Mycorrhizal colonization and grain Cd concentration of field-grown durum wheat in response to tillage, preceding crop and phosphorus fertilization

Managing mineral phosphorus application with soil residual phosphorus reuse in Canada

With limited phosphorus (P) supplies, increasing P demand, and issues with P runoff and pollution, developing an ability to reuse the large amounts of residual P stored in agricultural soils is increasingly important. In this study, we investigated the potential for residual soil P to maintain crop yields while reducing P applications and losses in Canada. Using a P cycling model coupled with a soil P dynamics model, we analyzed soil P dynamics over 110 years across Canada's provinces. We found that using soil residual P may reduce mineral P demand as large as 132 Gg P year-1 (29%) in Canada, with the highest potential for reducing P applications in the Atlantic provinces, Quebec, Ontario, and British Columbia. Using residual soil P would result in a 21% increase in Canada's cropland P use efficiency. We expected that the Atlantic provinces and Quebec would have the greatest runoff P loss reduction with use of residual soil P, with the average P loss rate decreasing from 4.24 and 1.69 kg ha-1 to 3.45 and 1.38 kg ha-1 , respectively. Ontario, Manitoba, and British Columbia would experience relatively lower reductions in P loss through use of residual soil P, with the average runoff P loss rate decreasing from 0.44, 0.36, and 4.33 kg ha-1 to 0.19, 0.26, and 4.14 kg ha-1 , respectively. Our study highlights the importance of considering residual soil P as a valuable resource and its potential for reducing P pollution.

The role of roots and rhizosphere in providing tolerance to toxic metals and metalloids

Human activity and natural processes have led to the widespread dissemination of metals and metalloids, many of which are toxic and have a negative impact on plant growth and development. Roots, as the first point of contact, are essential in endowing plants with tolerance to excess metal(loid) in the soil. The most important root processes that contribute to tolerance are: adaptation of transport processes that affect uptake efflux and long-distance transport of metal(loid)s; metal(loid) detoxification within root cells via conjugation to thiol rich compounds and subsequent sequestration in the vacuole; plasticity in root architecture; the presence of bacteria and fungi in the rhizosphere that impact on metal(loid) bioavailability; the role of root exudates. In this review, we provide details on these processes and assess their relevance on the detoxification of arsenic, cadmium, mercury and zinc in crops. Furthermore, we assess which of these strategies have been tested in field conditions and whether they are effective in terms of improving crop metal(loid) tolerance.

Comparative Small RNA Profiling and Functional Exploration on Wheat With High- and Low-Cadmium Accumulation

Cadmium is a toxic metal widely found in workplaces and plant soil because of extensive industrialization. Wheat is an important source of food generated from plant soil. The different responses of wheat against different omic levels of cadmium have been observed and widely studied worldwide. With the development of high-throughput sequencing, micro-level biological research has extended to the microRNA level. In this study, high-cadmium-accumulating wheat cultivars (Annong9267) and low-cadmium-accumulating wheat cultivars (Qian 102032) were used as experimental models. The two cultivars were treated by Cd for 2 h to explore the microRNA profiles in root and leaf tissues through small RNA sequencing. Important small RNAs, such as tae-miR9663-5p and tae-miR6201, and potential small RNA-mediated mechanisms associated with cadmium accumulation were identified by summarizing specific microRNA profiling patterns and their respective target genes. At the wheat roots and leaves, differentially expressed small RNAs related to cadmium accumulation in different plant tissues (roots or leaves) were identified, and functional enrichment analyses on target genes of differentially expressed miRNAs in low- and high-cadmium-accumulating wheat cultivars in different plant tissues (roots or leaves) obtained some known mature miRNAs and new miRNAs. The identified miRNA will be regarded as a potential screening biomarker for low-cadmium-accumulating wheat.

Insights into the antibacterial activity of cottonseed protein-derived peptide against Escherichia coli

In the study, antibacterial peptides were separated and identified from cottonseed protein hydrolysates and the interactions between antibacterial peptides and Escherichia coli were further investigated. Firstly, by using a combined strategy of Amberlite CG-50 ion exchange chromatography and reversed-phase high-performance liquid chromatography, three peptides with antibacterial activity were purified and identified, including HHRRFSLY, KFMPT, and RRLFSDY. Interestingly, HHRRFSLY and RRLFSDY exhibited higher inhibition activity with the IC50 value of 0.26 mg mL-1 and 0.58 mg mL-1 (p < 0.05), respectively. Flow cytometry results showed that the incubation of antibacterial peptides with E. coli could cause damage to the integrity of the E. coli cell membrane. Transmission electron microscopy and scanning electron microscopy results revealed the damage caused to the bacterial cell surface and the leakage of cytoplasmic content by the antibacterial peptides. Molecular docking studies indicated that HHRRFSLY, KFMPT, and RRLFSDY have a good binding affinity to the active sites of the surface protein (OmpF) mainly through a hydrogen bond and salt bridge. The results here showed that the antibacterial peptides derived from cottonseed protein could be used as a good choice for functional foods or related drugs, and also shed light on further studies of antibacterial mechanism.

Management of trace element-contaminated agricultural land by in situ stabilization combined with phytoexclusion over a three years crop rotation

This study assessed in situ stabilization combined with phytoexclusion in practical application on agricultural land contaminated strongly, and spatially heterogeneous, with metals (Cd, Pb, and Zn) and As. Single and combined lime marl and phosphate treatments were consecutively planted with two cultivars each of rape, wheat, and barley differing in trace elements (TE) accumulation. The effects on soil acidity, NH₄NO₃-soluble, and straw and grain TE concentrations were evaluated. The combined fertilizer treatment most effectively reduced metals mobility, but neither amendment mitigated plant TE status, which correlated more with pseudo-total than NH₄NO₃-soluble TE in soil. The cultivar choice reduced grain Cd by 39 or 21% in barley or wheat, respectively, simultaneously decreased grain Zn, but conversely affected As uptake in wheat grains. The lack of correlations between grain TE concentrations suggests the potential for breeding cultivars with low Cd and As accumulation without causing Zn malnutrition. The cereals had relatively low yields, particularly on highly polluted areas, and only rape and barley grains unexceptionally suited for animal consumption. Agricultural measures and climatic conditions influenced TE mobility. The cultivars' TE uptake varied less than in greenhouse studies, stressing the importance of field studies for an adequate estimation of phytoexclusion potentials.

Soil-indigenous arbuscular mycorrhizal fungi and zeolite addition to soil synergistically increase grain yield and reduce cadmium uptake of bread wheat (through improved nitrogen and phosphorus nutrition and immobilization of Cd in roots)

Soil pollution with heavy metals is a major problem in industrial areas. Here, we explored whether zeolite addition to soil and indigenous arbuscular mycorrhizal fungi (AMF) can reduce cadmium (Cd) uptake from soil by bread wheat. We conducted a pot experiment, in which the effects of indigenous soil AMF, zeolite addition, and Cd spiking to soil [0, 5, 10, and 15 mg (kg soil)^-1] were tested. Zeolite addition to soil spiked with 15 mg Cd kg^-1 decreased the Cd uptake to grains from 11.8 to 8.3 mg kg^-1 and 8.9 to 3.3 mg kg^-1 in the absence and presence of indigenous AMF, respectively. Positive growth, nitrogen (N), and phosphorous (P) uptake responses to mycorrhization in Cd-spiked soils were consistently magnified by zeolite addition. Zeolite addition to soil stimulated AMF root colonization. The abundance of AMF taxa changed in response to zeolite addition to soil and soil Cd spiking as measured by quantitative polymerase chain reaction. With increasing Cd spiking, the abundance of Funneliformis increased. However, when less Cd was spiked to soil and/or when zeolite was added, the abundance of Claroideoglomus and Rhizophagus increased. This study showed that soil-indigenous AMF and addition of zeolite to soil can lower Cd uptake to the grains of bread wheat and thereby reduce Cd contamination of the globally most important staple food.

Spatial distribution and risk assessment of heavy metals in contaminated paddy fields - A case study in Xiangtan City, southern China

An extensive investigation on spatial distribution and environmental risk assessment based on total content and fractions of heavy metals, as well as the cancer risk of Cd from seven adjacent contaminated paddy fields at Xiangtan City, southern China, was conducted in this study. A total of 63 soil samples were analyzed for soil physical properties and concentrations of eight heavy metals (Cd, Cr, Co, Cu, Mn, Ni, Pb, Zn). The results showed that concentrations of metals except for Cr, Mn and Ni exceeded the background values to varying degrees, and particularly, content of Cd was as 57.4-612 times higher than background values. Principal components analysis and correlation analysis revealed three groups: industry activities for Cd and Zn; natural sources mainly for Cu, Pb, Ni and Cr, with some slight anthropogenic activities for Cu and Pb accumulation; and manganese ore associated with cobalt for Co and Mn. Combined with different indices, Cd and Zn were the major contributors to the ecological risk, and cancer risk of Cd indicated an unacceptable degree in this area. Altogether, results from this study will facilitate a better understanding of metals distribution characteristics and provide a scientific basis for further comprehensive management for these paddy fields. Combination of functional microbial agent and plants promises to be a feasible and effective remediation method for cadmium pollution in the study area.

Little evidence that farmers should consider abundance or diversity of arbuscular mycorrhizal fungi when managing crops

Contents Summary 1092 I. Introduction 1093 II. Investigating activity of AMF in agroecosystems 1093 III. Crop benefit from AMF: agronomic and mycorrhizal literature differ 1094 IV. Flawed methodology leads to benefits of mycorrhizas being overstated 1094 V. Rigorous methodology suggests low colonisation by AMF can sometimes reduce crop yield 1095 VI. Predicting when mycorrhizas matter for crop yield 1096 VII. Crop genotype 1099 VIII. Fungal genotype 1100 IX. Complex interactions between the mycorrhizal fungal and soil microbial communities 1102 X. Phosphorus-efficient agroecosystems 1102 XI. Conclusions 1103 Acknowledgements 1104 References 1104 SUMMARY: Arbuscular mycorrhizal fungi (AMF) are ubiquitous in agroecosystems and often stated to be critical for crop yield and agroecosystem sustainability. However, should farmers modify management to enhance the abundance and diversity of AMF? We address this question with a focus on field experiments that manipulated colonisation by indigenous AMF and report crop yield, or investigated community structure and diversity of AMF. We find that the literature presents an overly optimistic view of the importance of AMF in crop yield due, in part, to flawed methodology in field experiments. A small body of rigorous research only sometimes reports a positive impact of high colonisation on crop yield, even under phosphorus limitation. We suggest that studies vary due to the interaction of environment and genotype (crop and mycorrhizal fungal). We also find that the literature can be overly pessimistic about the impact of some common agricultural practices on mycorrhizal fungal communities and that interactions between AMF and soil microbes are complex and poorly understood. We provide a template for future field experiments and a list of research priorities, including phosphorus-efficient agroecosystems. However, we conclude that management of AMF by farmers will not be warranted until benefits are demonstrated at the field scale under prescribed agronomic management.

Trace elements bioavailability to winter wheat (Triticum aestivum L.) grown subsequent to high biomass plants in a greenhouse study

Multielement-contaminated agricultural land requires the adaptation of agronomic practices to meet legal requirements for safe biomass production. The incorporation of bioenergy plants with, at least, moderate phytoextraction capacity into crop rotations with cereals can affect trace elements (TE) phytoavailability and, simultaneously, constitute economic revenues for farmers outside the food or forage sector. Hence, in a crop rotation pot study sunflower (Helianthus annuus L.), modified for high biomass and TE accumulation by chemical mutagenesis, was compared to winter oilseed rape (Brassica napus L.) as pre-crop. On two agricultural soils with different TE loads, the crops´ potential for phytoextraction and for impacts on TE uptake by subsequent winter wheat (Triticum aestivum L.) was studied. The results showed that rape tolerated high-level mixed contamination with metals (Cd, Pb and Zn) and As more than sunflower. In both soils, labile metals concentration increased and soil acidity remained high following sunflower. Furthermore, enhanced grain As accumulation in subsequent wheat was observed. By contrast, soil acidity and Cd or Zn accumulation of subsequent wheat decreased following rape. In the short term, moderate phytoextraction was superimposed by nutrient use or rhizosphere effects of pre-crops, which should be carefully monitored when designing crop rotations for contaminated land.

Soil inoculation with symbiotic microorganisms promotes plant growth and nutrient transporter genes expression in durum wheat

In a field experiment conducted in a Mediterranean area of inner Sicily, durum wheat was inoculated with plant growth-promoting rhizobacteria (PGPR), with arbuscular mycorrhizal fungi (AMF), or with both to evaluate their effects on nutrient uptake, plant growth, and the expression of key transporter genes involved in nitrogen (N) and phosphorus (P) uptake. These biotic associations were studied under either low N availability (unfertilized plots) and supplying the soil with an easily mineralizable organic fertilizer. Regardless of N fertilization, at the tillering stage, inoculation with AMF alone or in combination with PGPR increased the aboveground biomass yield compared to the uninoculated control. Inoculation with PGPR enhanced the aboveground biomass yield compared to the control, but only when N fertilizer was added. At the heading stage, inoculation with all microorganisms increased the aboveground biomass and N. Inoculation with PGPR and AMF+PGPR resulted in significantly higher aboveground P compared to the control and inoculation with AMF only when organic N was applied. The role of microbe inoculation in N uptake was elucidated by the expression of nitrate transporter genes. NRT1.1, NRT2, and NAR2.2 were significantly upregulated by inoculation with AMF and AMF+PGPR in the absence of organic N. A significant down-regulation of the same genes was observed when organic N was added. The ammonium (NH4 (+)) transporter genes AMT1.2 showed an expression pattern similar to that of the NO3 (-) transporters. Finally, in the absence of organic N, the transcript abundance of P transporters Pht1 and PT2-1 was increased by inoculation with AMF+PGPR, and inoculation with AMF upregulated Pht2 compared to the uninoculated control. These results indicate the soil inoculation with AMF and PGPR (alone or in combination) as a valuable option for farmers to improve yield, nutrient uptake, and the sustainability of the agro-ecosystem.

Metabolomics Suggests That Soil Inoculation with Arbuscular Mycorrhizal Fungi Decreased Free Amino Acid Content in Roots of Durum Wheat Grown under N-Limited, P-Rich Field Conditions

Arbuscular mycorrhizal fungi (AMF) have a major impact on plant nutrition, defence against pathogens, a plant’s reaction to stressful environments, soil fertility, and a plant’s relationship with other microorganisms. Such effects imply a broad reprogramming of the plant’s metabolic activity. However, little information is available regarding the role of AMF and their relation to other soil plant growth—promoting microorganisms in the plant metabolome, especially under realistic field conditions. In the present experiment, we evaluated the effects of inoculation with AMF, either alone or in combination with plant growth–promoting rhizobacteria (PGPR), on the metabolome and changes in metabolic pathways in the roots of durum wheat (Triticum durum Desf.) grown under N-limited agronomic conditions in a P-rich environment. These two treatments were compared to infection by the natural AMF population (NAT). Soil inoculation with AMF almost doubled wheat root colonization by AMF and decreased the root concentrations of most compounds in all metabolic pathways, especially amino acids (AA) and saturated fatty acids, whereas inoculation with AMF+PGPR increased the concentrations of such compounds compared to inoculation with AMF alone. Enrichment metabolomics analyses showed that AA metabolic pathways were mostly changed by the treatments, with reduced amination activity in roots most likely due to a shift from the biosynthesis of common AA to γ-amino butyric acid. The root metabolome differed between AMF and NAT but not AMF+PGPR and AMF or NAT. Because the PGPR used were potent mineralisers, and AMF can retain most nitrogen (N) taken as organic compounds for their own growth, it is likely that this result was due to an increased concentration of mineral N in soil inoculated with AMF+PGPR compared to AMF alone.

Trace elements in feed, manure, and manured soils

Modern animal feeds often include nutritional mineral supplements, especially elements such as Cu, P, Se, and Zn. Other sources of trace elements also occur in livestock systems, such as pharmaceutical use of As and Zn to control gut flora, Bi in dairy for mastitis control, and Cu as hoof dips. Additionally, potential exists for inadvertent inclusion of trace elements in feeds or manures. There is concern about long-term accumulation of trace elements in manured soil that may even exceed guideline "safe" concentrations. This project measured ∼60 elements in 124 manure samples from broiler, layer, turkey, swine grower, swine nursery, sow, dairy, and beef operations. The corresponding feeds were also analyzed. In general, concentrations in manure were two- to fivefold higher than those in feed: the manure/feed concentration ratios were relatively consistent for all the animal-essential elements and were numerically similar for many of the non-nutrient elements. To confirm the potential for accumulation in soil, total trace element concentrations were measured in the profiles of 10 manured and 10 adjacent unmanured soils. Concentrations of several elements were found to be elevated in the manured soils, with Zn (and P) the most common. One soil from a dairy standing yard had concentrations of B that exceeded soil health guideline concentrations. Given that the Cu/P and Zn/P ratios found in manure were greater than typically reported in harvested crop materials, these elements will accumulate in soil even if manure application rates are managed to prevent accumulation of P in soil.

Effect of silicon on reducing cadmium toxicity in durum wheat (Triticum turgidum L. cv. Claudio W.) grown in a soil with aged contamination

Agricultural soil contamination and subsequently crops still require alternative solutions to reduce associated environmental risks. The effects of silica application on alleviating cadmium (Cd) phytotoxicity in wheat plants were investigated in a 71-day pot experiment conducted with a historically contaminated agricultural soil. We used amorphous silica (ASi) that had been extracted from a diatomite mine for Si distribution at 0, 1, 10 and 15 ton ASi ha(-1). ASi applications increased plant biomass and plant Si concentrations, reduced the available Cd in the soil and the Cd translocation to shoots, while Cd was more efficiently sequestrated in roots. But ASi is limiting for Si uptake by plants. We conclude that significant plant-available Si in soil contributes to decreased Cd concentrations in wheat shoots and could be implemented in a general scheme aiming at controlling Cd concentrations in wheat.