Some Investigators Predict That the Continued Use of Chemical Fertilizer

Table 1 shows that the SOM, AN, AP and AK contents in the rhizosphere soil were the highest in T2 and the lowest in CK of the five different fertilizer treatments on day 15 after anthesis.The SOM, AN, AP and AK contents in the rhizosphere soil were the highest in M-T1 and the lowest in M-CK of the five different fertilizer treatments on day 75 after anthesis.Table 1 Effects of different fertilizer treatments on the properties of grape rhizosphere soil on days 15 and 75 after anthesis.On day 15 after anthesis, the TN, TP and TK contents of grape roots were the highest of the five different fertilizer treatments in T2 and the lowest in CK (Table 2).On day 75 after anthesis, the TN, TP and TK contents in the grape roots of M-CK were the lowest in all treatments, whereas the TN content in grape roots treated with increased organic fertilizer and reduced chemical fertilizer (M-T1, M-T2, and M-T3) were higher than that of M-T0 (P > 0.05), and the difference between M-T0 and M-T3 was not significant (P > 0.05).The contents of TN, TP and TK in grape leaves were the highest of five different fertilizer treatments in M-T2 and the lowest in M-CK.Figure 1 Effects of different fertilizer treatments on the Chao1 and Shannon indexes of bacteria in grape rhizosphere soil on days 15 and 75 after anthesis.Effects of different fertilizer treatments on bacterial communities at the phylum level in grape rhizosphere soil.Proteobacteria, Actinobacteria, Acidobacteria, Gemmatimonadetes and Chloroflexi were the dominant phyla, demonstrating >10% relative abundance in at least one rhizosphere soil sample.The relative abundance of Chloroflexi in T0 was significantly lower than that of CK on days 15 and 75 after anthesis (P < 0.05), and the relative abundance of Chloroflexi in soils treated with increased organic fertilizer and reduced chemical fertilizer (T1, T2, and T3) was significantly lower than that in CK and T0 (P < 0.05) (Table 3).On day 15 after anthesis, the relative abundances of Gemmatimonadetes and Bacteroidetes were the highest in T2 and the lowest in CK in the five different fertilizer treatments.Figure 2 Effects of different fertilizer treatments on bacterial communities at the phylum level on days 15 and 75 after anthesis.Table 3 Effects of different fertilizer treatments on bacterial communities at the phylum level in grape rhizosphere soil.On day 75 after anthesis, the relative abundance of Proteobacteria was highest in M-T2 and lowest in M-CK of the five different fertilizer treatments.Effects of different fertilizer treatments on N and P metabolism-related bacteria in grape rhizosphere soil at the genus level.On day 15 after anthesis, the relative abundance of Nitrospira in T2 was the highest of the five different fertilizer treatments and that in CK was the lowest.Table 4 Effects of different fertilizer treatments on bacteria related to the metabolism of N and P in the grape rhizosphere soil at the genus level.SOM, AN, AP and AK were positively correlated with TN, TP, TK, TN.R, TP.R and TK.R on days 15 and 75 after anthesis (Fig.The Chao1 and Shannon index values and the abundances of Arthrobacter, Pseudomonas, Nitrosopira and Bacillus were negatively correlated with pH and conductivity on days 15 and 75 after anthesis (Fig.The Chao1 and Shannon index values and the abundances of Arthrobacter, Pseudomonas, Nitrosopira and Bacillus were positively correlated with SOM, AN, AP and AK. .

Effects of the continuous use of organic manure and chemical

Effects of the continuous use of organic manure and chemical

This difference could be attributed to the efficiency of OM, which was significantly lower than that of CF; this finding agrees with a previous report18.The removal of P by crops caused the soil available P to constantly decrease under the CK treatment, in which no P was applied.After four consecutive cropping seasons, the balance of soil P was positive under both OM and CF treatments.Moreover, P input was much higher than P output in soil because the application of P fertilizer was far greater than the plant P uptake.Excessive fertilization resulted in a low URP under both the OM and CF treatments, ranging from 4.64 to 5.75% and 9.29 to 12.81%, respectively.The O-P and Ca 10 -P contents were relatively stable in the four-year experiment, which confirmed that the large amount of P fixed in the calcareous soil is responsible for the long-term release of P by pedological processes26.This observation suggested that non-labile P was almost not affected by the excessive addition of fertilizer P. However, a decline in the O-P status of the CK treatment soil was observed because extracellular phosphate enzymes released by plants and microbes facilitate the mineralization of P 0 when the available P concentration of the soil solution is low27.This trend was also reported by Zhang et al.28, who found that the soil P 0 of non-fertilized plots decreased by 14% of the initial value over 5 years of maize production.As shown in Table 6 and compared with data from 2009, the soil organic carbon content increased under the OM treatment and decreased under the CF and CK treatments in 2013, which suggests that the application of OM is necessary to improve the soil organic carbon supply in the vegetable greenhouse.Other studies32 reported no clear change in organic carbon in the soil of rice systems even without fertilizer application, which is mainly due to crop residues remaining in the fields.However, a decreasing pH was observed under the CF treatments due to the heavy application of inorganic N fertilizer, which is common in soil utilized for growing vegetables33.The result suggested that N was an important limiting factor for vegetable growth, particularly under the OM treatments.The lack of available N is a common problem in organic cultivation in China and results in lower crop yields and more P surplus in the soil because there is a much lower N content than P content in OM, and plant N uptake and N losses are also much greater than P losses in the soil. .

The effects of chemical and organic fertilizer usage on rhizosphere

The effects of chemical and organic fertilizer usage on rhizosphere

Inductively coupled plasma mass spectrometry (ICP-MS) and high-throughput sequencing technology analyses were used to investigate heavy metals content and bacterial composition in rhizosphere soils.Our results indicated that organic fertilizer treatment significantly decreased Cu, Pb and Cd contents in rhizosphere soil sample.The results also showed that treatment with organic fertilizer significantly decreased the contents of Cd, Pb and As in tea leaves.https://doi.org/10.1371/journal.pone.0217018 Editor: Fuzhong Wu, Sichuan Agricultural University, CHINA Received: December 13, 2018; Accepted: May 2, 2019; Published: May 28, 2019 Copyright: © 2019 Lin et al.Introduction Camellia sinensis, commonly known as tea plant, is a mountainous crop and an important agricultural product for many farmers in China.Therefore, it is essential to understand the impact of nitrogen fertilizers beyond their effects on crop yield in order to achieve a balance between benefits and harms in modern agricultural practices.The potential benefits of organic fertilizers have been documented in a number of studies in which investigators observed a raise in soil microbial activities, which in turn improved crop growth and restrained pests and diseases [6–7].Moreover, the effects of long-term use of organic fertilizer on rhizosphere bacterial composition and heavy metals in tea gardens have not been carefully investigated.In this study, we have used ICP-MS and high-throughput sequencing technology to determine the effects of organic and chemical fertilizers on bacterial taxa and heavy metals content in the rhizosphere of tea orchards.Materials and methods Field experiment and soil sampling The experimental station is located in the Zudun township of Nanping in the Fujian Province of China (27°24ʹN, 118°33ʹE).Tea polyphenols and caffeine contents were determined using a Waters HPLC system (C18 column: Inertsil ODS-SP, 4.6 × 250 mm, 5 μm).TN, TP, and TK were determined using Kjeldahl digestion, sodium carbonate fusion, and NaOH melts flamer methods, respectively [18].AP was extracted with hydrochloric acid and ammonium fluoride, and contents were measured using the molybdenum blue method.The contents of these metals were determined by Inductively coupled plasma mass spectrometry (ICP-MS, PerkinElmer NexION 300X, U.S.A), using parameters listed in Table 1.The PCR reactions were conducted in a 50 μL mixture system, using TransStart Fastpfu DNA Polymerase (TransGen Biotechnology, Beijing, U.S.A).Differences among the treatments were calculated and statistically analyzed using the analysis of variance (ANOVA) and the LSD multiple range tests (p < 0.05).In order to prevent food shortage worldwide and maximize crop yield, large amounts of chemical fertilizers have been applied to arable fields over the past few decades [29–30].Furthermore, our data showed that organic fertilizer treatment improved soil pH, and increased the contents of tea polyphenols and amino acids.The future research should focus the potential mechanism of intrinsic linkages between microbial community and heavy metal under the organic fertilizer treatments.Our data are in agreement with the findings of Sun et al. [29], who reported that the NPK chemical fertilizers caused a significant decrease in bacterial diversity.Significant differences in soil bacterial composition were also observed in tea orchards under long-term treatment with chemical or organic fertilizers.Further analysis showed that Acidothermus, Acidobacterium and Acidicaldus, increased significantly in soil samples treated with chemical fertilizer, which are acidophilic and capable of proliferating in an acidic environment.Our previous study have shown the plant–microbe interactions contribute to the increased acidity and create a new environment to mediate changes in the microbial community structure in the R.

pseudostellariae rhizosphere under continuous monoculture regimes [46].Positive plant-soil feedback depends on beneficial interactions between plant roots and microorganisms for growth promotion, nutrient acquisition and disease suppression [4].Nitrospira is a ubiquitous bacterium that has a role in the nitrogen cycle by performing nitrite oxidation in the second step of nitrification [51–52].These results suggested that organic fertilizer could improve the soil environment to create a new condition for the growth of potentially beneficial microbes.Our findings suggest that organic fertilizer can shape microbial composition and recruit beneficial bacteria into the rhizosphere of tea. .

Chemical Fertiliser - an overview

In medieval Europe, between one-third and one-half of the arable land was left fallow.Spreading animal manures in the field, as well as inclusion of leguminous crops, helped to add nitrogen, a principal nutrient, to the soil.Consequently, yields began to decline.Necessity impelled the development of artificial fertilizers, which are chemical substances containing, in forms readily available to plants, the elements that improve the growth and productivity of crops.The three major nutrient elements that a crop needs are nitrogen, phosphorus, and potassium.Lawes later founded the world's first agricultural experiment station on his own estate of Rothamsted, not far from London. .

Long-term impact of fertilization on soil pH and fertility in an apple

At present, N utilization rate has reached 400 to 600 kg ha -1 in apple orchards in China with an annually increasing trend ( Hao et al. 2012 ).Excessive N fertilizer application might not only decrease the N utilization efficiency and the agricultural production benefits, but also lead to negative impact on soil quality and nitrate pollution in groundwater and surface waters ( Ju et al., 2006 ).At the end of October in each year, apple fruits were harvested, we also recorded the FW in each tree in the three N application treatments, and sampled and analyzed the total N content.Winter pruning was carried out in December-January, the branches mass removed per tree was recorded, and a subsample was taken, dried, and stored for total N content analysis.In agricultural ecosystems, crop uptake of base cations (i.e., Na + , K + , Mg 2+ , and Ca 2+ ) and anions (H 2 PO 4 - and SO 4 2- ) can be considered as the dominant source of acidity and alkalinity, respectively ( Equation 1 , 2 , and 3 ) ( Barak et al., 1997 ; Guo et al., 2010 ), assuming that the uptake and removal of these ions from soil leave an equivalent H + or OH - in the soil:.Considering the four biochemical processes (N cycling, uptake of BCs, P, and S), the net H + production was calculated in the three N fertilization treatments ( Figure 4 ).After 28 years, the soil pH in CK, NPK and NPKM treatments were 0.16, 1.04 and 0.74 units lower than the initial value in 1988.Although SOC and TN concentration increased in all treatments, soil C/N ratio decreased compared to control ( Figure 1 ).N fertilizer may increase both the amount of crop residue and the N concentration; the latter would likewise influence its rate of mineralization (Chen et al., 2010).In our experiment, with the prolonged fertilizing time, the content of SOC and TN significantly increased, but the soil C/N ratio decreased.Our research also showed that soil available nutrient (AN, AP, and EK) concentration were significantly affected by different fertilization treatments.Although fertilization significantly increased the soil available nutrient concentrations, continuous high fertilizer input may bring about many negative impacts, such as: 1) excess nutrients entering into the deep soil along with rain or irrigation and, thus, influencing the safety of groundwater (Ju et al., 2006); and 2) the higher AK content in soil may affect the absorption of calcium and lead to calcium deficiency and bitter pit, which frequently occurs in this apple production area (Milošević and Miloševi, 2015).Some studies demonstrated that the soil pH was decreased to a certain extent with different fertilizer treatments, and the annual decline rate was from 0.01 to 0.07 units (Daugelene and Butkute, 2008; Zhang et al., 2009).Through the three-year experiment from 2012 to 2014, further analysis shows that the recent soil acidification in China's apple orchards resulted mainly from high-N fertilizer inputs.However, this is rather low compared with China's greenhouse vegetable systems (220 kmol H+ ha-1 y-1, N fertilizer rates above 4000 kg N ha-1 y-1 with N use efficiencies below 10%) (Guo et al., 2010).Increasing N fertilizer applications have been a major management technique thought to drive high fruit yield.At the current fertilization levels (～900 kg N hm2), approximately 64.8 tons of dry biomass (fruit, pruned branches, and fallen leaves) are harvested annually in the apple systems, leading to an estimated H+ production rate by the BCs uptake of 41.4 kmol ha-1 y-1. .

Fifteen-Year Application of Manure and Chemical ...

Fifteen-Year Application of Manure and Chemical ...

High-throughput quantitative PCR and sequencing technologies were employed to assess the effects of long-term manure or chemical fertilizer application on the distribution of ARGs and microbial communities.In addition, manure application increased the abundance of mobile genetic elements (MGEs), which were significantly and positively correlated with most types of ARGs, indicating that horizontal gene transfer via MGEs may play an important role in the spread of ARGs.Furthermore, the application of manure and chemical fertilizers significantly affected microbial community structure, and variation partitioning analysis showed that microbial community shifts represented the major driver shaping the antibiotic resistome.Taken together, our results provide insight into the long-term effects of manure and chemical fertilization on the dissemination of ARGs in intensive agricultural ecosystems.The increasing dissemination and propagation of antibiotic resistance genes (ARGs) in various environments has aroused great concern worldwide (Zhu et al., 2013; Fahrenfeld et al., 2014) and might threaten antibiotic effectiveness and public health in the 21st century (Berendonk et al., 2015).China is the largest consumer of antibiotics in the world, with a total usage of approximately 162 kt in 2013, and half of the total antibiotics consumed in China were used to treat animal diseases and promote animal growth (Zhang et al., 2015).The overuse of antibiotics in modern livestock husbandry has been proven to be a potential key driver of the expansion of environmental ARG reservoirs (Boxall et al., 2003; Brandt et al., 2009).Indeed, prior studies have demonstrated that manure is an important reservoir of antibiotic-resistant bacteria (ARB), ARGs and mobile genetic elements (MGEs) (Heuer et al., 2011; Su et al., 2014; Udikovic-Kolic et al., 2014; Chen Q. et al., 2016).Importantly, horizontal gene transfer (HGT) by MGEs can promote the ready dissemination of ARGs among microbial communities (Xie et al., 2018a).Furthermore, previous studies assumed that environmental ARGs could be transferred into the food chain through HGT mechanisms, creating great risks to human health (Berendonk et al., 2015; Wang et al., 2015).The excessive use of chemical fertilizers in this region has caused serious negative environmental effects, such as soil acidification, ammonia volatilization, and nitrate contamination in groundwater (Chen et al., 2018; Wang et al., 2018).Applying organic manure to replace some amount of conventional chemical fertilizer has been proven to be an effective approach on the NCP with respect to crop yield and soil carbon and nitrogen stocks (Gai et al., 2018).Moreover, ARGs were observed to be stable in the microbial community of a soil that regularly received manure application (Heuer and Smalla, 2007).In addition, chemical fertilizer application can induce significant changes in soil properties and microbial communities (Wang et al., 2018; Xie et al., 2018b).Therefore, the importance of investigating and controlling ARGs and microbial communities in agricultural soils cannot be understated.However, only a few studies to date have systematically assessed the distribution and transport of ARGs in soil under long-term manure and chemical fertilizer application.In the present study, high-throughput quantitative PCR technology combined with high-throughput sequencing technology was employed to explore the influence of the application of chemical fertilizer and pig manure on the resistome profile, MGEs, and microbial communities of soil.This study contributes to a better understanding of the dissemination and persistence of soil ARGs caused by manure application and chemical fertilization.The long-term field experiment was set up in 2001 at the Luancheng Ecological Station, Hebei Province, China (37°53'N, 114°41'E) with a winter wheat-summer maize rotation.Detailed information about the experimental design and the fertilization scheme is shown in Supplementary Figures S1, S2, respectively.Fresh manure was applied as a base fertilizer to the agricultural soil in the M and MN treatments before wheat sowing every year (early October).Sampling occurred in the winter, when the wheat plants were small and had basically stopped growing.Briefly, soil organic matter (OM) was determined using the K 2 Cr 2 O 7 oxidation method.Soil available phosphorus (AP) was extracted with 0.5 M NaHCO 3 and determined using the molybdenum blue method.Available potassium (AK) was extracted with 1 M ammonium acetate and measured using flame photometry (ZEENIT®700P, Analytik Jena AG, Germany).The quality and quantity of the extracted DNA were examined using a Nanodrop spectrophotometer (NanoDropTM One, Thermo Fisher Scientific, United States).The relative abundance of each ARG/MGE was calculated using a formula from a previous study (Chen Q.

et al., 2016): relative gene abundance = 10 ( ( 31 - C ⁢ t ( t ⁢ a ⁢ r ⁢ g ⁢ e ⁢ t ) ) / ( 10 / 3 ) ) 10 ( ( 31 - C ⁢ t ( 16 ⁢ s ) ) / ( 10 / 3 ) ) , where Ct (target) and Ct ( 16 S) referred to the threshold cycles of the ARGs/MGEs and the 16S rRNA gene, respectively.Fold changes were calculated to illustrate the enrichment of soil ARGs under the application of manure or chemical fertilizers according to a previous study (Wang et al., 2014b).Genes were regarded as statistically enriched compared with the CK treatment if the range calculated by two standard deviation of the mean fold change was entirely >1.To depict bacterial communities, the 341F/785R primer pair was used to amplify the V3-V4 region of the 16S rRNA gene (Yasir et al., 2015).The clean data generated were analyzed using Quantitative Insights Into Microbial Ecology (QIIME) software.Operational taxonomic units (OTUs) were determined at the 97% similarity level using the UCLUST program (Edgar, 2010).The sequencing data were deposited in the European Nucleotide Archive database under accession number PRJEB29291.In this study, the long-term application of chemical fertilizers (N, NP, and NPK) significantly reduced soil pH (P < 0.05), while the increases in the soil OM, TC, TN, and AP were not significant (except that of AP in the NP and NPK treatments).Compared to the chemical fertilizer treatments, the application of manure fertilizer significantly decreased the pH and the C/N ratio and increased the concentrations of OM, TC, TN, AK, and AP (P < 0.05) (Supplementary Table S1).The total relative abundance of ARGs was 1.31 (±0.21) copies/16S rRNA gene copies in the PM (Supplementary Table S3).The 114 ARGs detected in soil samples potentially encoded resistance to major types of antibiotics, including multidrug antibiotics (18%), MLSB (18%), aminoglycoside (16%), beta_lactamase (17%), tetracycline (15%), FCA (fluoroquinolone, quinolone, florfenicol, chloramphenicol and amphenicol) (3%), vancomycin (6%), and sulfonamides (4%) (Supplementary Figure S3A), covering three major resistance mechanisms: antibiotic deactivation (39%), efflux pump (31%) and cellular protection (27%) (Supplementary Figure S3B).Compared with the CK and chemical-fertilized treatments, manure application significantly increased the ARG abundance, with total relative abundances of ARGs in the M and MN of 0.13 (2.6 times) and 0.23 (4.6 times) copies/16S rRNA gene copies, respectively (Figure 2B).FCA, fluoroquinolone, quinolone, florfenicol, chloramphenicol, and amphenicol; MLSB, macrolide-lincosamide-streptogramin B; MGEs, mobile genetic elements.(A) Venn diagram illustrating the ARGs shared by the CK, N, NP, and NPK treatments.(C) Venn diagram illustrating the ARGs shared by the CK, M, and MN treatments and PM.(D) The relative abundance of ARGs shared among the CK, M, and MN treatments and PM.The PCoA based on Bray-Curtis distance showed that the ARG distributions in the CK treatment and fertilized soil samples were separated (Supplementary Figure S4B).In addition, the changes in soil properties caused by fertilization might contribute to the structural variances in ARGs.RDA showed that the selected soil properties explained a total of 47.9% of the structural variance in ARGs.Among them, the pH and the C/N ratio were negatively correlated with the abundance of ARGs in soil, whereas other soil properties, such as TC, OM, TN, AK, and AP, were positively correlated with ARG abundance (P < 0.05) (Supplementary Figure S6).The total enrichment of ARGs in fertilized soils displayed marked differences, ranging from 482.1-fold (NP) to 3574.9-fold (MN) compared with the CK treatment (Figure 4).Genes encoding resistance to aminoglycoside, multidrug and tetracycline were the three most dominant types of ARGs in the fertilized treatments.The distribution of each ARG subtype in fertilized soils determined using Circos software (http://circos.ca/).Numbers on the outer ring represent the percentages of ARG subtypes in each fertilization treatment.Additionally, the total relative abundance of MGEs was significantly correlated with the total relative abundances of aminoglycoside (r = 0.89, P < 0.001), beta_lactamase (r = 0.59, P < 0.05), FCA (r = 0.64, P < 0.01), MLSB (r = 0.79, P < 0.001), sulfonamide (r = 0.92, P < 0.001), tetracycline (r = 0.93, P < 0.001), and vancomycin (r = 0.56, P < 0.05) resistance genes, based on Pearson's correlation analysis (Figure 5B).Differences in the composition of microbial communities among the CK, manure-fertilized and chemical-fertilized treatments were also clearly identified (Supplementary Figure S11).The soil properties, i.e., TC, TN, OM, AK, AP, pH, and C/N ratio, were important factors in the separation of the microbial communities, explaining a total of 35.9% of the structural variance in the microbial community (Supplementary Figure S12).Network analysis was performed to illustrate the correlations between ARG subtypes and bacterial taxa (at the family level).The resulting network was composed of 52 nodes and 196 edges, including 28 unique ARG subtypes, 1 intI1 gene, and 23 families (Figure 6).These 23 bacterial taxa were affiliated with the phyla Bacteroidetes, Actinobacteria, Proteobacteria, Planctomycetes, and Firmicutes and had strong correlations with various ARGs (Spearman's r2 > 0.36, P < 0.01).In addition, other families, such as Nocardioidaceae, Sphingomonadaceae, and Pirellulaceae, also had significant correlations with diverse ARGs (P < 0.01) (Figure 6).Edges are dependent on the coefficient values, and node size is weighted based on the relative abundance of ARGs/bacterial taxa.Redundancy analysis was employed to evaluate the relationships among the microbial community, soil properties, and ARGs (Figure 7A).Three phyla (Actinobacteria, Planctomycetes, and Gemmatimonadetes) exhibited significant correlations with ARGs in soil (P < 0.05).In addition, VPA was applied to explore the effects of the microbial community, MGEs, and soil properties on the distribution of ARGs (Figure 7B) and illustrated that the microbial community, MGEs and soil properties contributed to 27.6, 7.1, and 9.9% of the ARG variation, respectively.(A) Redundancy analysis (RDA) revealing correlations among ARGs, main phyla taxa (>1% in any sample) and soil properties.After 15 years of continuous manure amendment, the diversity and abundance of ARGs were significantly increased in manure-fertilized soil (Figure 2), and the antibiotic deactivation and efflux pump mechanisms were the two most dominant resistance mechanisms (Supplementary Figure S3).The PCoA also showed that manure application influenced the ARG composition (Supplementary Figure S4).Previous studies have shown that manure application correlates with the emergence and proliferation of ARGs in indigenous microbiota (Su et al., 2014; Chen Q. et al., 2016).This may have been caused by the introduction of new types of ARGs and ARB from animal manure (Heuer et al., 2011; Chen et al., 2017; Pu et al., 2018) or by selection pressure forced by antibiotics, heavy metals and disinfectants in the manure-fertilized soils (Knapp et al., 2010; Su et al., 2014; Udikovic-Kolic et al., 2014; Xie et al., 2018a).Moreover, as indicated by the network analysis, genes that encoded resistance to different types of antibiotics were placed in the same module (Supplementary Figure S8); they might change and transfer together under the selection pressure imposed by manure application because these ARGs may be located on the same DNA fragment or in the same host bacterium (Qian et al., 2018).The variation in the ARG profile between chemical fertilization treatments and the CK treatment was likely caused by alterations in the soil properties and the microbial community composition, including ARB already in the soil (Forsberg et al., 2014; Xie et al., 2018b).The existence of ARGs in unfertilized soil has traditionally been explained by the presence of antibiotic producers that harbor genes to protect themselves from these secondary metabolites (Heuer et al., 2011).Previous studies have also shown that antibiotic resistance is an ancient phenomenon, as confirmed by the detection of ARGs in permafrost sediments (D'Costa et al., 2011), pristine forests (Zhu et al., 2013; Wang et al., 2014a), and the Tibetan environment (Chen B.

et al., 2016).Only manure amendment dramatically increased the relative abundance of MGEs in soil, while chemical fertilizer did not (Figure 5), indicating that MGEs originating from manure-derived bacteria could be established well in manured soils (Heuer et al., 2011).HGT of ARGs via MGEs, such as integrons, transposons, interactive conjugative elements and plasmids, from manure to soil microbes is a potential pathway for the spread and propagation of ARGs (Stokes and Gillings, 2011) since some of the bacteria from manure might not be well adapted to soil and may only survive from weeks to months in the environment (Heuer et al., 2011).A previous study demonstrated that ARGs could undergo "mobilization" when they appeared on MGEs (Stokes and Gillings, 2011).The Soil Microbial Community Is the Main Driver Shaping ARG Profiles.In this study, the five most abundant phyla in soils, Proteobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Firmicutes, were assumed to be possible bacterial hosts for ARGs, as revealed by the network analysis (Figure 6).These bacterial phyla have been recognized as important hosts for ARGs that encode resistance to multiple antibiotics in metagenomics analysis (Forsberg et al., 2014).A previous study demonstrated that manure application could induce a significant selective advantage for ARGs affiliated with the Micromonosporaceae family (Xiong et al., 2018).Another study showed that the genera Bacillus and Mycobacterium were possible bacterial pathogen hosts of ARGs that were enriched in a tetracycline-added soil treatment (Xia et al., 2019).Therefore, since these ARB could readily grow there, their eventual antibiotic exposure would be much more likely to contribute to the selection pressure for resistance during environmental dissemination.A pronounced difference in the diversity and structure of the microbial community was found between the manure-fertilized soils and the CK and chemical-fertilized treatments (Supplementary Figure S10).Multiple factors could result in this phenomenon, such as plant species, root growth, exudate production, and soil properties (Chaparro et al., 2014; Wang et al., 2015).Importantly, the variation in the microbial community played the main role in causing the shifts in the antibiotic resistome, rather than soil properties or MGEs (Figure 7B), since to the extent of the manure application, all soil microbes would have been exposed to selection for the resistance and mobilization of ARGs (Su et al., 2015; Chen Q. et al., 2016; Han et al., 2018).Previous studies have demonstrated that microbial community structure is closely related to the ARGs harbored in different environments (Forsberg et al., 2014; Johnson et al., 2016; Xie et al., 2018b).In addition, soil has been deemed an important reservoir of ARGs due to its complex microbial community and diverse antibiotic-producing microbes (Su et al., 2014), and the establishment of ARGs in the soil microbial community can be promoted by the periodic addition of manure (Heuer and Smalla, 2007).In summary, this study demonstrated that long-term manure application markedly enhanced the abundance and diversity of ARGs that encode resistance to a variety of antibiotics, such as aminoglycoside and tetracycline.FW, WH, and SC collected the soil samples and performed the laboratory measurements and data analysis.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.We would like to thank Prof. Yongguan Zhu, Prof. Jianqiang Su, Prof.

Xiaofang Li, Prof. Zheng Chen, and Dr.

Ruibo Sun for their constructive suggestions on this manuscript.Increased pollution-induced microbial community tolerance to sulfadiazine in soil hotspots amended with artificial root exudates.Metagenomic analysis revealing antibiotic resistance genes (ARGs) and their genetic compartments in the Tibetan environment.Long-term field application of sewage sludge increases the abundance of antibiotic resistance genes in soil.Tetracycline antibiotics: mode of action, applications, molecular biology, and epidemiology of bacterial resistance.Effect of manure application on abundance of antibiotic resistance genes and their attenuation rates in soil: field-scale mass balance approach.Long-term benefits of combining chemical fertilizer and manure applications on crop yields and soil carbon and nitrogen stocks in North China Plain.Antibiotic resistance genes and associated bacterial communities in agricultural soils amended with different sources of animal manures.Manure and sulfadiazine synergistically increased bacterial antibiotic resistance in soil over at least two months.Structural and functional response of the soil microbial community to application of manure from difloxacin-treated pigs.Metagenomic and network analysis reveal wide distribution and co-occurrence of environmental antibiotic resistance genes.The prevalence of integrons as the carrier of antibiotic resistance genes in natural and man-made environments.Co-occurrence of resistance genes to antibiotics, biocides and metals reveals novel insights into their co-selection potential.BMC Genomics 16:964. doi: 10.1186/s12864-015-2153-5 PubMed Abstract | CrossRef Full Text | Google Scholar.Diversity, abundance, and persistence of antibiotic resistance genes in various types of animal manure following industrial composting.Prevalence of erm genes encoding macrolide-lincosamide-streptogramin (MLS) resistance among clinical isolates of Staphylococcus aureus in a Turkish university hospital.High throughput profiling of antibiotic resistance genes in urban park soils with reclaimed water irrigation.Effects of tetracycline residuals on humification, microbial profile and antibiotic resistance genes during vermicomposting of dewatered sludge.Application of manure containing tetracyclines slowed down the dissipation of tet resistance genes and caused changes in the composition of soil bacteria.Exploring variation of antibiotic resistance genes in activated sludge over a four-year period through a metagenomic approach.Comprehensive evaluation of antibiotics emission and fate in the river basins of China: source analysis, multimedia modeling, and linkage to bacterial resistance.Plasmid metagenome reveals high levels of antibiotic resistance genes and mobile genetic elements in activated sludge. .

Inorganic Fertiliser - an overview

Manure and inorganic fertilizer are the principal sources of agricultural nitrogen that are easiest to document and compare globally.The most outstanding feature in these data is the dramatic increase of fertilizer in Asia since the 1970s, although Western Europe currently uses the largest unit-area amount on cropland.In North America, Asia, Western and Eastern Europe, approximately twice as much nitrogen comes from inorganic fertilizer compared to manure.If the trend of increasing size of livestock operations is global, there may be an accompanying trend of increasing nitrogen contamination of groundwater from both point sources of manure storage systems and non-point sources of manure disposal on fields near large livestock facilities.The processes in agricultural systems that generate nitrate support both plant growth and water contamination.Immobilization by soil microorganisms may be offset by the opposing process of mineralization, both of which generally occur continuously (Keeney, 1986). .

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