol/d/g) and phytase enzymes activities (broad bean = 2.45 μmol/min/g; soybean = 5.91 μmol/min/g), transcript abundance of phoN/phoC genes and microbial biomass P (MBP) in rhizosphere soil. In crux, the findings of this study suggest that long term Mo application enhanced P bioavailability through increased available P, MBP, P related enzymes activities and their genes expressions which may represent a strategy of Mo to encounter P deficiencies in the soil system. • Mo application showed a complementary effect on plant dry matter yield and uptake of P in the leguminous cropping system. • Understanding the characteristics of the rhizosphere can rapidly deliver info on the P acquisition efficiency. • Available P and microbial biomass P were higher in the Mo-enriched soil. • The higher P concentration in soils was primarily indorsed to the organic P hydrolysis by the enzymes. • From the perspective of P nutrient management, Mo application could mediate the rhizosphere biochemical process. [ABSTRACT FROM AUTHOR]

Different nitrogen (N) sources have been reported to significantly affect the activities and expressions of N metabolism enzymes and mineral elements concentrations in crop plants. However, molybdenum-induced effects in winter wheat cultivars have still not been investigated under different N sources. Here, a hydroponic study was carried out to investigate these effects on two winter wheat cultivars ('97003' and '97014') as Mo-efficient and Mo-inefficient, respectively, under different N sources (NO3−, NH4NO3, and NH4+). The results revealed that the activities of nitrate reductase (NR) and nitrite reductase (NiR) followed the order of NH4NO3 > NO3− > NH4+ sources, while glutamine synthetase (GS) and glutamate synthase (GOGAT) followed the order of NH4+ > NH4NO3 > NO3− in both the wheat cultivars. However, Mo-induced effects in the activities and expressions of N metabolism enzymes under different N sources followed the order of NH4NO3 > NO3− > NH4+ sources, indicating that Mo has more complementary effects towards nitrate nutrition than the sole ammonium source in winter wheat. Interestingly, under −Mo-deprived conditions, cultivar '97003' recorded more pronounced alterations in Mo-dependent parameters than '97014' cultivar. Moreover, Mo application increased the proteins, amino acids, ammonium, and nitrite contents while concomitantly decreasing the nitrate contents in the same order of NH4NO3 > NO3− > NH4+ sources that coincides with the Mo-induced N enzymes activities and expressions. The findings of the present study indicated that Mo plays a key role in regulating the N metabolism enzymes and assimilatory products under all the three N sources; however, the extent of complementation exists in the order of NH4NO3 > NO3− > NH4+ sources in winter wheat. In addition, it was revealed that mineral elements profiles were mainly affected by different N sources, while Mo application generally had no significant effects on the mineral elements contents in the winter wheat leaves under different N sources. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is highly toxic, even at very low concentrations, to both animals and plants. Pollen is extremely sensitive to heavy metal pollutants; however, less attention has been paid to the protection of this vital part under heavy metal stress. A pot experiment was designed to investigate the effect of foliar application of Se (1 mg/L) and Mo (0.3 mg/L) either alone or in combination on their absorption, translocation, and their impact on Cd uptake and its further distribution in Brassica napus, as well as the impact of these fertilizers on the pollen grains morphology, viability, and germination rate in B. napus under Cd stress. Foliar application of either Se or Mo could counteract Cd toxicity and increase the plant biomass, while combined application of Se and Mo solutions on B. napus has no significant promotional effect on plant root and stem, but reduces the seeds’ weight by 10–11%. Se and Mo have decreased the accumulated Cd in seeds by 6.8% and 9.7%, respectively. Microscopic studies, SEM, and pollen viability tests demonstrated that pollen grains could be negatively affected by Cd, thus disturbing the plant fertility. Se and Mo foliar application could reduce the toxic symptoms in pollen grains when the one or the other was sprayed alone on plants. In an in vitro pollen germination test, 500 μM Cd stress could strongly inhibit the pollen germination rate to less than 2.5%, however, when Se (10 μM) or Mo (1.0 μM) was added to the germination medium, the rate increased, reaching 66.2% and 39.4%, respectively. At the molecular level, Se and Mo could greatly affect the expression levels of some genes related to Cd uptake by roots (IRT1), Cd transport (HMA2 and HMA4), Cd sequestration in plant vacuoles (HMA3), and the final Cd distribution in plant tissue at the physiological level (PCS1). [ABSTRACT FROM AUTHOR]