Elevated temperature shifts soil N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification across global terrestrial ecosystems.

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta-analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N2 O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N2 O emission demonstrated significant positive relationships with rates of CO2 emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia-oxidizing archaea amoA gene, ammonia-oxidizing bacteria amoA and nirK genes. This study provides the first global-scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.

Long-term nitrogen fertilization decreases bacterial diversity and favors the growth of Actinobacteria and Proteobacteria in agro-ecosystems across the globe.

Long-term elevated nitrogen (N) input from anthropogenic sources may cause soil acidification and decrease crop yield, yet the response of the belowground microbial community to long-term N input alone or in combination with phosphorus (P) and potassium (K) is poorly understood. We explored the effect of long-term N and NPK fertilization on soil bacterial diversity and community composition using meta-analysis of a global dataset. Nitrogen fertilization decreased soil pH, and increased soil organic carbon (C) and available N contents. Bacterial taxonomic diversity was decreased by N fertilization alone, but was increased by NPK fertilization. The effect of N fertilization on bacterial diversity varied with soil texture and water management, but was independent of crop type or N application rate. Changes in bacterial diversity were positively related to both soil pH and organic C content under N fertilization alone, but only to soil organic C under NPK fertilization. Microbial biomass C decreased with decreasing bacterial diversity under long-term N fertilization. Nitrogen fertilization increased the relative abundance of Proteobacteria and Actinobacteria, but reduced the abundance of Acidobacteria, consistent with the general life history strategy theory for bacteria. The positive correlation between N application rate and the relative abundance of Actinobacteria indicates that increased N availability favored the growth of Actinobacteria. This first global analysis of long-term N and NPK fertilization that differentially affects bacterial diversity and community composition provides a reference for nutrient management strategies for maintaining belowground microbial diversity in agro-ecosystems worldwide.

Assessment of Bacterial Communities and Predictive Functional Profiling in Soils Subjected to Short-Term Fumigation-Incubation.

Previous investigations observed that when soil was fumigated with ethanol-free CHCl3 for 24 h and then incubated under appropriate conditions, after the initial flush of CO2 was over, soil organic carbon (SOC) mineralization continued at the same rate as in the non-fumigated soil. This indicates that, following fumigation, the much diminished microbial population still retained the same ability to mineralize SOC as the much larger non-fumigated population. We hypothesize that although fumigation drastically alters the soil bacterial community abundance, composition, and diversity, it has little influence on the bacterial C-metabolic functions. Here, we conducted a 30-day incubation experiment involving a grassland soil and an arable soil with and without CHCl3 fumigation. At days 0, 7, and 30 of the incubation, the bacterial abundances were determined by quantitative PCR, and the bacterial community composition and diversity were assessed via the 16S rRNA gene amplicon sequencing. PICRUSt was used to predict the metagenome functional content from the sequence data. Fumigation considerably changed the composition and decreased the abundance and diversity of bacterial community at the end of incubation. At day 30, Firmicutes (mainly Bacilli) accounted for 70.9 and 94.6 % of the total sequences in the fumigated grassland and arable soil communities, respectively. The two fumigated soil communities exhibited large compositional and structural differences during incubation. The families Paenibacillaceae, Bacillaceae, and Symbiobacteriaceae dominated the bacterial community in the grassland soil, and Alicyclobacillaceae in the arable soil. Fumigation had little influence on the predicted abundances of KEGG orthologs (KOs) assigned to the metabolism of the main acid esters, saccharides, amino acids, and lipids in the grassland soil community. The saccharide-metabolizing KO abundances were decreased, but the acid ester- and fatty acid-metabolizing KO abundances were elevated by fumigation in the arable soil community. Our study suggests functional redundancy regarding the bacterial genetic potential associated with SOC mineralization.

Engineering soil organic matter quality: Biodiesel Co-Product (BCP) stimulates exudation of nitrogenous microbial biopolymers.

Biodiesel Co-Product (BCP) is a complex organic material formed during the transesterification of lipids. We investigated the effect of BCP on the extracellular microbial matrix or 'extracellular polymeric substance' (EPS) in soil which is suspected to be a highly influential fraction of soil organic matter (SOM). It was hypothesised that more N would be transferred to EPS in soil given BCP compared to soil given glycerol. An arable soil was amended with BCP produced from either 1) waste vegetable oils or 2) pure oilseed rape oil, and compared with soil amended with 99% pure glycerol; all were provided with 15N labelled KNO3. We compared transfer of microbially assimilated 15N into the extracellular amino acid pool, and measured concomitant production of exopolysaccharide. Following incubation, the 15N enrichment of total hydrolysable amino acids (THAAs) indicated that intracellular anabolic products had incorporated the labelled N primarily as glutamine and glutamate. A greater proportion of the amino acids in EPS were found to contain 15N than those in the THAA pool, indicating that the increase in EPS was comprised of bioproducts synthesised de novo. Moreover, BCP had increased the EPS production efficiency of the soil microbial community (µg EPS per unit ATP) up to approximately double that of glycerol, and caused transfer of 21% more 15N from soil solution into EPS-amino acids. Given the suspected value of EPS in agricultural soils, the use of BCP to stimulate exudation is an interesting tool to consider in the theme of delivering sustainable intensification.

Interaction between the microbial community and invading Escherichia coli O157:H7 in soils from vegetable fields.

The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G(-)) to Gram-positive (G(+)) bacterial PLFAs (G(-)/G(+) ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G(-)/G(+) ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.

Arsenic species uptake and subcellular distribution in Vallisneria natans (Lour.) Hara as influenced by aquatic pH.

Vallisneria natans (Lour.) Hara, a widely distributed submerged aquatic plant, is a promising species for arsenic (As) removal from contaminated water. We investigated the effects of pH on the accumulation, subcellular distribution and detoxification of As in V. natans. The results showed that the optimum pH for submerged V. natans growth is close to 7.0. The accumulation of As in the plant increased with the increase of pH (p < 0.05). This may have been due to arsenic/phosphate transporters with a higher affinity for the more highly electronegative AsO4 (3-) than for HAsO4 (2-) and H2AsO4 (-). After As(V) was accumulated by plants, more than 80 % was reduced to As(III), but As reduction decreased with increased pH. The majority of accumulated As and reduced As(III) (47 %-66 %) was found in the vacuoles. Higher As concentrations in vacuoles could be considered as an important mechanism for As detoxification in submerged plants.

Metallic micronutrients are associated with the structure and function of the soil microbiome.

The relationship between metallic micronutrients and soil microorganisms, and thereby soil functioning, has been little explored. Here, we investigate the relationship between metallic micronutrients (Fe, Mn, Cu, Zn, Mo and Ni) and the abundance, diversity and function of soil microbiomes. In a survey across 180 sites in China, covering a wide range of soil conditions the structure and function of the soil microbiome are highly correlated with metallic micronutrients, especially Fe, followed by Mn, Cu and Zn. These results are robust to controlling for soil pH, which is often reported as the most important predictor of the soil microbiome. An incubation experiment with Fe and Zn additions for five different soil types also shows that increased micronutrient concentration affects microbial community composition and functional genes. In addition, structural equation models indicate that micronutrients positively contribute to the ecosystem productivity, both directly (micronutrient availability to plants) and, to a lesser extent, indirectly (via affecting the microbiome). Our findings highlight the importance of micronutrients in explaining soil microbiome structure and ecosystem functioning.

Three source-partitioning of CO2 fluxes based on a dual-isotope approach to investigate interactions between soil organic carbon, glucose and straw.

Inputs of available organic materials into soil alter the decomposition of soil organic matter (SOM), a process called priming effect. Organic carbon (C) inputs in terrestrial ecosystems are common from various sources (e.g. rhizodeposits, plant residues, microbial necromass) simultaneously, but their interactions as well as mutual effects on SOM decomposition are unknown because multisource partitioning of pools and fluxes was not available. A dual-isotope approach (identical materials except for straw being possessed two 13C abundances) was adopted to partition total CO2 emission from three C sources: SOM, glucose and straw. Cumulative CO2 efflux was quantified into straw-derived (558 µg C g-1), glucose-derived (480 µg C g-1) and SOM-derived (58 µg C g-1) CO2 during the first 7 days of incubation. Glucose or straw addition induced positive SOM priming, whereas glucose combined with straw resulted in higher SOC loss than that induced by single addition of glucose or straw after day 7. The Spearman's correlation showed that the interactions between glucose and straw shifted from increased CO2 evolved during their intensive decomposition (days 1 to 3) to mutual constraint on mineralization during the late stage (days 5 to 7). This study provides evidences for the suitability of the dual-isotope approach to partition multiple sources of CO2 fluxes and C pools, and evaluates their individual or mutual contributions to SOM priming, thus, implicating C sequestration in terrestrial ecosystems.

Lack of correlation between turnover of low-molecular-weight dissolved organic carbon and differences in microbial community composition or growth across a soil pH gradient.

We studied how soil pH (pHs 4 to 8) influenced the mineralization of low-molecular-weight (LMW)-dissolved organic carbon (DOC) compounds, and how this compared with differences in microbial community structure. The mineralization of LMW-DOC compounds was not systematically connected to differences in soil pH, consistent with soil respiration. In contrast, the microbial community compositions differed dramatically. This suggests that microbial community composition data will be of limited use in improving the predictive power of soil C models.

Changes in microbial community structure due to chronic trace element concentrations in different sizes of soil aggregates.

Studies on the effects of trace elements (TEs) (e.g. Cu, Cd, Zn) on soil microbial communities have provided useful information on the toxicity of TEs to microbes. However, previous studies mainly focused on the effects of TEs on microbial community structure in intact soil, while there are few studies on the impact of TEs on microbial community structure in soil aggregates. In this study, soils previously polluted for 20 years, and now containing low and high TE concentrations derived from, now abandoned, metal smelters were sampled from the surface layer (0-15 cm) of two adjacent Chinese paddy fields. The aim was to determine the effects of TEs on the soil microbial biomass and community structure in different sized soil aggregates. Long-term high TE pollution decreased microbial biomass concentration and species, changed the proportion of bacteria and fungi and decreased the diversity of bacteria in the different sized aggregates. The microbial communities in soil aggregates became clustered with increasing TE concentrations.

Performance and mechanisms for remediation of Cd(II) and As(III) co-contamination by magnetic biochar-microbe biochemical composite: Competition and synergy effects.

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe3O4 biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g-1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation.

Effects of magnetic biochar-microbe composite on Cd remediation and microbial responses in paddy soil.

There is growing global interest in the bioremediation of cadmium (Cd) using combinations of biochar and microorganisms. However, the interactions among biochar, introduced and indigenous microorganisms remain unclear. Accordingly, a 90 day microcosm experiment was conducted to investigate this by adding Bacillus sp. K1 strain inoculated rice straw biochar (SBB) and magnetic straw biochar (MBB) into a Cd contaminated paddy soil from Hunan, China. All treatments were incubated aerobically (60% water holding capacity) or anaerobically for 90 d. During both soil incubations, Bacillus sp. K1 successfully colonized in soil with composites applications. Soil pH was significantly increased from acid to neutral, and available Cd decreased with the addition of both composites. The better remediation efficiency of MBB than SBB under anerobic conditions was attributed to the transformation of acetic acid-extractable Cd into the residual fraction, caused by Cd2+ bonding with crystal Fe3O4. The application of the two kinds of composites caused similar changes to both microbial communities. There was a slight decrease in indigenous microbial alpha diversity with the MBB aerobic application, while the total population number of bacteria was increased by 700%. Both the redundancy analysis and Mantel analyses indicated that pH and microbial biomass C contributed to the colonization of Bacillus sp. K1 with SBB under aerobic conditions, and with MBB under anerobic conditions, respectively. The research provides a new insight into interactive effects and investigates immobilization mechanisms involved of bacterial/biochar composites in anaerobic and aerobic soils.

Response of soil native microbial community to Eschericia coli O157:H7 invasion.

The presence of Eschericia coli O157:H7 in the natural environment is a serious threat to human health. The native microbial community in soil plays an important role in resisting E. coli O157:H7 invasion. This study examined the responses of soil microbial community to E. coli O157:H7 invasion during a 32-day incubation. The E. coli O157:H7 persisted longer in γ-irradiated soil than non-irradiated soil while glucose addition decreased its persistence in the irradiated soil which was associated with an increasing recovery of the native community. The invasion of E. coli O157:H7 increased soil organic carbon mineralization, an indicator of microbial activity, in both non-irradiated and irradiated soils, while glucose addition significantly promoted the carbon mineralization process. The 16S rRNA sequencing data showed the gradual recovery of the native bacterial population including specific taxa such as proteobacteria and actinobacteria following irradiation. It is concluded that soil microbial function and structure can affect persistence of E. coli O157:H7 and that lower biodiversity of the native community favors its persistence.

Maize straw biochar addition inhibited pentachlorophenol dechlorination by strengthening the predominant soil reduction processes in flooded soil.

Biochar has received increasing attention for its multifunctional applications as a soil amendment. The dual effect of biochar on reductive organic pollutants and soil biogeochemical processes under anaerobic environments in parallel has yet to be fully explored. In this study, anaerobic batch experiments were conducted to examine the effect of biochar on both reductive transformation of pentachlorophenol (PCP) and soil redox processes in flooded soil. Compared to biochar-free controls, the reductive dechlorination of PCP was significantly inhibited following biochar addition, with the inhibition degree increased with increasing amount of biochar. Dissimilatory iron and sulfate reduction, as well as the production of methane, were significantly enhanced following biochar addition. The bacterial and archaeal communities showed a functional selection responded to the addition of biochar and PCP, with the core functional groups at the genus level including Dethiobacter, Clostridium, Geosporobacter, Desulfuromonas, Desulfatitalea, and Methanosarcina. These findings indicated that biochar could affect soil microbial redox processes and may act as an electron mediator altering electron distribution from PCP dechlorination to the predominant soil reduction processes, and increase understanding regarding biochar's comprehensive effects on the remediation of natural flooded soil polluted by chlorinated organic pollutants that can be degraded reductively.

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems.

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Contrasting soil pH effects on fungal and bacterial growth suggest functional redundancy in carbon mineralization.

The influence of pH on the relative importance of the two principal decomposer groups in soil, fungi and bacteria, was investigated along a continuous soil pH gradient at Hoosfield acid strip at Rothamsted Research in the United Kingdom. This experimental location provides a uniform pH gradient, ranging from pH 8.3 to 4.0, within 180 m in a silty loam soil on which barley has been continuously grown for more than 100 years. We estimated the importance of fungi and bacteria directly by measuring acetate incorporation into ergosterol to measure fungal growth and leucine and thymidine incorporation to measure bacterial growth. The growth-based measurements revealed a fivefold decrease in bacterial growth and a fivefold increase in fungal growth with lower pH. This resulted in an approximately 30-fold increase in fungal importance, as indicated by the fungal growth/bacterial growth ratio, from pH 8.3 to pH 4.5. In contrast, corresponding effects on biomass markers for fungi (ergosterol and phospholipid fatty acid [PLFA] 18:2omega6,9) and bacteria (bacterial PLFAs) showed only a two- to threefold difference in fungal importance in the same pH interval. The shift in fungal and bacterial importance along the pH gradient decreased the total carbon mineralization, measured as basal respiration, by only about one-third, possibly suggesting functional redundancy. Below pH 4.5 there was universal inhibition of all microbial variables, probably derived from increased inhibitory effects due to release of free aluminum or decreasing plant productivity. To investigate decomposer group importance, growth measurements provided significantly increased sensitivity compared with biomass-based measurements.

Co-transport of phenanthrene and pentachlorophenol by natural soil nanoparticles through saturated sand columns.

Mobile colloids such as nanoparticles (NPs) are often considered to affect the fate and transport of various contaminants by serving as carriers. Many studies have focused on the effect of engineered NPs on contaminant transport. To date, very little information is available on the co-transport of natural soil NPs with typical organic contaminants. This study investigated the co-transport of phenanthrene (PHE) and pentachlorophenol (PCP) by three soil NPs through saturated sand columns. Soil NPs with high organic matter and particle concentration were the most effective in transporting PHE through columns. In addition, soil NPs significantly increased the transport of low-level PHE (0.2 mg L-1) but there was no obvious increase at 1.0 mg L-1 PHE. This is attributed to a higher ratio of NP-associated PHE to total PHE at a low-level than at a high-level during transport. In contrast to PHE, the chemical speciation of PCP determined its mobility, which was highly dependent on solution pH. At pH 6.5, anionic PCP became dominant and soluble in the effluent. This could account for the negligible effect of soil NPs on PCP mobility. At pH 4.0, however, neutral molecular PCP dominated and, as expected, decreased mobility of PCP occurred. Soil NPs considerably enhanced the transport of neutral PCP in NP-associated forms compared to controls, due to the high hydrophobicity and sorption affinity of PCP to NPs. The mobility of soil NPs was little affected by PHE and PCP under tested conditions. This study indicated that highly mobile soil NPs may be effective carriers for organic contaminants and give a new direction to polluted site remediation by using a natural material, e.g., soil.

Soil available phosphorus content drives the spatial distribution of archaeal communities along elevation in acidic terrace paddy soils.

Archaea play crucial roles in geochemical cycles and influence the emission of greenhouse gases in acidic soils. However, little is known about the distribution pattern of total archaeal diversity and community composition with increasing elevation, especially in acidic agricultural ecosystems. Terraces, characterized by vertical climate changes and unique hydrological properties, are "natural experiments" to explore the spatial distribution of microorganisms along elevation in paddy soils. Here we investigated the diversity and structure of soil archaeal communities in nine increasingly elevated acidic paddy soils of the Yunhe terrace, China. Archaeal communities were dominated by Methanomicrobia of Euryarchaeota (38.5%), Group 1.1a-associated cluster (SAGSCG-1) of Thaumarchaeota (22.0%) and Subgroup-6 (previously described as crenarchaeotal group 1.3b) of Bathyarchaeota (17.8%). The archaeal phylotype richness decreased with increasing elevation. Both the species richness and phylogenetic diversity of the archaeal communities were significantly negatively correlated with soil available phosphorus (AP) content according to linear regression analyses. The archaeal communities differed greatly between soils of increasing elevation, and were roughly clustered into three groups, mostly in relation to AP contents. A variation partitioning analysis further confirmed that edaphic factors including the content of AP (17.1%), nitrate (7.83%), soil organic carbon (4.69%), dissolved organic carbon (4.22%) and soil pH (4.07%) shaped the archaeal community. The variation of soil properties were probably induced by elevation. The co-occurrence network indicated a modular structure of the archaeal community. Overall, our results emphasized that soil AP content was the best predictor of archaeal diversity and community structure, and the impacts of elevation on soil archaeal communities were not diminished by long-term rice cultivation, although minor compared with the effects of soil properties.

Remediation of heavy metal contaminated soils by biochar: Mechanisms, potential risks and applications in China.

There are global concerns about heavy metal (HM) contamination in soils, which in turn has produced an increased demand for soil remediation. Biochar has been widely documented to effectively immobilize metals in contaminated soils and has received increasing attention for use in soil remediation. Here, we review recent progresses in understanding metal-biochar interactions in soils, potential risks associated with biochar amendment, and application of biochar in soil remediation in China. These recent studies indicate that: (1) the remediation effect depends on the characteristics of both biochar and soil and their interactions; (2) biochar applications could decrease the mobility/bioavailability of HMs in soils and HM accumulation in plants; and (3) despite its advantages, biochar applications could pose ecological and health risks, e.g., by releasing toxic substances into soils or by inhalation of biochar dust. Research gaps still exist in the development of practical methods for preparing and applying different biochars that target specific HMs. In the future, the long term effects and security of biochar applications on soil remediation, soil organisms and plant growth need to be considered.

Sorption of pentachlorophenol and phenanthrene by humic acid-coated hematite nanoparticles.

Hematite nanoparticles (NPs) exist naturally and ubiquitously in soil, and they are always associated with soil organic matter by forming organic-inorganic complexes. In this work, hematite NPs coated with peat humic acid (HApeat) and soil humic acid (HAsoil) were chosen as sorbents for hydrophobic organic contaminants (HOCs) to simulate the sorption processes in soil. Ionizable pentachlorophenol (PCP) and non-ionizable phenanthrene (PHE) were selected as representative HOCs. Compared with sorption isotherms of uncoated hematite NPs, the coating of HA onto the surface of hematite NPs substantially increased its sorption affinity for PCP and PHE by about 1-2 orders of magnitude, and the increasing degree was positively correlated to the HA content. These phenomena emphasized the dominant role of HA in the sorption process. The reduced polarity and the introduction of functional groups contributed to the enhanced sorption of HOCs on HA-coated hematite NPs. Furthermore, HApeat-hematite NPs showed higher sorption affinity for both PCP and PHE than HAsoil-hematite NPs, which was mainly due to the lower polarity and higher hydrophobicity of HApeat-hematite NPs. The sorption of PCP and PHE on HA-coated hematite NPs was inhibited obviously with increasing pH values and the pH effect on PCP sorption was more significant than that of PHE, due to the deprotonation of functional groups within adsorbed HA, the loose structure of adsorbed HA and the dissociation of PCP. Our findings elucidated the mechanisms involved in HOCs sorption processes by HA-hematite NPs and provided a theoretical basis for environmental remediation with natural NPs (e.g., hematite NPs).