Root Zn Concentrations Research Articles

Synergism and antagonisms between nutrients induced by copper toxicity in grapevine rootstocks: Monocropping vs. intercropping

The long-term use of Cu-containing fungicides contaminates vineyards soils, which can induce Cu toxicity and nutrient imbalances in several plant species. The aim of this work was to evaluate the effect of Cu toxicity on two grapevine rootstocks, Fercal and 196.17, and to elucidate if intercropping with oat can alleviate grapevine Cu toxicity. Plants were hydroponically-cultivated and treated with different Cu concentrations. At harvest the biomass accumulation, the SPAD index and the symplastic and apoplastic root and leaves ionome were measured to evaluate possible synergistic and/or antagonistic effects on other micro- and macronutrients. The root exudation analysis was correlated with genes expression (VvPEZ-like), whereas PCA analysis performed on the grapevine and oat ionome revealed that both mono- and intercropped 196.17 rootstock display a positive effect on Zn and Mn in the root tissues at high Cu concentrations. An increase of Zn and Mn in roots was also reported for the intercropped Fercal rootstock at high Cu concentrations while an antagonistic relation was reported for root Zn concentration in the monocropped Fercal rootstock. Our results showed that grapevine and oat compete for nutrient uptake and that this phenomenon can possibly alleviate grapevine Cu toxicity. However, Fercal rootstock is able to take advantage from oat, while 196.17 is disadvantaged by the intercropping system. Even though intercropping system seems to be a valuable tool to counteract grapevine Cu toxicity, the application of this agricultural practice has shown to be species dependent and should be evaluated for each rootstock.

Effects on Eichhornia crassipes under Zn stress.

Eichhornia crassipes is a macrophyte widely used in phytoremediation, demonstrating a high ability to remove metals from water. The aim of this work was to evaluate its enzymatic detoxification strategies and metal accumulation when it is exposed to different Zn concentrations (0, 2, 4, 6, and 9ppm) for periods of 24, 48, and 72h. Zn concentration in roots was significantly higher than in aerial parts. Independently of the treatment, in the first 48h, concentrations of photosynthetic pigments were not affected. However, a significant increase (between 19 and 34%) in Chl-b concentrations for all treatments was observed at 72h. Carotenoid concentration was not affected during the first 48h, while at 72h, there was a significant increase regarding the control (between 11 and 24%) for all treatments. Malondialdehyde concentration in aerial parts and roots was not affected during the experiment. Nonetheless, a significant increase in the enzymatic activity of the antioxidant system was observed. Results suggest that Zn could have potential antioxidant properties, which may result in the activation of different antioxidant enzymes involved in the protection against metal stress.

Combined effects of ZnO NPs and Cd on sweet sorghum as influenced by an arbuscular mycorrhizal fungus

Both metals and metal-based nanoparticles (NPs) can easily accumulate in soil, posing risks for plants and microbes. However, the interaction between NPs and toxic metals coexisting in soil is not yet well understood. Here, we studied the combined effects of ZnO NPs and Cd on sweet sorghum inoculated with or without the arbuscular mycorrhizal (AM) fungus Funneliformis caledonium. Plants were grown in soil amended with ZnO NPs (50, 250, and 500 mg/kg), alone or in combination with 5 mg/kg Cd. The two higher doses of ZnO NPs inhibited plant growth, leading to synergistic toxicity with Cd. However, at the lowest dose, ZnO NPs were non-phytotoxic, displaying antagonistic interactions with Cd on plant growth. When added with high doses of ZnO NPs, Cd significantly increased root Zn concentrations, but decreased shoot Zn concentrations at the low dose. Conversely, all doses of ZnO NPs significantly decreased shoot and root Cd concentrations. Furthermore, high doses of ZnO NPs generally inhibited soil enzyme activities, but Cd addition showed no significant or even stimulative effects, and mitigated the inhibitory effects of ZnO NPs. AM inoculation increased plant growth and P nutrition, and soil enzyme activities. When the low dose of ZnO NPs was added alone or in combination with Cd, AM inoculation decreased shoot Zn concentrations. Our results reveal complex interactions between ZnO NPs and Cd on plant growth and nutrition, plant Zn and Cd accumulation, and soil enzyme activities, while AM inoculation can help diminish the adverse effects induced by ZnO NPs and Cd.

Interactions Between Environmental Factors and Zinc Concentrations in Porewater and Roots of Rhizophora sp. in Ampallas, Mamuju, West Sulawesi, Indonesia

The study was to determine the concentrations of Zn in porewater and fine roots of Rhizophora sp., and to examine their interactions with mangrove densities and physico-chemical. Porewater samples, fine roots, and sediments were collected in a 100 m2 plot at each site with different mangrove densities. The average Zn concentrations in mangrove roots in the study area were 0 – 58.21 mg/kg, suggested the capability of mangrove roots in retaining Zn. The average dissolved Zn concentrations in porewater were 0.63 mg/L – 3.50 mg/L, illustrated the amount of Zn bioavailable form and its potential release to the adjacent environment. The Zn concentrations in porewater did not correlate significantly with the densities of mangroves. The concentrations of Zn in roots increased as the densities were higher, which is possibly caused by the absence of mangrove at Site 1. The study discovered the important roles of organic content and silt/clay in Zn sorption thus affect Zn levels in porewater. The concentrations of Zn in mangrove roots increased as the pH of sediment and porewater decreased.

Zinc deficiency tolerance in maize is associated with the up-regulation of Zn transporter genes and antioxidant activities.

Zinc (Zn) is an essential micronutrient for the growth and development of plants. However, Zn deficiency is a common abiotic stress causing yield loss in crop plants. This study elucidates the mechanisms of Zn deficiency tolerance in maize through physiological and molecular techniques. Maize lines tolerant (PAC) and sensitive (DAC) to Zn deficiency were examined physiologically and by atomic absorption spectrometry (AAS). Proteins, H2 O2 , SOD, POD, membrane permeability and gene expression (using real-time PCR) of roots and shoots of both maize lines were assessed. Zn deficiency had no significant effect on root parameters compared with control plants in PAC and DAC but showed a substantial reduction in shoot parameters in DAC. AAS showed a significant decrease in Zn concentrations in both roots and shoots of DAC but not PAC under Zn deficiency, implying that Zn deficiency tolerance mechanisms exist in PAC. Consistently, total protein and membrane permeability were significantly reduced in DAC but not PAC in both roots and shoots under Zn deficiency in comparison with Zn-sufficient plants. Real-time PCR showed that expression of ZmZIP1, ZmZIP4 and ZmIRT1 transporter genes significantly increased in roots of PAC, but not in DAC due to Zn deficiency compared with controls. The H2 O2 concentration dramatically increased in roots of DAC but not PAC. Moreover, tolerant PAC showed a significant increase in POD and SOD activity due to Zn deficiency, suggesting that POD- and SOD-mediated antioxidant defence might provide tolerance, at least in part, under Zn deficiency in PAC. This study provides an essential background for improving Zn biofortification of maize.

Synergic effect of arbuscular mycorrhizal fungi and bradyrhizobia on biomass response, element partitioning and metallothionein gene expression of soybean-host under excess soil zinc

The synergic effect of rhizobia (R) and arbuscular mycorrhizal (AM) fungi on the bioproduction, trace element partitioning and metallothionein gene expression of soybean-host was investigated under normal and elevated soil zinc conditions. In a completely randomized 3×4 factorial design, the experimental treatments – Zn addition (0, 200, and 400 mg Zn kg−1 soil) and inoculation (uninoculated control, R, AM, and RAM dual inoculation) were set up in the greenhouse for nine weeks. While the inoculants effectiveness was decreased in 400 mg Zn kg−1 soils, RAM induced significantly higher biomass production under all soil Zn treatments. The biomass response indicated that AM modulated stem and root bioproduction in favor of leaf/pod, while rhizobium favored root production and potentiated AM effect in dual inoculation. The partitioning of Zn and Mn in the hosts indicated synergic effects between AM and R, in RAM plants. Compared with control, AM lowered leaf Zn concentrations by reducing root Zn concentrations and modulating root-to-stem and stem-to-leaf Zn translocations. Compared to AM, RAM plants achieved lower leaf and pod Zn concentrations by mainly reducing root-to-stem Zn translocation. Zn treatment increased leaf and pod Mn in control plants, but symbionts countered this by regulating root-to-stem Mn translocation, especially in RAM. Type 1 metallothionein gene expression in roots was highest in RAM and lowest in control plants, but Zn effects were not dose-dependent. Synergisms in symbionts root colonization, number and greenness of leaves, element partitioning and metallothionein gene expression are indicated as important mechanisms underlying the effective partnership between AM and R, in the dual inoculation.

Macrophytes as potential biomonitors in peri-urban wetlands of the Middle Parana River (Argentina).

The aims of this study were to measure the concentrations of nutrients and pollutants in peri-urban wetlands, to analyze the plant morphology of the most representative macrophyte species, and to determine their potential use as biomonitors. Four wetlands in the Middle Paraná River floodplain evidencing contamination or anthropogenic impact were studied. The studied species were Typha domingensis Pers., Eichhornia crassipes (Mart.) Solms., Alternanthera philoxeroides (Mart.) Griseb., and Pistia stratiotes L. Besides, the same plant species from an uncontaminated wetland considered as control were studied. A. philoxeroides showed the highest total phosphorus (TP) concentration in leaves throughout the study, while the other species showed a higher TP concentration in roots than in leaves. Since metal concentration in A. philoxeroides tissues was always higher than in sediment, further studies focused on its phytoremediation capacity should be carried out. T. domingensis exhibited the highest Zn concentrations in roots followed by Pb, and E. crassipes presented the highest values of Pb concentrations in roots. The aerial part height of the plants from peri-urban wetlands was significantly higher than that of the plants from the control, while the root length was significantly lower. The root length of P. stratiotes showed a negative correlation with soluble reactive phosphorus (SRP) concentration in water. All the root anatomical parameters of T. domingensis and E. crassipes showed a positive correlation with nitrate and ammonium concentrations in water. The studied macrophytes evidenced a high tolerance, enabling them to grow and survive in peri-urban wetlands that receive pollution from different sources. The use of aquatic and wetland plants as contaminant bioindicators and bioaccumulators in the Middle Paraná River floodplain is completely feasible.

Assessment of the adaptive capacity of plant species in copper mine tailings in arid and semiarid environments

The objective of this work was to identify hyperaccumulator plants and evaluate their capacity on copper mine tailings in the Antofagasta Region (Chile), considered one of the most arid in the world. Two native plant species, Gazania rigens and Pelargonium hortorum, were grown during 11 weeks on mine tailings. The physico-chemical characterization of the mine tailings under study indicated that the substrate required conditioning to support a phytoremediation system. In this respect, organic and inorganic amendments and mycorrizhal fungi were added to the substrate. Three treatments were designed to assess the effects of the amendments through an analysis of variance. Indicators of plant growth and development were measured weekly, and concentrations of Cd, Cu, Fe, Mn, Pb, Al, and Zn in roots of tailing-grown plants and substrate were measured at the end of the experiment. The results were used to determine the bioconcentration factor (BCF), which demonstrated that both species act as excluders of Fe, Mn, Pb, Al, and Zn. In addition, it was found that both species present characteristics of potential accumulators of Cu.

Fluorine and metals in Polygonum arenastrum Bor. from areas influenced by various types of industry

A herbaceous plant Polygonum arenastrum Bor. (=P. aequele Lindm., Polygonum aviculare ssp. aequale (Lindman) Ascherson & Graebner) (equal-leaved knotgrass), is a widespread, good coloniser, able to survive in wastelands where other species became extinct. Therefore, the bioindication abilities of this species for F, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn were investigated. P.arenastrum was collected from 90 sites affected by six polluting factories: copper smelter, chlor-alkali plant, former ferrous-chromium smelter and active combustion smelter, power plant, cement plant and coke plant. Plant samples were collected at 0.75, 1.5, 3 and 4.5km from each of these polluters in N, S, W and E directions. For comparison, a control site with 16 sampling points was selected in an area relatively free from pollution. Concentrations of Cr, Cu, Fe, Pb and Zn in shoots and roots positively correlated with those in soil (both total and plant-available). Cu, Pb and Zn in P.arenastrum were within the values reported in literature as toxic for other plants with the highest bioaccumulation factor (BF) from soil to shoots for Cr and the highest translocation factor (TF) from roots to shoots for Co and Pb for more and less polluted and control sites. Polygonum arenastrum has a potential to accumulate Cr even in sites with low chromium concentration in soil. Polygonum arenastrum does not show any form of shoot injury at increased levels of F and metals in its tissues. Based on these characteristics we conclude that the ubiquitous P.arenastrum may be utilised as a relevant indicator of contamination in industrial zones and may function as an early warning system of increased toxicity in the environment.

Effect of different nitrogen forms on the toxicity of Zn in wheat seedling root: a modeling analysis.

Heavy metal stress in culture media is always rhizotoxic. Our study aims to investigate the role of negative potential (ψ 0) at root cell membrane surface (CMs) on modeling Zn2+ toxicity to wheat seedling roots and to examine the effects of different nitrogen forms (NH4+ and NO3-) on ψ 0 and Zn rhizotoxicity. Solution culture experiments were conducted to measure the root elongation and Zn accumulation under Zn2+ exposure. The role of two nitrogen forms in affecting Zn2+ toxicity was compared, giving particular consideration to ψ 0 and Zn2+ activities at CMs ({Zn2+}0). Results showed that NH4+ alleviates Zn2+ rhizotoxicity and NO3- increases Zn2+ rhizotoxicity. In modeling the rhizotoxicity, root length correlated better with {Zn2+}0 than {Zn2+}b, and the predictive accuracy (r 2) of NH4+ treatment increased from 0.748 to 0.917 when incorporation of {Zn2+}0 and {Ca2+}0 into analysis. Oppositely, ψ 0 played a limited role in modeling Zn2+ rhizotoxicity and bioavailability in NO3- treated medium (r 2=0.609). Moreover, higher concentration of Zn in roots was found in NO3- treatment, compared with the NH4+ treatment. ψ 0 rather than the rhizotoxicity data correlated better with Zn accumulation especially in the NO3- treatment (r 2>0.7), which meant the electrical driving force at CMs playing a dominant role in modeling the metal accumulation. In conclusion, the alleviatory role of NH4+ on Zn toxicity and uptake was well explained and modeled by electrostatic effects at CMs. Though our data do not explore mechanisms for the NO3--Zn2+ interactions, we propose that ψ 0 worked better in affecting the driving force for root Zn uptake, than influencing metal bioavailability at CMs.

The influences of arbuscular mycorrhizal fungus on phytostabilization of lead/zinc tailings using four plant species

ABSTRACTA greenhouse experiment was conducted to investigate the effects of the arbuscular mycorrhizal fungus Funneliformis mosseae on three parameters: Pb, Zn, Cu and Cd accumulation, translocation and plant growth in perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea), showy stonecrop (Hylotelephium spectabile) and Purple Heart (Tradescantia pallida). The purpose of this work is to enhance site-specific phytostabilization of lead/zinc mine tailings using native plant species. The results showed that mycorrhizal fungi inoculation significantly increased plant biomass of F. arundinacea, H. spectabile and T. pallida. The Pb, Zn, Cu and Cd concentrations in roots were higher than those in shoots both with and without mycorrhizae, with the exception of the Zn concentration in H. spectabile. Mycorrhizae generally increased metal concentrations in roots and decreased metal concentrations in shoots of L. perenne and F. arundinacea. In addition, it was found that the majority of the bioconcentration and translocation factors were lower than 1 and mycorrhizal fungi inoculation further reduced these values. These results suggest that appropriate plant species inoculated with mycorrhiza might be a potential approach to revegetating mine tailing sites and that H. spectabile is an appropriate plant for phytostabilization of Pb/Zn tailings in northern China due to its higher biomass production and lower metal accumulation in shoots.

Zinc uptake by roots and accumulation in maize plants as affected by phosphorus application and arbuscular mycorrhizal colonization

Phosphorus (P) application reduces the zinc (Zn) concentration of cereal grain, but the mechanisms, including root Zn accumulation, remain controversial. Field and pot experiments were conducted to determine the degree to which root Zn accumulation, root arbuscular mycorrhizal (AM) colonization, and other factors contribute to the negative interaction between P and Zn. Root Zn accumulation was positively related to shoot Zn accumulation. In responding to P application, root Zn accumulation was more affected by changes in AM colonization than by changes in root dry weight (RDW). In the pot experiment without Zn supply, root Zn concentration (RZnC), RDW, and AM colonization together explained 98% (adjusted R2 value) of the decrease in root Zn accumulation with P application, while AM colonization and RDW explained 66% (adjusted R2 value) of decrease in total Zn accumulation. In the pot experiment with Zn sufficient supply, RZnC and RDW explained 89% (adjusted R2 value) of the decrease in root Zn accumulation with increasing P application, while RDW, RZnC, and AM colonization explained 53% (adjusted R2 value) of the decrease in total Zn accumulation. Especially in Zn-deficient soil, root Zn accumulation explains much of the negative interaction between P and Zn, and root Zn accumulation is greatly affected by AM colonization.

Physiological Role of Exogenous Nitric Oxide in Improving Performance, Yield and Some Biochemical Aspects of Sunflower Plant Under Zinc Stress

The present study was undertaken to examine the possible roles of sodium nitroprusside in protection against oxidative damage due to zinc toxicity in sunflower plants. Physiochemical parameters in sunflower plants exposed to Zn2+ (100, 200 and 300 mg/kg soil) alone or combined with SNP were measured. The results showed that excess of Zn decreased plant growth, seed yield components and photosynthetic pigments content. On the other hand, Zn stress increased the level of non-enzymatic antioxidants (ascorbic acid and reduced glutathione) and enzymatic antioxidants (superoxide dismutase, ascrobate peroxidase and glutathione reductase), coupled with the appearance of novel protein bands. Furthermore, Zn stress increased Zn content in roots and shoots. The amounts of Zn in roots were higher than shoots. A marked increase in total saturated fatty acids accompanied by a decrease in total unsaturated fatty acids was observed. Exogenously application of SNP (20 µM) increased growth parameters, photosynthetic pigments content, ascorbic acid and glutathione contents, antioxidant enzyme activities and the quality of the oil in favour of the increase of unsaturated fatty acids. Moreover, SNP application increased Zn concentration in roots and inhibited Zn accumulation in shoots. Therefore, it is concluded that SNP treatment can help reduce Zn toxicity in sunflower plants.

Effect of biochar on cadmium bioavailability and uptake in wheat (Triticum aestivum L.) grown in a soil with aged contamination

Cadmium (Cd) is a well-known and widespread toxic heavy metal while the effects of biochar (BC) on Cd bioavailability and toxicity in wheat, especially in soils with aged contamination are largely unknown. In the present study, the effect of rice straw BC on Cd immobilization in soil and uptake by wheat in an agricultural contaminated-soil was investigated. Different levels of rice straw BC (0%, 1.5%, 3.0% and 5% w/w) were incorporated into the soil and incubated for two weeks. After this, wheat plants were grown in the amended soil until maturity. The results show that the BC treatments increased the soil and soil solution pH and silicon contents in the plant tissues and in the soil solution while decreased the bioavailable Cd in soil. The BC application increased the plant-height, spike-length, shoot and root dry mass and grain yield in a dose additive manner when compared with control treatment. As compared to control, BC application increased the photosynthetic pigments and gas exchange parameters in leaves. Biochar treatments decreased the oxidative stress while increased the activities of antioxidant enzymes in shoots compared to the control. The BC treatments decreased the Cd and Ni while increased Zn and Mn concentrations in shoots, roots, and grains of wheat compared to the control. As compared to the control, Cd concentration in wheat grains decreased by 26%, 42%, and 57% after the application of 1.5%, 3.0%, and 5.0% BC respectively. Overall, the application of rice straw BC might be effective in immobilization of metal in the soil and reducing its uptake and translocation to grains.

Decrease in the genotoxicity of metal-contaminated soils with biochar amendments.

Biochar amendments, i.e., the solid product of biomass pyrolysis, reduce soil metal availability, which may lower the toxicity of metal-contaminated soils. A direct link between the decrease in soil metal availability and improved plant development is however often difficult to establish, as biochar may induce undesirable side effects on plant growth, e.g., a modification to plant nutrition. In order to investigate toxicity processes at a cellular level, roots of Vicia faba were exposed for 7days to three metal-contaminated substrates and one control soil, amended with a 0 or 5% (w/w) addition of a wood-derived biochar. Exposure to pure biochar was also tested. Root tip cells were then observed to count the number of micronuclei as an estimation of DNA damage and the number of cells at mitosis stage. Results showed that biochar amendments led to a significant decrease in soil metal availability (Cd, Cu, Ni, Pb, and Zn) and to enhance root development on acidic substrates. The micronucleus frequency in root tip cells was positively correlated and the number of mitotic cells negatively, to the extractability of Zn in soils and to the concentration of Zn in secondary roots. Exposure to pure biochar caused a lower production of roots than most soil substrates, but led to the lowest number of observed micronuclei. In conclusion, biochar amendments can reduce the genotoxicity associated with the presence of metallic contaminants in soils, thereby potentially improving plant growth.

Biochemical and molecular mechanisms associated with Zn deficiency tolerance and signaling in rice (Oryza sativa L.)

ABSTRACTIn this study, zinc (Zn) deficiency caused a significant reduction in growth parameters and tissue Zn concentrations in BRRI 33 (sensitive) but not in Pokkali (tolerant). The increase of proton extrusion in both genotypes under high pH suggests that it gets triggered as a common consequence of reducing pH and solubilization of Zn. Real-time PCR showed pronounced upregulation of OsZIP4, OsDMAS1, OsNAS2 and OsPCS1 in Zn-deficient roots of Pokkali, and to a lesser extent in BRRI 33 only for OsZIP4 and OsPCS1. This suggests that OsDMAS1, OsNAS2 and OsPCS1 functions as secondary consequences leading to higher chelation and uptake of Zn under Zn deficiency in Pokkali. Further, a major increase in CAT, POD, SOD, GR and key metabolites suggests that high antioxidant defense plays a critical role in Zn deficiency tolerance in Pokkali. Further, Pokkali self-grafts and plants having Pokkali rootstock combined with BRRI 33 scion showed no significant decline in plant height, root dry matter and Zn concentration along with upregulation of Zn transporters (OsZIP4 and OsIRT1) under Zn deficiency, suggesting that signal driving mechanisms for Zn deficiency tolerance mechanisms are generated in the root and Zn-inefficient BRRI 33 is not capable of producing signals or sensing them.

Root Fungal Endophytes Enhance Heavy-Metal Stress Tolerance of Clethra barbinervis Growing Naturally at Mining Sites via Growth Enhancement, Promotion of Nutrient Uptake and Decrease of Heavy-Metal Concentration.

Clethra barbinervis Sieb. et Zucc. is a tree species that grows naturally at several mine sites and seems to be tolerant of high concentrations of heavy metals, such as Cu, Zn, and Pb. The purpose of this study is to clarify the mechanism(s) underlying this species’ ability to tolerate the sites’ severe heavy-metal pollution by considering C. barbinervis interaction with root fungal endophytes. We measured the heavy metal concentrations of root-zone soil, leaves, branches, and fine roots collected from mature C. barbinervis at Hitachi mine. We isolated fungal endophytes from surface-sterilized root segments, and we examined the growth, and heavy metal and nutrient absorption of C. barbinervis seedlings growing in sterilized mine soil with or without root fungal endophytes. Field analyses showed that C. barbinervis contained considerably high amounts of Cu, Zn, and Pb in fine roots and Zn in leaves. The fungi, Phialocephala fortinii, Rhizodermea veluwensis, and Rhizoscyphus sp. were frequently isolated as dominant fungal endophyte species. Inoculation of these root fungal endophytes to C. barbinervis seedlings growing in sterilized mine soil indicated that these fungi significantly enhanced the growth of C. barbinervis seedlings, increased K uptake in shoots and reduced the concentrations of Cu, Ni, Zn, Cd, and Pb in roots. Without root fungal endophytes, C. barbinervis could hardly grow under the heavy-metal contaminated condition, showing chlorosis, a symptom of heavy-metal toxicity. Our results indicate that the tree C. barbinervis can tolerate high heavy-metal concentrations due to the support of root fungal endophytes including P. fortinii, R. veluwensis, and Rhizoscyphus sp. via growth enhancement, K uptake promotion and decrease of heavy metal concentrations.

The role of lupin shoot P and Zn status in root allocation and nutrient uptake in soil with heterogeneous P and Zn distribution

Many plants have been found to show preferential root growth allocation to soil patches with locally increased nutrient availability. Little is known about the influence of the plants’ nutrient status on these responses. Addressing this question, we conducted a climate chamber experiment to investigate how foliar phosphorus (P) and zinc (Zn) application (alone or in combination) would affect root allocation and nutrient uptake by white lupin (Lupinus albus L.) seedlings growing on soil with constructed heterogeneity in P and Zn distribution. The same soil packing was used in all pots. One quarter section of each packing was enriched with Zn, one with P, one with Zn and P, while neither Zn nor P was added to the fourth section (opposite to the section with the combined Zn and P amendment). Neither foliar P nor foliar Zn application had a fertilization effect on plant growth. The allocation of root length growth showed a clear preference for P-enriched soil sections, when no foliar fertilizer was applied. With foliar P or Zn application these preferences disappeared. Cluster root allocation and root P concentration showed a similar behavior. In the treatments with foliar Zn application, root length growth was also preferentially allocated in Zn-enriched soil, while without foliar Zn there was only a tendency for such a response. Root Zn concentrations were always much higher in soil sections with than without Zn amendment. The foliar treatments had no effect on root Zn concentration. While the responses to foliar P application can be understood in terms of an optimization strategy in root allocation for P foraging, the effects of foliar Zn application on root growth allocation cannot be interpreted in this way and require further investigation.

The Role of the Arbuscular Mycorrhizal Maize (Zea mays L.) and Phosphorus levels in the phytoremediation of zinc contaminated soil.

The factorial experiment under greenhouse condition was conducted to investigate the effects of AMF on phytoremediation of zinc contaminated soil. Maize plants inoculated and non-inoculated with Glomus mossea were grown under five levels of Zinc addition (0, 100, 300, 600, and 900〖 mg kg〗^(-1) ) and three levels of phosphorus addition (0, 25, 50 mg kg^(-1)). No mycorrhizal colonization was detected in the roots of non-inoculated plants. The higher value of colonized roots in inoculated plants was in treatment (+MP0Zn4) 69% while the lower value was in the treatment (+MP2Zn3) 35%. An addition of phosphorus fertilization significantly decrease colonization rate of roots. Inoculation with AMF increased shoots and roots dry matter weight, Zn uptake in shoots and phosphorus concentration and uptake in shoots and roots. Inoculation with AMF decreases Zn concentration in shoots and increases Zn concentration in roots in moderate and high levels of Zn addition. Dry matter weight of shoots and roots significantly decreases with increase of Zinc addition in non mycorhizal plants; however, there is no significant effect of the zinc addition on shoots and roots dry matter weight in mycorrhizal plants. These results are good evidence that AMF increases host plant tolerance to Zn contamination. An addition of phosphorus increases shoots and roots dry matter, phosphorus concentration and uptake. This study suggests that AMF protect maize plants from Zn toxicity and enhance phytoremediation of Zn contaminated soil by two mechanisms: dilutions effects and accumulate Zn in roots and fungi mycelium

Zinc uptake and accumulation in winter wheat relative to changes in root morphology and mycorrhizal colonization following varying phosphorus application on calcareous soil

Although phosphorus (P) is known to reduce zinc (Zn) uptake by roots and root-to-shoot translocation, how this interaction is affected by changes in root morphology and arbuscular mycorrhizae (AM) are poorly understood. The current study determined the effects of P application rate (0, 25, 50, 100, 200, and 400kgPha−1) on Zn uptake by roots and root-to-shoot translocation in a high-yielding winter wheat system on calcareous soil. Root dry weight (RDW), root length density (RLD), and root surface area (RSA) significantly increased as P application increased from 0 to 50kgha−1 but were unaffected by rates >50kgha−1. Zn accumulation (mgm−2 or μgm−2) by roots at flowering increased with application of 25 and 50kgPha−1 but slightly decreased with application of 100–400kgPha−1. Zn accumulation in roots and in shoots at flowering and grain yield at maturity were positively correlated with RDW, RLD, and RSA. Root Zn accumulation was increasing with increased AM colonization from low AM (<10%) to 30% AM colonization. Whereas, continuously increasing AM colonization induced root Zn accumulation decrease, which may be mainly due to the decrease of root dry weight affected by P deficiency. P application rate did not significantly affect the ratio of Zn concentrations in roots vs. shoots or the ratio of Zn accumulation in roots vs. total Zn accumulation in the plant, indicating that Zn translocation from roots to shoots is not the primary factor limiting Zn concentrations in grain. These results indicate 1) that P application affects the Zn accumulation of wheat by affecting Zn uptake by roots and 2) that the changes in Zn uptake by roots and Zn accumulation following P application reflect changes in root morphology and AM colonization of roots.