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Aims: Terrestrial carbon (C) sequestration is derived mainly from plant photosysthetically-fixed C deposition but soil organic C (SOC) content in saline soils is generally low due to low deposition of C from restricted plant growth. It is important to explore the effects of soil salinity on the allocation of photosynthetically-fixed C to better understand C sequestration in saline wetland soils. Methods: We conducted a pot experiment in which reed ( Phragmites australis) was grown in a low salinity (LS) soil and a high salinity (HS) soil from the Yellow River Delta under flooded conditions. The allocation of photosynthetically-fixed C into plant tissues, SOC, dissolved organic C (DOC), microbial biomass C (MBC), particulate organic C (POC), and mineral-associated organic C (MAOC) was determined using a C pulse-labeling method after four labeling events during the 125-day-long reed growing season and destructive sampling immediately at the end of six hours of pulse labeling (end 6-h) and on the final harvest day (final day). Results: In most cases soil salinity, reed growth stage, or reed biomass significantly ( P < 0.05) affected the deposition of photosynthetically-fixed C into the plant-soil system. At all four pulses at end 6-h the high salinity soil had significantly ( P < 0.05) lower percentage net assimilated C in the roots and significantly higher ( P < 0.05) percentage net assimilated C in the soil than did the low salinity soil. At both end 6-h and on the final day the high salinity soil had significantly ( P < 0.05) lower SOC, and significantly ( P < 0.05) higher DOC/SOC ratio than the low salinity soil except for pulses 3 and 4 on the final day. The majority of photosynthetically-fixed C in soil was deposited into MAOC pools and >80 % of deposited SOC was present as MAOC in the high salinity soil due to its significantly ( P < 0.05) higher clay content compared with the low salinity soil. Conclusions: Soil salinity affected the allocation of photosynthetically-fixed C in the plant-soil system, and soil texture altered the allocation of rhizodeposition C in different soil particles. [ABSTRACT FROM AUTHOR]

A comprehensive synthesis of 32 long-term experiments in China is performed by comparing yields and SOM contents and their time by nutrient management responses (TNMR) to determine whether and to what extent combined application of organics amendments and fertilizers (organics + fertilizers) can increase productivity and soil organic matter (SOM) content and enhance the sustainability of diverse cropping systems. TNMR is defined as percentage changes over time in yields and SOM contents in external nutrient input treatments relative to initial and control plots and represents the net effects of nutrient management strategies on yields and SOM contents. Organics + fertilizers significantly increased yields over three crops (wheat, maize and rice) on average by 29% relative to sole organics and 8% to fertilizer only. Higher TNMR values in yields were found with organics + fertilizers in the sequence wheat (53%) > maize (40%) > rice (8%). Significant and positive time trends in TNMR of organics + fertilizers in wheat and maize yield may imply enhanced sustainability of cropping systems. Addition of organics (alone or combined with fertilizers) increased SOM contents and their TNMR over fertilizers applied alone. However, benefits varied between organics and organics + fertilizers by land use type. The latter led to higher SOM contents than (for dry land) and similar to the former (for dry-flooded and flooded systems). 2.3 and 1.4 times higher TNMR of organics + fertilizers in SOM content in dry land than dry-flooded and flooded systems implies that dry land was more responsive in SOM content increase upon adoption of organics + fertilizers than the latter. Overall, despite variation in the quantitative magnitude in crop or land use type, compared with application of organics or fertilizers only, a combination of both represents the most effective way to produce more food, build up SOM and enhance sustainability, especially in dry land cropping systems. [ABSTRACT FROM AUTHOR]

A solvent extraction method coupled to high-performance liquid chromatography with tandem mass spectrometry detection (HPLC–MS/MS) was developed and validated for the simultaneous determination of soil diphenylarsinic acid (DPAA) and phenylarsinic acid (PAA). Several extraction solvents were evaluated with respect to the degree of soil extract-induced matrix effects and the recovery values for DPAA and PAA in the four studied soil matrices. Validation data showed that solvent extraction had a negligible impact on the accurate quantification of DPAA. In contrast, only with disodium hydrogen phosphate extraction did the method give both limited matrix effects (102–107%) with a coefficient of variation < 3% ( n = 4) and efficient recoveries (77–109%) at two spiking levels (20 and 50 mg kg − 1 ) for PAA. The selection of an appropriate extractant was the approach to reduce matrix effects while guaranteeing satisfactory recoveries of soil DPAA and PAA. Chromatographic separation was completed in 37 min and the analytes were detected in positive mode using selected reaction monitoring. MS/MS operating conditions were optimized for both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources. Under optimal conditions the detection limit was 0.01 and 1.00 μg L − 1 for DPAA and PAA. The method detection limits (MDLs) obtained ranged from 2.52 to 3.42 μg kg − 1 for DPAA and from 0.23 to 0.33 mg kg − 1 for PAA depending on the soil types, and the intraday and interday precision was less than 5% for both analytes at two different concentrations. The method was successfully applied for the simultaneous determination of DPAA and PAA in one-month aged soils, satisfactory recoveries (> 74.03%) were obtained for both analytes. The results show that the proposed solvent extraction method coupled to HPLC–MS/MS analysis can provide accurate and reliable determinations of DPAA and PAA in soil samples. [ABSTRACT FROM AUTHOR]

Plastic film mulching has played an important role in Chinese agriculture, especially in vegetable production, but large amounts of film residues can accumulate in the soil. The present study investigated the effects of plastic film residues on the occurrence of soil PAEs and microbial activities using a batch pot experiment. PAE concentrations increased with increasing plastic film residues but the soil microbial carbon and nitrogen, enzyme activities and microbial diversity decreased significantly. At the end of the experiment the PAE concentrations were 0–2.02 mg kg −1 in the different treatments. Soil microbial C and N, enzyme activities, AWCD value, and Shannon-Weaver and Simpson indices declined by about 28.9–76.2%, 14.9–59.0%, 4.9–22.7%, 23.0–42.0% and 1.8–18.7%, respectively. Soil microbial activity was positively correlated with soil PAE concentration, and soil PAE concentrations were impacted by plastic color and residue volume. Correlations among, and molecular mechanisms of, plastic film residues, PAE occurrence and microbial activity require further study. [ABSTRACT FROM AUTHOR]

Diphenylarsinic acid (DPAA) is a major contaminant in environments polluted by chemical weapons and abandoned after World Wars I and II and poses high risks to biota but remediation methods for this contaminant are rare. Here, the photodegradtion of DPAA was studied under high-pressure Hg lamp irradiation. DPAA was degraded completely into inorganic arsenic species in 30 min under UV-C irradiation. The photodegradation of DPAA depended mainly on its direct photolysis through excited-state DPAA. By contrast, the generation of 1 O 2 during the photodegradation of DPAA was confirmed by electron paramagnetic resonance (EPR) studies, but 1 O 2 had little effect on the photodegradation of DPAA. Phtotodegradation of DPAA was also studied in soil leachates and groundwater and the photolytic rate of DPAA was controlled by the total organic carbon (TOC) content in soil leachates and by the NO 3 − concentration in groundwater. Finally, studies on the effects of common solutes on the photodegradation of DPAA show that Cl − can increase the photolytic rate of DPAA by prolonging the lifetime of excited-state DPAA. Moreover, NO 3 − , NO 2 − , and humic acid (HA) can decrease the photolytic rate of DPAA by suppressing the production of excited-state DPAA. This research shows the detailed mechanism of DPAA photodegradation and provides a new and effective method for DPAA decontamination. [ABSTRACT FROM AUTHOR]

Adsorption by minerals is a common geochemical process of dissolved organic matter (DOM) which may induce fractionation of DOM at the mineral-water interface. Here, we examine the molecular fractionation of DOM induced by adsorption onto three common iron oxyhydroxides using electrospray ionization coupled with Fouriertransform ion cyclotron resonance mass spectrometry (ESI-FT-ICRMS). Ferrihydrite exhibited higher affinity to DOM and induced more pronounced molecular fractionation of DOM than did goethite or lepidocrocite. High molecular weight (>500 Da) compounds and compounds high in unsaturation or rich in oxygen including polycyclic aromatics, polyphenols and carboxylic compounds had higher affinity to iron oxyhydroxides and especially to ferrihydrite. Low molecular weight compounds and compounds low in unsaturation or containing few oxygenated groups (mainly alcohols and ethers) were preferentially maintained in solution. This study confirms that the double bond equivalence and the number of oxygen atoms are valuable parameters indicating the selective fractionation of DOM at mineral and water interfaces. The results of this study provide important information for further understanding the behavior of DOM in the natural environment. [ABSTRACT FROM AUTHOR]

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulatorSedum plumbizincicola (S. plumbizincicola)was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment “S. plumbizincicolaintercropped with maize” was higher than inS. plumbizincicolamonocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha−1gave the maximum rate. These results indicated thatS. plumbizincicolaat an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction. [ABSTRACT FROM AUTHOR]

The widespread and increasing application of chlorothalonil (CTN) raises concerns about its non-target impacts, but little information is available on the effect of CTN on the key functional genes related to soil nitrogen (N) cycling, especially in the case of repeated applications. In the present study, a microcosm incubation was conducted to determine CTN residues and the impacts on the abundances of key functional genes related to N cycling after repeated CTN applications. The results demonstrated that repeated CTN applications at the recommended application rate and five times the recommended rate led to the accumulation of CTN residue in soil at concentrations of 5.59 and 78.79 mg kg − 1 , respectively, by the end of incubation. Real time PCR (RT-PCR) revealed that repeated CTN applications had negative effects on the chi A and apr A gene abundances. There were significantly negative correlations between CTN residues and abundances of AOA and AOB genes. In addition, the abundances of key functional genes involved in soil denitrification were declined by repeated CTN applications with the sole exception of the nos Z gene. This study suggests that repeated CTN applications could lead to the accumulation of CTN residue and generate somewhat inconsistent and erratic effects on the abundances of key functional genes related to soil N cycling. [ABSTRACT FROM AUTHOR]

Diphenylarsinic acid (DPAA) is formed during the leakage of arsenic chemical weapons in sites and poses a high risk to biota. However, remediation methods for DPAA contaminated soils are rare. Here, the photocatalytic oxidation (PCO) process by nano-sized titanium dioxide (TiO 2 ) was applied to degrade DPAA in soil. The degradation pathway was firstly studied, and arsenate was identified as the final product. Then, an orthogonal array experimental design of L 9 (3) 4 , only 9 experiments were needed, instead of 81 experiments in a conventional one-factor-at-a-time, was used to optimize the operational parameters soil:water ratio, TiO 2 dosage, irradiation time and light intensity to increase DPAA removal efficiency. Soil:water ratio was found to have a more significant effect on DPAA removal efficiency than other properties. The optimum conditions to treat 4 g soil with a DPAA concentration of 20 mg kg − 1 were found to be a 1:10 soil: water ratio, 40 mW cm − 2 light intensity, 5% TiO 2 in soil, and a 3-hour irradiation time, with a removal efficiency of up to 82.7%. Furthermore, this method (except for a change in irradiation time from 3 to 1.5 h) was validated in nine different soils and the removal efficiencies ranged from 57.0 to 78.6%. Removal efficiencies were found to be negatively correlated with soil electrical conductivity, organic matter content, pH and total phosphorus content. Finally, coupled with electron spin resonance (ESR) measurement, these soil properties affected the generation of OH• by TiO 2 in soil slurry. This study suggests that TiO 2 photocatalytic oxidation is a promising treatment for removing DPAA from soil. [ABSTRACT FROM AUTHOR]

Excessive N fertilization is a problem in the intensive cropping systems on the North China Plain. Proper N management is essential to maximize N efficiency and sustain agricultural production while minimizing negative impacts on the environment. The aim of the present study was to investigate N dynamics, maize yields and soil fertility in response to short term compost application and straw return vs. inorganic fertilization. A field experiment (2012–2014) was conducted for three years on a calcareous soil in Quzhou county, Heibei province, north China. There were four treatments: unfertilized control (T1), inorganic fertilizer (100% NPK, T2), compost (cattle wastes) + 70% NPK (T3), T3 + wheat straw (T4). No significant differences in biomass accumulation or N uptake among the fertilized treatments were observed across the maize growing season. Compost application for three years tended to increase grain yields particularly in the second and third years, and the average yield increase was approximately 7–15% over T2. Residual N min down the soil profile (1 m) in the compost treatments (T3 and T4) decreased by 50% deeper in the soil (60–100 cm depth) at the maize harvest in 2014. Compared to T2, the compost treatments significantly increased NUE and soil available P and K contents. Correlation analysis indicates that maize yield in 2014 was significantly correlated with soil available P and K and with soil organic carbon (SOC). Overall, straw return did not have a significant influence on any measured parameters in either soil or plant samples. Our results demonstrate that 30% replacement of N fertilizer by compost is an effective nutrient management strategy to maintain N uptake and yield of maize, reduce N loss and also increase soil fertility. A considerable increase in invertase activity in the compost treatments highlights that the critical importance of integrating the management of carbon and nitrogen for sustainable agricultural production in this region of highly intensive production. [ABSTRACT FROM AUTHOR]

Chronic nutrient addition to grassland soils can strongly influence the composition and abundance of nitrifying microbial communities. Despite the fact that nitrifying microbes play a crucial role in regulating ecosystem nitrogen (N) cycling, our understanding of how long-term N fertilization might influence nitrifying microbial groups is still limited. Here we used soil from a 44-year-old grassland fertilization experiment and performed high-throughput pyrosequencing analyses (and real-time quantitative PCR) to determine whether and how the identity and abundance of nitrifying microbes has changed in response to chronic inorganic (chemical fertilizer) and organic (cattle slurry) N additions. We found that the amoA genes of ammonia-oxidizing archaea (AOA) significantly increased under organic N additions, whereas ammonia-oxidizing bacteria (AOB) increased with the addition of inorganic N. Proportional changes of AOA, AOB and nitrite-oxidizing bacteria (NOB) demonstrate that nitrifying phylotypes are influenced by chronic N additions. We also found that AOA/AOB ratios increased with higher application rates of cattle slurry suggesting that AOA may affect N cycling more in soils receiving animal manures, whereas AOB are functionally more important in chemically fertilized soils. Phylogenetic analysis shows that shifts in AOA and AOB community structure occurred through time across N fertilization treatments. For example, (a) fosmid 29i4-like AOA, (b) Nitrosospira cluster 3-like AOB, and (c) Nitrospira -like NOB dominated nitrifying communities in fertilized soils. Finally, high-throughput pyrosequencing of 16S rRNA genes show that N fertilization (either inorganic or organic) increased the abundance of Actinobacteria in soils while it decreased the abundance of Proteobacteria. Our study is one of the first to show that long-term N additions to soils can greatly affect nitrifying communities, and that phylogenetically and functionally distinct nitrifiers have developed through time in response to chronic N fertilization. [ABSTRACT FROM AUTHOR]

Background and aims: Few studies have addressed the effects of root physiological plasticity on interspecific interactions. The present study aimed to investigate the plasticity of wheat and maize roots and their responses to nitrogen (N) application rates and neighboring species in wheat/maize intercropping. Methods: The roots of wheat and maize were sampled three times by auger after about 90 days of co-growth in the intercropping treatment with five levels of N application and sole crops at one N application rate. Results: Intercropped wheat altered its root length density (RLD) and lateral root distribution with different N application regimes, while lateral root distribution of intercropped maize was less sensitive to N application regimes. In addition, wheat had a 54.5 % (38-69 days) −375 % (0-37 days) higher N uptake rate per unit root length (NURl) when intercropped with maize compared with sole cropping but intercropped maize had either 58.3 % lower (0-37 days) or similar NURl than did sole cropped maize at the same N application rate. Conclusions: Our findings suggest that the competitive ability of the plant species for underground resources is conducive to plasticities in RLD, lateral root distribution in response to soil N, and N uptake efficiency to neighboring species. [ABSTRACT FROM AUTHOR]

Livestock farming produces slurry, which is normally recycled by land-spreading; but this raises questions about the long-term impact of slurry on soil fauna and soil processes. To examine the long-term effects of slurry on earthworms, cattle and pig excreta slurries and inorganic fertiliser were applied to a ryegrass silage sward for 33 years in a replicated experiment, and earthworms sampled for four consecutive years at three seasonal intervals (March, May and October). Animal slurries were applied at three rates (50, 100 and 200 m 3 ha −1 yr −1 ) and inorganic fertiliser as 200 kg N, 32 kg P and 160 kg K ha −1 yr −1 . Epigeic earthworms, Lumbricus rubellus , Lumbricus juveniles, and the endogeic Allolobophora chlorotica responded strongly and positively to cattle slurry inputs. In the case of L. rubellus , biomass was five times greater in the highest input cattle slurry plots than in the untreated controls. In contrast to Al. chlorotica adults, other endogeic earthworms and juvenile Allolobophora were more associated with the inorganic fertiliser treatment. Aporrectodea juveniles, in particular, had significantly greater biomass in the inorganic fertiliser treatment. However, no such response was demonstrated by adult Aporrectodea caliginosa , the commonest species found, suggesting niche separation between adults and juveniles. Pig slurry applications produced relatively little change in earthworm biomass compared to controls, despite residual copper concentrations; suggesting that organic matter input was counterbalancing the sublethal effects of copper. [ABSTRACT FROM AUTHOR]

Meeting the future food security challenge without further sacrificing environmental integrity requires transformative changes in managing the key biophysical determinants of increasing agronomic productivity and reducing the environmental footprint. Here, we focus on Chinese rice production and quantitatively address this concern by conducting 403 on-farm trials across diverse rice farming systems. Inherent soil productivity, management practices and rice farming type resulted in confounded and interactive effects on yield, yield gaps and greenhouse gas (GHG) emissions (N2O, CH4 and CO2-equivalent) with both trade-offs and compensating effects. Advances in nitrogen, water and crop management (Best Management Practices—BMPs) helped closing existing yield gaps and resulted in a substantial reduction in CO2-equivalent emission of rice farming despite a tradeoff of increase N2O emission. However, inherent soil properties limited rice yields to a larger extent than previously known. Cultivating inherently better soil also led to lower GHG intensity (GHG emissions per unit yield). Neither adopting BMPs only nor improving soils with low or moderate productivity alone can adequately address the challenge of substantially increasing rice production while reducing the environmental footprint. A combination of both represents the most efficient strategy to harness the combined-benefits of enhanced production and mitigating climate change. Extrapolating from our farm data, this strategy could increase rice production in China by 18%, which would meet the demand for direct human consumption of rice by 2030. It would also reduce fertilizer nitrogen consumption by 22% and decrease CO2-equivalent emissions during the rice growing period by 7% compared with current farming practice continues. Benefits vary by rice-based cropping systems. Single rice systems have the largest food provision benefits due to its wider yield gap and total cultivated area, whereas double-rice system (especially late rice) contributes primarily to reducing GHG emissions. The study therefore provides farm-based evidence for feasible, practical approaches towards achieving realistic food security and environmental quality targets at a national scale. [ABSTRACT FROM AUTHOR]

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO3-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N2O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO3-N decreased. When15NO3-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg−1only 1.1 ± 0.4 mg kg−1NO3-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N2O-N emissions were at levels of only micrograms kg−1soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N2O. [ABSTRACT FROM PUBLISHER]

The diversity of arbuscular mycorrhizal fungi ( AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of K obresia pygmaea C. B. Clarke and C arex pseudofoetida Kük. in alpine K obresia pastures along an elevational transect (4149-5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae ( EMH) and total glomalin-related soil protein ( T-GRSP). The influence of plant richness was mainly due to its indirect influence on T-GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co-occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands. [ABSTRACT FROM AUTHOR]

Plant community productivity and species composition are primarily constrained by water followed by nitrogen ( N) availability in the degraded semi-arid grasslands of Inner Mongolia. However, there is a lack of knowledge on how long-term N addition and water availability interact to influence the community structure of arbuscular mycorrhizal ( AM) fungi, and whether AM fungi contribute to the recovery of degraded grasslands. Soils and roots of the dominant plant species S tipa grandis and A gropyron cristatum were sampled under two water levels and N) rates after 8 years. The abundance and diversity of AM fungi remained relatively resilient after the long-term addition of water and N. Variation in the AM fungal communities in soils and roots were affected primarily by watering. AM fungal abundance and operational taxonomic unit ( OTU) richness were significantly correlated with average aboveground net primary productivity and biomass of plant functional groups. Hyphal length density was significantly correlated with plant richness, the average biomass of S . grandis and perennial forbs. Both water and plant biomass had a considerable influence on the AM fungal assemblages. The tight linkages between AM fungi with aboveground plant productivity highlight the importance of plant-microbe interactions in the productivity and sustainability of these semi-arid grassland ecosystems. [ABSTRACT FROM AUTHOR]

Zero-valent iron (ZVI) is widely used to mitigate environmental pollutants such as chlorinated pesticides through reductive reactions accompanied by extensive impacts on the soil microbial community. However, whether and how ZVI changes the biodegradation of target compounds remain poorly understood. Here, we monitor the fate of lindane using a 14C-labled tracer and evaluate the growth and functions of the bacterial community in ZVI-stressed conditions in a historically γ-hexachlorocyclohexane (lindane)-contaminated soil using a combination of isotopic (18O-H 2 O) and metagenomic methods. ZVI promoted the biomineralization of lindane in a dose-dependent manner. Soil bacteria were inhibited by amendment with ZVI during the initial stages of incubation (first three days) but recovered during the subsequent six weeks. Metagenomic study indicates that the todC1 / bedC1 genes involved in the oxidation of dechlorinated lindane intermediates were upregulated in the 18O-labeled bacterial community but the presence of the lin genes responsible for lindane dechlorination was not confirmed. In addition, the benzoate biodegradation pathway that links to downstream catabolism of lindane was enhanced. These findings indicate successive chemical and biological degradation mechanisms underlying ZVI-enhanced lindane mineralization and provide a scientific basis for the inclusion of an extended bioremediation stage in the environmental application of ZVI materials. [Display omitted] • ZVI enhanced lindane removal by increasing mineralization and NER formation. • ZVI promoted the biomineralization of lindane in a dose-dependent manner. • Bacterial growth was inhibited by ZVI in the initial stage but recovered later. • Lin gene responsible for lindane dechlorination was not confirmed. • Pathway that links to downstream catabolism of lindane was enhanced by ZVI. [ABSTRACT FROM AUTHOR]

Cadmium (Cd)-bearing sphalerite and smithsonite ore particles are ubiquitous in soils near metal-mining areas. Previous studies indicate that smithsonite is more readily dissolved in acidic waters and soils than sphalerite but the mobility of Cd and zinc (Zn) derived from these ores in soils is unknown. Using microcosm incubation experiments and microscopic and spectroscopic analysis, we found that the mobility of Cd and Zn derived from smithsonite is higher than from sphalerite. The mobilization rates of Cd (16.6%) and Zn (13.7%) released from smithsonite in soils after 30-day incubation experiments were higher than those from sphalerite (Cd, ~ 1.42%; Zn, ~ 0.75%). Moreover, the percentages of Cd2+ and Zn2+ in soil pore water showed a dynamic increase in smithsonite-spiked treatments but a decrease in sphalerite-spiked treatments. HRTEM-EDX-SAED analysis further indicates the occurrence of dynamic transformation of amorphous Cd and Zn species in soil pore water to crystalline ZnS and iron oxides in sphalerite-spiked soil but crystalline ZnCO 3 nanoparticles were dynamically transformed to amorphous metal-bearing species in smithsonite-spiked soil. The opposite transformation trends in pore water of Zn ore-spiked soils provide new insights into the Cd environmental risks in soils affected by Zn mining. [Display omitted] • High mobility or bioavailability of Cd and Zn were found in SM-spiked soils. • First-order kinetic well-fitted the release of Cd and Zn derived from Zn ores. • Crystalline Zn-bearing nanoparticle dynamic transformed to amorphous colloids in SM-spike soil pore water. • Zn-bearing amorphous colloids dynamic transformed to nano-crystals in SP-spiked soil pore water. • The formation of metal-bearing nano-crystals may be frequent in the karst soil pore water. [ABSTRACT FROM AUTHOR]

Bacterial type IV coupling proteins (T4CPs) bind and mediate the delivery of DNA substrates through associated type IV secretion systems (T4SSs). T4CPs consist of a transmembrane domain, a conserved nucleotide-binding domain (NBD), and a sequence- variable helical bundle called the all-alpha domain (AAD). In the T4CP structural prototype, plasmid R388-encoded TrwB, the NBD assembles as a homohexamer resembling RecA and DNA ring helicases, and the AAD, which sits at the channel entrance of the homohexamer, is structurally similar to N-terminal domain 1 of recombinase XerD. Here, we defined the contributions of AADs from the Agrobacterium tumefaciens VirD4 and Enterococcus faecalis PcfC T4CPs to DNA substrate binding. AAD deletions abolished DNA transfer, whereas production of the AAD in otherwise wild-type donor strains diminished the transfer of cognate but not heterologous substrates. Reciprocal swaps of AADs between PcfC and VirD4 abolished the transfer of cognate DNA substrates, although strikingly, the VirD4-AADPcfC chimera (VirD4 with the PcfC AAD) supported the transfer of a mobilizable plasmid. Purified AADs from both T4CPs bound DNA substrates without sequence preference but specifically bound cognate processing proteins required for cleavage at origin-of-transfer sequences. The soluble domains of VirD4 and PcfC lacking their AADs neither exerted negative dominance in vivo nor specifically bound cognate processing proteins in vitro. Our findings support a model in which the T4CP AADs contribute to DNA substrate selection through binding of associated processing proteins. Furthermore, MOBQ plasmids have evolved a docking mechanism that bypasses the AAD substrate discrimination checkpoint, which might account for their capacity to promiscuously transfer through many different T4SSs. IMPORTANCE: For conjugative transfer of mobile DNA elements, members of the VirD4/TraG/TrwB receptor superfamily bind cognate DNA substrates through mechanisms that are largely undefined. Here, we supply genetic and biochemical evidence that a helical bundle, designated the all-alpha domain (AAD), of T4SS receptors functions as a substrate specificity determinant. We show that AADs from two substrate receptors, Agrobacterium tumefaciens VirD4 and Enterococcus faecalis PcfC, bind DNA without sequence or strand preference but specifically bind the cognate relaxases responsible for nicking and piloting the transferred strand through the T4SS. We propose that interactions of receptor AADs with DNA-processing factors constitute a basis for selective coupling of mobile DNA elements with type IV secretion channels. [ABSTRACT FROM AUTHOR]

A better understanding of Glomeromycotan biogeography is essential for the conservation of arbuscular mycorrhizal (AM) fungal species and the ecosystem services that they provide worldwide. Here, we examine the spatial dynamics of AM fungi along two slopes (4149 m a.s.l. to the summit at 5033 m a.s.l.) of Mount Mila on the Tibetan Plateau. Our hypothesis was that AM fungal communities at higher elevation would show distinct assemblages with lower diversity in conditions of increasing environmental harshness. A total of 52 operational taxonomic units (OTUs) spanning all four orders were detected and some OTUs were habitat specific. Nearly 30% of the OTUs were new phylotypes, including two family-like clades. Distinct communities of AM fungi were found at the higher elevation, demonstrating potential niche differentiation along the elevation gradient. Elevation patterns of taxon richness/diversity differed between the two transects, decreasing with increasing elevation on the eastern slope and unimodal (or no pattern) on the western slope. Taken together, we provide evidence for significant spatial structure of AM fungi across the elevation gradient, and the distribution patterns are regulated simultaneously by the plant communities, soil properties and climatic conditions in this plateau montane ecosystem. [ABSTRACT FROM AUTHOR]

Long-term application of sewage sludge resulted in soil cadmium (Cd) and zinc (Zn) contamination in a pot experiment conducted to phytoextract Cd/Zn repeatedly usingSedum plumbizincicolaandApium graceolensin monoculture or intercropping mode eight times. Shoot yields and soil physicochemical properties changed markedly with increasing number of remediation crops when the two plant species were intercropped compared with the unplanted control soil and the two monoculture treatments. Changes in soil microbial indices such as average well colour development, soil enzyme activity and soil microbial counts were also significantly affected by the growth of the remediation plants, especially intercropping withS. plumbizincicolaandA. graveolens. The higher yields and amounts of Cd taken up indicated that intercropping of the hyperaccumulator and the vegetable species may be suitable for simultaneous agricultural production and soil remediation, with larger crop yields and higher phytoremediation efficiencies than under monoculture conditions. [ABSTRACT FROM PUBLISHER]

Background: Overyielding (i.e., mixtures of crops yielding higher than expected when compared with monocultures) and increased nutrient acquisition have been found in many intercropping systems. However, there are very few published studies on long-term changes in soil chemical and biological properties in intercropping systems compared to sole cropping. Methods: A field experiment was established in 2003 in Gansu province, northwest China. The treatments comprised three intercropping systems (either continuous or rotational wheat/maize, wheat/faba bean, maize/faba bean intercropping), rotational cropping (wheat-maize, wheat-faba bean, faba bean-maize, and wheat-maize-faba bean rotations), and monocropping (sole wheat, faba bean and maize) systems. In 2011 (ninth year of the experiment) and 2012 (tenth year) the yields and some soil chemical and biological properties were examined after all crop species were harvested. Results: There was overyielding by 6.6 % and 32.4 % in wheat/maize intercropping in 2011 and 2012, respectively. Faba bean/maize intercropping was enhanced by 34.7 % and 28.6 %, respectively but not wheat/faba bean intercropping. Soil organic matter, total nitrogen, Olsen P, exchangeable K and cation exchange capacity in all intercropping systems did not differ from the monocultures except for soil pH in wheat/maize and faba bean/maize intercropping in 2011 and soil exchangeable K and cation exchange capacity (CEC) in 2012. Soil pH in wheat/maize and faba bean/maize intercropping was significantly reduced by 3.2 % and 1.9 %, respectively. Soil exchangeable K in wheat/maize, faba bean/maize and wheat/faba bean intercropping declined markedly by 15 %, 21.7 % and 12.1 %, respectively. Soil cation exchange capacity in wheat/maize, faba bean/maize and wheat/faba bean intercropping was notably lower than the corresponding monocultures by 17.5 %, 23.3 % and 18.3 %, respectively. Soil enzyme activities after 9 and 10 years of intercropping differed little from monocultures or rotations. Conclusions: The results indicate that intercropping overyielded compared with monocropping or rotational cropping and also maintained the stability of most of the soil chemical and enzyme activities relative to rotations and monocropping in the relatively fertile soil studied. [ABSTRACT FROM AUTHOR]

The large consumption of groundwater for irrigating winter wheat has resulted in a continuous decline in the groundwater table on the North China Plain in recent decades. Alternative cropping systems have been proposed to substitute for the conventional winter wheat–summer maize rotation system for the sustainable use of groundwater in the future. However, the impact of these cropping systems on net global warming potential (net GWP), and greenhouse gas emissions on the basis of per unit of yield (greenhouse gas intensity, GHGI) is poorly documented. Measurements of greenhouse gases were conducted over a four-year period to gain insight into net GWP and GHGI on a crop rotation scale based on an ongoing long-term field experiment on the North China Plain. The cropping systems investigated include one conventional winter wheat–summer maize system (Chem. W/M) as the control and four alternative cropping systems, namely an optimized winter wheat–summer maize system (Opt. W/M), two winter wheat–summer maize (or soybean)–spring maize system with three crops in two years (W/M–M, W/S–M), and a single spring maize per year (M). Compared with the Chem. W/M control, the grain yields in Opt. W/M increased significantly by 19% while the net GWP, GHGI and fertilizer N decreased by 29%, 40% and 40%, respectively, but still consumed as much groundwater (264 mm yr −1 ) as Chem. W/M. In the two-year rotation cycle fertilizer N, groundwater use, net GWP and GHGI in W/M–M, W/S–M and M declined by 56–70%, 43–63%, 50–58% and 30–50%, respectively, compared to Chem. W/M. Moreover, these cropping systems consumed only 108–159 mm yr −1 groundwater for irrigation, a value close to the theoretical value of 150 mm yr −1 to avoid a continuing decline in the groundwater table in this region. However, W/S–M treatment had grain yield reductions of −23% and M treatment had −30%, and only W/M–M maintained grain yields relative to Chem. W/M. We therefore recommend the W/M–M management package as a preferred option to maintain grain yields together with low GWP and GHGI while mitigating the decline in the groundwater table in areas with a high water deficit. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction bySedum plumbizincicolausing different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl)thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg−1of Cd and 241 mg kg−1Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH4)2SO4+DCD treatment produced higher NH4+−N concentrations in soil solution than the (NH4)2SO4and NaNO3treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg−1, respectively. The (NH4)2SO4+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO3treatment. Plant shoots grown with NaNO3had higher Cd concentrations than (NH4)2SO4+DCD treatment at 24.0 and 15.4 mg kg−1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively. [ABSTRACT FROM PUBLISHER]

The transport behavior of titanium dioxide nanoparticles (TiO NPs, 30 nm in diameter) was studied in well-defined porous media composed of clean quartz sand over a range of solution chemistry under acidic conditions. Transport of TiO NPs was dramatically enhanced by humic substances (HS) at acidic pH (4.0, 5.0 and 6.0), even at a low HS concentration of 0.5 mg L. Facilitated transport of TiO NPs was likely attributable to the increased stability of TiO NPs and repulsive interaction between TiO NPs and quartz sands due to the adsorbed HS. The mobility of TiO NPs was also increased with increasing pH from 4.0 to 6.0. Although transport of TiO NPs was insensitive to low ionic strength, it was significantly inhibited by high concentrations of NaCl and CaCl. In addition, calculated Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy indicated that high energy barriers were responsible for the high mobility of TiO NPs, while the secondary energy minimum could play an important role in the retention of TiO NPs at 100 mmol L NaCl. Straining and gravitational settlement of larger TiO NPs aggregates at 1 mg L HS, pH 5.0, and 2 mmol L CaCl could be responsible for the significant retention even in the presence of high energy barriers. Moreover, more favorable interaction between approaching TiO NPs and TiO NPs that had been already deposited on the collector resulted in a ripening-shape breakthrough curve at 2 mmol L CaCl. Overall, a combination of mechanisms including DLVO-type force, straining, and physical filtration was involved in the retention of TiO NPs over the range of solution chemistry examined in this study. [ABSTRACT FROM AUTHOR]

Background and aims: The objectives of this study were to elucidate the mechanisms of interaction between root exudates of tall fescue and functional bacteria associated with petroleum degradation and whether components of the exudates can enhance petroleum removal from soil. Methods: Root exudates of tall fescue were collected through a continuous root exudate trapping system and identified by GC-MS. Chemotaxis, swarming, and in vitro assay were conducted to assess the effects of the organic acids of root exudates on Klebsiella sp. D5A (plant growth promoting rhizobacterium), Pseudomonas sp. SB (biosurfactant producing bacterium), and Streptomyces sp. KT (petroleum-degrading bacterium). A pot experiment with organic acid amendment was conducted to study the effects of these components of root exudates on petroleum remediation. Microbial physiological metabolisms affected by organic acids were tested using Biolog Eco plates. Results: Palmitic acid was found to be most effective in promoting D5A colonization on tall fescue. ρ-Hydroxybenzoic and palmitic acids significantly stimulated the growth of strains D5A, SB, and KT. Furthermore, palmitic acid amendment significantly enhanced petroleum removal in pot experiment. Conclusions: Palmitic acid was the critical organic acid to facilitate petroleum removal during phytoremediation. These findings provide insight into the mechanisms by which tall fescue enhances the degradation of petroleum. [ABSTRACT FROM AUTHOR]

E nterococcus faecalis pCF10 transfers at high frequencies upon pheromone induction of the prg Q transfer operon. This operon codes for three cell wall-anchored proteins - PrgA, PrgB (aggregation substance) and PrgC - and a type IV secretion system through which the plasmid is delivered to recipient cells. Here, we defined the contributions of the Prg surface proteins to plasmid transfer, biofilm formation and virulence using the C aenorhabditis elegans infection model. We report that a combination of PrgB and extracellular DNA ( eDNA), but not PrgA or PrgC, was required for extensive cellular aggregation and pCF10 transfer at wild-type frequencies. In addition to PrgB and eDNA, production of PrgA was necessary for extensive binding of enterococci to abiotic surfaces and development of robust biofilms. However, although PrgB is a known virulence factor in mammalian infection models, we determined that PrgA and PrgC, but not PrgB, were required for efficient killing in the worm infection model. We propose that the pheromone-responsive, conjugative plasmids of E . faecalis have retained Prg-like surface functions over evolutionary time for attachment, colonization and robust biofilm development. In natural settings, these biofilms are polymicrobial in composition and constitute optimal environments for signal exchange, mating pair formation and widespread lateral gene transfer. [ABSTRACT FROM AUTHOR]

Background and aims: The foraging capability of extraradical mycelium (ERM) of arbuscular mycorrhizal (AM) fungi to high soil phosphorus (P) supply and carry-over effect of ERM on new host plants remain to be explored. This study investigated whether the inhibition of ERM at high P supply varies between fungal species and whether ERM have carry-over effects when they encounter new hosts. Methods: A two-compartment device was designed to spatially separate hyphae from host roots and the carry-over effect was investigated using two-stage growth experiments. P fertilizers were applied only to hyphal compartments at a gradient of 0, 35, 150, 300, or 1,000 mg P∙kg. Maize plants were inoculated with Glomus mosseae, Rhizophagus irregularis or remained uninoculated. Results: The biomass of G. mosseae in the hyphal compartment was on average higher than that of R. irregularis and the difference was greater at the second harvest. The biomass of G. mosseae increased slightly at P35 and thereafter decreased significantly with increasing P level. The biomass of R. irregularis increased slightly at P35 and did not differ significantly at higher P levels from that at P0. In general, inoculation significantly increased the biomass and P uptake of donor and receiver plants. The mycorrhizal growth responsiveness (MGR) and mycorrhizal phosphorus responsiveness (MPR) of both donor and receiver plants decreased at higher P supply level. The ratios of MGR and MPR between donor and receiver plants were close to 1 for both fungal species and were independent of P level. Inoculation with R. irregularis significantly enhanced root P uptake efficiency and alkaline phosphatase activity (ALP) in both donor and receiver plants across all P levels. Conclusions: Our results demonstrate that fungal species differ in their responses to soil P availability. R. irregularis was less sensitive to soil P gradients, and compensated for growth promotion and P uptake of the host by increasing ALP and root P uptake efficiency. The carry-over effects of ERM imply that the maintenance of mycorrhizal networks is of particular importance in intensive agricultural ecosystems. [ABSTRACT FROM AUTHOR]

A glasshouse pot experiment was conducted to study the effects of phytoextraction bySedum plumbizincicolaand application of rapeseed cake (RSC) on heavy metal accumulation by a subsequent rice(Oryza sativa L.)crop in a contaminated paddy soil collected from east China. After phytoextraction byS. plumbizincicolathe soil and brown rice Cd concentrations effectively declined. After phytoextraction, RSC application reduced brown rice Cd concentrations in the subsequent rice crop to 0.23–0.28 mg kg−1, almost down to the standard limit (0.2 mg kg−1). After phytoextraction and then application of RSC, the soil solution pH, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations increased during early stages of rice growth resulting directly and indirectly in lowering the bioavailability of the heavy metals. Thus the grain yield of the subsequent rice crop increased and the heavy metals in the brown rice declined significantly. In this contaminated acid soil, growing the hyperaccumulatorS. plumbizincicolaand rice in rotation together with RSC application may therefore be regarded as a viable strategy for safe grain production and bioremediation. [ABSTRACT FROM PUBLISHER]

ABSTRACT The co-metabolism of benzo[a]pyrene (B[a]P) and the capacity of the fungusTrichoderma reeseiFS10-C to bioremediate an aged polycyclic aromatic hydrocarbon (PAH)-contaminated soil were investigated. The fungal isolate removed about 54% of B[a]P (20 mg L−1) after 12 days of incubation with glucose (10 g L−1) supplementation as a co-metabolic substrate. Bioaugmented microcosms showed a 25% decrease in total PAH concentrations in soil after 28 days, and the degradation percentages of 3-, 4-, and 5(+6)-ring PAHs were 36%, 35%, and 25%, respectively. In addition, bioaugmented microcosms exhibited higher dehydrogenase (DHA) and fluorescein diacetate hydrolysis (FDAH) activities and increased average well-color development (AWCD), Shannon-Weaver index (H), and Simpson index (D) significantly. Principal component analysis (PCA) also distinguished clear differentiation between treatments, indicating that bioaugmentation restored the microbiological function of the PAH-contaminated soil. The results suggest that bioaugmentation byT. reeseiFS10-C might be a promising bioremediation strategy for aged PAH-contaminated soils. [ABSTRACT FROM PUBLISHER]

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic (As) and cadmium (Cd) in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3-16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid (from 11.3% to 61.7%) made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal(loid)s in the grain of rice grown in soils polluted with both As and Cd. [ABSTRACT FROM AUTHOR]

The efficiency of heavy metal removal from soil by EDTA leaching was assessed in a column leaching experiment at the laboratory scale and field heap leaching at the pilot scale using a sandy loam sierozem agricultural soil contaminated with Cd, Cu, Pb, and Zn. Soil amendment and aging were conducted to recover leaching soils. The percentages of Cd, Cu, Pb, and Zn removed by column leaching were 90%, 88%, 90%, and 67%, respectively, when 3.9 bed volumes of 50 mM EDTA were used. At the pilot scale, on-site metal removal efficiencies using the selected leaching procedure were 80%, 69%, 73% and 62% for Cd, Cu, Pb and Zn, respectively. EDTA leaching decreased soil CEC, total P, total K and available K concentrations but increased organic matter and total Kjeldahl N concentrations. The subsequent amendment and soil aging further reduced the DTPA-extractable heavy metals in the leached soils. Growth of the first crop of pak choi in the leached soil was inhibited but the second crop grew well after the soil was aged for one year and the concentrations of Cd and Pb in the edible parts were below the Chinese statutory limits. The results demonstrate the potential feasibility of the field leaching technique using EDTA combined with subsequent amendment and soil aging for the remediation of heavy metal-contaminated agricultural soils. [ABSTRACT FROM AUTHOR]

Phthalate esters (PAEs) are widely used as plasticizers in both industrial and commercial products and have aroused considerable concern over their widespread distribution and potentially hazardous impacts on the environment. The present study investigated the distribution (concentrations at different sites) of PAEs in typical riverine sediments in southern Jiangsu Province and its relationship with the physical and chemical properties of the sediments. PAEs were detected in all 34 sediment samples analyzed, and the total concentrations of the six priority control PAEs in sediments ranged from 2.3 to 80.1 mg kg − 1 with a mean concentration of 13.2 ± 14.7 mg kg − 1 . Land use significantly ( p < 0.05) influenced the PAE concentrations in the river sediments. The average PAE concentrations in mixed industrial and commercial districts were 27.8 ± 18.2 mg kg − 1 , three and eight times higher than those in suburban areas (8.8 ± 3.7 mg kg − 1 ) and an agricultural field (3.4 ± 0.9 mg kg − 1 ), respectively. The concentrations of PAEs showed significant linear positive correlations with sediment organic matter and phosphorus but no significant correlation with sediment pH. Di(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DnBP) were the dominant PAE compounds present in all examined sediment samples. These PAEs have relatively high ecotoxicology, but the potential risk of their transfer to the food chain needs further study. [ABSTRACT FROM AUTHOR]

Yield and nutrient acquisition advantages are frequently found in intercropping systems. However, there are few published reports on soil fertility in intercropping relative to monocultures. A field experiment was therefore established in 2009 in Gansu province, northwest China. The treatments comprised maize/faba bean, maize/soybean, maize/chickpea and maize/turnip intercropping, and their correspoding monocropping. In 2011 (the 3rd year) and 2012 (the 4th year) the yields and some soil chemical properties and enzyme activities were examined after all crop species were harvested or at later growth stages. Both grain yields and nutrient acquisition were significantly greater in all four intercropping systems than corresponding monocropping over two years. Generally, soil organic matter (OM) did not differ significantly from monocropping but did increase in maize/chickpea in 2012 and maize/turnip in both years. Soil total N (TN) did not differ between intercropping and monocropping in either year with the sole exception of maize/faba bean intercropping receiving 80 kg P ha−1 in 2011. Intercropping significantly reduced soil Olsen-P only in 2012, soil exchangeable K in both years, soil cation exchangeable capacity (CEC) in 2012, and soil pH in 2012. In the majority of cases soil enzyme activities did not differ across all the cropping systems at different P application rates compared to monocrops, with the exception of soil acid phosphatase activity which was higher in maize/legume intercropping than in the corresponding monocrops at 40 kg ha−1 P in 2011. P fertilization can alleviate the decline in soil Olsen-P and in soil CEC to some extent. In summary, intercropping enhanced productivity and maintained the majority of soil fertility properties for at least three to four years, especially at suitable P application rates. The results indicate that maize-based intercropping may be an efficient cropping system for sustainable agriculture with carefully managed fertilizer inputs. [ABSTRACT FROM AUTHOR]

Aim: There have been only two studies of the smoking prevalence outside bars/cafés worldwide, both undertaken in Australia. The aim of this study was to further develop the assessment of the prevalence of smoking outside bars/cafés in a busy urban area. It is important for smokefree places policymaking to have baseline data on smoking visibility at these places, so as to be able to gauge the effects of policy changes that may alter levels of smoking. Methods: Researchers observed smoking during eight 15-minute periods (during 12-1 pm and 7-8 pm) in April 2013 at 14 bar/café locations in central Wellington, New Zealand. Results: Of 2600 people observed in the outdoor areas of bars/cafés, 15.8% were observed smoking (95% confidence interval (CI): 14.5%-17.5%); 18.5% in the evening (95% CI: 16.8%-20.4%) compared to 9.1% at midday (95% CI: 7.2%-11.4%). Conclusion: Smoking was observed in the outdoor areas of the bars/cafés at a prevalence of double that found in the previous Australian studies. This may be accounted for by observation method or observation times, or may be due to a much wider range of premises in the Australian cities with outdoor areas, which are open later, or a much wider variety of patrons who used such areas, compared to in Wellington. We found twice the prevalence of smoking outside bars/cafés in evenings compared to midday. Such differences may be related to a greater consumption of alcohol in evenings or to a different patronage then. Smokefree policies covering these settings could help denormalize smoking. [ABSTRACT FROM AUTHOR]

Appropriate nitrogen (N) management is important to minimize N losses from intensively managed agricultural ecosystems. Understanding the community structure of arbuscular mycorrhizal fungi ( AMF) in response to N management can be of great ecological significance, particularly with the recent emphasis on the role of AMF in N cycling. A comprehensive study of both the vertical distribution of AMF in the soil profile and the temporal changes in community structure in maize roots was conducted over a 5-year period at a field site on the North China Plain. The N treatments consisted of zero N, conventional farming practice, and optimum N based on an in-season soil Nmin test. Terminal restriction fragment length polymorphism and clone sequencing were used to analyse the AMF community. Optimum N mitigated the decline in richness of AMF in the conventional N treatment in the surface soil. Diverse and species-rich AMF communities occurred deep in the soil profile. A significant difference in AMF community structure was observed between the control and fertilizer N treatments but not between the two N application strategies. AMF communities deeper in the soil profile were subsets of those richer communities in the surface soil and the loss of AMF taxa was mostly due to the absence of rare taxa. Soil pH and Nmin contents were major soil properties affecting the soil AMF communities among the N treatments while vertical distribution was influenced mainly by soil electrical conductivity. Crop phenology had a stronger influence than N treatment on the temporal shifts in AMF communities in maize roots. Our results provide evidence for the importance of N management in maintaining AMF diversity. Changes in soil chemical properties due to N fertilization, in particular declining soil pH, should be integrated in N management strategies to reduce the negative impacts on AMF communities induced by N fertilization. Excessive N inputs induced significant changes in soil physicochemical properties, especially soil acidification, and may have negative impacts on AMF communities. [ABSTRACT FROM AUTHOR]

Knowledge about the distribution pattern and function of soil microbial communities is essential for understanding their vital role in ecosystem functioning. However, little is known about the elevational patterns of microbial communities at high altitudes on the Tibetan Plateau, a region that is very sensitive to global change. We investigated the microbial community composition and functional patterns along an elevational gradient (3100-4600 m above sea level) on Mount Segrila using phospholipid fatty acids (PLFAs) and community level physiological profiles (CLPP). Soil microbes were abundant even at higher altitudes and ranged from 1.52 to 3.53 μmol per g organic carbon (OC) by total PLFAs. Soil microbial biomass (expressed as Total PLFAs) declined at higher elevations, and the highest abundance was observed at the low-elevation site. Fungal to bacterial ratio decreased with increasing elevation. While no consistent elevational pattern was observed for PLFA profiles, richness and diversity of carbon source utilization by the microbial community decreased significantly at higher altitudes. Soil microbes at higher altitudes had the potential to metabolize relatively more recalcitrant carbon components while microbes at lower altitudes tended to utilize labile carbon sources. The results were in line with the chemical composition of soil organic matter. Increasing O-alkyl C and decreasing alkyl C content indicate slow decomposition at higher elevations. Variations in structure and activity of microbial community were mainly attributable to MAT, pH, and litter C:N. Our results indicate that pH is a major factor affecting microbial communities, and the impact of soil pH is closely correlated with temperature and vegetation changes along the elevational gradient. As future climate warming may lead to temperature increases and an upward migration of vegetation, our results provide fundamental knowledge of soil microbial communities in the Tibetan alpine region and may help to predict responses of the belowground community to global climate change. [ABSTRACT FROM AUTHOR]

Highlights: [•] Leaching characteristics of a paddy field with straw retention were monitored in situ. [•] Nitrogen and phosphorus leaching losses under different N application rates with straw retention were evaluated. [•] The percolation rate declined with time after rice transplanting in first-order index attenuation. [•] N leaching occurred mainly at basal fertilization stage and straw incorporation reduced N leaching but stimulated P leaching. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated the long term effects of K application on K use and soil status. [•] K increased grain yield, but this effect decreased with excessive application. [•] Returned straw, deep soil K utilization, weathering soil K pools may alleviate soil K deficits. [ABSTRACT FROM AUTHOR]

Abstract: The impacts of different crop rotation systems with their corresponding management practices on grain yield, greenhouse gas emissions, and fertilizer nitrogen (N) and irrigation water use efficiencies are not well documented. This holds especially for the North China Plain which provides the staple food for hundreds of millions of people and where groundwater resources are polluted with nitrate and depleted through irrigation. Here, we report on fertilizer N and irrigation water use, grain yields, and nitrous oxide (N2O) and methane (CH4) emissions of conventional and optimized winter wheat–summer maize double-cropping systems, and of three alternative cropping systems, namely a winter wheat–summer maize (or soybean)–spring maize system, with three harvests in two years; and a single spring maize system with one crop per year. The results of this two-year study show that the optimized double-cropping system led to a significant increase in grain yields and a significant decrease in fertilizer N use and net greenhouse gas intensity, but the net greenhouse gas N2O emissions plus CH4 uptake and the use of irrigation water did not decrease relative to the conventional system. Compared to the conventional system the net greenhouse gas emissions, net greenhouse gas intensity and use of fertilizer N and irrigation water decreased in the three alternative cropping systems, but at the cost of grain yields except in the winter wheat–summer maize–spring maize system. Net uptake of CH4 by the soil was little affected by cropping system. Average N2O emission factors were only 0.17% for winter wheat and 0.53% for maize. In conclusion, the winter wheat–summer maize–spring maize system has considerable potential to decrease water and N use and decrease N2O emissions while maintaining high grain yields and sustainable use of groundwater. [Copyright &y& Elsevier]

A modified in-growth core technique was employed to determine the contribution of indigenous arbuscular mycorrhizal fungi (AMF) to plant growth and nutrient uptake in intensive agroecosystems at two Experimental field sites at Shangzhuang (Experiment I) and Quzhou (Experiment II) in North China. The growth cores (26.5 cm depth, 5 cm diameter for maize plants, and 4 cm for alfalfa and tomato plants) were covered with 40-μm nylon mesh (restriction of hyphal growth) and buried in the soil. They either remained static (static mesh) or were regularly rotated (rotated mesh) to disrupt hyphal penetration into the cores. A non-rotated 0.45-μm mesh (block mesh, inhibition of hyphal growth) treatment which remained static was also included to compare with the rotated mesh treatment (Experiment I). Growth cores from the two experimental sites had different soil types and two contrasting low P levels. The soil in the growth cores was sieved and sterilized before being placed into the growth core. Three plant species, namely maize, tomato and alfalfa were selected. The growth periods for maize plants were 35 days (Experiment I) and 39 days (Experiment II), respectively, and the corresponding growth periods for tomato and alfalfa were 67 days (Experiment I) and 53 days (Experiment II). At harvest the AMF species inside and outside the in-growth cores were identified by polymerase chain reaction (PCR), cloning and sequencing. Irrespective of plant species or genotype (maize), root colonization rates and hyphal length density (Experiment I) were generally suppressed in the rotated mesh treatment. The inhibition of hyphal growth by block mesh was comparable to that by the rotated mesh treatment. The growth of all three plant species in static mesh at the two Experimental sites, at both low (Experiment I) and sub-optimal soil P supply levels (Experiment II), was significantly higher than in the rotated (or block mesh) treatment. Root colonization rates of three maize genotypes were positively correlated with plant P concentration (Experiment II). Uptake efficiencies of P and N were significantly higher in static mesh than in the rotated (or block) treatment. AMF species detected (Experiment I) were all Glomerales, including the genera Glomus and Rhizophagus. One identified species of Rhizophagus intraradices and one Glomus viscosum-like phylotype were the dominant species. We conclude that the indigenous AM are crucial for early seedling growth, particularly for plants with small seeds and low P reserves and when seedlings exhibit P deficiency. The facilitation effect is highly relevant to enhanced root P (and possibly N) uptake and P delivery by the fungal mycelium. Our results have implications for the importance of maintenance of intact hyphal networks in intensive agroecosystems. [ABSTRACT FROM AUTHOR]

Aims: Phytoextration of metal polluted soils using hyperaccumulators is a promising technology but requires long term successive cropping. This study investigated the dynamics of plant metal uptake and changes in soil metals over a long remediation time. Methods: A soil slightly polluted with metals (S1) was mixed with highly polluted soil (S4) to give two intermediate pollution levels (S2, S3). The four resulting soils were repeatedly phyto-extracted using nine successive crops of Cd/Zn-hyperaccumulator Sedum plumbizincicola over a period of 4 years. Results: Shoot Cd concentration decreased with harvest time in all soils but shoot Zn declined in S1 only. Similar shoot Zn concentrations were found in S2, S3 and S4 although these soils differed markedly in metal availability, and their available metals decreased during phytoextraction. A possible explanation is that plant active acquisition ability served to maintain plant metal uptake. Plant uptake resulted in the largest decrease in the acid-soluble metal fraction followed by reducible metals. Oxidisable and residual fractions were less available to plants. The coarse soil particle fractions made the major contribution to metal decline overall than the fine fractions. Conclusion: Sedum plumbizincicola maintained long term metal uptake and the coarse soil particles played the most important role in phytoextraction. [ABSTRACT FROM AUTHOR]

Abstract: Rational soil/rhizosphere-plant phosphorus (P) management strategies in intercropping systems are poorly understood. Three years of field experiments with different rates of P fertilizer (0, 40 and 80kgha−1) as main effects and maize (Zea mays L.) intercropping with oilseed rape (Brassica napus L.), turnip (Brassica campestris L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.) and soybean (Glycine max L.) with the respective monocultures as subplot effects were carried out to study the influence of fertilizer P application on productivity, shoot P content, apparent recovery of fertilizer P and soil Olsen-P in intercrops and monocultures. Average total grain yields and shoot P contents of maize/turnip, maize/faba bean, maize/chickpea and maize/soybean intercropping increased by 30.7%, 24.8%, 24.4%, and 25.3% and by 44.6%, 30.7%, 39.1%, and 28.6%, respectively, compared with the weighted means of the corresponding monocultures, and were highest at 40kgPha−1. Moreover, the average apparent recovery of fertilizer P of the intercropping systems increased from 6.1% to 30.6% at 40kgPha−1 and from 4.8% to 14.5% at 80kgPha−1 compared with overall monoculture systems on average over three years. The results indicate that intercropping and a rational P application rate (e.g. 40kgPha−1) maintained maximum total grain production and shoot P content, P balance of inputs/outputs and soil Olsen-P at an appropriate level (21.3mgkg−1), and maximum apparent recovery of fertilizer P (30.6%) through exploitation of the biological potential for efficient acquisition of P and other resources by interspecific interactions toward a sustainable and productive agricultural system. [Copyright &y& Elsevier]

We monitored soil respiration (Rs), soil temperature (T) and volumetric water content (VWC%) over four years in one typical conventional and four alternative cropping systems to understand Rs in different cropping systems with their respective management practices and environmental conditions. The control was conventional double-cropping system (winter wheat and summer maize in one year - Con.W/M). Four alternative cropping systems were designed with optimum water and N management, i.e. optimized winter wheat and summer maize (Opt.W/M), three harvests every two years (first year, winter wheat and summer maize or soybean; second year, fallow then spring maize - W/M-M and W/S-M), and single spring maize per year (M). Our results show that Rs responded mainly to the seasonal variation in T but was also greatly affected by straw return, root growth and soil moisture changes under different cropping systems. The mean seasonal CO2 emissions in Con.W/M were 16.8 and 15.1 Mg CO2 ha−1 for summer maize and winter wheat, respectively, without straw return. They increased significantly by 26 and 35% in Opt.W/M, respectively, with straw return. Under the new alternative cropping systems with straw return, W/M-M showed similar Rs to Opt.W/M, but total CO2 emissions of W/S-M decreased sharply relative to Opt.W/M when soybean was planted to replace summer maize. Total CO2 emissions expressed as the complete rotation cycles of W/S-M, Con.W/M and M treatments were not significantly different. Seasonal CO2 emissions were significantly correlated with the sum of carbon inputs of straw return from the previous season and the aboveground biomass in the current season, which explained 60% of seasonal CO2 emissions. T and VWC% explained up to 65% of Rs using the exponential-power and double exponential models, and the impacts of tillage and straw return must therefore be considered for accurate modeling of Rs in this geographical region. [ABSTRACT FROM AUTHOR]

Highlights: [•] Low Cu has no significant effect on Sedum plumbizincicola plant growth and Cd and Zn uptake. [•] Plant held Cu in unactive areas and insoluble forms as de-toxification mechanisms. [•] Influence of Cu on Zn and Cd uptake and translocation were different. [•] Cu accumulation in leaf veins may restrain Cd/Zn unloading to the leaves [ABSTRACT FROM AUTHOR]

Highlights: [•] A ‘competition–recovery–overyielding’ process was found in dynamics of root length growth and distribution of intercropped maize. [•] The stronger the associated crop roots, the more depressed the intercropped maize root development and shoot biomass. [•] Root lengths in 0–1.0m at jointing and in 0–0.3m of soil profiles at grain-filling were response to P fertilization. [•] Dynamics of root length growth and distribution correlated well with corresponding shoot biomass accumulation of maize. [ABSTRACT FROM AUTHOR]

The remediation effects of hydrogen peroxide (H 2 O 2) oxidation and surfactant-leaching alone or in combination on three typical oilfield sludges were studied. The removal efficiency of total petroleum hydrocarbons (TPHs) of Jidong, Liaohe and Jiangsu oil sludges by hydrogen peroxide oxidation alone was very poor (6.5, 6.8, and 3.4 %, respectively) but increased significantly (p < 0.05), especially of long-chain hydrocarbons, by combining the use of H 2 O 2 with surfactants (80.0, 79.8 and 82.2 %, respectively). Oxidation combined with leaching may impair microbial activity and organic manure was therefore added to the treated sludges for biostimulation and the composition and function of the microbial community were studied. The addition of manure rapidly restored sludge microbial activity and significantly increased the relative abundance of some salt-tolerant and alkali-tolerant petroleum-degrading bacteria such as Corynebacterium , Pseudomonas , Dietzia and Jeotgalicoccus. Moreover, the relative abundance of two classic petroleum-degrading enzyme genes, alkane 1-monooxygenase and catechol 1, 2-dioxygenase, increased significantly. • Peroxide combined with surfactant leaching enhanced C16–C40 fraction of TPH removal. • Manure application can rapidly restore the ecological function of treated sludges. • Relative abundances of two petroleum degradation genes increased significantly in treated sludge. [ABSTRACT FROM AUTHOR]