Shoot Zn Uptake Research Articles

High-Zn wheat alleviates P-Zn antagonism by improving Zn activation, acquisition, and translocation at key growth stages

Context or problemApplication of phosphorus (P) fertilizer has achieved a remarkable increase in yield but has also resulted in decreased zinc (Zn) concentration and its bioavailability in cereal grains. ObjectivesSelecting, breeding, and understanding the mechanism for wheat cultivars with high-yield and high-grain Zn under P application is urgent and difficult, with the purpose of alleviating P-Zn antagonism and solving Zn malnutrition globally. MethodsIn a five-year field experiment on the southern Loess Plateau, China, selected high-yield wheat cultivars with contrasting grain Zn concentrations were assessed for rhizosphere Zn activation, root Zn acquisition, and Zn translocation among plant parts at the key growth stages under different P fertilization rates. ResultsResults showed that although the grain Zn concentration decreased with P application, it decreased less and still remained around 49–65 mg/kg in the grain of high Zn (HZn) cultivars. This was 58–72% higher than that of the low Zn (LZn) cultivars on soil with 2.7 mg/kg Olsen-P and 0.55 mg/kg DTPA-Zn due to 32.9–55.4% higher shoot Zn uptake in HZn cultivars at harvest. P application enhanced the rhizosphere Zn activation of HZn cultivars by 21.6% higher than that of LZn cultivars at the jointing stage. However, P application inhibited the root Zn acquisition of both types of cultivars, except for that of the HZn cultivars at the anthesis. The Zn translocation from root to shoot was remarkably enhanced at the grain-filling stage, but much more for HZn cultivars with P application, with the transfer factor being 154% for HZn cultivars and 7.9% for LZn cultivars, respectively. ConclusionsTherefore, HZn cultivars alleviated the P-Zn antagonism and achieved higher grain Zn concentration than the recommended target of 40–60 mg/kg, by maintaining higher rhizosphere Zn activation at the jointing stage, stable high Zn acquisition at the anthesis, and higher Zn translocation capacity from root to shoot during the grain-filling stage. ImplicationsBreeding and selecting cultivars with excellent acquisition performance and translocation capacity for Zn, accompanied by relatively lower soil available P and reasonable P application, may be an applicable Zn biofortification strategy for wheat and other cereals, overcoming the P-Zn antagonism.

Nano-zinc and plant growth-promoting bacteria is a sustainable alternative for improving productivity and agronomic biofortification of common bean

Background and aimsNano-zinc (Zn) fertilizer is an easily adaptable and environmentally safe alternative option that can effectively improve growth, yield and biofortification of common bean. Plant growth-promoting bacteria (PGPBs) could promote plant growth and nutrients availability in sustainable manner. Therefore, this study aimed to investigate the influence of foliar nano-Zn application in association with seed co-inoculations of PGPBs on growth, yield, biofortification and Zn use efficiencies in common bean cultivation. Two field experiments were performed with seven co-inoculations of PGPBs and three foliar nano-Zn doses applied 50% at R5 and 50% at R8 stages of common bean to determine plant height, shoot dry matter, grain yield, Zn concentration and uptake in shoot and grains, Zn partitioning index, daily Zn intake and Zn use efficiencies for agronomic biofortification.ResultsThe combined foliar nano-Zn application and co-inoculation of R. tropici + B. subtilis enhance grain yield, leaf chlorophyll index, total protein content, grain Zn concentration and uptake, daily Zn intake, Zn use efficiency, applied Zn recovery and Zn utilization efficiency in common beans in 2019 and 2020 cropping seasons. Foliar nano-Zn application at a dose of 1.5 kg ha−1 increased plant height, shoot dry matter, shoot Zn uptake, Zn partitioning and agro-physiological efficiency under co-inoculation with R. tropici + B. subtilis in both cropping years.ConclusionsThe treatments with foliar nano-Zn application at a dose of 1.5 ha−1 and co-inoculation with R. tropici + B. subtilis improved performance, chlorophyll index, protein content, grain yield, and Zn efficiencies that can lead to better biofortification of common bean in tropical savannah. Therefore, it is recommended that applying nano-Zn via foliar along with co-inoculation of PGPBs could be the better option for productivity and biofortification of common bean.Graphical

Enhancing Zinc Biofortification of Wheat through Integration of Zinc, Compost, and Zinc-Solubilizing Bacteria

Zinc (Zn) deficiency is a fairly widespread agronomic constraint in many of the world’s cereal (wheat, rice, corn, barley, etc.) production regions. Zinc is an imperative micronutrient required for optimum plant growth and development. Low Zn availability in about 50% of global land has resulted in Zn deficiency in cereal grains. A two-year field experiment was conducted at the Agronomy Research Farm, The University of Agriculture, Peshawar, during Rabi season 2018–19 (Y1) and 2019–20 (Y2) to study the impact of Zn levels (0, 5, 10 and 15 kg Zn ha−1), compost types (control, composted sheep manure (SMC), composted poultry manure (PMC) and farmyard manure compost (FYMC), and Zn-solubilizing bacteria (ZnSB) (with (+) and without (-) on Zn biofortification in order to overcome Zn deficiency. The experiment was set up in three replications in a randomized complete block design. The wheat variety “Pirsabak-2013” was planted in a 30 cm row-to-row spacing. The plot size was kept at 9 cm2, with 10 rows plot−1, and the seed was sown at a rate of 100 kg ha−1. The results showed that ZnSB application increased ShZnC (shoot Zn concentration) to a maximum level of 29.3 mg kg−1, ShZnUp (shoot Zn uptake) to 176.0 g ha−1, SZnUp (straw Zn uptake) to 116.67 g ha−1, and TZnUp (total Zn uptake) to 230.3 g ha−1. In the case of compost types, PMC resulted in maximum grain Zn uptake (GZnUp) (28.9 mg kg−1), ShZnUp (192.9 g ha−1), GZnC (33.4 mg kg−1), GZnUp (125.06 g ha−1), SZnUp (125.26 g ha−1), and TZnUp (250.3 g ha−1). In the case of Zn levels, higher ShZnC (31.5 mg kg−1), ShZnUp (191.3 g ha−1), GZnC (34.4 mg kg−1), SZnC (23.5 mg kg−1), GZnUp (128.98 g ha−1), SZnUp (129.29 g ha−1), and TZnUp (258.3 g ha−1) were calculated with the use of the highest rate of 15 kg Zn ha−1, which was either statistically similar to or followed by 10 kg Zn ha−1. A strong positive correlation was found among uptake by different plant parts (ZnG, ZnS, ShZnUp, GZnUp, SZnUp, and TZnUp). It was concluded that the combined application of PMC and 10 kg Zn ha−1 along with ZnSB (+) improved Zn biofortification and uptake in wheat crop under Zn-deficient soils.

Wheat grain zinc concentration as affected by soil nitrogen and phosphorus availability and root mycorrhizal colonization

Nitrogen (N) fertilization increases zinc (Zn) acquisition in cereal crops. However, little is known about the effects of N fertilization on grain Zn concentration in relation to availability of soil N and phosphorous (P) and root mycorrhizal colonization. The present study used a 12-year location-fixed field experiment with winter wheat grown at five N fertilization rates (0, 80, 160, 240 and 320 kg N ha−1). The objective was to assess effects of phytoavailability of soil N and P and root mycorrhizal colonization on wheat Zn nutrition during three-year field measurements. Zinc concentration in wheat grains was increased with N fertilization in a linear-plateau fashion, and it reached the plateau of 30.3 ± 0.4 mg kg−1 when soil mineral N (nitrate-N) levels were 8.5 ± 1.0 mg kg−1 and above at maturity. Similarly, total shoot Zn uptake and Zn remobilization from vegetative tissues to grains were also increased significantly and then attained a plateau as the N rates increased. The enhancements in grain Zn concentration by N fertilization mainly occurred in the crease tissue, embryo and aleurone fractions of the grain. Long-term N fertilization was also associated with increases in root mycorrhizal colonization up to 8.8 ± 2.9 mg kg−1 soil available mineral N at maturity. Shoot Zn uptake at maturity increased quadratically with the increase in shoot N uptake and root mycorrhizal colonization rate, whereas there was an inverse relationship between shoot Zn uptake and soil P availability. The results suggest that grain Zn concentration of wheat plants grown under long-term N fertilization was closely related to the soil mineral N status and showed clear increases with decreased soil available P concentration and improved root mycorrhizal colonization rates.

Biofortification of Silage Maize with Zinc, Iron and Selenium as Affected by Nitrogen Fertilization.

Agronomic biofortification is one of the main strategies for alleviation of micronutrient deficiencies in human populations and promoting sustainable production of food and feed. The aim of this study was to investigate the effect of nitrogen (N)fertilization on biofortification of maize crop (Zea mays L.) with zinc (Zn), iron (Fe) and selenium (Se) grown on a micronutrient deficient soil under greenhouse conditions. Factorial design experiment was set under greenhouse conditions. The experiment consisted of two levels of each N, Zn, Fe and Se. The levels for N were 125 and 250 mg N kg−1 soil; Zn were 1 and 5 mg Zn kg−1 soil; levels of Fe were 0 and 10 mg Fe kg−1 soil; levels of Se were 0 and 0.02 mg Se kg−1 soil. An additional experiment was also conducted to study the effect of the Zn form applied as a ZnO or ZnSO4 on shoot growth, shoot Zn concentration and total shoot Zn uptake per plant. Shoot Zn concentrations increased by increasing soil Zn application both with ZnSO4 and ZnO treatments, but the shoot Zn concentration and total Zn uptake were much greater with ZnSO4 than the ZnO application. Under given experimental conditions, increasing soil N supply improved shoot N concentration; but had little effect on shoot dry matter production. The concentrations of Zn and Fe in shoots were significantly increased by increasing N application. In case of total uptake of Zn and Fe, the positive effect of N nutrition was more pronounced. Although Se soil treatment had significant effect, N application showed no effect on Se concentration and accumulation in maize shoots. The obtained results show that N fertilization is an effective tool in improving the Zn and Fe status of silage maize and contribute to the better-quality feed.

Interactive effects of drought, organic fertilizer, and zinc oxide nanoscale and bulk particles on wheat performance and grain nutrient accumulation

Drought (40% field moisture capacity), organic fertilizer (O-F; 10%), and nano vs. bulk-ZnO particles (1.7 vs. 3.5 mg Zn/kg) were assessed in soil to determine their interactive effects on wheat performance and nutrient acquisition. Drought significantly reduced (6%) chlorophyll levels, whereas nano and bulk-ZnO alleviated some stress, thereby increasing (14–16%) chlorophyll levels, compared to the control. O-F increased (29%) chlorophyll levels and counteracted Zn's effect. Drought delayed (3-days) panicle emergence; O-F, nano and bulk-ZnO each accelerated (5-days) panicle emergence under drought, relative to the control and absence of O-F. Drought reduced (51%) grain yield, while O-F increased (130%) yield under drought. Grain yield was unaffected by Zn treatment under drought but increased (88%) under non-drought condition with bulk-ZnO, relative to the control. Drought lowered (43%) shoot Zn uptake. Compared to the control, nano and bulk-ZnO increased (39 and 23%, respectively) shoot Zn in the absence of O-F, whereas O-F amendment enhanced (94%) shoot Zn. Drought increased (48%) grain Zn concentration; nano and bulk-ZnO increased (29 and 18%, respectively) grain Zn, relative to the control, and O-F increased (85%) grain Zn. Zn recovery efficiency was in the order O-F > nano-ZnO > bulk-ZnO, regardless of the water status. Grain Fe concentration was unaffected by drought, under which O-F significantly reduced grain Fe, and nano-ZnO significantly reduced grain Fe, in the absence of O-F. Nano and bulk-ZnO also significantly reduced grain Fe, with O-F amendment under drought. Drought can have dire consequences for food and nutrition security, with implications for human health. This study demonstrated that drought-induced effects in food crops can be partially or wholly alleviated by ZnO particles and Zn-rich O-F. Understanding the interactions of drought and potential mitigation strategies such as fertilization with Zn-rich organic manure and ZnO can increase options for sustaining food production and quality under adverse conditions.

Dynamic Zinc Accumulation and Contributions of Pre- and/or Post-Silking Zinc Uptake to Grain Zinc of Maize as Affected by Nitrogen Supply.

Nitrogen (N) supply could improve the grain yield of maize, which is of great importance to provide calories and nutrients in the diets of both humans and animals. Field experiments were conducted in 2009 and 2010 to investigate dynamic zinc (Zn) accumulation and the pre-silking and post-silking Zn uptake and their contributions to grain Zn accumulation of maize with different N supply under field conditions. Results showed that only 1.2% to 39.4% of grain Zn accumulation derived from pre-silking Zn uptake, with Zn remobilization being negatively affected by increasing N supply. However, post-silking Zn uptake (0.8–2.3 mg plant–1) and its substantial contribution to grain Zn accumulation (60.6%–98.8%) were progressively enhanced with the increasing N supply. Furthermore, grain Zn concentration was positively associated with grain N concentration (r = 0.752***), post-silking N uptake (r = 0.695***), and post-silking Zn uptake (r = 738***). A significant positive relationship was also found between post-silking uptake of N and Zn (r = 0.775***). These results suggest that N nutrition is a critical factor for shoot Zn uptake and its allocation to maize grain. Dry weight, and N and Zn concentration of grain and straw were significantly enhanced with the increasing N from “no N” to “optimal N” supply (150 kg N ha−1 in 2009 and 105 kg N ha−1 in 2010), but further increasing N supply (250 kg N ha−1) generally resulted in a non-significant increase in both cropping seasons. During the grain development, N supply also generally tended to improve grain N and Zn concentrations, but decrease phosphorus (P) concentration and the molar ratio of P to Zn compared with null N application. These results suggest that grain Zn accumulation mainly originates from post-silking Zn uptake. Applying N at optimal rates ensures better shoot Zn nutrition and contributes to post-silking Zn uptake, maintaining higher grain Zn availability by decreasing the molar ratio of P to Zn, and resulting in benefits to human nutrition.

Critical concentration of available soil phosphorus for grain yield and zinc nutrition of winter wheat in a zinc-deficient calcareous soil

The decrease in cereal grain zinc (Zn) caused by phosphorus (P) application has attracted wide attention. However, optimizing P fertilization for both satisfactory grain yield and grain Zn concentration is still a problem due to a poor understanding of the relationship between P application rates and available soil P, and that of available soil P and soil Zn availability, relevant soil factors, and plant Zn uptake and utilization. A location-fixed field experiment was initiated in 2004 with winter wheat (Triticum aestivum L.) grown at five P rates of 0, 50, 100, 150, and 200 kg P2O5 ha−1, and soil and plant samples were collected during the three growing seasons of 2013–2016. Winter wheat grain yield increased, and the grain Zn concentration decreased with increasing available soil P in a linear-plus-plateau manner. The grain yield plateau, averaging 6009 ± 155 kg ha−1, was reached at an available soil P concentration of 10.2 ± 2.5 mg kg−1, and the grain Zn plateau, averaging 22.4 ± 0.9 mg kg−1, was reached at an available soil P of 14.2 ± 1.8 mg kg−1. Shoot Zn uptake after flowering was not affected, while Zn remobilization from vegetative parts to grains and the Zn harvest index increased with P application at available soil P levels below 11.6 mg kg−1. The available soil Zn increased, and root mycorrhizal colonization was unaffected at lower available soil P levels. The decrease in wheat grain Zn concentration with increasing P application at lower available soil P levels was primarily explained by yield dilution effects, not the changes in available soil Zn and root mycorrhizal colonization. Under the experimental conditions, the available soil P would have to be as low as 0.7 ± 0.4 mg kg−1 to achieve the target grain Zn concentration of 40 mg kg−1, and at this level, the grain yield would only be 4127 ± 252 kg ha−1.

Identification of high-yield and high-Zn wheat cultivars for overcoming “yield dilution” in dryland cultivation

Abstract The most effective measure to address human zinc (Zn) deficiency worldwide is genetic Zn biofortification of cereal grains, namely breeding crop cultivars with both high yield and high grain Zn concentration. This has been not easy due to the widely reported yield dilution effect on grain Zn, while the Zn uptake and its distribution, as sources for grain Zn filling, were much less investigated for overcoming the yield dilution. A field study was conducted in a calcareous low-Zn soil in dryland with 123 modern wheat cultivars planted for two years, and different traits were determined at maturity to characterize cultivars with high or low grain Zn at the same yield levels. For all tested cultivars, grain Zn concentration showed no significant correlation with yield in both years. Then 19 cultivars were identified with consistent yield and grain Zn performances across years, and classified into four groups: low-Zn low-yield (n = 4), high-Zn low-yield (n = 4), low-Zn high-yield (n = 7), and high-Zn high-yield (n = 4). For low-yield cultivars, grain Zn was more closely related to shoot Zn uptake, while for high-yield cultivars, both shoot Zn uptake and Zn harvest index were closely related to grain Zn. From the seven high-yield low-Zn (7142 kg ha−1, 14.7 mg kg−1) to the four high-yield high-Zn cultivars (7287 kg ha−1, 20.8 mg kg−1), there was no yield dilution effect on grain Zn because the latter possessed both high shoot Zn uptake (190 g Zn ha−1) and high Zn harvest index (79%). In conclusion, yield dilution is not necessarily an obstacle for increasing wheat grain Zn concentration. Enhancing the Zn uptake and its distribution to grain make it possible to achieve high grain Zn and high yield simultaneously, promoting the success of genetic Zn biofortification for dryland wheat.

The effects of arbuscular mycorrhizal fungus and water stress on some antioxidant enzymes activities and nutrients uptake of two citrus rootstocks

ABSTRACT-Water stress is the main cause for crop yield reduction in the majority of agricultural regions of the world because it affects almost all plant functions. The effects of Glomus mosseae on growth, nutrients uptake, and antioxidant enzymes of sour orange (Citrus aurantium) and rough lemon) Citrus jambheri) rootstocks were assessed in sterilized soil under greenhouse conditions. A three-factor experiment was set up in a completely randomized design with three replicates of each treatment. Treatments consisted of water stress at four levels (irrigation intervals of 2, 4, 6, and 8 days) and mycorrhizal treatments at two levels (inoculation with G. mosseae and non-mycorrhizal control). Mycorrhizal seedlings of two citrus rootstocks were successfully infected by G. mosseae. As water stress increased, root colonization, shoot dry weight, shoot N, P, Mn, Cu, and Fe uptake of two citrus rootstocks significantly decreased but shoot Zn uptake and the antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (G-POD) and ascorbate peroxidase (APX)] activities of two citrus rootstocks leaves increased. With inoculation of seedlings by G. mosseae compared with control, shoot dry weight, N and P uptake, and antioxidant enzymes activities increased. It may be concluded that mycorrhizal inoculation notably influenced shoot nutrients uptake and leaves antioxidant enzymes activities in citrus and an increase in these parameters alleviated water stress.

Effect of uneven root allocation on shoot Zn uptake by crop plants growing on soil with heterogeneous P and Zn distribution

Many plants are known to preferentially allocate root growth to soil patches with elevated availability of growth-limiting nutrients. Little is known about how this influences the uptake of other nutrients such as trace metals. Here we investigated zinc (Zn) uptake by different crop plants in soil with heterogeneous phosphorus (P) and Zn distribution. Triticum aestivum L. (spring wheat), Cucumis sativus L. (cucumber) and Lupin albus L. (white lupin) were grown in rhizoboxes on low-P soil treated with local P and Zn amendments. A treatment with homogeneous P amendment was used as control. Root system development was monitored over 55days using neutron radiography and Winrhizo. The treatments had no effect on total root and shoot biomass, but root growth responded positively to local soil P enrichment but not to local Zn enrichment in all three plants. Wheat and cucumber responded with preferential allocation of root length, while in white lupin cluster root (CR) allocation was shifted to the P-enriched soil patches. Shoot Zn uptake was increased in wheat and cucumber when Zn- and P-enrichment were co-located and decreased when they were disjunct, indicating that shoot Zn uptake was related to root length growth in these two plants. In contrast, preferential CR allocation in lupin was not associated with a treatment effect on shoot Zn uptake.

Root growth and Zn uptake of three common crop plants in response to heterogeneity in soil texture and Zn distribution

The responses of root growth to non-uniformities in soil conditions can be of great importance for the acquisition of soil nutrients by plants. Here we monitored the root growth response of white lupin, cucumber and spring wheat to constructed horizontal heterogeneity in soil texture (and thereby also soil moisture) and zinc (Zn) distribution in rhizoboxes filled with sandy low-Zn soil using neutron radiography imaging. We investigated how the position of Zn-enriched soil relative to the heterogeneity in soil texture and moisture distribution affected Zn uptake, as compared to a control treatment with homogeneous texture. In all treatments the same total amount of water was added to the rhizoboxes. In cucumber heterogeneity in texture and moisture increased root length, root biomass and, independent of the position of Zn enrichment, also Zn uptake. In lupin it decreased cluster root formation and root biomass and in wheat specific root length, but in both of them it had no effect on total root length and shoot Zn uptake. The effects on root traits were associated with increased shoot biomass in wheat and cucumber, but not in lupin. Spatial differences in root growth between opposite sections in the heterogeneous packings were limited to the treatment in which coarse texture was combined with Zn enrichment. The results indicate that the responses in root system development were dominated by systemic factors with little modification by local responses and that the morphological root traits studied here were not limiting plant Zn uptake.

Erratum to: Predicting zinc bioavailability to wheat improves by integrating pH dependent nonlinear root surface adsorption

Aim Our aim was to improve the prediction of Zn bioavailability to wheat grown on low-Zn soils. The classical approach that directly relates Zn in a certain soil extract to Zn uptake has been shown to be inadequate in many cases. We tested a stepwise approach where the steps of the uptake process are characterized with, respectively, Zn solid-solution distribution, adsorption of Zn to root surface, Zn uptake into root and Zn translocation to shoot. Methods Two pot experiments were done with wheat grown on nine low-Zn soils varying widely in pH, clay and organic matter content. Soluble Zn concentrations in two soil extracts (DTPA and CaCl2) were measured. Free Zn ion concentrations in CaCl2 soil extracts were determined with the Donnan Membrane Technique. These Zn concentrations were then related to plant Zn uptake following both the direct and the stepwise approach. Results In the direct approach, Zn in the DTPA extract was a better predictor for shoot Zn uptake than Zn in the CaCl2 extract. In the stepwise approach, the relationship between Zn in CaCl2 extracts and the root surface adsorbed Zn was pH-dependent and nonlinear. Root surface adsorbed Zn was linearly related to root Zn uptake, and the latter was linearly related to the shoot Zn uptake. The stepwise approach improved the Zn uptake prediction compared to the direct approach and was also validated for different wheat cultivars. Conclusions The adsorption of Zn on the root surface is pH dependent and nonlinear with respect to the soil Zn concentration, and a useful proxy for bioavailable Zn over a wide range of soils.

Australian native plant species Carpobrotus rossii (Haw.) Schwantes shows the potential of cadmium phytoremediation.

Many polluted sites are typically characterized by contamination with multiple heavy metals, drought, salinity, and nutrient deficiencies. Here, an Australian native succulent halophytic plant species, Carpobrotus rossii (Haw.) Schwantes (Aizoaceae) was investigated to assess its tolerance and phytoextraction potential of Cd, Zn, and the combination of Cd and Zn, when plants were grown in soils spiked with various concentrations of Cd (20-320 mg kg(-1) Cd), Zn (150-2,400 mg kg(-1) Zn) or Cd + Zn (20 + 150, 40 + 300, 80 + 600 mg kg(-1)). The concentration of Cd in plant parts followed the order of roots > stems > leaves, resulting in Cd translocation factor (TF, concentration ratio of shoots to roots) less than one. In contrast, the concentration of Zn was in order of leaves > stems > roots, with a Zn TF greater than one. However, the amount of Cd and Zn were distributed more in leaves than in stems or roots, which was attributed to higher biomass of leaves than stems or roots. The critical value that causes 10% shoot biomass reduction was 115 μg g(-1) for Cd and 1,300 μg g(-1) for Zn. The shoot Cd uptake per plant increased with increasing Cd addition while shoot Zn uptake peaked at 600 mg kg(-1) Zn addition. The combined addition of Cd and Zn reduced biomass production more than Cd or Zn alone and significantly increased Cd concentration, but did not affect Zn concentration in plant parts. The results suggest that C. rossii is able to hyperaccumulate Cd and can be a promising candidate for phytoextraction of Cd from polluted soils.

Tolerance to Zn deficiency and P-Zn interaction in wheat seedlings cultured in chelator-buffered solutions

Zinc deficiency is a common constraint for wheat production in the regions with limited precipitation, particularly in the regions with high levels of available phosphate (P) in soil. Two experiments were conducted using chelator-buffered nutrient solutions to characterize differences in tolerance to Zn deficiency among three winter wheat (Triticum aestivum L.) genotypes and to investigate the relationship between P and Zn nutrition in wheat species. Four indices, Zn efficiency, relative shoot-to-root ratio, total Zn uptake in shoot, and shoot dry weight were used to compare the tolerance to Zn deficiency among three wheat genotypes. The results indicated that the four indices could be used in breeding selection for Zn uptake-efficient genotypes. The genotype H6712 was the most tolerant to Zn deficient, followed by M19, and then X13. Specifically, H6712 had the highest Zn uptake efficiency among the three genotypes. The addition of P to the growth medium increased Zn uptake and translocation from roots to shoots. Total Zn content of the wheat plant was 43% higher with 0.6 mmol/L P treatment than that of control with 0 mmol /L P treatment. The Zn translocation ratios from roots to shoots were increased by 16% and 26% with 0.6 mmol/L P treatment and 3 mmol/L P treatment, respectively, compared with 0 mmol/L P treatment. In contrast, high Zn concentrations in the growth medium inhibited P translocation from roots to shoots, but the inhibitive effects were not strong. Sixty-six percent of P taken up by wheat plants was translocated to the wheat shoots at 0 μmol/L Zn treatment, while the percent was 60% at 3 μmol/L Zn treatment. The result may be due to the fact that the wheat plants need more P than Zn.

Kinetics of zinc release from ground tire rubber and rubber ash in a calcareous soil as alternatives to Zn fertilizers

Ground rubber contains 15–20 g Zn kg−1 but very low levels of Cd and could serve as an inexpensive byproduct Zn fertilizer. The aim of this investigation was to test Zn release in a soil treated with ground tire rubber and rubber ash compared with commercial Zn fertilizer and a laboratory grade zinc sulfate. A Zn-deficient soil was chosen from wheat fields in Isfahan province, central Iran, and the ground rubber, rubber ash and fertilizer-Zn and laboratory ZnSO4 were added at 0.5 and 2 mg Zn kg−1; 0.5 kg ha−1 would usually correct Zn deficiency in such pot tests. The soil DTPA-extractable Zn was then measured with time and the results were described examining first order, Elovich, power function and parabolic diffusion kinetics models. In the pot experiment, corn (Zea mays L.) plants were exposed to three rates of Zn (0, 20, 40 mg Zn kg−1) from two different sources (ZnSO4 and ground rubber). Ground rubber was applied as 2–3 mm and <1 mm diameter particles. Zinc treatments were mixed with the soils before planting. At harvest, concentrations of Zn, Pb, and Cd in roots and shoots of corn were measured. Results showed that ground rubber and rubber ash significantly increased the concentration of DTPA-Zn in the soil and this increase was higher than achieved with the commercial Zn fertilizer. At the lower Zn application rate, Zn release followed parabolic diffusion, while at the higher rate the kinetics of release followed power function and Elovich models. There was an increase in Zn concentration of corn shoot and roots by adding of Zn regardless the source of applied Zn. With increase in the rate of rubber used, the shoot Zn uptake increased. The Pb concentration of shoot and Cd concentrations of shoot and roots were low (less than 0.02 mg kg−1) in all treatments. The results showed that the soil DTPA Zn decreases over time if the soil is amended with a soluble form of Zn whereas the reverse was observed if the Zn is added as ground rubber which only gradually transforms. Thus ground rubber and rubber ash offer strong value as Zn fertilizer for Zn deficient soils.

Influence of early stages of arbuscular mycorrhiza on uptake of zinc and phosphorus by red clover from a low-phosphorus soil amended with zinc and phosphorus.

In a pot experiment, red clover (Trifolium pratense) was grown in sterilized Zn-amended low available P soil (0, 50 or 400 mg Zn kg(-1)) with or without 100 mg kg(-1) added P and with or without inoculation with the arbuscular mycorrhizal (AM) fungus G. mosseae. When the plants were harvested after 40 days, AM colonization of the roots was still at an early stage, with only 14-38% of total root length colonized on average. AM colonization was highest in low-P soil, and was lowest in soil amended with 400 mg Zn kg(-1). Shoot yields were highest in AM plants with added P, but root yields were unaffected by AM inoculation. Shoot and root yields were higher with 100 mg added P kg(-1) soil, but lower with 400 mg Zn kg(-1) than 50 mg Zn kg(-1) or controls unamended with Zn. Shoot and root P concentrations were seldom higher in AM plants, but shoot P offtakes were higher in AM plants with added P. Concentrations of Zn and Cu were much higher in the roots than in the shoots. Shoot and root Zn and shoot Cu were lower, but root Cu was higher, in AM plants. Soil residual pH after plant growth was higher in AM treatments, and residual total Zn was also higher, indicating lower Zn uptake by AM plants. Soil solution pH was higher in AM treatments, and soil solution Zn was lower in the presence of mycorrhiza. The results are discussed in terms of AM protection of the plants against excessive shoot Zn uptake.

Seed zinc content influences early vegetative growth and zinc uptake in oilseed rape (Brassica napus and Brassica juncea) genotypes on zinc-deficient soil

Low-Zn seed (around 80 ng Zn per seed) and high-Zn seed (around 160 ng Zn per seed) of Zhongyou 821 (a traditional Brassica napus genotype from China found to be Zn-inefficient in our previous experiments), Narendra (Zn-efficient B. napus genotype from Australia) and CSIRO-1 (a Zn-efficient B. juncea genotype from Australia) oilseed rape genotypes were sown in pots containing Zn-deficient siliceous sand fertilized with low Zn supply (0.05 mg Zn kg−1 soil) or high Zn supply (2.0 mg Zn kg−1 soil) in a controlled environment. After six weeks, plants derived from the high-Zn seed had better seedling vigour, increased root and shoot growth, more leaf area and chlorophyll concentration in fresh leaf, and higher Zn uptake in shoot compared to those from low-Zn seed at low Zn supply; the impact of high-Zn seed was more marked in Zhongyou 821 compared with CSIRO-1 and Narendra. The influence of high-Zn seed was dissipated at high Zn supply. CSIRO-1 was superior in terms of shoot dry matter production and Zn uptake in shoots at low Zn supply. The results demonstrate that although oilseed rape has very small seeds (about 3 mg per seed weight) compared with wheat (30 mg per seed weight), Zn reserves present in this very small seed still have a strong impact on early vegetative growth as well as on Zn uptake of plants in Zn-deficient soils. The results suggest that sowing high-Zn seed coupled with growing Zn-efficient genotypes may help in sustaining the production of oilseed rape in Zn-deficient soils, and this has implications for improved seed technology.

Effects of mycorrhizae and fertilizer amendments on zinc tolerance of plants

In soils containing elevated levels of zinc, plant growth may be impaired because of Zn interference with P uptake by plants and because of detrimental effects of Zn toxicity itself. Because mycorrhizal fungi are known to improve uptake of plant P, the beneficial effects of mycorrhizal symbiosis on Zn tolerance of Andropogon gerardii Vitm. were assessed in soil amended with various levels of Zn and P. In the absence of P amendment, mycorrhizal fungi stimulated plant growth, but the degree of benefit depended on the inoculum source and the soil Zn level. Mycorrhizal fungi from a Zn contaminated site were more effective in increasing plant biomass at higher levels of Zn in the soil, whereas plant growth at lower levels of soil Zn was greater with mycorrhizal fungi from a non-contaminated site. Mycorrhizal fungus inoculation had no effect on shoot Zn concentration; however, inoculation significantly improved the plant P nutrition and therefore resulted in a high shoot P/Zn concentration ratio at all the soil Zn levels. To a certain extent, addition of P to the soil alleviated the Zn toxicity that had inhibited plant growth, but plant biomass tended to decrease with increasing soil Zn levels. Although P amendment improved P uptake, it also resulted in increased shoot Zn uptake.