Electrical and optical enhancement of ITO/Mo bilayer thin films via laser annealing

ITO/Mo bilayer thin films were sputtered on n-type silicon and glass substrates and annealed with a Nd:YAG pulsed laser. The structural results show that both the as-deposited and the annealed ITO/Mo thin films have a polycrystalline structure, and that the annealing treatment enhanced the crystallinity of samples. Moreover, the XRD patterns exhibited a cubic structure preferentially oriented along the (222) and (400) planes. The AFM analysis shows that grain size and RMS roughness increased from 16.02 to 36.19 nm and 0.4 to 2.6 nm, respectively, when the laser energy was increased to 120 mJ. The as-deposited sample has an optical transmittance of nearly 80% in the 300-800 nm range. The laser annealing yielded a higher transmittance of 94% and increased the bandgap energy from 2.76 to 2.88 eV at 120 mJ. The annealing treatment decreased the resistivity from 15.63 × 10^-4 to 1.73 × 10^-4 Ω/cm^-1. Additionally, the figure of merit of the ITO/Mo structure improved significantly from 6.63 × 10^-4 Ω^-1 of the as-deposited sample to 17.6 × 10^-3 Ω^-1 of the the annealed structure. The results indicate that the laser annealing could improve the efficiency of the transparent conductive layer, which can be potentially applied in optoelectronic devices.

Evaluation of Soil Contamination with Industrial Waste Effluent in Riyadh, Saudi Arabia

BACKGROUND AND OBJECTIVE

Currently, in Saudi Arabia, wastewater production has increased manifolds due to onset of mega projects. The main objective of this study was to evaluate the soil contamination due to land disposal of industrial waste effluents.

MATERIALS AND METHODS

Soil and water samples were collected from different depth and distances from the wastewater pond. Soil and water samples were analyzed for physical and chemical contents. The regression and other statistically techniques were applied for data analysis.

RESULTS

Soil texture was sandy loam to sandy clay loam and was calcareous. Soil salinity was 80.3 dS m-1 near the pond and was normal after 100 m from the pond. Among the various heavy metals Cr showed more mobility than As and Mo.

CONCLUSION

Soil was sandy loam to sandy clay loam containing gravels between 29.2-43.6% and was calcareous. Soil salinity was 80.3 and 3.2 dS m-1 near the pond and at 100 m distance, respectively. The mobility index of Cr was high followed by As and Mo in descending order.

Natural variation in a molybdate transporter controls grain molybdenum concentration in rice

Molybdenum (Mo) is an essential micronutrient for most living organisms, including humans. Cereals such as rice (Oryza sativa) are the major dietary source of Mo. However, little is known about the genetic basis of the variation in Mo content in rice grain. We mapped a quantitative trait locus (QTL) qGMo8 that controls Mo accumulation in rice grain by using a recombinant inbred line population and a backcross introgression line population. We identified a molybdate transporter, OsMOT1;1, as the causal gene for this QTL. OsMOT1;1 exhibits transport activity for molybdate, but not sulfate, when heterogeneously expressed in yeast cells. OsMOT1;1 is mainly expressed in roots and is involved in the uptake and translocation of molybdate under molybdate-limited condition. Knockdown of OsMOT1;1 results in less Mo being translocated to shoots, lower Mo concentration in grains and higher sensitivity to Mo deficiency. We reveal that the natural variation of Mo concentration in rice grains is attributed to the variable expression of OsMOT1;1 due to sequence variation in its promoter. Identification of natural allelic variation in OsMOT1;1 may facilitate the development of rice varieties with Mo-enriched grain for dietary needs and improve Mo nutrition of rice on Mo-deficient soils.

Nutrient limitation of terrestrial free-living nitrogen fixation

Nitrogen (N) fixation by free-living bacteria is a primary N input pathway in many ecosystems and sustains global plant productivity. Uncertainty exists over the importance of N, phosphorus (P) and molybdenum (Mo) availability in controlling free-living N fixation rates. Here, we investigate the geographic occurrence and variability of nutrient constraints to free-living N fixation in the terrestrial biosphere. We compiled data from studies measuring free-living N fixation in response to N, P and Mo fertilizers. We used meta-analysis to quantitatively determine the extent to which N, P and Mo stimulate or suppress N fixation, and if environmental variables influence the degree of nutrient limitation of N fixation. Across our compiled dataset, free-living N fixation is suppressed by N fertilization and stimulated by Mo fertilization. Additionally, free-living N fixation is stimulated by P additions in tropical forests. These findings suggest that nutrient limitation is an intrinsic property of the biochemical demands of N fixation, constraining free-living N fixation in the terrestrial biosphere. These findings have implications for understanding the causes and consequences of N limitation in coupled nutrient cycles, as well as modeling and forecasting nutrient controls over carbon-climate feedbacks.

Molybdenum and phosphorus limitation of moss-associated nitrogen fixation in boreal ecosystems

Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a ¹⁵ N₂ tracer technique to assess the ARA to N₂ fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA : ¹⁵ N₂ ratios increased with increasing Mo additions. These findings show that N₂ fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.

Molybdenum and iron mutually impact their homeostasis in cucumber (Cucumis sativus) plants

Molybdenum (Mo) and iron (Fe) are essential micronutrients required for crucial enzyme activities in plant metabolism. Here we investigated the existence of a mutual control of Mo and Fe homeostasis in cucumber (Cucumis sativus). Plants were grown under single or combined Mo and Fe starvation. Physiological parameters were measured, the ionomes of tissues and the ionomes and proteomes of root mitochondria were profiled, and the activities of molybdo-enzymes and the synthesis of molybdenum cofactor (Moco) were evaluated. Fe and Mo were found to affect each other's total uptake and distribution within tissues and at the mitochondrial level, with Fe nutritional status dominating over Mo homeostasis and affecting Mo availability for molybdo-enzymes in the form of Moco. Fe starvation triggered Moco biosynthesis and affected the molybdo-enzymes, with its main impact on nitrate reductase and xanthine dehydrogenase, both being involved in nitrogen assimilation and mobilization, and on the mitochondrial amidoxime reducing component. These results, together with the identification of > 100 proteins differentially expressed in root mitochondria, highlight the central role of mitochondria in the coordination of Fe and Mo homeostasis and allow us to propose the first model of the molecular interactions connecting Mo and Fe homeostasis.

Biological nitrogen fixation by alternative nitrogenases in boreal cyanolichens: importance of molybdenum availability and implications for current biological nitrogen fixation estimates

Cryptogamic species and their associated cyanobacteria have attracted the attention of biogeochemists because of their critical roles in the nitrogen cycle through symbiotic and asymbiotic biological fixation of nitrogen (BNF). BNF is mediated by the nitrogenase enzyme, which, in its most common form, requires molybdenum at its active site. Molybdenum has been reported as a limiting nutrient for BNF in many ecosystems, including tropical and temperate forests. Recent studies have suggested that alternative nitrogenases, which use vanadium or iron in place of molybdenum at their active site, might play a more prominent role in natural ecosystems than previously recognized. Here, we studied the occurrence of vanadium, the role of molybdenum availability on vanadium acquisition and the contribution of alternative nitrogenases to BNF in the ubiquitous cyanolichen Peltigera aphthosa s.l. We confirmed the use of the alternative vanadium-based nitrogenase in the Nostoc cyanobiont of these lichens and its substantial contribution to BNF in this organism. We also showed that the acquisition of vanadium is strongly regulated by the abundance of molybdenum. These findings show that alternative nitrogenase can no longer be neglected in natural ecosystems, particularly in molybdenum-limited habitats.