In order to improve the research and development level of prevention and control techniques for agricultural nonpoint source and heavy metal polluted croplands, a National Key R & D Program of China titled with “research and development on comprehensive prevention and control techniques for agricultural non-point source and heavy metal polluted croplands” was initiated during the 13rd Five-Year Period, in the context of national research project reform. This program was designed throughout the industrial chain, including 35 research missions into three categories, such as fundamental research, common key techniques, and technique integration and demonstration. This paper introduced the backgrounds, objectives and research missions of the program, analyzed the progress and major characteristics for the research missions initiated in the years 2016 and 2017, and discussed the program management mechanism, so as to provide references for enhancing application, approval and management of National Key R & D Program of China.
Soil is a complex redox system where many active biogeochemical processes co-occurred, such as denitrification, iron/sulfate reduction, methanogenesis and reductive dehalogenation, etc. Due to their frequent and close interaction, these typical redox processes make a great contribution in regulating the transformation/transportation of elements and pollutants in a natural soil ecosystem. Recently, with the development of molecular biology technology, studies regarding the microbial community structure, distribution characteristics and relative abundance in soil environment, based on functional gene biomarkers, become a hot topic around the world. The key genes encoding for specific functional enzymes in typical redox processes have been continually improved. This greatly advanced our understanding with respect to the specific metabolic pathway of elements and pollutants in soils, and promoted the in-depth development in studies on environmental microbial ecology. However, due to the diversity of microorganisms and functional genes, the influence of different environmental factors, and their extensive interactions in the natural soil environment, our knowledge currently available for demonstrating the complicated metabolic pathways and the coupling mechanism among different elements and pollutants are still finite. Therefore, the key functional genes and their diversity involved in several major reduction processes in soils were reviewed in this paper. Through comprehensive analysis of the microbial community structure and functional properties during the reduction processes of NO3－, Fe(Ⅲ) and SO42－, the process of methanogenesis, and the reductive dehalogenation of halogenated organic pollutants, we aim to explore the coupling mechanism between typical soil redox processes and the reductive removal of halogenated organic pollutants, thereby developing an improved strategy for pollution remediation.
The bioremediation of organic pollutants is regarded as a safe, economical and efficient strategy. Nevertheless, biodegradation efficiency is not only associated with the degrading capability of bacteria, but also depends on the bioavailability of pollutants, which is influenced by microbial mobility in addition to the soil medium and nature of the pollutants. On account of the high hydrophobicity, most of the soil organic pollutants are strongly adsorbed to soil and the bioavailability is poor. In the past few years, many studies have shown that most motile bacteria can sense and access pollutants through the process of chemotaxis. The chemotactic movement of bacteria can increase the bioavailability of organic pollutants, which in turn have a beneficial role in bioremediation. Chemotaxis has been extensively studied in Escherichia coli, but the E. coli chemosensory system reflects only a small fraction of the diversity of bacterial chemotactic responses. A limited number of compounds like amino acids, organic acids and sugars are the primary attractants for E. coli. Whereas for many free-living bacteria, a much wider range of attractants have been documented, such as naphthalene, toluene, biphenyl, polychlorinated biphenyls, benzoic acid, chlorobenzoic acids, nitroaromatics, methyl parathion and atrazine. The involved species include Pseudomonas sp., Ralstonia sp., Azospirillum sp., Rhizobium sp., Burkholderia sp. and Arthrobacter sp. At present, there is sufficient evidence indicating that chemotaxis can increase the bioavailability of organic pollutants. The best studied example is the degrading capacity of Pseudomonas putida G7 to naphthalene. In addition, studies about the chemotaxis of Ralstonia sp. SJ98 towards p-nitrophenol and Pseudomonas putida DLL-1 to methyl parathion demonstrated that chemotaxis could enhance in situ bioremediation of soil pollution. The effect of bacterial chemotaxis on degradation implies a significant link between chemotaxis and degradation. Chemotaxis is now only observed towards compounds which can be degraded by the microorganisms, while non-substrate compounds are not found to be chemoattractants. And the observation that specific pollutant chemoreceptors were co-localized with the degradation genes on plasmids combined with the coordinately expression of transport, chemoreceptor, and degradation genes, which strongly suggests an inherent link between chemotaxis and degradation. In sum, this paper reviewed recent research progress on bacterial chemotaxis, including signal transduction mechanism, bacterial chemotaxis to typical organic pollutants, with a special focus on the intimate link between chemotaxis and degradation.
Escherichia coli is a kind of facultative anaerobic bacteria which is commonly found in the host gastrointestinal tract and natural environments. The presence of pathogenic E. coli in manure and sewage is a serious threat to the health of humans and animals, which can spread to consuming agricultural products and enter the food industry chain. In the above processes, these pathogens can survive and spread in the form of surface-associated biofilm. Initial attachment is the first step of the biofilm development. When cells attached on the surface, physiological properties of bacteria are altered. It can reshape cell morphology and behavior by changing the expressions of different genes, such as, those related to cell motility and metabolism. Therefore, the attachment on various biotic (plant roots or leaves) and abiotic (soil particles) surfaces is the key step for bacterial survival in different environments. The way that cells sense a surface and respond upon surface attachment is referred as“surface sensing”, which consists of a great many behaviors, including the workings of the apparatus that allows perception of proximal surfaces, the apparatus that allows selection of different surfaces for attachment, and the biochemical cascade and physical consequences that follow the recognition of surfaces. E. coli is a one of the most studied microorganisms in surface sensing. The bacteria can sense the solid surface by the cell surface structure and regulate attachment by controlling cell motility and surface properties through the intracellular signaling system. E. coli can sense solid surfaces through flagella, type I fimbriae, membrane proteins (such as OmpX and NlpE), lipopolysaccharide (LPS) and exopolymeric substances (EPS). In addition, cell density can also affect cell attachment. The buoyant density of bacteria is usually 1.06-1.13 g/mL, which leads to the slow deposition of cells onto surfaces from suspension in bulk liquid. The buoyant density of E. coli increases as they enter stationary phase, which facilitates their rapid deposition on surfaces. Two-component system is the main intracellular signaling system induced by attachment. Specifically, the regulation of pili by two-component system is an important way to control surface sensing. As far as we know, the CpxAR, RcsAB and EnvZ-OmpR pathways can respond to surface signals and regulate pili expression in attachment. Nonetheless, bacterial surface sensing is a phenomenon that is still not well understood at the level of physical chemistry, biochemistry, genetics, and cell biology. The surface sensing of E. coli is a complex, multi- step and coordinated process which may be regulated and/or affected by many factors, particularly in complicated soil systems. A further understanding of the mechanisms of surface sensing will improve our knowledge on not only how microbes, especially pathogens, survive and transmit in soils, but also how soil biofilm is formed.
Global spread of antibiotic resistance has hampered the infection therapies by antibiotics and posed great threat to human health. Agroecosystem is the source and sink of antibiotic resistance genes (ARGs) and strongly associated with human health. Antibiotics have been extensively used in human medicine and animal production for prevention and treatment of disease, and promotion of animal growth. Animal farms and sewage treatment plants are the hotspots for dissemination of ARGs in environments. Application of animal wastes and sludges contributes largely to the increased resistance in agroecosystems via directly introduction of antibiotic resistant bacteria or ARGs, or through introduction of antibiotic residues and selection of indigenous resistant bacteria. However, discriminating their contribution to the ARGs level in agroecosystem is difficult. Both culture-dependent and culture-independent technologies, including metagenomic, microarray and high-throughput quantitative polymerase chain reaction have been utilized in the characterization of ARGs in agroecosystem, and each has its strength and weakness. Numerous researches have investigated the diversity and abundance of ARGs in agroecosystems. However, the baseline or background data of ARGs and the knowledge of biogeography of ARGs in agroecosystems are limited. Lack of standard surveillance system hinders the comparison of results from various studies. Horizontal gene transfer (HGT) plays a pivotal role in the dissemination of ARGs in environments. Plasmids, integrons, bacterial phages and extracellular DNA are important mobile genetic elements (MGEs) mediating HGT in agroecosystems. The concentration of antibiotics, heavy metals and other chemicals contribute to the HGT of ARGs. The primary risk of ARGs is that they could be transferred from environmental bacteria to human or animal pathogens, resulting in antibiotic treatment failure. However, knowledge gaps remain in evaluating the impact of ARGs in agroecosystems to human health. ARGs in environments are ubiquitous and diverse, prioritizing the risk of ARGs in the environments is an essential step to human health risk assessment (HHRA). Then to investigate the dissemination of these highly risk ARGs, particularly estimate the likelihood of their introduction into human pathogens is necessary. Finally, the lack of quantitative estimates of human exposure to these ARGs and their link with large-scale epidemiological survey are the key data gaps in the assessment of human health risk.
Phthalic acid esters (PAEs) are typical organic pollutants widely distributed in various environments, including soil, water, atmosphere and sediments, etc. Meanwhile, PAEs are well known to have endocrine disruption and toxicological effects of teratogenicity, carcinogenicity and mutagenicity, causing great threats to human health and ecosystem security. In this paper, we review the distribution characteristics of PAEs pollution in the soil- plant system, summarize the multi-interfacial (soil-air, soil-water and soil-plant) migration and transformation of PAEs in the soil and its function mechanism, the in vivo metabolism, microbial degradation process and interactive mechanisms of PAEs, compared and analyzed the bioavailability of PAEs in soils, the toxicological effects at different physiological-biochemical and tissues levels, and the effects of PAEs on microbial ecological function, elaborated the pivotal techniques for preventing and control of PAEs pollution and novel strategies of agronomic regulation, and proposed the research trends on migration and transformation of PAEs in soils and associated bioavailability problems.
Chlorpyrifos (O, O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate, CPF) is one of the most widely used pesticides in agriculture, with broad-spectrum, high efficiency, and moderate toxicity. Unfortunately, only less than 1% of CPF applied can be directly utilized by plants, and up to 99% were released into the environment. Continuous and excessive use of CPF has already led to widespread environmental contamination. Recently, great concern has been raised regarding its residue problems and the risk to the ecological environment. In this paper, the fate and environmental behavior of CPF in soils were reviewed. Adsorption/desorption and degradation were two critically important courses on this issue. CPF adsorption/desorption in soils may be fitted by Freundlich model or linear model. The parameters of CPF adsorption in soils are greatly related to soil properties. Soil organic matter contents are the key parameter controlling CPF’s adsorption, as well as CPF’s desorption. However, adsorption process is also affected by other soil characteristics, such as pH and temperature. It is therefore generally assumed that the sorption mechanisms of CPF in soils should be dominated by the binding between CPF and the hydrophobic site on the surface of soil particles. The degradation of CPF in the natural environment is mainly controlled by biotic processes. Bacteria and fungi are the main microorganisms that can degrade CPF by co-metabolism or mineralization into 3,5,6-trichloro-2-pyridinol and dicethylthiophospshate. The degradation of the intermediate degradation product 3,5,6-trichloro-2-pyridinol is the limiting factor for the CPF degradation process. Indigenous microorganism is effective for the degradation of 3,5,6-trichloro-2-pyridinol, leading a good remediation of CPF contaminated site. The use of indigenous or genetically modified microorganisms and/or plants has enhanced the degradation for in- situ bioremediation of contaminated sites. In conclusion, it is necessary to establish an adsorption/desorption model to describe the complex relation between CPF and other factors in soils. Furthermore, a novel gene technology can be further studied to enhance the degradation of CPF by microorganism and/or plants in soils.
Quinclorac is one of the typical quinolinecarboxylic acid herbicides existing in farmland ecosystems. The research progress in effect of quinclorac on crops, community structure of soil microorganisms, enzyme activities and its degradation by microorganisms was reviewed comprehensively. The future works focusing on mechanisms of microbial degradation, screening of degradative bacteria, and application in farmlands were also proposed. The main contents are as follows: Quinclorac is relatively stable in the environment; quinclorac residues in soil can lead to changes of genes and functional enzymes in crops, thus causing damage to crops and resistance of some weeds; the presence of quinclorac in environment may cause animal dysplasia, metamorphosis and reproductive abnormality, thus affecting the diversity and abundance of animals; regular application rate has little effect on community structure of soil microorganisms and soil enzyme activities. Quinclorac often exists for a long time in natural environment, and the bioremediation based on microbial degradation is an effective way to control the quinclorac pollution. At present, researches on microbial degradation of quinclorac are conducted mainly in China, and several highly effective strains for degrading quinclorac isolated from contaminated soils and tobacco roots are mostly identified as bacteria. The degradation of quinclorac may attribute to the combination of decarboxylation reaction and dechlorination reaction. Temperature, humidity and pH are the main influencing factors of microbial degradation. Usually in a certain range, the degradation of quinclorac in soil accelerated with the increase of temperature and humidity. However, excessively high temperature or humidity would reduce the efficiency of microbial degradation. pH value mainly affected the microbial degradation of quinclorac in two aspects. Quinclorac is weak acidic and shows higher dissociation degree in slight alkaline soil, which is more easily degraded; on the other hand, the pH of soil has direct effect on the species and quantity of soil microbial communities, which has a great impact on the effect of microbial degradation. In conclusion, to reveal the complex physiological and biochemical processes and mechanism of soil microbial degradation, and explore the remediation technology for quinclorac contaminated soil, future work should focus on: 1) investigating the mechanism of quinclorac degradation at molecular biological level by the application of advanced molecular biological technology and tandem mass spectrometry technology, and constructing highly effective strains in degrading quinclorac through genetic engineering; 2) focusing on complex degradation of quinclorac by multiple strains; 3) verifying the effect of the currently isolated quinclorac-degrading strains in the field.
Steroid estrogens are a group of biologically active compounds synthesized from cholesterol and have a cyclopentan-o-perhydrophenanthrene ring in common. Steroid estrogens can be classified into natural and synthetic types, and have been intensively reported for wide distribution in water bodies and farmland soils. Trace steroid estrogens in the environment can pose severe threat to the ecosystems. For example, these steroid estrogens can promote synthesis and secretion of vitellogenin in male fish, and this female-specific protein can lead to feminization of the male fish population and result in extinction of fish species. Recently, steroid estrogens have been frequently detected in surface waters, such as lakes and rivers, but little attention was paid to steroid estrogen accumulation in soils, and the potential steroid estrogen pollution caused by application of manure in greenhouse vegetable farmland. In addition to the sewage treatment plant effluent outfalls, large amounts of animal wastes and biosolids applied to agricultural fields might run off into nearby water bodies or infiltrate through the soil into groundwater. Cattle and poultry manure has been reported as a source of the environmental loadings of steroid estrogens. In this paper, the migration and transformation process of steroid estrogens was reviewed, and the environmental behavior including adsorption, degradation and associated influence factors was discussed. The distribution and partitioning of steroid estrogens in the environment were determined by their physicochemical properties and site-specific environmental conditions. Due to low solubility in water, the persistence and bioavailability of hydrophobic steroid hormones in the aquatic systems depend greatly on their sorption to particulate matter. The adsorption behavior of steroid estrogens in environmental media is influenced not only by their physical and chemical properties, but also by soil type, environmental pH, and types and contents of organic matters. Furthermore, degradation of steroid hormones in the environment includes photodegradation, chemical degradation, and microbial degradation, and the degradation process can greatly reduce the concentration of steroid estrogens, but is affected by multiple factors. Finally, the research trends of steroid estrogens were suggested as follows: 1) to explore the pattern of environmental behaviors of manure- borne- steroid estrogens in the farmland soil, especially in the greenhouse soil; 2) to investigate research in the field, especially under multi- interface conditions, which make more sense than experimental simulations in the lab; 3) to discover the environmental behaviors of steroid estrogens coexisting with other pollutants.
Several mineral nutrient elements of plants can reduce Cd availability in soil by precipitation and adsorption, and decrease Cd absorption of plants by the competition between Cd and plant nutrients for the same membrane transporters. Nutrient management is one of the most important agronomic practices for better crop growth. Accordingly, it is regarded as a low cost, short period and high efficient way to alleviate Cd accumulation in crops by proper management of nutrients and proper treatment of the interactions between Cd and plant nutrients. In addition, other agronomic measures and molecular plant breeding, which could modulate the interactions between Cd and plant nutrients, might also be two relatively inexpensive and effective strategies to minimize Cd contamination in crops. The main objective of this review is to highlight how the interactions between mineral nutrient elements and Cd affect the availability of Cd in soil, and the Cd absorption of plants. Examples include that, the competition between Fe, Ca, Zn, Mn and Cd uptake by root can decrease Cd levels in plants, and iron supply prevents Cd uptake by inhibiting iron- regulated transporter1 (IRT1) expression. The strategies of using these interactions to minimize Cd accumulation in the edible parts of crops were also focused in this review. For example, the application of P fertilizer can precipitate with Cd to reduce Cd uptake by plants. In addition, Si and Se fertilizer foliage application can decrease Cd translocation from roots to shoots in plants, thus reducing Cd accumulation in edible organs and improving food safety.
Organic pollutants including chemical pesticides, petroleum compounds, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), have caused serious environmental problems and posed new threats to human health when released into environments. Therefore, studies on the remediation of organic pollutants in contaminated-sites have received great concern. Plant-microorganism combined remediation of organic pollutants is a method to enrich, fix and degrade organic pollutants in soil by means of plant-microbe composite system, which is highly efficient, environmentally friendly and cheap, and has been paid more and more attention. On one hand, the roots of plants continue to provide secretions and other metabolites for microorganisms, improve the contents of soil organic matter in roots, thus increasing the microbial diversity and microbial activity, and promoting the ability of microbial remediation of organic pollutants. On the other hand, rhizosphere microorganisms secrete organic acids and other substances, are able to change the existing state or redox state of organic pollutants in the environment, and reduce the toxicity of organic compounds to plants, strengthen the tolerance of plants, and promote the absorption, transfer and enrichment of organic pollutants. Plant-microorganism is mutually beneficial to each other, which can enhance the effect of phytoremediation. The combined forms of phytoremediation include plant- rhizosphere microorganisms, plant- mycorrhizal fungi, plantendophyte and plant-specific degrading bacteria. In recent years, a series of advances have been made in phytoremediation of plant-microorganism combination. Such as, the interaction of alfalfa and soil microbial could greatly reduce the concentration of PCBs in soil; the inoculation of rhizobium and mycorrhizal fungi enhanced the ability of alfalfa to remove PCBs. Regarding the problems raised in the development of bioremediation, the following three aspects should be emphasized in the study of plant-microorganism remediation in the future: 1) Screen selected microbial strains and plant materials to improve the remediation efficiency of microbe and resistance of plants; 2) strengthen the real- time monitoring ability of bioremediation process of organic pollutants, optimize and control the living environment of plants and microorganisms, and improve the efficiency of remediation; 3) improve the degradation efficiency by enhancing the bioavailability of pollutants to strengthen the bioremediation effect.
Oilseed rape (Brassica napus L.) is one of the most widely grown oil crops and ranks the top-one edible oil in China. However, a significant proportion of the rapeseed oil in China relies on importation from abroad. In recent years, the planting area of oilseed rape in China continuously decreased and there was a paucity of cultivars which have wide adaption to adverse environment and resistance against a range of diseases. Above all, low seed oil content became a prominent problem. In order to improve rapeseed quality especially the seed oil content and change the passive situation of the country on international edible oil market, reinforcing the fundamental basic on the mechanism of seed oil formation seems necessary. In this review, we highlighted the influence of lipid decomposition during seed maturation on final seed oil content, and the phenomenon that seed oil rapidly decreases after reaching to a peak point about one week before harvest in rainy years. Some aspects, such as the metabolism of fatty acid in seeds, the acquisition of seed dormancy, and the association between post-peak seed oil decomposition and the acquisition of seed dormancy, were well illustrated to clarify the impact of seed dormancy on fatty acid accumulation. Finally, some constructive suggestions referring to the enhancement of rapeseed oil content in breeding practice were discussed.
