Insights in to iron-based nanoparticles (hematite and magnetite) improving the maize growth (Zea mays L.) and iron nutrition with low environmental impacts.

The possible potential application of Fe-NPs on Fe nutrition, heavy metals uptake and soil microbial community needs to be investigated. In the current research, a pot experiment was used to examine the implications of Fe-NPs (α-Fe2O3 and Fe3O4) on maize growth, Fe uptake and transportation, soil microbial community, and environmental risk. Fe3O4, α-Fe2O3, FeSO4 at a rate of 800 mg Fe kg-1 were applied in soils with four replications under a completely randomized design for a period of 60 days. Results showed that Fe uptake by maize roots were increased by 107-132% than control, with obvious variations across different treatments (Fe3O4> α-Fe2O3> FeSO4> control). Similarly, plant height, leaf surface area, and biomass were increased by 40-64%, 52-91% and 38-109% respectively, with lower values by FeSO4 application. The elevated level of chlorophyll contents and carotenoids and significant effects with control on antioxidant enzymes activities (i.e., catalase, and superoxide dismutase) suggested that application of Fe-NPs improved overall biochemical processes. The differential expression of important Fe transporters (i.e., ZmYS1 and ZmFER1) as compared to control indicated the plant strategic response for efficient uptake and distribution of Fe. Importantly, Fe-NPs reduced the heavy metals uptake (i.e., chromium, cadmium, arsenic, nickel, copper) by complex formation, and showed no toxicity to the soil microbial community. In summary, the application of Fe-NPs can be a promising approach for improving crop productivity and Fe nutrition without negatively affecting soil microbial community, and fostering sustainable agricultural production.

Maize zinc uptake is influenced by arbuscular mycorrhizal symbiosis under various soil phosphorus availabilities.

The antagonistic interplay between phosphorus (P) and zinc (Zn) in plants is well established. However, the molecular mechanisms mediating those interactions as influenced by arbuscular mycorrhizal (AM) symbiosis remain unclear. We investigated Zn concentrations, root AM symbiosis, and transcriptome profiles of maize roots grown under field conditions upon different P levels. We also validated genotype-dependent P-Zn uptake in selected genotypes from a MAGIC population and conducted mycorrhizal inoculation experiments using mycorrhizal-defective mutant pht1;6 to elucidate the significance of AM symbiosis in P-Zn antagonism. Finally, we assessed how P supply affects Zn transporters and Zn uptake in extraradical hyphae within a three-compartment system. Elevated P levels led to a significant reduction in maize Zn concentration across the population, correlating with a marked decline in AM symbiosis, thus elucidating the P-Zn antagonism. We also identified ZmPht1;6 is crucial for AM symbiosis and confirmed that P-Zn antagonistic uptake is dependent on AM symbiosis. Moreover, we found that high P suppressed the expression of the fungal RiZRT1 and RiZnT1 genes, potentially impacting hyphal Zn uptake. We conclude that high P exerts systemic regulation over root and AM hyphae-mediated Zn uptake in maize. These findings hold implications for breeding Zn deficiency-tolerant maize varieties.

Characterization of Root and Foliar-Applied Iron Oxide Nanoparticles (α-Fe2O3, γ-Fe2O3, Fe3O4, and Bulk Fe3O4) in Improving Maize (Zea mays L.) Performance.

Iron (Fe) oxide nanoparticles (NPs) improve crop growth. However, the comparative effect of root and foliar-applied different sources of Fe oxide NPs on plant performance at morphological and physiological levels still needs to be discovered. In this study, we characterized the growth and physiological responses of hydroponic-cultured maize seedlings to four sources of Fe (i.e., α-Fe2O3, γ-Fe2O3, Fe3O4 NPs, and bulk Fe3O4) and two application methods (root vs. foliar). Results showed that Fe concentration in root and shoot increased by elevating the level of NPs from 100 mg L-1 to 500 mg L-1. Overall, the responses of maize seedlings to different sources of Fe oxide NPs were as follows: Fe3O4 > γ-Fe2O3 > α-Fe2O3 > bulk Fe3O4. The application of Fe at concentrations ranging from 100 mg L-1 to 500 mg L-1 had no significant effects on various growth parameters of maize, including biomass, chlorophyll content, and root length. Iron oxide NPs increased the plant biomass by 23-37% by root application, whereas it was 5-9% by foliar application. Chlorophyll contents were increased by 29-34% and 18-22% by foliar and root applications, respectively. The non-significant response of reactive oxygen species (i.e., superoxide dismutase, catalase, and peroxidase) suggested optimum maize performance for supplementing Fe oxide NPs. A confocal laser scanning microscope suggested that Fe oxide NPs entered through the epidermis and from the cortex to the endodermis. Our results provide a scientific basis that the root application of Fe3O4 at the rate of 100 mg L-1 is a promising approach to obtain higher maize performance and reduce the quantity of fertilizer used in agriculture to minimize environmental effects while improving crop productivity and quality. These findings demonstrated the tremendous potential of Fe NPs as an environmentally friendly and sustainable crop approach.

Global food nutrients analysis reveals alarming gaps and daunting challenges.

Eliminating both overt and hidden hunger is at the core of the global food and nutrition security agenda. Yet, the collective state of nutrition security at the population level is not known. Here we quantify food-based availability of 11 essential nutrients for 156 countries using a food production-consumption-nutrition model, followed by assessment of the nutrient availability status as a ratio of recommended intake. For the baseline year 2017, global per capita availability was adequate for calorie and protein but in severe deficit for vitamin A and calcium (intake ratios, <0.60, where 1.0 is adequate) and moderate deficit for vitamin B12 (intake ratio, 0.76). At the country level, more than half of the 156 countries were in various degrees of deficit for all nine micronutrients. Disparities across regions or countries were enormous. We explore intervention strategies from an agriculture-food system perspective and discuss the daunting challenges of addressing nutrition security broadly.

The long non-coding RNA PILNCR2 increases low phosphate tolerance in maize by interfering with miRNA399-guided cleavage of ZmPHT1s.

The open reading regions of ZmPHT1s (inorganic phosphate [Pi] transporters) in maize possess target sites of microRNA399 (miR399). However, the relationship between miR399 and ZmPHT1s and its functional importance in response to Pi deficiency remain to be explored. We show here that ZmPHT1;1, ZmPHT1;3, and ZmPHT1;13 are the targets of ZmmiRNA399. We found that a long non-coding RNA, PILNCR2 (Pi-deficiency-induced lncRNA 2), is transcribed from the opposing DNA strand of ZmPHT1;1 and predominantly localized in the cytoplasm. A ribonuclease protection assay and an RNA-RNA binding assay showed that PILNCR2 and ZmPHT1s could form the RNA/RNA duplexes in vivo and in vitro. A co-expression assay in N. benthamiana revealed that the PILNCR2/ZmPHT1 RNA/RNA duplexes interfere with miR399-guided cleavage of ZmPHT1 mRNAs. Overexpression of PILNCR2 increased low-Pi tolerance in maize, whereas its knockout and knockdown decreased low-Pi tolerance in maize. Consistently, ZmPHT1;3 and ZmPHT1;13 mRNA abundance was increased in transgenic plants overexpressing PILNCR2 but reduced in its knock-out mutants, suggesting that PILNCR2 positively regulates the mRNA abundance of ZmPHT1;3 and ZmPHT1;13 in maize. Collectively, these results indicate that PILNCR2 plays an important role in maize Pi homeostasis by interfering with miRNA399-guided cleavage of ZmPHT1 mRNAs.

The auxin signaling pathway contributes to phosphorus-mediated zinc homeostasis in maize.

Although the interaction between P and Zn has long been recognized in plants, the physiological and molecular mechanisms underlying P and Zn interactions are poorly understood. We show here that P supply decreases the Zn concentration in maize shoots and roots. Compared to +P + Zn (addition of both P and Zn), +P-Zn reduced and -P-Zn increased the total length of 1° lateral roots (LRs). Under +P + Zn, both P and Zn concentrations were lower in the sl1 mutant roots than in wild-type (WT) maize roots, and P accumulation did not reduce the Zn concentration in ll1 mutant roots. Transcriptome profiling showed that the auxin signaling pathway contributed to P-mediated Zn homeostasis in maize. Auxin production and distribution were altered by changes in P and Zn supply. Cytosolic Zn co-localized with auxin accumulation under +P + Zn. Exogenous application of 1-NAA and L-Kyn altered the P-mediated root system architecture (RSA) under Zn deficiency. -P-Zn repressed the expression of miR167. Overexpression of ZmMIR167b increased the lengths of 1° LRs and the concentrations of P and Zn in maize. These results indicate that auxin-dependent RSA is important for P-mediated Zn homeostasis in maize.HighlightAuxin-dependent RSA is important for P-mediated Zn homeostasis in maize.

Co-incorporation of Chinese milk vetch (Astragalus sinicus L.), rice straw, and biochar strengthens the mitigation of Cd uptake by rice (Oryza sativa L.).

Soil cadmium (Cd) contamination is becoming a widespread concern because of its threat to global ecosystem health and food security. Co-incorporation of Chinese milk vetch (MV) and rice straw (RS) is a common agricultural practice in Southern China; however, the effects of combining these two materials with biochar on Cd bioavailability remain unclear. This study investigated the effects of MV, RS, rape straw biochar (RB), iron-modified biochar (FB), and their combinations on Cd uptake by rice through incubation and field experiments. The results showed that compared with the control without material input (CK), MV + RS (MR), MV + RS + RB (MRRB), and MV + RS + FB (MRFB) considerably reduced the Cd concentration in brown rice by 61.20 %, 65.38 %, and 62.65 %, respectively. Furthermore, the treatments increased the formation of iron­manganese plaque (IMP) at different growth stages; MRRB and MRFB exhibited the highest increase rates among the treatments. Quantitatively, the Fe plaque and Mn plaque were increased by 20.61 %-47.23 % and 80.18 %-172.74 %, respectively. Compared with CK, the MRRB and MRFB treatments reduced the soil available Cd by 35.09 %-54.45 % and 38.20 %-50.20 %, respectively, at all stages. This decrease was substantially lower than that observed in the MV, RS, and MR treatments. Similar trends were observed in the incubation experiment. Additionally, the Community Bureau of Reference Sequential Extraction Analysis indicated that the MRRB and MRFB treatments converted the bioavailable Cd fractions into a stable form. Partial least squares path model and redundancy analysis revealed that pH was the major factor influencing Cd bioavailability. This study emphasized that the dual impact factors from the enhancement of Cd passivation capability and IMP formation jointly result in the reduction of Cd uptake by rice. Consequently, the co-incorporation of MV, RS, and biochar is promising for remediating Cd-contaminated paddy soils in Southern China.

A sustainable phosphorus management in agriculture: Assessing trade-offs between human health risks and nutritional yield regarding heavy metals in maize grain.

High-quality products in sustainable agriculture require both limited health risks and sufficient dietary nutrients. Phosphorus (P) as a finite and non-renewable resource is widely used in agriculture, usually exerting influence on the accumulation of heavy metals (HMs) in soil and crops. The present research explores, for the first time, the combined effects of long-term P fertilizer and repeated zinc (Zn) application in field on the human health risks and nutritional yield regarding trace elements in maize grain. A field experiment was conducted using maize with six P application rates (0, 12.5, 25, 50, 100, and 200 kg P ha-1) and two Zn application rates (0 and 11.4 kg Zn ha-1). The results showed that the concentrations of Zn, copper (Cu), and lead (Pb) in the maize grain were significantly affected by P application and can be further affected by Zn application. The concentrations of chromium (Cr) and arsenic (As) showed opposite tendency as affected by P fertilizer rates while did not affected by additional Zn application. Zn application decreased the cadmium (Cd) concentration at high P levels and Pb concentration at low P levels, particularly. No HMs contamination or direct health risk was found in maize grain after receiving long-term P and repeated Zn fertilizer. The threshold hazard quotient of an individual and all investigated HMs in this study were acceptable for human digestion of maize grain. While the carcinogenic risk of Cr was non-negligible in case of maize was taken as one of daily staple food for local residents. Combination use of P (25 kg ha-1) and Zn fertilizer on maize enhanced its nutritional supply ability regarding Zn and Cu, and simultaneously mitigated potential human health risks associated with Cd and Pb.

Foliar Zinc Application to Wheat May Lessen the Zinc Deficiency Burden in Rural Quzhou, China.

Zinc (Zn) malnutrition is a common health problem, especially in developing countries. The human health and economic benefits of the replacement of conventional flour with Zn-biofortified wheat flour in rural household diets were assessed. One hundred forty-five wheat flour samples were collected from rural households in Quzhou County. Then, field experiments were conducted on wheat at two Zn levels (0 and 0.4% ZnSO4 · 7H2O foliar application) under 16 diverse agricultural practices in Quzhou County. Foliar Zn application significantly increased the Zn concentration and bioavailability in wheat grain and flour. If rural households consumed Zn-biofortified flour instead of self-cultivated flour or flour purchased from supermarkets, 257-769 or 280-838, 0.46-1.36 million or 0.50-1.49 million disability-adjusted life years (DALYs) lost, respectively, could be saved in Quzhou County and China. Amounts of 2.3-12.0 million and 5.5-22.6 billion RMB could be obtained via Zn-biofortified flour in Quzhou County and China, respectively. The current study indicates that Zn-biofortified flour via foliar Zn application is a win-win strategy to maintain the yield and combat human Zn deficiency in rural households in China. More health and economic benefits could be obtained in rural household dependent on wheat flour purchased from supermarkets than in those dependent on self-cultivated wheat flour.

Life cycle assessment of a long-term multifunctional winter wheat-summer maize rotation system on the North China Plain under sustainable P management.

In sustainable agriculture, sufficient crop yields and nutrients must be produced while maintaining environmental protection. Considering the role of phosphorus (P) fertilizer in influencing crops yield and environmental security, life cycle assessment was used to examine the environmental impacts of long-term P application on the grain yield and nutritional quality of winter wheat and summer maize. Thus, a long-term field experiment with six P application rates for winter wheat (0, 25, 50, 100, 200, and 400 kg P ha-1) and summer maize (0, 12.5, 25, 50, 100, and 200 kg P ha-1) was conducted on the North China Plain (NCP). The results showed that the cradle-to-farm gate eutrophication potential (EP), energy depletion (ED), and P depletion (PD) were significantly affected by the P application rate applied in winter wheat and summer maize production. The critical P rate required to ensure food security for wheat and maize was in line with the optimal rate for sustainable environmental development in terms of grain production and nutrient levels. On the NCP, the ED and PD of summer maize with optimized P management over 10 years were less than those of winter wheat regardless of using yield or nutrient level as the functional unit. However, the EP of the nutrient supply in winter wheat was less than that in summer maize under optimized P fertilization. The specific nutritional components that limited improvements in environment of wheat and maize production under the optimal P rate were energy (calories) and protein, respectively. In conclusion, in a multifunctional winter wheat-summer maize rotation system, optimized P fertilization (50 kg ha-1 for winter wheat and 25 kg ha-1 for summer maize) combined with the planting of high-yield wheat varieties and high-protein maize varieties showed great potential to reduce the environmental impacts of wheat and maize production.

Innovative management programme reduces environmental impacts in Chinese vegetable production.

China produces half of the world's vegetables. The production uses 1.7% of the global harvest area of crops but accounts for 7.8% of the chemical fertilizers and 6.6% of crop-sourced greenhouse gas (GHG) emissions worldwide. Using an innovative management programme, the integrated knowledge and products strategy (IKPS), we demonstrate opportunities for producing more vegetables with lower environmental impacts in China's vegetable production systems. Combining soil-crop system management practices with enhanced-efficiency fertilizer products, IKPS was tested through 54 site-year field experiments in China's major agro-ecological zones by a national research network over 12 years. Compared with current farming practices, the adoption of IKPS decreased the nitrogen (N) application rate by 38%, N surplus by 65% and GHG emissions by 28%, while increasing yield by 17%. Scenario analyses showed that adoption of IKPS in China's vegetable production could mitigate resource and environmental burdens while enhancing food and nutrition security.

Responses in Zinc Uptake of Different Mycorrhizal and Non-mycorrhizal Crops to Varied Levels of Phosphorus and Zinc Applications.

Negative effects of high phosphorus (P) application on zinc (Zn) nutrition have been observed in many crops. This study investigated the Zn responses of three typical crops to varied P and Zn applications. A pot experiment was conducted using two mycorrhizal crops (maize and soybean) and one non-mycorrhizal crop (oilseed rape) under three levels of P, two levels of Zn, and two levels of benomyl. Results showed that P application significantly decreased shoot and root Zn concentrations, Zn uptake, and Zn acquisition efficiency (ZnAE) of the three crops irrespective of Zn rate, and that these reductions were greater for maize and soybean than for oilseed rape. Zn application alleviated the P inhibition of Zn uptake in the three crops. The arbuscular mycorrhizal fungi (AMF) colonization of maize and soybean contributed most to the negative effects of increasing P application on Zn uptake, explaining 79-89 and 64-69% of the effect, respectively. For oilseed rape, root dry weight and root Zn concentration explained 90% of the decrease in Zn uptake caused by P application. These results suggest that there is another pathway in addition to the mycorrhizal pathway regulating Zn uptake under mediation by P supply.

Simultaneous Biofortification of Rice With Zinc, Iodine, Iron and Selenium Through Foliar Treatment of a Micronutrient Cocktail in Five Countries.

Widespread malnutrition of zinc (Zn), iodine (I), iron (Fe) and selenium (Se), known as hidden hunger, represents a predominant cause of several health complications in human populations where rice (Oryza sativa L.) is the major staple food. Therefore, increasing concentrations of these micronutrients in rice grain represents a sustainable solution to hidden hunger. This study aimed at enhancing concentration of Zn, I, Fe and Se in rice grains by agronomic biofortification. We evaluated effects of foliar application of Zn, I, Fe and Se on grain yield and grain concentration of these micronutrients in rice grown at 21 field sites during 2015 to 2017 in Brazil, China, India, Pakistan and Thailand. Experimental treatments were: (i) local control (LC); (ii) foliar Zn; (iii) foliar I; and (iv) foliar micronutrient cocktail (i.e., Zn + I + Fe + Se). Foliar-applied Zn, I, Fe or Se did not affect rice grain yield. However, brown rice Zn increased with foliar Zn and micronutrient cocktail treatments at all except three field sites. On average, brown rice Zn increased from 21.4 mg kg-1 to 28.1 mg kg-1 with the application of Zn alone and to 26.8 mg kg-1 with the micronutrient cocktail solution. Brown rice I showed particular enhancements and increased from 11 µg kg-1 to 204 µg kg-1 with the application of I alone and to 181 µg kg-1 with the cocktail. Grain Se also responded very positively to foliar spray of micronutrients and increased from 95 to 380 µg kg-1. By contrast, grain Fe was increased by the same cocktail spray at only two sites. There was no relationship between soil extractable concentrations of these micronutrients with their grain concentrations. The results demonstrate that irrespective of the rice cultivars used and the diverse soil conditions existing in five major rice-producing countries, the foliar application of the micronutrient cocktail solution was highly effective in increasing grain Zn, I and Se. Adoption of this agronomic practice in the target countries would contribute significantly to the daily micronutrient intake and alleviation of micronutrient malnutrition in human populations.

The responses of soil enzyme activities, microbial biomass and microbial community structure to nine years of varied zinc application rates.

Zinc (Zn) fertilizer application can certainly improve the production and nutritional quality of cereal crops. However, Zn accumulation in the soil may lead to some deleterious environmental impacts in agroecosystems. The effects of long-term Zn application on soil microbial properties remain unclear, but it is imperative to understand such effects. In this study, we collected soil samples from a nine-year field experiment in a wheat-maize system that continuously received Zn applied at various rates (0, 2.3, 5.7, 11.4, 22.7 and 34.1 kg ha-1) to evaluate the soil enzymes, microbial biomass and microbial community structure. The results showed that Zn application at the rate of 5.7 kg ha-1 significantly increased the activities of urease, invertase, alkaline phosphatase and catalase in the soil, while the rate of 34.1 kg ha-1 significantly decreased the evaluated enzyme activities. The microbial biomass carbon (C) and nitrogen (N) were not affected by Zn application rates, although an increase in the microbial biomass C was observed in the 11.4 kg ha-1 treatment. Moreover, the alpha diversity of the bacterial and fungal communities did not vary among the nil Zn, optimal Zn (5.7 kg ha-1) and excess Zn (34.1 kg ha-1) treatments. However, the bacterial communities in the soil receiving the optimal and excess Zn application rates were slightly changed. Compared to the nil Zn treatment, the other Zn application rates increased the relative abundances of the Rhodospirillales, Gaiellales and Frankiales orders and decreased the abundance of the Latescibacteria phylum. The redundancy analysis further indicated that the soil bacterial community composition significantly correlated with the concentrations of soil DTPA-Zn and total Zn. These results highlight the importance of optimal Zn application in achieving high production and high grain quality while concurrently promoting soil microbial activity, improving the bacterial community and further maintaining the sustainability of the agroecological environment.

Identifying key drivers for geospatial variation of grain micronutrient concentrations in major maize production regions of China.

Micronutrient deficiencies are prevalent health problems worldwide. The maintenance of adequate concentrations of micronutrients in maize grain is crucial for human health. We investigated the overall status and geospatial variation of micronutrients in Chinese maize grains and identified their key drivers. A field survey was conducted in four major maize production areas of China in 2017 with 980 pairs of soil and grain samples collected from famers' fields. At a national scale, grain zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) concentrations varied substantially, with average values of 17.4, 17.3, 4.9, and 1.5 mg kg-1, respectively, suggesting a solid gap between grain Zn and Fe concentrations and the biofortification target values. Significant regional difference in the concentrations of Zn, Mn and Cu, but not Fe, were observed in grain, with much higher levels in Southwest China. The nutritional yields of Zn, Fe and Cu were lower than the energy and Mn yields, indicating an unbalanced output between energy and micronutrients in current maize production system. Grain Zn, Fe, Mn and Cu correlated negatively with maize yield in most test regions. Increased nitrogen (N) rate positively affected grain Zn and Cu, while increased phosphorus (P) rate negatively affects grain Zn and Fe. Apart from Fe, available Zn, Mn and Cu in soil exerted significant positive effects on grain Zn, Mn and Cu concentrations, respectively. Decrease in soil pH and increase in the organic matter content may increase the accumulation of Fe and Mn in grain. Grain Zn and Cu concentrations increased as available soil P decreased. Of the factors considered in this study, grain yield, N and P rates, soil pH and organic matter were the main factors that affect grain micronutrient status and should be more extensively considered in the production and nutritional quality of maize grain.

Integrated systematic approach increase greenhouse tomato yield and reduce environmental losses.

High input - high output greenhouse vegetable systems are responsible for nutrient surpluses and environmental losses. Integrated strategies that improve soil, crop and nutrient management are needed to ensure more sustainable production systems. We conducted a two-year field experiment to evaluate the potential of integrated soil-crop system management (ISSM) practices to improve the productivity and environmental outcomes from an intensive greenhouse tomato production system in the Yangtze River Basin, China. Four treatments were tested: i) farmers' practice (FP); ii) soil remediation (SR), where lime nitrogen with compost addition was the only management strategy; iii) a treatment that combined soil remediation with optimized crop planting density (SRCO), which increased planting density for improving crop yield; and iv) integrated soil-crop system management (ISSM), as a systematic integrated approach, which included the combined optimization of soil remediation, crop optimization, and nutrient management. In the integrated soil-crop system management treatment, nutrient management was optimized through adoption of the most appropriate type (formula) of fertilizer for the crop, rate and application timing of synthetic fertilizer, and by substituting poultry manure with compost. Our results indicated that the fruit yield of the integrated soil-crop system management treatment was 104 t ha-1, 13.4%-37.3% higher than that of the other three treatments. The mean reactive nitrogen loss (81.1 kg N ha-1) and the greenhouse gas emissions (6495 kg CO2-eq ha-1) in the farmers' practice treatment were much higher than in the other three treatments (reactive nitrogen loss: 47.9-54.3 kg N ha-1; and greenhouse gas emissions: 4926-5468 kg CO2-eq ha-1, respectively). The mean nitrogen and carbon footprints of the integrated soil-crop system management treatment were significantly lower than those of other treatments, as a result of both the lower fertilizer nitrogen use and the greater yield. This study indicates that integrated soil-crop system management could produce greater yields and increase net profit with reduced nitrogen inputs, whilst reducing the environmental cost associated with conventional farmers' practice in plastic-greenhouse vegetable production systems.

Soil Application of Zinc Fertilizer Increases Maize Yield by Enhancing the Kernel Number and Kernel Weight of Inferior Grains.

Improving the development of inferior grains is important for increasing maize yield under high-density conditions. However, the effect of micronutrients, especially zinc (Zn), on the development of inferior grains and maize yield under field conditions has not been evaluated to date. A field experiment with six Zn application rates (0, 2.3, 5.7, 11.4, 22.7, and 34.1 kg/ha) was conducted to investigate the effects of soil application of Zn fertilizer on the development of inferior grains. Pollen viability was measured at the tasseling stage. The maize spike was divided into apical (inferior grain), middle, and basal sections for further measurement at harvest. Results showed that soil application of Zn fertilizer increased maize yield by 4.2-16.7% due to increased kernel number and weight in the apical, but not in the middle and basal sections. Zn application also significantly increased pollen viability at the tasseling stage. The critical Zn concentrations in shoots at the tasseling stage for obtaining high pollen viability and high kernel numbers of inferior grains were 31.2 and 35.6 mg/kg, respectively. Zn application also increased the 1,000-kernel weight of inferior grain due to high biomass accumulation. Furthermore, the grain Zn concentration of inferior grain with Zn application increased by 24.3-74.9% compared with no Zn application. Thus, soil application of Zn fertilizer successfully increased grain yield of maize by improving pollen viability, kernel number, and kernel weight of inferior grains (apical section), also contributing to grain Zn biofortification.

Health risk assessment associated with heavy metal accumulation in wheat after long-term phosphorus fertilizer application.

Phosphorus (P) fertilizer is widely used to increase wheat yield. However, it remains unclear whether prolonged intake of wheat grain that received long-term P application may promote human health risks by influencing heavy metal(loid)s (HMs) accumulation. A 10-year field experiment was conducted to evaluate the effects of continuous P application (0, 25, 50, 100, 200, and 400 kg P ha-1) on human health risks of HMs, including zinc (Zn), copper (Cu), cadmium (Cd), lead (Pb), arsenic (As), nickel (Ni), and chromium (Cr), by ingesting wheat grain. The results showed that P application facilitated Zn, Pb, Cd, and As accumulation in the topsoil. The Zn, Cu, Pb, and Ni concentrations in grain were decreased, while Cd and As were increased by P application. All HMs concentrations of both soil and grain were in the ranges of corresponding safety thresholds at different P levels. The accumulation abilities of Zn, Cu, Pb, and Ni from soil and straw to grain were suppressed by P addition while of As was enhanced. There was no significant difference in the hazard index (HI) of the investigated HMs in all treatments except 25 kg ha-1. The threshold cancer risk (TCR) associated with As and Cd was enhanced, while that of Pb was alleviated as P application increased. Behaviors of Cr from soil to wheat and to humans were not affected by P application. Phosphorus application at a rate of 50 kg ha-1 decreased total non-cancer and cancer risks by 15% and 21%, respectively, for both children and adults, compared to the highest value. In conclusion, long-term optimal application of 50 kg P ha-1 to wheat did not result in additional adverse effects on the total non-carcinogenic or carcinogenic risk caused by the studied HMs to humans through the ingestion of wheat grain.

Soil Microbial Composition and phoD Gene Abundance Are Sensitive to Phosphorus Level in a Long-Term Wheat-Maize Crop System.

Microbes associated with phosphorus (P) cycling are intrinsic to soil P transformation and availability for plant use but are also influenced by the application of P fertilizer. Nevertheless, the variability in soil P in the field means that integrative analyses of soil P cycling, microbial composition, and microbial functional genes related to P cycling remain very challenging. In the present study in the North China Plain, we subjected the bacterial and fungal communities to amplicon sequencing analysis and characterized the alkaline phosphatase gene (phoD) encoding bacterial alkaline phosphatase in a long-term field experiment (10 years) with six mineral P fertilization rates up to 200 kg P ha-1. Long-term P fertilization increased soil available P, inorganic P, and total P, while soil organic P increased until the applied P rate reached 25 kg ha-1 and then decreased. The fungal alpha-diversity decreased as P rate increased, while there were no significant effects on bacterial alpha-diversity. Community compositions of bacteria and fungi were significantly affected by P rates at order and family levels. The number of keystone taxa decreased from 10 to 3 OTUs under increasing P rates from 0 to 200 kg ha-1. The gene copy numbers of the biomarker of the alkaline phosphatase phoD was higher at moderate P rates (25 and 50 kg ha-1) than at low (0 and 12.5 kg ha-1) and high (100 and 200 kg ha-1) rates of P fertilization, and was positively correlated with soil organic P concentration. One of the keystone taxa named BacOTU3771 belonging to Xanthomonadales was positively correlated with potential functional genes encoding enzymes such as glycerophosphoryl diester phosphodiesterase, acid phosphatase and negatively correlated with guinoprotein glucose dehydrogenase. Altogether, the results show the systematic effect of P gradient fertilization on P forms, the microbial community structure, keystone taxa, and functional genes associated with P cycling and highlight the potential of moderate rates of P fertilization to maintain microbial community composition, specific taxa, and levels of functional genes to achieve and sustain soil health.

Health risk assessment of heavy metals (Zn, Cu, Cd, Pb, As and Cr) in wheat grain receiving repeated Zn fertilizers.

Soil application of Zn fertilizer is an effective approach to improve yield and Zn accumulation in wheat grain. However, it remains unclear whether repeated Zn application can result in high accumulation of heavy metals (HMs) in soils and grains and thus represents a potential risk for human consumption. This study aimed to evaluate the health risk assessment of HMs in a wheat production system which had continuously received 8 years of Zn application at varying rates (0, 2.3, 5.7, 11.4, 22.7, 34.1 kg Zn ha-1). The results showed that Zn application significantly increased the soil total Zn concentration without affecting concentrations of As, Pb, Cd, Cu and Cr. Across Zn rates, Zn application increased grain concentrations of Zn, Pb and Cd by 75%, 51% and 14%, respectively, and reduced grain As concentration by 14%. The human health risk assessment revealed that the threshold hazard quotients for the individual HM were below 1, independent of Zn rates. The hazard index (HI) values at Zn rates of 11.4, 22.7 and 34.1 kg Zn ha-1 were significantly greater than that at null Zn treatment. Furthermore, exposures to As, Cu and Zn accounted for 97% of HI at all Zn rates. Analysis of the threshold cancer risk with Pb and As showed that ingestion of wheat grain even from highest Zn application rate wouldn't bring the lifetime carcinogenic risk. In contrast, long-term Zn application significantly reduced the carcinogenic risk of As by 9.7-26.5%. In conclusion, repeated soil applications of Zn at optimal rate (5.7 kg Zn ha-1) didn't cause health risk for Zn, Cu, Cd, Pb, Cr, and As, while improving productivity and grain Zn concentration of wheat to meet human recruitment. Our study highlights the importance of appropriate Zn fertilizer management in improving grain quality while reducing HMs risks from human consumption.