Grazing weakens competitive interactions between active methanotrophs and nitrifiers modulating greenhouse-gas emissions in grassland soils

This work was financially supported by Natural Science Foundation of China (41977033, 41907026, and 41721001), Fundamental Research Funds for the Central Universities (2019QNA6011), National Key Basic Research Program of China (2014CB138801), Shandong Provincial Natural Science Foundation (ZR2019BD032), China Postdoctoral Science Foundation (2020T130387 and 2019M652448). CG-R was funded by a Royal Society University Research Fellowship (UF150571). Special thanks to ChunMei Meng, Yu Luo, and Yan Zheng for their assistance in laboratory analyses.Peer reviewedPublisher PD

Enrichment of soil fertility and salinity by tamarisk in saline soils on the northern edge of the Taklamakan Desert

To better understand the influence of Tamarix spp. (tamarisk shrubs) on soil fertility and salinity and the implication for saline soil management in northwestern China, several soil physical and chemical characteristics were measured beneath tamarisk canopies from the upper, middle, and lower regions of the Taklamakan Desert alluvial plain. The measured properties included soil organic matter (SOM), plant-available phosphorus (P), extractable soil potassium (K) soil electric conductivity (EC), sodium (Na+), total potassium (K+), and pH. The enrichment ratios for soil nutrients (i.e., available P. extractable K, and SOM) and salinity (i.e., EC, Na+, K+, and pH) were used to evaluate fertility and salinity islands in tamarisk mounds. SOM, available P, and extractable K were higher within mounds than in open, tamarisk-free land in each of the three sampled locations. The SOM enrichment ratios were highest at the middle region of the alluvial plain and lowest at the lower region of the alluvial plain, a pattern that is consistent with the growth patterns of tamarisk plants. The variation in SOM enrichment ratios in surface soils was mainly affected by the shoot biomass of tamarisk shrubs. The positive effect of tamarisk on soil fertility indicates that tamarisk may be beneficial for vegetation restoration and improving utilization of saline land. Nevertheless, soil salinity and pH increased under tamarisk canopy, especially EC and K+ in surface soil from the middle alluvial plain. The EC enrichment ratio was highest in the middle alluvial plain and, depending on soil depth, lowest in the upper and lower alluvial plain. These results reflect negative effects of tamarisk on soil chemical characteristics. (C) 2009 Elsevier B.V. All rights reserved

Plant growth-promoting rhizobacteria enhance the growth and Cd uptake of Sedum plumbizincicola in a Cd-contaminated soil

This study aimed to isolate plant growth-promoting rhizobacteria (PGPR) that exhibit heavy metal resistance to examine their influence on Cd uptake and soil microbial community structure during phytoremediation. Heavy metal-tolerant PGPR were isolated from the roots of possible hyperaccumulators using plates with 1-aminocyclopropane-1-carboxylate (ACC) as sole nitrogen source. Minimal inhibitory concentrations (MICs) of each isolate were determined by the plate dilution method. The impacts of isolated PGPR on the growth and Cd accumulation of Sedium plumbizincicola were conducted in a pot experiment. In addition, the effect of PGPR inoculation on the microbial community during phytoextraction by S. plumbizincicola was studied by 454 pyrosequencing. A total of nine Cd-resistant strains were isolated from the roots of Cd accumulators, and their plant growth-promoting activities were characterized. Isolates were able to produce indole-3-acetic acid (IAA) (28-133 mg L-1) and solubilize phosphate (65-148 mg L-1). In a pot experiment, the inoculation of isolates NSX2 and LCR1 significantly enhanced the growth of and uptake of Cd by the Cd hyperaccumulator S. plumbizincicola. 454 pyrosequencing revealed that the inoculation of the PGPR lead to a decrease in microbial community diversity in the rhizopshere during phytoextraction. Specifically, indigenous heavy metal-tolerant PGPR such as Actinospica, Bradyrhizobium, Rhizobium, Mesorhizobium, and Mycobacterium were selectively enriched in the treatments in which PGPR were added. It is suggested that a unique constitution of microbial communities in inoculated treatments plays a key role in enhancing Cd phytoremediation. Inoculation of strains Rhodococcus erythropolis NSX2 and Cedecea davisae LCR1 could promote S. plumbizincicola growth and enhance the remediation efficiency. The introduced PGPR could also affect the indigenous microbial community structure and the diversity in Cd-contaminated soil during phytoremediation.This study aimed to isolate plant growth-promoting rhizobacteria (PGPR) that exhibit heavy metal resistance to examine their influence on Cd uptake and soil microbial community structure during phytoremediation

Time-resolved x-Ray fluorescence analysis of element distribution and concentration in living plants: an example using manganese toxicity in cowpea leaves

The distribution and concentration of nutrients and contaminants affect almost every metabolic process in plants but analytical limitations have hindered the determination of microscopic changes over time within living plant tissues. We developed a novel method using synchrotron-based micro X-ray fluorescence (μ-XRF) that, for the first time, allows quantification of the spatial and temporal changes of multiple elements in the same area of living leaves. The utility of this approach was tested by examining changes over 48 h in unifoliate leaves of 7-d-old cowpea (Vigna unguiculata) plants simultaneously at 0.2 and 30 μM Mn in nutrient solution, with 30 μM Mn known to be toxic to cowpea and cause the formation of Mn-dense lesions. The fast X-ray fluorescence detector system reduced dwell on living leaf samples. This produced no evidence of tissue damage through repeated μ-XRF scanning, thereby overcoming previously noted experimental artifacts. This permitted, for the first time, visual and quantitative assessments of spatial and temporal changes in nutrient concentrations. By focusing on changes in Mn status, this study illustrated extension of two-dimensional μ-XRF scans to a three-dimensional geometry of Mn kinetics in the same area of leaves. The multi-element potential of this method was exemplified through the measurement of distributions and concentrations of K, Ca, Fe, Cu, and Zn within living plant leaves. This novel method and accompanying information on changes in Mn distribution showed the potential for microscopic, time-resolved, in vivo examination of changes in elemental distribution. We consider that this method will be of benefit for a wide range of studies, including functional characterization of molecular biology, examining changes in the distribution of nutrients, and understanding the movement and toxicity of contaminants

Biogeographic Distribution Patterns of the Archaeal Communities Across the Black Soil Zone of Northeast China

Although archaea are ubiquitous in various environments, the knowledge gaps still exist regarding the biogeographical distribution of archaeal communities at regional scales in agricultural soils compared with bacteria and fungi. To provide a broader biogeographical context of archaeal diversity, this study quantified the abundance and community composition of archaea across the black soil zone in northeast China using real-time PCR and high-throughput sequencing (HTS) methods. Archaeal abundances across all soil samples ranged from 4.04 × 107 to 26.18 × 107 16S rRNA gene copies per gram of dry soil. Several soil factors were positively correlated with the abundances including soil pH, concentrations of total C, N, and P, and available K in soil, and soil water content. Approximately 94.2, 5.7, and 0.3% of archaeal sequences, and 31, 151, and 3 OTUs aligned within the phyla Thaumarchaeota, Euryarchaeota, and Crenarchaeota, respectively. Within the phylum of Thaumarchaeota, group 1.1b was a dominating genus accounting for an average of 87% archaeal sequences and phylogenetically classified as Nitrososphaera, a genus of ammonia oxidizing archaea. The response of dominating OTUs to environmental factors differed greatly, suggesting the physiological characteristics of different archaeal members is diversified in the black soils. Although the number of OTUs was not related with any particular soil parameters, the number of OTUs within Thaumarchaeota and Euryarchaeota was marginally related with soil pH. Archaeal community compositions differed between samples, and a Canonical correspondence analysis (CCA) analysis indicated that soil pH and the latitude of sampling locations were two dominating factors in shifting community structures. A variance partitioning analysis (VPA) analysis showed that the selected soil parameters (32%) were the largest drivers of community variation, in particular soil pH (21%), followed by geographic distances (19%). These findings suggest that archaeal communities have distinct biogeographic distribution pattern in the black soil zone and soil pH was the key edaphic factor in structuring the community compositions

Soldering in magnesium high pressure die casting and its preservation by surface engineering

Magnesium alloys are the lightest structural metallic materials and their importance in a range of industries has been rising in the last ten years. To the automotive and electronics industries, the most attractive properties of magnesium alloys are their light weight, strength to weight ratio, higher strength of thin/very thin section, high quality surface finish and precise dimension of cast components. With the increased use of magnesium alloys especially in high pressure die casting, the phenomenon of soldering of magnesium alloys is attracting more attention. Soldering is the sticking of casting alloy to the die surface and leaving of drag marks on both the die and casting surface after part ejection. Soldering increases the rejection rate and the machine downtime, and serious soldering may damage the die which can cost hundreds of thousands, or even a million dollars to make. Because thin walled casting is one of the major advantages of magnesium high pressure die casting compared to other alloys, slight soldering can result in serious production problem. This project is aimed at understanding the soldering problem in the magnesium high pressure die casting process and applying surface engineering approaches to reduce or even eliminate it

Role of manganes in the soldering reaction in magnesium high pressure die casting

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