Zinc uptake kinetics in the low and high‐affinity systems of two contrasting rice genotypes

Rice (Oryza sativa L.) cultivars differ widely in their susceptibility to zinc (Zn) deficiency. The physiological basis of Zn efficiency (ZE) is not clearly understood. In this study, the effects of Zn‐sufficient and Zn‐deficient pretreatments on the time and concentration‐dependent uptake kinetics of Zn were examined at low (0–160 nM) and high Zn supply levels (0–80 μM) in two contrasting rice genotypes (Zn‐efficient IR36 and Zn‐inefficient IR26). The results show that ⁶⁵Zn²⁺ influx rate was over 10 times greater for the Zn‐deficient pretreatment plants than for the Zn‐sufficient pretreatment plants. At low Zn supply, significant higher ⁶⁵Zn²⁺ influx rates were found for the Zn‐efficient genotype than for the inefficient genotype, with a greater difference (over three‐fold) at Zn supply > 80 nM in the Zn‐deficient pretreatments. At high Zn supply levels, however, a difference (2.5‐fold) in ⁶⁵Zn²⁺ influx rate between the two genotypes was only noted in the Zn‐deficient pretreatments. Similarly, the ⁶⁵Zn²⁺ accumulation in the roots and shoots of Zn‐efficient IR36 pretreated with Zn‐deficiency were sharply increased with time and higher than that in the Zn‐inefficient IR26 with an over four‐fold difference at 2 h absorption time. However, with Zn‐deficient pretreatments, the Zn‐efficient genotype showed a higher shoot : root ⁶⁵Zn ratio at higher Zn supply. Remarkable differences in root and shoot ⁶⁵Zn²⁺ accumulation were noted between the two genotypes in the Zn‐deficiency pretreatment, especially at low Zn level (0.05 μM), with 2–3 times higher values for IR36 than for IR26 at an uptake time of 120 min. There appear to be two separate Zn transport systems mediating the low and high‐affinity Zn influx in the efficient genotype. The low‐affinity system showed apparent Michaelis–Menten rate constant (K_m) values ranging from 10 to 20 nM, while the high‐affinity uptake system showed apparent K_m values ranging from 6 to 20 μM. The V_max value was significantly elevated in IR36 and was 3–4‐fold greater for IR36 than for IR26 at low Zn levels, indicating that the number of root plasma membrane transporters in low‐affinity uptake systems play an important role for the Zn efficiency of rice.     

Effects of mycorrhizal inoculation of upland rice on uptake kinetics of arsenate and arsenite

We assessed the effect of mycorrhizal inoculation on short‐term uptake kinetics of arsenate and arsenite by excised roots of upland rice (Oryza sativa L. cv. Zhonghan 221). A concentration of 0.01–0.05 mM arsenic (As) differentially affected the influx rates of both arsenate and arsenite into rice roots non‐inoculated or inoculated with Glomus mosseae and G. versiforme. While V_max for arsenate uptake by non‐mycorrhizal roots was 1.02 µmol g^?1 fresh weight h^?1, it was reduced by a factor of 2.4 for mycorrhizal roots (about 0.42 µmol g^?1 fresh weight h^?1) in the high‐affinity uptake system. However, at high concentrations of 0.5–2.5 mM As only G. versiforme was able to reduce As influx. The results show that mycorrhizal effects on As uptake of upland rice are both concentration and species‐specific.     

Effects of soil water content on growth,tillering, and manganese uptake of lowland rice grown in the water‐saving ground‐cover rice‐production system (GCRPS)

A 2‐year field experiment and a pot experiment were carried out to compare Mn uptake, tillering, and plant growth of lowland rice grown under different soil water conditions in the ground‐cover rice‐production system (GCRPS) in Beijing, North China. The field experiment was conducted in 2001 and 2002, including two treatments: lowland‐rice variety (Oryza sativa L. spp. japonica) grown under thin (14 μm) plastic‐film soil cover (GCRPS_plastic) at 80%–90% water‐holding capacity (WHC) and traditional lowland rice (paddy control) grown with 3 cm standing‐water table. The pot experiment was conducted in a greenhouse with four treatments: (1) traditional lowland rice: paddy control; (2) GCRPS, water‐saturated soil: GCRPS_saturated; (3) GCRPS at 90% water‐holding capacity (WHC): GCRPS_90%WHC; and (4) GCRPS at 70% WHC: GCRPS_70%WHC. Results of the field experiment showed that dry‐matter production, number of tillers, as well as N and Mn concentrations in rice shoots of GCRPS were significantly lower than in paddy control, while there was no significant difference in shoot Fe, Cu, Zn, and P concentration and nematode populations. In the pot experiment, shoot Mn concentration significantly decreased with decreasing soil water content, while soil redox potential increased. Shoot–dry matter production and tiller number of GCRPS_saturated were significantly higher than in other treatments. Significant correlations were observed between the shoot Mn concentration and tiller number at maximum tillering stage in the field and pot experiment, respectively. We therefore conclude that the limitation of Mn acquisition might contribute to the growth and yield reduction of lowland rice grown in GCRPS. The experiment provides evidence that GCRPS_plastic combined with nearly water‐saturated soil conditions helps saving water and achieving optimum crop development without visual or latent Mn deficiency as observed under more aerobic conditions.     

Non‐protein thiols and glutathione S‐transferase alleviate Cd stress and reduce root‐to‐shoot translocation of Cd in rice

A hydroponic experiment was conducted to investigate the dynamic variations of cadmium (Cd) uptake and transport, non‐protein thiols (NPT) and glutathione (GSH) concentrations, glutathione S‐transferase (GST) activity and lipid peroxidation under Cd stress in order to clarify the role of NPT and GST in reducing Cd toxicity and translocation in rice (Oryza sativa L.). Cadmium accumulation was initially fast and then slowed down with increasing time of Cd exposure. However, the rice growth inhibition and lipid peroxidation were not intense until 5d after Cd treatment, even though Cd kept accumulating in root and shoot, suggesting that Cd may be effectively detoxified. The concentrations of NPT in root increased gradually until 5d after Cd stress, whereas those in shoot showed no significant changes. The concentration of shoot GSH was progressively enhanced upon Cd treatment, while it gradually declined in root after an initial increase. The GST activity varied similarly in root and shoot, reaching the maximum level on 3rd day, followed by a significant decrease 5 d after Cd application. Significant increases of lipid peroxidation and root‐to‐shoot translocation on 7th day indicate that the equilibrium in Cd‐thiol interaction in rice might be disturbed upon the prolonged Cd exposure. In summary, our results suggest that Cd may be retained and detoxified in rice root through chelation with thiol compounds and subsequent sequestration.     

The Cd‐tolerant rice mutant cadH‐5 is a high Cd accumulator and shows enhanced antioxidant activity

To investigate the mechanism of cadmium (Cd) detoxification in rice (Oryza sativa L.), a Cd‐tolerant mutant cadH‐5, obtained by an Agrobacterium tumefaciens‐based gene‐delivery system, was used for a Cd‐tolerance and accumulation study. After 15 d of exposure to 0.75 mM CdCl₂, significant phenotypic differences were observed between the wild type (WT) and cadH‐5. When exposed to 0.5 mM CdCl₂, higher Cd levels were accumulated in cadH‐5 root cell wall, root cytosol, and membranes than those in WT. However, Cd concentrations in root tissues varied in both WT and cadH5. No significant difference of hydrogen peroxide (H₂O₂) concentrations was observed between WT and cadH‐5, while contents of cell‐wall polysaccharides and phytochelatins (PCs) in the mutant were higher compared to WT. The ratios of reduced glutathione to oxidized glutathione (GSH : GSSG) and ascorbate to dehydroascorbate (ASC : DHA) were lower in WT than in cadH‐5, while the NADPH : NADP⁺ ratio was different to the ratios of GSH : GSSG and ASC : DHA; the ascorbate peroxidase (APX, EC 1.11.1.11), glutathione peroxidase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities were lower in WT compared to cadH‐5. Our results indicate that under long‐term Cd stress, cadH‐5 plants can accumulate more Cd with more PC. Also, the redox status of ASC‐GSH cycle was more inhibited in WT than in cadH‐5 plants, rendering WT less able to scavenge reactive oxygen species (ROS). The cadH‐5 mutant maintains relatively high ASC, GSH, and NADPH concentrations, ratios of ASC : DHA, GSH : GSSG, and NADPH : NADP⁺, as well as antioxidative enzymatic activities and PC concentrations. Thus, it is tolerant of relatively high Cd accumulation.     

Catalase and ascorbate peroxidase activities are not directly involveded in the silicon‐mediated alleviation of ferrous iron toxicity in rice

Silicon (Si) is the second most abundant element in the soil and can alleviate several abiotic stresses in many plant species. However, the mechanisms involved in alleviating ferrous iron (Fe²⁺) toxicity by Si are still largely unknown, and no study has investigated the role of Si on the Fe²⁺‐induced oxidative stress and antioxidant system in rice. Four cultivars of Asian and African rice (Oryza sativa L. and Oryza glaberrima Steud) were grown for 4 weeks under hydroponic conditions with or without Fe²⁺ (250 mg Fe²⁺ L^?1) and with or without Si (250 mg SiO₂ L^?1). The plants that were treated with Fe²⁺ suffered Fe²⁺ toxicity, and Si helped to alleviate the toxicity symptoms. The bronzing index and the Fe concentration in the foliar tissue increased in the presence of Fe²⁺ but decreased significantly with the application of 250 mg SiO₂ L^?1. The concentration of malonyldialdehyde, that is commonly used as an indicator of oxidative stress, increased in the foliar tissue in the presence of 250 mg Fe²⁺ L^?1 in the nutrient solution. The application of 250 mg SiO₂ L^?1 in the plant nutrient solution treated with Fe²⁺ considerably limited the increase of malonyldialdehyde. However, no significant effect of Si application on the activities of antioxidant enzymes (catalase and ascorbate peroxidase) and non‐enzymatic antioxidants (total ascorbate, reduced ascorbate, oxidized ascorbate, and the ratio of the reduced to oxidized forms) was observed in the rice plants that were grown in the presence of Fe²⁺. These results suggest that Si does not act directly on the antioxidant defense system of rice but reduces the plant Fe²⁺ concentration, which reduces the oxidative stress.     

Organ-specific allocation pattern of acquired phosphorus and dry matter in two rice genotypes with contrasting tolerance to phosphorus deficiency

ABSTRACT

Our earlier study demonstrated that the landrace of Japonica rice, Akamai exhibits low-P (phosphorous) tolerance mechanisms compared to the conventional type cultivar, Koshihikari. The present study examined the genotypic difference of yield, plasticity of root growth, and internal utilization of acquired P (allocation pattern of biomass and P among different vegetative and reproductive organs) of two contrasting cultivars in response to P-deficiency. Each cultivar was grown until maturity with (+P) and without (–P) P supply in pots (two plants per pot) filled with 15 kg of Regosol soil. Grain yield and yield components were determined along with biomass and P accumulation in different vegetative and reproductive organs. To assess the plasticity of root growth, the soil column in the pot was divided into two equal portions (upper and lower soil layers) in which the root dry weight and length were measured separately. Among the investigated yield components, the number of filled grains per panicle was the key parameter determining genotypic differences of grain yield of two cultivars. P-deficiency had a marked influence on grain filling of Koshihikari where the filled grain percentage under –P condition was reduced by 29% compared to that under +P condition. However, the respective reduction for Akamai was only 11%. Low-P tolerance ability of Akamai imparts a yield advantage over Koshihikari under P-deficient conditions because of the production of the higher number of filled grains per panicle. Akamai explored both upper and lower soil layers of the pot more efficiently in search of P through greater root biomass and length. Akamai grown under P-deficient conditions had remarkably lower P concentrations in less active vegetative tissues (partly and fully senesced leaves) than those of Koshihikari; whereas, more active organs (green leaves and panicles) contained a greater amount of P. Akamai’s higher plasticity to external P availability can be a genetic resource for developing low-P tolerant, high-yielding rice genotypes suitable for predicted future P-limited environments.     

Seasonal soil nitrogen dynamics in rice‐wheat cropping systems of Nepal

The rice‐wheat annual double cropping system occupies some 0.5 million ha in the Himalayan foothills of Nepal. Alternating soil drying and wetting cycles characterize the 6–10 weeks long dry‐to‐wet season transition period (DWT) after wheat harvesting and before wetland rice transplanting. Mineral fertilizer use in the predominant smallholder agriculture is low and crops rely largely on native soil N for their nutrition. Changes in soil aeration status during DWT are likely to stimulate soil N losses. The effect of management options that avoid the nitrate build‐up in soils during DWT by N immobilization in plant or microbial biomass was studied under controlled conditions in a greenhouse (2001/2002) and validated under field conditions in Nepal in 2002. In potted soil in the greenhouse, the gradual increase in soil moisture resulted in a nitrate N peak of 20 mg (kg soil)^–1 that rapidly declined as soil moisture levels exceeded 40 % water‐filled pore space (equiv. 75 % field capacity). Similarly, the maximum soil nitrate build‐up of 40 kg N ha^–1 under field conditions was followed by its near complete disappearance with soil moisture levels exceeding 46 % water‐filled pore space at the onset of the monsoon rains. Incorporation of wheat straw and/or N uptake by green manure crops reduced nitrate accumulation in the soil to < 5 mg N kg^–1 in pots and < 30 kg N ha^–1 in the field (temporary N immobilization), thus reducing the risk for N losses to occur. This “saved” N benefited the subsequent crop of lowland rice with increases in N accumulation from 130 mg pot^–1 (bare soil) to 185 mg pot^–1 (green manure plus wheat straw) and corresponding grain yield increases from 1.7 Mg ha^–1 to 3.6 Mg ha^–1 in the field. While benefits from improved soil N management on lowland rice are obvious, possible carry‐over effects on wheat and the feasibility of proposed options at the farm level require further studies.     

双季稻田冬闲期土壤细菌数量及结构对施氮的响应

[目的]研究不同施氮水平对湖南双季稻区冬闲期土壤细菌结构与数量的影响,为双季稻区水稻可持续生产提供理论依据。[方法]依托湖南省双季稻区连续8年的定位试验,选取3个氮肥水平处理:CK(不施氮肥)、N1(施N 100 kg/hm^2)、N2(施N 200 kg/hm^2),取稻田冬闲期5—20 cm耕层土样,采用高通量测序和荧光定量PCR方法测定了土壤细菌数量与结构。[结果]与CK相比,N1、N2处理显著增加了双季稻产量,提升了冬闲期土壤总氮、全碳含量,降低了土壤pH、硝态氮及碳氮比(P<0.05)。N1和N2处理的细菌16s rDNA基因拷贝数分别为CK的48.25和40.31倍。施氮显著增加土壤总细菌丰度,土壤细菌丰度与土壤全氮、碳氮比呈显著正相关,与土壤全碳呈显著负相关。施氮改变了冬闲期稻田土壤细菌的多样性及群落结构。与CK相比,N1处理提高了稻田土壤微生物多样性;N2处理显著增加稻田土壤细菌丰富度,但显著降低稻田土壤细菌多样性。此外,3个处理土壤菌群相对丰度最高的是Proteobacteria(变形菌门),达40.16%~51.16%。N2处理的变形菌门相对丰度显著高于CK与N1,N1处理的变形菌门相对丰度显著低于CK。3个处理属水平细菌相对丰度较高的是Anaerolineaceae_uncultured(厌氧绳菌属)和Nitrospira(硝化螺旋菌属),其相对丰度分别为8.6%~14.56%和8.16%~11.46%。Spearman相关性分析显示,11个优势门菌群数量均与土壤化学性质存在显著相关性。稻田11个优势菌群的数量与土壤化学性质显著相关。[结论]湖南双季稻区施氮降低冬闲期稻田土壤pH和C/N比,低施氮水平可增加稻田微生物多样性,高施氮量虽然增加稻田细菌丰富度,但降低了微生物多样性。     

早晚季不同水稻籽粒灌浆表现及其与耐光氧化特性的关系研究

试验研究早晚季不同水稻材料籽粒灌浆特性与耐光氧化反应特性的关系结果表明,耐光氧化反应特性强的适强光生态型水稻品种其达最大灌浆速率的时间较迟,且灌浆生长盛期终止亦迟,各参数在早晚季灌浆结实期保持相对稳定;而不耐光氧化的适弱光生态型品种则反之,其达最大灌浆速率的时间早,且生长盛期结束亦早,各参数在早晚季灌浆结实期稳定性相对较差。     

Comparison of transgenic Bt rice and its non‐Bt counterpart in adaptability to nitrogen deficiency

Resistances of newly bred Bacillus thuringiensis (Bt) crops have been dramatically improved because of the effective and high expression of Bt protein in the plant. However, poorer adaptabilities to environmental stresses were observed in some Bt crops compared to their non‐Bt counterparts. The biological reasons for the poorer adaptabilities were still unclear. A nitrogen (N) deficiency experiment was conducted to investigate variations in growth and physiology characteristics of a newly bred Bt rice [Oryza sativa L. line MH63 (Cry2A*)] compared to its non‐Bt counterpart MH63. MH63 (Cry2A*) showed lower grain yields and lower biomass under low N levels compared to MH63. Earlier leaf senescence associated with disorder in protein metabolism was observed in MH63 (Cry2A*) when the N concentration was lower than 13.50 mg g^?1 in MH63 (Cry2A*) leaves and the ratio of Bt protein to soluble protein (BT : SP) was higher than 2203 μg g^?1 in MH63 (Cry2A*) leaves. The lower grain yield, the lower biomass and the earlier leaf senescence associated with disorder in protein metabolism in MH63 (Cry2A*) were correlated to the high BT : SP in MH63 (Cry2A*) leaves. The results suggest that MH63 (Cry2A*) has a poorer adaptability to N deficiency compared to its non‐Bt counterpart MH63. This poorer adaptability might be related to the high Bt protein expression in MH63 (Cry2A*).     

Soil N transformations after application of 15N‐labeled biomass in incubation experiments with repeated soil drying and rewetting

The effects of repeated soil drying and rewetting on microbial biomass N (N_bio) and mineral N (N_min) were measured in incubation experiments simulating typical moisture and temperature conditions for soils from temperate climates in the post‐harvest period. After application of in vitro ¹⁵N‐labeled fungal biomass to a silty loam, one set of soils was exposed to two drying‐rewetting cycles (treatment DR; 14 days to decrease soil moisture to 20 % water‐holding capacity (WHC) and subsequently 7 days at 60 % WHC). A control set (treatment CM) was kept at constant moisture conditions (60 % WHC) throughout the incubation. N_bio and N_min as well as the ¹⁵N enrichment of these N pools were measured immediately after addition of ¹⁵N‐labeled biomass (day 0) and after each change in soil moisture (day 14, 21, 35, 42). Drying and rewetting (DR) resulted in higher N_min levels compared to CM towards the end of the incubation. Considerable amounts of N_bio were susceptible to mineralization as a result of soil drying (i.e., drying enhanced the turnover of N_bio), and significantly lower N_bio values were found for DR at the end of each drying period. Immediately after biomass incorporation into the soil (day 0), 22 % of the applied ¹⁵N was found in the N_min pool. Some of this ¹⁵N_min must have been derived from dead cells of the applied microbial biomass as only about 80 % of the microbes in the biomass suspension were viable, and only 52 % of the ¹⁵N_bio was extractable (using the fumigation‐extraction method). The increase in ¹⁵N_min was higher than for unlabeled N_min, indicating that added labeled biomass was mineralized with a higher rate than native biomass during the first drying period. Overall, the effect of drying and rewetting on soil N turnover was more pronounced for treatment DR compared to CM during the second drying‐rewetting cycle, resulting in a higher flush of mineralization and lower microbial biomass N levels.     

Development of a quick on‐farm test to determine nitrate levels in soil

Crop management can be optimized and nitrogen (N) losses can be reduced with a better knowledge of soil‐nitrogen availability, especially if this information becomes directly available on‐site in a fast and cost‐effective way. In this paper, simple on‐farm methods to determine nitrate‐N in field‐moist soil samples immediately after sampling are described. The procedures include volumetric soil sampling, extraction based on manual shaking with tap water as universally available extractant, filtering soil/extractant mixtures on‐site, on‐site determination of the soil water content, and reflectometric nitrate measurements based on test strips. Using correction factors can compensate the impact of the temperature during the final nitrate measurement. An excellent agreement was found between the developed quick‐test procedures and the standard laboratory procedure. The proposed quick‐test has great potential to enable economical savings for farmers as well as benefiting the environment.     

Capacity,selectivity, and reversibility for nitrate exchange of a layered double‐hydroxide (LDH) mineral in simulated soil solutions and in soil

The leaching of nitrate is an important way of N losses from agricultural soils in humid regions. Nitrate leaching is difficult to control as most soils under crop production do not have anion‐exchange properties, and nitrate remains mobile in the solution. The present work evaluated the potential use of a synthetic layered double‐hydroxide (LDH) mineral as a nitrate exchanger in soil. The LDH used was a chloride form of a magnesium‐aluminum layered double hydroxide with the formula: [Mg²⁺_0.82Al³⁺_0.18(OH)₂]^0.18+[(Cl^–)_0.18 0.5(H₂O)]^0.18–. Experiments were carried out in aqueous solutions as well as in soil with the following objectives: (1) to characterize the nitrate adsorption capacity on the LDH, (2) to study its selectivity for nitrate adsorption in solution, (3) to evaluate the reversibility for nitrate exchange, and (4) to study the nitrate adsorption capacity and nitrate diffusion towards the LDH in soil.     

Eucalyptus biochar application enhances Ca uptake of upland rice,soil available P,exchangeable K,yield, and N use efficiency of sugarcane in a crop rotation system

It was hypothesized that the application of eucalyptus biochar enhances nutrient use efficiencies of simultaneously supplied fertilizer, as well as provides additional nutrients (i.e., Ca, P, and K), to support crop performance and residual effects on subsequent crops in a degraded sandy soil. To test this hypothesis, we conducted an on‐farm field experiment in the Khon Kaen province of Northeastern Thailand to assess the effects of different application rates of eucalyptus biochar in combination with mineral fertilizers to upland rice and a succeeding crop of sugarcane on a sandy soil. The field experiment consisted of three treatments: (1) no biochar; (2) 3.1 Mg ha^?1 biochar (10.4 kg N ha^?1, 3.1 kg P ha^?1, 11.0 kg K ha^?1, and 17.7 kg Ca ha^?1); (3) 6.2 Mg ha^?1 biochar (20.8 kg N ha^?1, 6.2 kg P ha^?1, 22.0 kg K ha^?1, and 35.4 kg Ca ha^?1). All treatments received the same recommended fertilizer rate (32 kg N ha^?1, 14 kg P ha^?1, and 16 kg K ha^?1 for upland rice; 119 kg N ha^?1, 21 kg P ha^?1, and 39 kg K ha^?1 for sugarcane). At crop harvests, yield and nutrient contents and nitrogen (N) use efficiency were determined, and soil chemical properties and pH₀ monitored. The eucalyptus biochar material increased soil Ca availability (117 ± 28 and 116 ± 7 mg kg^?1 with 3.1 and 6.2 Mg ha^?1 biochar application, respectively) compared to 71 ± 13 mg kg^?1 without biochar application, thus promoting Ca uptake and total plant biomass in upland rice. Moreover, the higher rate of eucalyptus biochar improved CEC, organic matter, available P, and exchangeable K at succeeding sugarcane harvest. Additionally, 6.2 Mg ha^?1 biochar significantly increased sugarcane yield (41%) and N uptake (70%), thus enhancing N use efficiency (118%) by higher P (96%) and K (128%) uptake, although the sugar content was not increased. Hence, the application rate of 6.2 Mg ha^?1 eucalyptus biochar could become a potential practice to enhance not only the nutrient status of crops and soils, but also crop productivity within an upland rice–sugarcane rotation system established on tropical low fertility sandy soils.     

Zinc uptake and distribution in tomato plants in response to foliar supply of Zn hydroxide‐nitrate nanocrystal suspension with controlled Zn solubility

The present study investigated the foliar uptake rate, distribution, and retranslocation patterns of novel, synthesized zinc hydroxide‐nitrate nanocrystals (ZnHN; solubility 30–50 mg Zn L^?1) applied on to the adaxial surface of tomato leaves (Solanum lycopersicum L. cv. Roma). The total Zn absorption from ZnHN suspension positively increased with ZnHN application rates, but the relative efficacy started to decline at > 400 mg Zn L^?1. Within the 3 weeks, total Zn recovery in the ZnHN‐treated plants was 16% of the total ZnHN‐Zn applied, compared to the near 90% total Zn recovery in the Zn(NO₃)₂‐plants at the same Zn rate. Foliar‐absorbed ZnHN‐Zn was distributed from the treated leaves into other plant parts and preferentially translocated into the roots. Distribution of Zn from ZnHN‐treated leaves to apical parts was not limited by Zn deficiency. These results demonstrate that ZnHN crystals with controlled solubility provided some sort of slow‐release Zn over a certain growth period at a rate slower (but quantitatively effective) than the soluble Zn(NO₃)₂. The efficacy of the prolonged foliar Zn supply could be enhanced if the ZnHN suspension is sprayed over a large leaf surface area at the peak vegetative or early flowering stage.