The connection between the antibiotic resistome and nitrogen-cycling microorganisms in paddy soil is enhanced by application of chemical and plant-derived organic fertilizers.

Antibiotic resistant genes (ARGs) present significant risks to environments and public health. In particular, there is increasing awareness of the role of soil nitrogen in ARG dissemination. Here, we investigated the connections between antibiotic resistome and nitrogen-cycling microbes in paddy soil by performing five-year field experiments with the treatments of no nitrogen fertilization (CK), reduced chemical nitrogen fertilization (LN), conventional chemical nitrogen fertilization (CN) and plant-derived organic nitrogen fertilization (ON). Compared with CK treatment, CN and ON treatments significantly increased soil NH4+ and TN concentrations by 25.4%-56.5% and 10.4%-20.1%, respectively. Redundancy analysis revealed significantly positive correlation of NH4+ with most ARGs, including tetA, macB and barA. Correspondingly, CN and ON treatments enhanced ARG abundances by 21.9%-23.2%. Moreover, CN and ON treatments promoted nitrate/nitrite-reducing bacteria and linked the corresponding N-cycling functional genes (narG, narH, nirK and nrfA) with most ARGs. Metagenomic binning was performed and identified Gemmatimonadaceae, Caulobacteraceae, Ilumatobacteraceae and Anaerolineaceae as hosts for both ARGs and nitrate/nitrite reduction genes that were enriched by CN and ON treatments. Soil resistome risk score analysis indicated that, although there was increased relation of ARG to nitrogen-cycling microorganisms with nitrogen fertilizer application, the environmental risk of ARGs was not increased due to the lower distribution of ARGs in pathogens. This study contributed to a deeper understanding of the role of soil nitrogen in shaping ARG profiles and controlling soil resistome risk.

Inhibition Roles of Calcium in Cadmium Uptake and Translocation in Rice: A Review.

Cadmium (Cd) contamination in rice grains is posing a significant threat to global food security. To restrict the transport of Cd in the soil-rice system, an efficient way is to use the ionomics strategy. Since calcium (Ca) and Cd have similar ionic radii, their uptake and translocation may be linked in multiple aspects in rice. However, the underlying antagonistic mechanisms are still not fully understood. Therefore, we first summarized the current knowledge on the physiological and molecular footprints of Cd translocation in plants and then explored the potential antagonistic points between Ca and Cd in rice, including exchange adsorption on roots, plant cell-wall composition, co-transporter gene expression, and transpiration inhibition. This review provides suggestions for Ca/Cd interaction studies on rice and introduces ionomics research as a means of better controlling the accumulation of Cd in plants.

Alleviation of aqueous nitrogen loss from paddy fields by growth and decomposition of duckweed (Lemna minor L.) after fertilization.

Runoff loss of nitrogen from paddy fields has received increasing attention in recent years. Duckweed is an aquatic plant frequently found in paddy fields. In this study, the effects of duckweed (Lemna minor L.) in floodwater on aqueous nitrogen losses from paddy fields were systematically investigated. Results demonstrated that the growth of duckweed decreased total nitrogen concentrations in floodwater and nitrogen runoff loss from paddy fields by 16.7%-18.3% and 11.2%-13.6%, respectively. Moreover, compared with NO3-, NH4+ was preferentially removed by duckweed. 15N isotope tracer experiments revealed that the growth and decomposition of duckweed acted as a "buffer" against the nitrogen variation in floodwater after fertilization. During the growth of duckweed, leaves were found to be the principal organ to assimilate NH4+ and release NO3- by using non-invasive micro-test technology. Duckweed degradation increased the content of hydrophobic acids and marine humic-like substances in floodwater, which promoted the migration of nitrogen from floodwater to soil. Redundancy analysis and structural equation models further illustrated that pH and temperature variation in floodwater caused by duckweed played a greater role in aqueous nitrogen loss reduction than the nitrogen accumulation in duckweed. This study suggested that the growth of duckweed in paddy fields was an effective supplementary method for controlling aqueous nitrogen loss during agricultural production.

Salicylic Acid, a Multifaceted Hormone, Combats Abiotic Stresses in Plants.

In recent decades, many new and exciting findings have paved the way to the better understanding of plant responses in various environmental changes. Some major areas are focused on role of phytohormone during abiotic stresses. Salicylic acid (SA) is one such plant hormone that has been implicated in processes not limited to plant growth, development, and responses to environmental stress. This review summarizes the various roles and functions of SA in mitigating abiotic stresses to plants, including heating, chilling, salinity, metal toxicity, drought, ultraviolet radiation, etc. Consistent with its critical roles in plant abiotic tolerance, this review identifies the gaps in the literature with regard to the complex signalling network between SA and reactive oxygen species, ABA, Ca2+, and nitric oxide. Furthermore, the molecular mechanisms underlying signalling networks that control development and stress responses in plants and underscore prospects for future research on SA concerning abiotic-stressed plants are also discussed.

Intercropping of Euonymus japonicus with Photinia × fraseri Improves Phytoremediation Efficiency in Cd/Cu/Zn Contaminated Field.

Intercropping plants for phytoremediation is a promising strategy in heavy metal-polluted soils. In this study, two typical greening plant species, Euonymus japonicus (E. japonicus) and Photinia × fraseri (P. × fraseri), were intercropped in a Cd/Cu/Zn-contaminated field. The phytoremediation efficiency was investigated by measuring the plant biomass, metal concentration, and mycorrhizal colonisation, as well as the effects on soil properties, including soil pH; soil total N; and available N, P, K, Cd, Cu, and Zn. The results showed that, compared with the monoculture system, intercropping significantly lowered the available Cd, Cu, and Zn contents, significantly improved the total and available N contents in rhizosphere soils of both plant species, and increased the hyphae colonisation rate of P. × fraseri. In both plants, intercropping significantly improved the total plant biomass. Furthermore, the concentrations Zn and Cd in the root of E. japonicus and Cu concentration in the root of P. × fraseri were enhanced by 58.16%, 107.74%, and 20.57%, respectively. Intercropping resulted in plants accumulating higher amounts of Cd, Cu, and Zn. This was particularly evident in the total amount of Cd in E. japonicus, which was 2.2 times greater than that in the monoculture system. Therefore, this study provides a feasible technique for improving phytoremediation efficiency using greening plants.

Synchronous response in methanogenesis and anaerobic degradation of pentachlorophenol in flooded soil.

Methanogenesis is commonly mass-produced under anaerobic conditions and serves as a major terminal electron accepting process driving the degradation of organic biomass. In this study, a cofactor of methanogenesis (coenzyme M, CoM) and a classic methanogensis inhibitor (2-bromoethanesulfonate, BES) were added at different concentrations to investigate how methanogenesis would affect PCP degradation in flooded soil. Strikingly, the processes of methanogenesis and PCP degradation were simultaneously promoted with CoM, or inhibited with BES, significantly (p < 0.05). High-throughput sequencing for soil bacterial and archaeal community structures revealed that members of Desulfitobacterium, Dethiobacter, Sedimentibacter, Bacillus and Methanosarcina might act as the core functional groups jointly perform PCP degradation in flooded soil, possibly through assisting microbial mediated dechlorination in direct organohalide-respiration, and/or indirect co-metabolization in complex anaerobic soil conditions. This study implied an underlying synergistic coupling between methanogenesis and dechlorination, and provided insights into a novel consideration with respect to coordinating methanogenesis while promoting anaerobic degradation of PCP for complex polluted soil environment, which is necessary for the improved all-win remediation.

Effects of Cd, Cu, Zn and their combined action on microbial biomass and bacterial community structure.

Heavy metal pollution can decrease the soil microbial biomass and significantly alter microbial community structure. In this study, a long-term field experiment (5 years) and short-term laboratory experiment (40 d) were employed to evaluate the effects of heavy metals (Cd, Cu, Zn), and their combinations at different concentrations, on the soil microbial biomass and the bacterial community. The ranges of heavy metal concentration in the long-term and short-term experiments were similar, with concentration ranges of Cd, Cu and Zn of about 0.3-1.5, 100-500, and 150-300 mg kg-1, respectively. Microbial biomass decreased with increasing soil heavy metal concentrations in both the long-term and short-term experiments. The interaction between soil physicochemical factors (pH, TN, TC) and heavy metals (Cd, Cu, Zn) played a major role in change in the bacterial community in long-term polluted soil. In the laboratory experiment, although each heavy metal had an adverse effect on the microbial biomass and community structure, Cu appeared to have a greater role in the changes compared to Cd and Zn. However, the synergistic effects of the heavy metals were greater than those of the single metals and the synergistic effect between Cu and Cd was greater than that of Cu and Zn.