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There is increasing and widespread interest in the maintenance of soil quality and remediation strategies for management of soils contaminated with organic pollutants and trace metals or metalloids. There is also a growing body of evidence that arbuscular mycorrhizal (AM) fungi can exert protective effects on host plants under conditions of soil metal contamination. Research has focused on the mechanisms involved and has raised the prospect of utilizing the mutualistic association in soil re-vegetation programmes. In this short paper we briefly review this research, summarize some recent work and highlight some new data which indicate that the alleviation of metal phytotoxicity, particularly Zn toxicity, by arbuscular mycorrhiza may occur by both direct and indirect mechanisms. Binding of metals in mycorrhizal structures and immobilization of metals in the mycorrhizosphere may contribute to the direct effects. Indirect effects may include the mycorrhizal contribution to balanced plant mineral nutrition, especially P nutrition, leading to increased plant growth and enhanced metal tolerance. Further research on the potential application of arbuscular mycorrhiza in the bioremediation or management of metal-contaminated soils is also discussed. [ABSTRACT FROM AUTHOR]

Background and aims: The addition of organic amendments to soils can significantly increase soil organic matter (SOM) content as well as the mass of large (e.g. 2000-250 μm) particulate organic matter (POM) fractions. Here we address whether the addition of organic amendments might affect both POM pools and the phytoextraction efficiency of Sedum plumbizincicola (S. plumbizincicola) in cadmium (Cd) polluted soils.Methods: We carried out a 442-days long pot experiment and measured Cd uptake by S. plumbizincicola for four successive plant crops in two polluted paddy soils subjected to rice straw (RS) amendment. We also measured soil pH, nutrient availability, pore water dissolved organic carbon (DOC) and Cd concentrations across different soil particle-size fractions.Results: We found that RS amendments had no significant effects on soil pH, DOC or Cd concentrations in bulk soils during repeated phytoextraction. However, RS amendments were associated with significant (1) increases (i.e. 14.3 to 20.7%) in Cd uptake by S. plumbizincicola plants from the first crop harvest, (2) increases in available soil nutrients content, (3) increases in the percentage of oxidizable Cd fractions and the mass of soil POM fractions, and (4) decreases in POM Cd concentrations after repeated phytoextraction. These findings suggest that POM fractions may represent important accessible pools of Cd for uptake by S. plumbizincicola plants.Conclusions: RS amendments enhance both Cd bioavailability within soil POM pools and Cd uptake by the hyperaccumulator S. plumbizincicola thus providing an effective management practice to improve Cd removal from polluted soils through phytoextraction. [ABSTRACT FROM AUTHOR]

Background and aims: Overyielding in intercropping compared to monoculture has been widely reported. One of the mechanisms may be the alteration of the microbial community in intercropping and especially the amelioration of the negative effects of pathogens that can accumulate in monocultures. Here we test whether inoculation with arbuscular mycorrhizal fungi (AMF) and wheat take-all disease influences overyielding and whether changes in the microbial communities generate feedbacks on plant growth. Methods: In Experiment 1, wheat and faba bean were grown in monoculture or intercropping to form three planting patterns. Plants were inoculated with or without wheat take-all disease ( Gaeumannomyces graminis), and one, six, or no AM fungi, to create 6 soil conditioned treatments. Soils from Experiment 1 were used as inocula in Experiment 2 to test the feedback on plant growth from monocultures and the legacy benefits of intercropping. Results: No significant influence of AMF on plant growth was observed in either experiment. In Experiment 1, AMF had no significant effect in suppressing take-all but take-all tended to decrease AMF colonization. Shoot biomass and competitive ability of wheat was suppressed by take-all in both experiments. Wheat and faba bean showed overyielding in both the take-all and non-take-all treatment in Experiment 1 but only overyielding in the take-all treatment in Experiment 2. Growth of wheat and faba bean were suppressed in conspecific soil, and this negative feedback was observed across all take-all and AMF treatments, and regardless of competition. Biomass of wheat and faba bean was higher in soil from intercropping than in monoculture soil, and this positive legacy benefit of intercropping did not depend on take-all, AMF or plant competition. Conclusions: We find support for alterations of the soil community causing negative plant soil feedback and positive legacy benefits of intercropping. Our results are consistent with microbial dynamics generating overyielding in intercropping by reducing the negative influence of soil pathogen build-up on conspecific host plants and simultaneously compensatively improving growth of neighbor plants. [ABSTRACT FROM AUTHOR]

Aims: The rhizosphere microbiome plays an important role in plant growth and behavior during phytoremediation. This work aims to explore how hyperaccumulating plant performance (shoot biomass and Cd uptake) and rhizosphere bacterial community are driven by plant development under a Cd concentration gradient and their relationship during plant growth. Methods: A pot experiment was conducted using the Cd hyperaccumulator Sedum plumbizincicola grown in soil spiked with 0, 5 and 20 mg Cd kg−1 for 13 weeks. Plant performance (shoot biomass and Cd uptake) was determined and the rhizosphere bacterial community was examined by weekly Illumina sequencing. Biomarker genera were identified by the Random Forest model and the functions were predicted by PICRUSt2. Results: The rhizospheres bacterial community tended to stabilize from the 6th or 7th week regardless of the soil Cd concentration, coinciding with the vigorous growth stage of the hyperaccumulator. Biomarker genera Paenibacillus and Streptacidiphilus enriched in the stable stage showed significant positive correlations with Cd uptake. In addition, some predicted gene abundances of enzymes related to plant growth promotion by the rhizosphere bacterial community were influenced to various degrees by plant development and soil Cd concentration. Conclusion: There exists a stable bacterial community in the rhizosphere of S. plumbizincicola during phytoremediation and biomarker taxa enriched at this stage were positively correlated with Cd uptake. Selecting microorganisms that match the developmental stages might further enhance phytoremediation. This provides some theoretical basis for modulating rhizosphere microbes at the appropriate time during phytoextraction to optimize the phytoremediation technique. [ABSTRACT FROM AUTHOR]

Effects of long-term applications (50, 100 and 200 m3 ha−1y−1) of pig and cow slurries on yield, botanical composition and nutrient content of herbage of an original perennial ryegrass sward were assessed in a three-cut silage system and compared with unamended and fertilized controls in the 36th year of the experiment. Cow slurry at 50 m3 ha−1 produced similar annual herbage DM yield to 200 kg ha−1 fertilizer N in 2006, whereas about 100 m3 ha−1 pig slurry were required to produce a similar amount of DM. The highest slurry application rate significantly influenced sward botanical composition without depressing DM yield. The principal invading species were creeping bent and meadow grasses (similar to findings at a previous assessment in 1981) except in the unamended control (which were common bent and Yorkshire fog). Perennial ryegrass remained a main species in plots receiving fertilizer (31 % annual DM yield) and low slurry rates (38 %) but declined to 3 % annual DM yield at the highest slurry rate where the ability of ryegrass to utilize slurry N and P may have been affected by chemically or physically induced deficiencies of other nutrients (e.g. Ca) or direct physical effects such as smothering. [ABSTRACT FROM AUTHOR]

Nutrient and water management is crucially important in shallow-rooted vegetable production systems characterized by high input and high environmental risk. A 2-year field experiment on greenhouse cucumber double-cropping systems examined the effects of root zone nitrogen management and planting of sweet corn as a catch crop in the summer fallow period on cucumber yield and soil Nmin dynamics compared to conventional practices. Cucumber fruit yields were not significantly affected by root zone N management and catch crop planting despite a decrease in N fertilizer application of 53% compared to conventional N management. Soil Nmin content to a depth of 0.9 m decreased markedly and root zone (0–0.3 m) soil Nmin content was maintained at about 200 kg N ha−1. Root zone N management efficiently and directly reduced apparent N losses by 44% and 45% in 2005 and 2006, respectively. Sweet corn, the summer catch crop, depleted Nmin residue in the soil profile of 1.8 m at harvest of winter–spring season cucumber by 304–333 kg N ha−1, which contributed 19–22% reduction in N loss. Compared to conventional N management, N loss was reduced by 56% under root zone N management and catch crop planting. [ABSTRACT FROM AUTHOR]

A split root device was designed to assess the possible role of AMF in translocation and detoxification of As by maize plants. Half of each maize root system grew in As-amended or unamended soil and the remainder was inoculated with either Glomus mosseae or Acaulospora morrowiae. External mycelium was collected from a third compartment. Neither shoot nor root As concentrations were affected by inoculation with either fungus. Soil As amendment produced higher As concentrations in roots in the second compartment and in the external mycelium. The As concentrations in the matrix solution of the second root compartment were lower in mycorrhizal treatments with no differences in soluble As in the hyphal compartments. Mycorrhiza exerted little effect on As translocation within plants but may have influenced root As efflux. Deposition of As in external mycelium indicates a possible role of mycorrhizal fungi in the detoxification of As in the host plants. [ABSTRACT FROM AUTHOR]

Aims: There is little information available on the potential influence of soil micro-arthropods on the phytoremediation of metal-contaminated soils using hyperaccumulator plants. We hypothesized that soil micro-arthropods may promote organic matter decomposition, thereby releasing nitrogen and enhancing the growth of and metal uptake by hyperaccumulators and thereby increase phytoextraction efficiency. Methods: Four highly contaminated soils with a range of metal contents were used in a pot experiment to study the effects of the collembolan Folsomia candida and the mite Hypoaspis aculeifer on phytoextraction by Sedum plumbizincicola, a cadmium (Cd) and zinc (Zn) hyperaccumulator. Results: Both micro-arthropods survived when the hyperaccumulator grew in the four soils. F. candida slightly increased the growth of S. plumbizincicola and shoot metal concentrations increased significantly in the presence of F. candida with or without H. aculeifer. Soil fauna increased shoot Cd accumulation by 27.9–66.3% compared to corresponding control soils. Similar shoot 15N abundances across treatments and decreasing shoot N content in two of the soils with addition of F. candida indicate that the promotion of phytoextraction was not associated with increasing plant nitrogen uptake from organic matter by F. candida. Conclusions: The mechanism of plant growth promotion might be an interaction between the soil fauna and the roots of the hyperaccumulator and this merits further investigation. This work highlights for the first time a potential role of soil micro-arthropods in the phytoextraction of metal-polluted soils. [ABSTRACT FROM AUTHOR]

Background and aims: Soil cadmium (Cd) contamination threatens food safety and human health. Increasing Cd phytoextraction efficiency by hyperaccumulators and growing safe products during remediation remain challenges. Methods: A pot experiment was conducted to explore the effects of different rates of sulfur (S) associated with alternating drying and wetting on a Sedum plumbizincicola-Oryza sativa rotation in Cd-contaminated neutral and calcareous soils. Results: The oxidation of added S under aerobic conditions significantly decreased soil solution pH and increased soluble sulfate (SO42−), Cd and iron (Fe) concentrations in both soils. During the rice growing season the soil solution redox (Eh) decreased to < −200 mV and the solution pH increased to neutral during the first few days of flooding. Soluble SO42− and Cd in the S treatments decreased significantly with increasing duration of flooding. Sulfur addition promoted shoot Cd concentrations of S. plumbizincicola by 1.7–5.5 times on calcareous soil and 1.7–2.3 times on neutral soil compared to the controls. Rice yields increased but Cd concentrations decreased at suitable S addition rates. Conclusions: Appropriate sulfur amendment combined with water management can be a feasible strategy to enhance the Cd remediation efficiency of the hyperaccumulator and reduce the accumulation of Cd in the rice grains in this rotation. [ABSTRACT FROM AUTHOR]

Aims: Plant roots can significantly alter soil pH and the chemical concentration and distribution of different elements in the rhizosphere environment. Here we ask whether cadmium (Cd) bioavailability in the rhizosphere of Cd-hyperaccumulator Sedum plumbizincicola can be influenced by root-induced effects on soil pH.Methods: The Cd-hyperaccumulator S. plumbizincicola and the Cd non-hyperaccumulator ecotype Sedum alfredii were both grown in four different Cd-contaminated soils. We used the planar optode imaging technique to produce two-dimensional and high-resolution measurements of soil pH. Shoot excess cation concentration, root architecture and Cd concentrations ([Cd]) in soil pore water were also measured. Spatial analyses based on kernel density estimate of roots (KDE) and a Moran's I correlogram were performed to assess spatial patterns and potential relationships among root distribution, soil pH and [Cd].Results: Both Sedum species showed root-induced increases in soil acidification (i.e. soil pH decreases of 0.1 to 0.62 units), which were clearly associated with greater root density of these plants. Remarkable excess cation uptakes by both Sedum species were detected and likely a driving factor for the root-induced acidification. The presence of the roots of S. plumbizincicola were then related to higher [Cd] in the rhizosphere than in bulk soil in Orthic Acrisol (+342%) and in Hydragric Antrosol soils (+296%). The hyperaccumulator S. plumbizincicola had larger root systems, higher acidification ability, and was associated with greater soil [Cd] than S. alfredii. Spatial patterns of root distribution and soil pH were similar between Sedum plants, however, spatial patterns of [Cd] differed across polluted soils.Conclusion: Rhizosphere acidification induced by S. plumbizincicola plants can play an important role on soil Cd mobilization, but overall effects on soil Cd bioavailability will depend on intrinsic soil biogeochemical properties. [ABSTRACT FROM AUTHOR]

Background and Aims: Studies verify that intercropping increases soil macro-aggregates but the mechanism underlying the increase is poorly understood.Methods: Three long-term field experiments were conducted starting in 2009 at three sites in an oasis in northwest China. The first was a split-plot design: Rhizobium (with or without inoculation) and three cropping systems (faba bean/maize intercropping and corresponding monocultures). The second and third experiments were both single-factorial randomized block designs with nine cropping systems (maize intercropped with faba bean, chickpea, soybean, or oilseed rape, and the corresponding monocultures). Soil aggregates were determined by the wet sieving method. Microbial biomass and community composition in 2015 and 2016 were determined by phospholipid fatty acid (PLFA) and high throughput sequencing analysis of 16S rRNA.Results: Soil macro-aggregates (> 2 mm) in intercropping systems increased by 15.5-58.6% across three sites and two years, an effect derived partly from increased relative abundance of soil Sordariales, from enhanced arbuscular mycorrhizal fungi biomass, or from reduced relative abundance of Nitrospirae, depending on soil type.Conclusions: Intercropping alters soil microbial community composition and further facilitates soil aggregation. These findings provide insights into the mechanisms underlying the maintenance of biodiversity in ecosystem functioning. [ABSTRACT FROM AUTHOR]

Aims: Recent research on the rhizosphere microbiome indicates that plants may benefit more from microbial communities than from individual members in a community. The link between soil microbiome and plant performance remains poorly understood during trace metal phytoremediation by hyperaccumulator plants. The effect of different microbiomes on the cadmium (Cd)/zinc (Zn) phytoextraction efficiency of Sedum plumbizincicola was therefore explored. Methods: Different microbiomes were set up using γ-irradiation and vancomycin addition and a pot experiment was conducted. The microbial communities were characterized using high-throughput sequencing and their functions were predicted. Results: Plant Cd and Zn contents in the vancomycin-amended treatment were about 38-46% and 35%-53% respectively lower than those in the other treatments. Bacterial composition and diversity were substantially changed by γ-irradiation and vancomycin addition but plant trace metal accumulation did not change subsequently. The bacterial functional profiles were very different following treatment with vancomycin compared with the other treatments at KEGG orthology hierarchy level 3. Genes related to up-regulated biofilm formation and down-regulated siderophore synthesis may partly contribute together to the low plant trace metal accumulation following vancomycin treatment. Conclusions: Specific bacterial community function rather than bacterial community diversity and composition may affect trace metal uptake by hyperaccumulator plants. [ABSTRACT FROM AUTHOR]

Background and aims: Intercropping often produces more biomass than the average of the corresponding monocultures, particularly in sustainable, low-input agriculture. Characterizing plant-plant interactions is fundamental for a better understanding of the ecological functioning of intercropping. However, there is little information on whether mycorrhizal networks exhibit different effects upon intra- and interspecific plant interactions in intercropping systems. Methods: Microcosms with one inner and three outer compartments were used. The inner compartment was separated from the outer compartments by a 30-μm nylon mesh or a solid barrier or remained open to allow full interactions between plants grown in the different compartments, creating three treatments, namely −Roots−CMNs (solid barrier), −Roots+CMNs (mesh), and +Roots+CMNs (no barrier). Either faba bean ( Vicia faba) or maize ( Zea mays) was grown as the donor plant in the inner compartment. Maize was combined with maize, wheat ( Triticum aestivum) or the weed species foxtail ( Setaria viridis) as the neighboring plant species. Faba bean was combined with faba bean, maize, or foxtail. The low-P soil was inoculated with the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae or remained uninoculated. Results: In the absence of AMF, plant growth was restricted by P deficiency and root interactions did not significantly affect plant-plant interactions. The presence of AMF enhanced plant biomass (maize by 104.5 %, faba bean by 61.6 %) and nutrient (N and P) uptake. Significant overyielding occurred in treatments where roots and hyphal networks of all plant species intermingled. The weed (foxtail) was suppressed by interspecific interactions while maize and faba bean benefitted from a mycorrhizal network and the presence of intermingling roots. Conclusions: In low-P soils, mycorrhizal networks contribute to overyielding in intercropping by enhancing the biomass and nutrient uptake of the mycorrhiza-dependent plant species. The biomass depression of weed species by AMF and/or root interactions may have ecological implications in weed control in intercropping systems. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

Increasing crop nitrogen use efficiency while also simultaneously decreasing nitrogen accumulation in the soil would be key steps in controlling nitrogen pollution from agricultural systems. Long-term field experiments were started in 2003 to study the effects of intercropping on crop N use and soil mineral N accumulation in wheat ( Triticum aestivum L. cv 2014)/maize ( Zea mays L. cv Shendan16), wheat/faba bean ( Vicia faba L. cv Lincan No. 5) and maize/faba bean intercropping and monocropping systems. Monocropping was compared with two types of strip intercropping: continuous intercropping (two crops intercropped continuously on the same strips of land every year) and rotational intercropping (two crops grown adjacently and rotated to the other crop's strip every year). Maize/faba bean intercropping had greater crop N uptake than did wheat/faba bean or wheat/maize. Wheat/maize accumulated more mineral N in the top 140 cm of the soil profile during the co-growth stage from maize emergence to maturity of wheat or faba bean. Continuously intercropped maize substantially decreased soil mineral N accumulation under wheat and faba bean rows (60-100 cm soil depth) at maize harvest. Soil mineral N accumulation under wheat rows increased with rotational intercropping with faba bean. Rotational intercropping may potentially alleviate the adverse effects of wheat on N use by other crops and increase the nitrogen harvest index of wheat, maize and faba bean. Intercropping using species with different maturity dates may be more effective in increasing crop N use efficiency and decreasing soil mineral N accumulation. [ABSTRACT FROM AUTHOR]

mospheric nitrogen (N) deposition is a serious problem on the North China Plain (NCP) because it imposes a considerable nutrient burden on the local environment. However, it also makes a substantial contribution to agricultural crop N requirements. The integrated total N input (ITNI) system is a method to quantify total atmospheric N deposition by using N-labeled monitor plants grown in pots. The effect of pot surface area and variety of indicator plant on the amount of airborne N input quantified by the ITNI system was investigated in this study. Total N deposition to the soil-maize/soil-wheat plant system at key growth stages was also quantified to improve N-fertilizer recommendations. When indicator plants having a high space requirement were used a correction factor was needed and this could be obtained only by simulating commercial field conditions, especially plant density, because the factor depends largely on pot area or the difference in plant density between pot conditions and field conditions. The total airborne N input measured by the ITNI system was not influenced by the variety of monitoring plant. N deposition was 20-25 kg N ha during growth from three expanded leaf to ten expanded leaf and also from ten expanded leaf to maturity of maize. N deposition was 29.1 kg N ha between planting and the jointing stage and 10.1 kg N ha from jointing to maturity of wheat. This high measured N deposition indicates that N deposition should be taken into account when calculating the N fertilizer requirements of maize and wheat in this region. [ABSTRACT FROM AUTHOR]

Interspecific interactions and soil nitrogen supply levels affect intercropping productivity. We hypothesized that interspecific competition can be alleviated by increasing N application rate and yield advantage can be obtained in competitive systems. A field experiment was conducted in Wuwei, Gansu province in 2007 and 2008 to study intercropping of faba bean/maize, wheat/maize, barley/maize and the corresponding monocultures of faba bean ( Vicia faba L.), wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.) and maize ( Zea mays L.) with N application rates of 0, 75, 150, 225 and 300 kg N ha. Total land equivalent ratios (TLER) were 1.22 for faba bean/maize, 1.16 for wheat/maize, and 1.13 for barley/maize intercropping over the 2-year study period. Maize was overyielding when intercropped with faba bean, but underyielding when intercropped with wheat or barley according to partial land equivalent ratios (PLER) based on grain yields of individual crops in intercropping and sole cropping. There was an interspecific facilitation between intercropped faba bean and maize, and interspecific competition between maize and either wheat or barley. The underyielding of maize was higher when intercropped with barley than with wheat. Fertilizer N alleviated competitive interactions in intercrops with adequate fertilizer N at 225 kg ha. Yield advantage of intercropping can be acquired with adequate nitrogen supply, even in an intensive competitive system such as barley/maize intercropping. This is important when using intercropping to develop intensive farming systems with high inputs and high outputs. [ABSTRACT FROM AUTHOR]

A field experiment was conducted for 5 years to examine the effects of non-flooded mulching cultivation on crop yield, internal nutrient efficiency and soil properties in rice–wheat (R–W) rotations of the Chengdu Plain, southwest China. Compared with traditional flooding (TF), non-flooded plastic film mulching (PM) resulted in 12 and 11% higher average rice ( Oryza sativa L.) yield and system productivity (combined rice and wheat yields), and the trends in rice and wheat ( Triticum aestivum L.) yields under PM were stable over time. However, non-flooded wheat straw mulching (SM) decreased average rice yield by 11% compared with TF, although no significant difference in system productivity was found between SM and TF. Uptakes of N and K by rice under PM were higher than those under TF and SM, but internal nutrient efficiency was significantly lower (N) or similar (K) under PM compared to SM and TF. This implies that more N and K accumulated in rice straw under PM. After 5-year rice–wheat rotation, apparent P balances (112–160 kg ha−1) were positive under all three cultivation systems. However, the K balances were negative under PM (−419 kg ha−1) and TF (−90 kg ha−1) compared with SM (45 kg ha−1). This suggests that higher K inputs from fertilizer, straw or manure may be necessary, especially under PM. After five rice seasons and four wheat seasons, non-flooded mulching cultivation led to similar (PM) or higher (SM) soil organic carbon (SOC), total N (TN) and alkali hydrolyzable N (AH-N) in the top 0–5 and 5–12 cm layers compared with TF. SOC, TN, AH-N and Olsen-P (OP) in the sub-surface layer (12–24 cm) were significantly higher under PM or SM than under TF, indicating that rice under non-flooded mulching conditions may fail to make use of nutrients from the subsoil. Thus, the risk of decline in soil fertility under non-flooded mulching cultivation could be very low if input levels match crop requirements. Our data indicate that PM and SM may be alternative options for farmers using R–W rotations for enhancement or maintenance of system productivity and soil fertility. [ABSTRACT FROM AUTHOR]

Growth, proton and oxalate efflux, K absorption and mineral depletion by one isolate of Cenococcum geophilum Fr., by a putative isolate of Pisolithus microcarpus and by two isolates of Pisolithus sp. were compared in pure liquid culture using either vermiculite or phlogopite as sole K source. An isolate from China (Pisolithus strain XC1) showed greatest biomass and K accumulation from both minerals. There were inverse correlations between reduction in HCl-extractable K and fungal proton efflux (r=-0.912, P<0.001) and between the ratio (total K lost from the substrate: K accumulation in hyphae) and oxalate efflux (r=-0.890, P<0.001). Protons effused from the fungi may have replaced interlayer K, and oxalate effused may have led to biological weathering of the minerals, especially under conditions of limited exchangeable K with phlogopite as K source. Pisolithus sp. and Pisolithus XC1 gave high depletion rates of CH3COONH4- and HCl-extractable K from the minerals and were therefore selected to study the growth and mobilization and utilization of K from the minerals by ectomycorrhizal eucalypt (Eucalyptus globulus Labill.) seedlings. Mycorrhizal seedlings extracted more K from the two minerals than did non-mycorrhizal controls, and those colonized by Pisolithus XC1 accumulated much more K than those inoculated with Pisolithus sp., a similar trend to fungal K accumulation in vitro. Non-mycorrhizal seedlings extracted very little HF-HClO4-extractable K from the minerals following sequential extraction with H2O, CH3COONH4 and HCl. In contrast, mycorrhizal seedlings significantly depleted K, although there was no difference between the two fungal strains. Patterns of depletion of sequentially extractable K fractions in the minerals by the fungi in pure culture in vitro differed from those exhibited by the fungus-root associations. [ABSTRACT FROM AUTHOR]

We report for the first time the establishment of an arbuscular mycorrhizal association between Glomus sinuosum (= Sclerocystis sinuosa) and transformed Ri T-DNA carrot (Daucus carota L.) roots in monoxenic culture. The G. sinuosum sporocarps survived not as single spores, but as sporocarps in the environment. The mode of germination of G. sinuosum was by extension of hyphae around the sporocarp. Numerous vegetative spores, arbuscules and vesicles were produced after the roots were infected by the hyphae. New mature sporocarps started to form after four months in the culture system. Forty-seven sporocarps were produced on average in each culture dish after six months, and these newly produced sporocarps were capable of germination in the growth medium. [ABSTRACT FROM AUTHOR]

Interactions between Se (as selenate) and I (as iodate) uptake by spinach plants (Spinacia oleracea L.) were studied under controlled conditions using solution culture. Spinach readily accumulated both Se and I in the edible parts, the leaves, with solution-to-leaf transfer factors ranging from 3.5 to 13.4. The distribution coefficients between leaves and roots ranged from 4.07 to 5.66 for I and 4.51 to 8.59 for Se. Selenium concentrations in plant tissues were unaffected by addition of I to the nutrient solution. Similarly, plant I concentrations were unaffected by addition of Se to the nutrient solution, except in nutrient solution with I at a concentration of 50 μM, in which addition of Se lowered shoot I concentrations significantly, but the effect was of low magnitude. These results indicate the possible feasibility of dual supplementation of plant growth substrates with Se and I to improve human nutrition where these two elements are deficient in the diet. The data also indicate the involvement of a positive feedback mechanism in the uptake of Se by spinach plants, since Se concentrations in leaves increased disproportionately with increasing Se concentration in the nutrient solution. [ABSTRACT FROM AUTHOR]

Enhancement of Pb and Zn uptake by Indian mustard (Brassica juncea (L.) Czern.) and winter wheat (Triticum aestivum L.) grown for 50 days in pots of contaminated soil was studied with application of elemental sulphur (S) and EDTA. Sulphur was added to the soil at 5 rates (0–160 mmol kg-1) before planting, and EDTA was added in solution at 4 rates (0–8 mmol kg-1) after 40 days of plant growth. Additional pots were established with the same rates of S and EDTA but without plants to monitor soil pH and CaCl2-extractable heavy metals. The highest application rate of S acidified the soil from pH 7.1 to 6.0. Soil extractable Pb and Zn and shoot uptake of Pb and Zn increased as soil pH decreased. Both S and EDTA increased soil extractable Pb and Zn and shoot Pb and Zn uptake. EDTA was more effective than S in increasing soil extractable Pb and Zn, and the two amendments combined had a synergistic effect, raising extractable Pb to ¿1000 and Zn to ¿6 times their concentrations in unamended control soil. Wheat had higher shoot yields than Indian mustard and increasing application rates of both S and EDTA reduced the shoot dry matter yields of both plant species to as low as about half those of unamended controls. However, Indian mustard hyperaccumulated Pb in all EDTA treatments tested except the treatment with no S applied, and the maximum shoot Pb concentration was 7100 mg kg-1 under the highest application rates of S and EDTA combined. Wheat showed similar trends, but hyperaccumulation (1095 mg kg-1) occurred only at the highest rates of S and EDTA combined. Similar trends in shoot Zn were found, but with lower concentrations than Pb and far below hyperaccumulation, with maxima of 777 and 480 mg kg-1 in Indian mustard and wheat. Despite their lower yields, Indian mustard shoots extracted more Pb and Zn from the soil (up to 4.1 and 0.45 mg pot-1) than did winter wheat (up to 0.72 and 0.28 mg pot-1), indicating that the effects of S and EDTA on shoot metal concentration were more important than yield effects in determining rates of metal removal over the growth period of 50 days. Phytoextraction of Pb from this highly contaminated soil would require the growth of Indian mustard for nearly 100 years and is therefore impractical. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to investigate the uptake of Zn from experimentally contaminated calcareous soil of low nutrient status by maize inoculated with the arbuscular mycorrhizal (AM) fungus Glomus caledonium. EDTA was applied to the soil to mobilize Zn and thus maximize plant Zn uptake. The highest plant dry matter (DM) yields were obtained with a moderate Zn addition level of 300 mg kg-1. Plant growth was enhanced by mycorrhizal colonization when no Zn was added and under the highest Zn addition level of 600 mg kg-1, while application of EDTA to the soil generally inhibited plant growth. EDTA application also increased plant Zn concentration, and Zn accumulation in the roots increased with increasing EDTA addition level. The effects of inoculation with G. caledonium on plant Zn uptake varied with Zn addition level. When no Zn was added, Zn translocation from roots to shoots was enhanced by mycorrhizal colonization. In contrast, when Zn was added to the soil, mycorrhizal colonization resulted in lower shoot Zn concentrations in mycorrhizal plants. The P nutrition of the maize was greatly affected by AM inoculation, with mycorrhizal plants showing higher P concentrations and P uptake. The results indicate that application of EDTA mobilized soil Zn, leading to increased Zn accumulation by the roots and subsequent plant toxicity and growth inhibition. Mycorrhizal colonization alleviated both Zn deficiency and Zn contamination, and also increased host plant growth by influencing mineral nutrition. However, neither EDTA application nor arbuscular mycorrhiza stimulated Zn translocation from roots to shoots or metal phytoextraction under the experimental conditions. The results are discussed in relation to the environmental risk associated with chelate-enhanced phytoextraction and the potential role of arbuscular mycorrhiza in soil remediation. [ABSTRACT FROM AUTHOR]