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Soybean–maize intercropping system can improve the utilization rate of farmland and the sustainability of crop production systems. However, there is a significant gap in understanding the interaction mechanisms between soil carbon (C), nitrogen (N), and phosphorus (P) cycling functional genes, rhizosphere microorganisms, and nutrient availability. To reveal the key microorganisms associated with soil nutrient utilization and C, N, and P cycling function in the soybean–maize intercropping system, we investigated the changes in soil properties, microbial community structure, and abundance of functional genes for C, N, and P cycling under soybean–maize intercropping and monocropping at different fertility stages in a pot experiment. We found that there was no significant difference in the rhizosphere microbial community between soybean–maize intercropping and monocropping at the seeding stage. As the reproductive period progressed, differences in microbial community structure between intercropping and monocropping gradually became significant, manifesting the advantages of intercropping. During the intercropping process of soybean and maize, the relative abundance of beneficial bacteria in soil rhizosphere significantly increased, particularly Streptomycetaceae and Pseudomonadaceae. Moreover, the abundances of C, N, and P cycling functional genes, such as abfA, mnp, rbcL, pmoA (C cycling), nifH, nirS-3, nosZ-2, amoB (N cycling), phoD, and ppx (P cycling), also increased significantly. Redundancy analysis and correlation analysis showed that Streptomycetaceae and Pseudomonadaceae were significantly correlated with soil properties and C, N, and P cycling functional genes. In brief, soybean and maize intercropping can change the structure of microbial community and promote the proliferation of beneficial bacteria in the soil rhizosphere. The accumulation of these beneficial bacteria increased the abundance of C, N, and P cycling functional genes in soil and enhanced the ability of plants to fully utilize environmental nutrients and promoted growth. [ABSTRACT FROM AUTHOR]

To investigate whether elevated CO2 (eCO2) changes the influence of nanoparticles (NPs) on soil microbial communities and the mechanisms, various nano-ZnO (0, 100, 300, and 500 mg·kg−1) and CO2 concentrations (400 and 800 µmol·mol−1) were applied to tomato plants (Solanum lycopersicum L.) in growth chambers. Plant growth, soil biochemical properties, and rhizosphere soil microbial community composition were analyzed. In 500 mg·kg−1 nano-ZnO-treated soils, root Zn content was 58% higher, while total dry weight (TDW) was 39.8% lower under eCO2 than under atmospheric CO2 (aCO2). Compared with the control, the interaction of eCO2 and 300 mg·kg−1 nano-ZnO decreased and increased bacterial and fungal alpha diversities, respectively, which was caused by the direct effect of nano-ZnO (r = − 1.47, p < 0.01). Specifically, the bacterial OTUs decreased from 2691 to 2494, while fungal OTUs increased from 266 to 307, when 800–300 was compared with 400–0 treatment. eCO2 enhanced the influence of nano-ZnO on bacterial community structure, while only eCO2 significantly shaped fungal composition. In detail, nano-ZnO explained 32.4% of the bacterial variations, while the interaction of CO2 and nano-ZnO explained 47.9%. Betaproteobacteria, which are involved in C, N, and S cycling, and r-strategists, such as Alpha- and Gammaproteobacteria and Bacteroidetes, significantly decreased under 300 mg·kg−1 nano-ZnO, confirming reduced root secretions. In contrast, Alpha- and Gammaproteobacteria, Bacteroidetes, Chloroflexi, and Acidobacteria were enriched in 300 mg·kg−1 nano-ZnO under eCO2, suggesting greater adaptation to both nano-ZnO and eCO2. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2) analysis demonstrated that bacterial functionality was unchanged under short-term nano-ZnO and eCO2 exposure. In conclusion, nano-ZnO significantly affected microbial diversities and the bacterial composition, and eCO2 intensified the damage of nano-ZnO, while the bacterial functionality was not changed in this study. [ABSTRACT FROM AUTHOR]

Intercropping systems can flexibly use resources such as sunlight, heat, water, and nutrients in time and space, improve crop yield and land utilization rates, effectively reduce continuous cropping obstacles and the occurrence of diseases and insect pests, and control the growth of weeds. Thus, intercropping is a safe and efficient ecological planting mode. The legume–cereal intercropping system is the most common planting combination. Legume crops fix nitrogen from the atmosphere through their symbiotic nitrogen fixation abilities, and the fixed nitrogen can be transferred to and utilized by cereal crops in various ways. The symbiotic nitrogen fixation efficiency of legume crops was improved by reducing the inhibition of soil nitrogen on nitrogenase activity through competitive absorption of soil nitrogen. However, the effects of nitrogen transformation and distribution in intercropping systems and microbial community structure characteristics on nitrogen transfer need to be further explored. In this review, (ⅰ) we present the transformation and distribution of nitrogen in the legume–cereal intercropping system; (ⅱ) we describe the soil microbial community characteristics in intercropping systems; and (ⅲ) we discuss the advantages of using modern biological molecular techniques to study soil microorganisms. We conclude that intercropping can increase the diversity of soil microorganisms, and the interaction between different plants has an important impact on the diversity and composition of the bacterial and fungal communities. The extensive application of modern biological molecular techniques in soil microbial research and the great contribution of intercropping systems to sustainable agriculture are particularly emphasized in this review. [ABSTRACT FROM AUTHOR]

Rhizo-microbe recruited by hyperaccumulating plants are crucial for the extraction of metals from contaminated soils. It is important, but difficult, to identify the specific rhizosphere microbes of hyperaccumulators shaped by root exudation. Continuous 13CO 2 labeling, microbial DNA-based stable isotope probing (DNA-SIP), and high throughput sequencing were applied to identify those rhizosphere microorganisms using exudates from the Cd hyperaccumulator Sedum alfredii. In contrast to its non-hyperaccumulating ecotype (NAE), the hyperaccumulating ecotype (HAE) of S. alfredii strongly changed the rhizosphere environment and extracted a 5-fold higher concentration of Cd from contaminated soil. Although both HAE and NAE harbored Streptomyces , Massilia , Bacillus, and WPS-2 Uncultured Bacteria with relative abundance of more than 1% in the rhizosphere associated with plant growth and immunity, the HAE rhizosphere specifically recruited Rhodanobacter (2.66%), Nocardioides (1.16%), and Burkholderia (1.01%) through exudates to benefit the extraction of Cd from soil. Different from the bacterial network with weak cooperation in the NAE rhizosphere, a closed-loop bacterial network shaped by exudates was established in the HAE rhizosphere to synergistically resist Cd. This research reveals a specific rhizosphere bacterial community induced by exudates assisted in the extraction of Cd by S. alfredii and provides a new perspective for plant regulation of the rhizo-microbe community beneficial for optimizing phytoremediation. [Display omitted] Hyperaccumulator S. alfredii (HAE) absorbed more Cd than non-hyperaccumulator (NAE). The HAE and NAE rhizosphere harbored common bacterial genera in Cd-contaminated soil. The HAE rhizosphere recruited specific bacterial genera with a closed-loop network. [ABSTRACT FROM AUTHOR]

Microplastic pollution has become an increasingly pervasive issue worldwide, but little is known about its effects on the soil environment. A soil microcosm experiment was conducted using low‐density polyethylene microplastics to estimate the effect of microplastic pollution on soil nutrient cycling and the soil microbial community structure. The results showed that microplastic addition significantly promoted soil carbon dioxide emissions but not soil nitrous oxide emissions. Soil pH, dissolved organic carbon, ammonia nitrogen, the contents of total phospholipid fatty acid (PLFA), and the ratios of gram‐positive bacteria to gram‐negative bacteria and saturated to monounsaturated PLFAs significantly increased. In addition, nitrate nitrogen and the ratios of fungi to bacteria, total iso‐branched fatty acids to total anteiso‐branched fatty acids, and cyclopropyl to precursor significantly decreased with increasing microplastic addition. The addition of microplastics decreased the abundance of ammonia oxidizing bacteria and nitrite reductase (nirS) but had little effect on the functional genes of ammonia oxidizing archaea, nitrite reductase (nirK), and nitrous oxide reductase. A principal coordinate analysis of the bacterial 16S ribosomal RNA gene and fungal internal transcribed spacer in the microplastic addition treatments revealed that the bacterial and fungal communities formed an obvious cluster. The average abundance of some microbial species with tolerance and degradability to microplastics, such as Nocardioidaceae, Amycolatopsis, Aeromicrobium, Cytophagaceae, Betaproteobacteria, Rhodoplanes, and Mortierella, in the microplastic addition treatments was significantly higher than that of the control treatment. The results suggested that microplastics have obvious influences on microbial communities and may affect global carbon and nitrogen cycles. Environ Toxicol Chem 2021;40:352–365. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Both drought and flooding are unfavorable for soil microorganisms, but nevertheless, are highly relevant to the extreme weather events that have been predicted to increase in the future. The switch of soil water status from drought to flooding can happen rapidly and microbial activity might be either stimulated or further inhibited, but we have insufficient understanding of the underlying microbial processes. Here, we tracked the changes in soil bacterial and fungal abundance and their community structures, assaying the total (DNA-based) and potentially active (RNA-based) communities in response to abrupt flooding of dry soil. Also, rates of soil respiration and enzyme activity were measured after flooding. Results showed that the bacterial community was found to be more responsive than the fungal community to flooding. The bacterial community responses were clearly classified into three distinct patterns in which the intermediate pattern displayed highly phylogenetic clustering. A transient flourish of Bacilli which belongs to Firmicutes was detected at 8–48 h of flooding, suggesting its potential importance in the microbial assemblage and subsequent ecosystem functioning. Finally, the accumulative amount of CO2 released was more closely related than enzyme activity to the change in structure of the bacterial community after flooding. In conclusion, these findings extended our understanding of the underlying soil microbial processes following abrupt water condition changes. [ABSTRACT FROM AUTHOR]

Bioleaching is a green recycling technology for recovering precious metals from waste printed circuit boards (WPCBs). However, this technology requires increasing cyanide production to obtain desirable recovery efficiency. Luria-Bertani medium (LB medium, containing tryptone 10 g/L, yeast extract 5 g/L, NaCl 10 g/L) was commonly used in bioleaching of precious metal. In this study, results showed that LB medium did not produce highest yield of cyanide. Under optimal culture conditions (25 °C, pH 7.5), the maximum cyanide yield of the optimized medium (containing tryptone 6 g/L and yeast extract 5 g/L) was 1.5 times as high as that of LB medium. In addition, kinetics and relationship of cell growth and cyanide production was studied. Data of cell growth fitted logistics model well. Allometric model was demonstrated effective in describing relationship between cell growth and cyanide production. By inserting logistics equation into allometric equation, we got a novel hybrid equation containing five parameters. Kinetic data for cyanide production were well fitted to the new model. Model parameters reflected both cell growth and cyanide production process. [ABSTRACT FROM AUTHOR]

Intensively fertilized acidic soils are global hotspots of nitrous oxide (N 2 O) emissions, contributing to net agronomic greenhouse gas outcomes. Identifying the key drivers of soil N 2 O emissions is hampered by the synergistic or antagonistic effects of multiple factors. Within a framework based on the predominant role of microbial communities producing N 2 O, the N 2 O emissions are affected either by proximal regulators: temporary soil property fluctuations affect N 2 O production transcriptionally, or by distal regulators: persistent genetic rearrangements in local microbial communities. The proximal regulators, individually or together, may spontaneously impact distal regulators. Here, we use acidic soils from tea (Camellia sinensis L.) plantations on a broader geographic scale as a model system. Based on amplicon sequencing and properties of 195 acidic (average pH = 5.0) soils, we determined the importance of proximal and distal regulation to N 2 O emissions. Microbial phylogenetic diversity as a distal regulator overwhelms mineral N content as a proximal regulator in explaining high N 2 O emissions. Low-abundance, diverse prokaryotic communities (e.g., Acidothermu) and specialized denitrifying fungal communities (e.g., Fusarium) were associated with high N 2 O emissions. Revisiting the impact of proximal regulators on distal regulators revealed that soil pH is the sole proximal regulator influencing the prokaryotic rare taxa that correlated with high N 2 O emissions. When considering proximal regulators together (here soil properties compiled as soil fertility index), the microbial diversity were independent of soil fertility. The microbial assembly was dominated by stochastic processes. Consequently, proximal regulators have a limited impact on distal regulators of N 2 O emissions from acidic soils. In conclusion, the framework underscored the importance of in situ microbial communities as distal regulators in explaining high N 2 O emissions from acidic soils. • Tea plantation soils as a model system for studying N 2 O emissions from acidic soils. • Microbial assembly processes are independent of soil fertility. • Microbial phylogenetic diversity explains more elevated N 2 O emissions. • Diverse prokaryotes and specialized fungi contributed to high N 2 O emissions. [ABSTRACT FROM AUTHOR]