Iron plaque formation and its effect on arsenic uptake by different genotypes of paddy rice

Background and aims

Iron plaque on roots has been hypothesized to be an effective restraint on the uptake of arsenic (As) by rice plants. Evaluating the formation of iron plaque and its effect on As uptake by various rice cultivars is valuable because selecting low As uptake rice cultivars results in reduced risks associated with rice consumption. This study examines iron plaque formation and its effect on As uptake by different genotypes of rice cultivars.

Methods

Hydroponic cultures were conducted in phytotron at day 25/night 20°C and the rice seedlings in fifth-leaf age were treated with Fe (II) at the levels of 0 and 100 mg L^?1 in the Kimura B nutrient solutions for 14 days. The amount of iron plaque formation of 28 rice cultivars was determined by using the DCB extractable Fe of roots. Four cultivars representing high and low iron plaque formation capability, from indica and japonica respectively, were selected out of the 28 cultivars and processed for Fe and As treatments. After Fe treatments for 4 days, the seedlings were fed with As (III) at levels of 0, 0.5, and 1 mg L^?1 for another 10 days. We were thus able to determine the amounts of iron plaque formation and the As content in iron plaque, roots, and shoots of the four tested cultivars.

Results

Iron plaque formation capability differed among tested twenty-eight rice cultivars. Feeding As to four tested cultivars enhanced iron plaque formation on roots; the As uptake by roots and shoots was decreased by the addition of Fe. Both the retention of As on iron plaque and the decrease of As uptake by the addition of Fe varied among tested cultivars and were not correlated with the iron plaque formation capability.

Conclusions

Iron plaque can sequestrate As on the roots and reduce rice’s As uptake. However, other factors also influence the As uptake, namely the differences in binding affinity of iron plaque to As, the existent As species in the rhizosphere, and the uptake capability of various As species by rice plants. These factors should also be considered when selecting low As uptake rice cultivars.     

Effects of waterlogging on the solubility and redox state of Sb in a shooting range soil and its uptake by grasses: a tank experiment

Aims

The effects of waterlogging on redox state and solubility of antimony (Sb) in a calcareous shooting range soil and its uptake by forage grass Lolium perenne L. and pasture weed Holcus lanatus L. were investigated.

Methods

Grasses were grown on semi-waterlogged or waterlogged shooting range soil in a laboratory tank. The soil solution was sampled at various depths over time and analyzed for the concentrations of Sb(III), Sb(V) and total Sb, as well as other trace elements.

Results

Although the reduction of Sb(V) to Sb(III) under increased waterlogging time decreased Sb solubility, it increased Sb uptake by L. perenne from 1.1 to 1.7 mg?kg^?1 (and to a lesser extent H. lanatus), implying preferential uptake of Sb(III) by this grass. The tank showed considerable variation in redox conditions with depth and plant treatment. The soil root zone (30 cm for L. perenne and 15 cm for H. lanatus) instead of the water saturated bottom, showed the highest manganese (Mn) and iron (Fe) concentrations in solution, accompanied by a higher proportion of Sb(III) in solution than the bottom zone of the tank.

Conclusions

Waterlogging can increase the risk of Sb entering the food chain from shooting range soil.     

Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims

Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant.

Methods

A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars.

Results

Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O₂ kg^?1 root d.w. h^?1), Fe plaque formation (Fe: 6,117–48,167 mg kg^?1; Mn: 127–1,089 mg kg^?1), heavy metals in shoot (Cd: 0.13–0.35 mg kg^?1; Pb: 4.8–8.1 mg kg^?1) and root tissues (Cd: 1.1–3.5 mg kg^?1; Pb: 45–199 mg kg^?1), and in Fe plaque (Cd: 0.54–2.6 mg kg^?1; Pb: 102–708 mg kg^?1). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues.

Conclusions

ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues.     

Nitrogen resorption in senescing leaf blades of rice exposed to free-air CO<Subscript>2</Subscript> enrichment (FACE) under different N fertilization levels

Background and Aims

The effects of Sb(V), alone or combined with Se, on the growth and root development of plants are unknown. The aim of this study is to investigate the interaction between selenite and different forms of Sb and the effects on their uptake in rice and on rice root morphology.

Methods

A hydroponic experiment was conducted that contained fourteen treatments. The treatment levels for Se were 0.5 and 1 mg L^?1, and the treatment levels for Sb(III) and Sb(V) were 5 and 15 mg L^?1.

Results

Sb(V) alone significantly reduced the surface area, mean diameter and volume of the roots, whereas Sb(III) alone reduced the values of most parameters of root morphology. The addition of 1 mg L^?1 Se significantly enhanced the surface area, number of medium roots, and Sb concentration in the roots subjected to 15 mg L^?1 Sb(V), but it decreased the number of root forks, the number and proportion of fine roots, and the shoot Sb concentration under exposure to 15 mg L^?1 Sb(III). When the plants were subjected to 1 mg L^?1 Se, the addition of 15 mg L^?1 Sb(III) markedly reduced the shoot and root Se concentrations and the number of root tips, root forks, and fine roots and increased the mean root diameter. However, the addition of Sb(V) did not significantly affect the root and shoot Se concentrations but significantly decreased the number of root forks and fine roots and increased the proportion of medium roots.

Conclusions

Se and Sb(III) showed antagonistic effects on uptake in the shoots, but not in the roots, of paddy rice. A range of Se concentrations could stimulate the uptake of Sb in both the shoots and roots of paddy rice exposed to Sb(V).

     

Contrasting grass nitrogen strategies reflect interspecific trade-offs between nitrogen acquisition and use in a semi-arid temperate grassland

Aims

The uptake and tolerance of antimonite [Sb(III)] and antimonate [Sb(V)] were investigated in two populations of Achillea wilhelmsii, one from strongly Sb-enriched mine soil, the other from uncontaminated soil, in comparison with non-metallicolous Silene vulgaris and Thlaspi arvense.

Methods

Tolerance was assessed from root elongation and biomass accumulation after exposure to a series of concentrations of Sb(III) or Sb(V) in hydroponics.

Results

For all the species Sb(III) was more toxic than Sb(V). S. vulgaris was the most Sb(III)-tolerant species, and A. wilhelmsii the most Sb(V)-tolerant one. There were no considerable interspecific differences regarding the root and shoot Sb concentrations. Sb(III) and Sb(V) tolerance and accumulation were not different between the metallicolous and the non-metallicolous A. wilhelmsii populations. Sb(III) uptake was partly inhibited by silicon. Sb(V) uptake was strongly inhibited by chloride.

Conclusions

There is uncorrelated variation among species in Sb(V) and Sb(III) tolerance, showing that plants sequester Sb(V) and Sb(III) in different ways. Sb(V) seems to be taken up via monovalent anion channels, and Sb(III) via silicon transporters, at least in part. The relatively high Sb(V) tolerance in A. wilhelmsii seems to be a species-wide property, rather than a product of local adaptation to Sb-enriched soil.

     

Comparison of As sequestration in iron plaque and uptake by different genotypes of rice plants grown in As-contaminated paddy soils

Background and aims

Limited information is available on comparing the iron plaque formation capabilities and their effect on arsenic (As) uptake by different rice plant genotypes grown in As-contaminated soils. This study investigates the effect of iron plaque on As uptake in different rice genotypes grown in As-contaminated soils from the Guandu Plain of northern Taiwan.

Methods

Twenty-eight rice genotypes including 14 japonica and 14 indica genotypes were used in this study. Rice seedlings were grown in As-contaminated soils for 38 days. The iron plaque formed on the rice roots were extracted using dithionite–citrate–bicarbonate. The concentrations of As, Fe, and P in soil solutions, iron plaque, and plants were measured. The speciation of As in the root’s iron plaque was determined by As K-edge X-ray absorption near-edge structure spectroscopy (XANES).

Results

The amounts of iron plaque formation on roots were significantly different among 28 tested rice genotypes, and 75.7–92.8 % of As uptake from soils could be sequestered in iron plaque. However, there were no significant negative correlations between the amounts of Fe or As in the iron plaque and the content of As accumulated in rice plants of tested genotypes. XANES data showed that arsenate was the predominant As species in iron plaque, and there were difference in the distribution of As species among different rice genotypes.

Conclusions

The iron plaque can sequester most of As uptake from soils no matter what rice genotypes used in this study. However, the iron plaque alone did not control the extent of As accumulation in rice plants from As-contaminated soils among 28 tested rice genotypes. Low As uptake genotypes of rice selected from this study can be recommended to be grown in the As-contaminated soils.     

Physiological and biochemical responses of the iron chlorosis tolerant grapevine rootstock 140 Ruggeri to iron deficiency and bicarbonate

Background and aims

Iron (Fe) deficiency chlorosis associated with high levels of soil bicarbonate is one of the main nutritional disorders observed in sensitive grapevine genotypes. The aim of the experiment was to assess both the independent and combined effects of Fe and bicarbonate nutrition in grapevine.

Methods

Plants of the Fe chlorosis tolerant 140 Ruggeri rootstock were grown with and without Fe(III)-EDTA and bicarbonate in the nutrient solution. SPAD index, plant growth, root enzyme (PEPC, MDH, CS, NADP⁺ ?IDH) activities, kinetic properties of root PEPC, organic acid concentrations in roots and xylem sap and xylem sap pH were determined. A factorial statistical design with two factors (Fe and BIC) and two levels of each factor was adopted: +Fe and ?Fe, and +BIC and ?BIC.

Results

This rootstock strongly reacted to Fe deficiency by activating several response mechanisms at different physiological levels. The presence of bicarbonate in the nutrient solution changed the activity of PEPC and TCA related enzymes (CS, NADP⁺-IDH) and the accumulation/translocation of organic acids in roots of Fe-deprived plants. Moreover, this genotype increased root biomass and root malic acid concentration in response to high bicarbonate levels in the substrate. Bicarbonate also enhanced leaf chlorophyll content.

Conclusions

Along with a clear independent effect on Fe nutrition, our data support a modulating role of bicarbonate on Fe deficiency response mechanisms at root level.     

Fe isotope fractionation caused by translocation of iron during growth of bean and oat as models of strategy I and II plants

Background

The determination of the plant-induced Fe-isotopic fractionation is a promising tool to better quantify their role in the geochemical Fe cycle and possibly to identify the physiological mechanisms of Fe uptake and translocation in plants. Here we explore the isotope fractionation caused by translocation of Fe during growth of bean and oat as representatives of strategy I and II plants.

Methods

Plants were grown on a nutrient solution supplemented with Fe(III)-EDTA and harvested at three different ages. We used the technique of multi-collector ICP-MS to resolve the small differences in the stable iron isotope compositions of plants.

Results

Total bean plants, regardless of their age, were found to be enriched in the light iron isotopes by ?1.2‰ relative to the growth solution throughout. During growth plants internally redistributed isotopes where young leaves increasingly accumulated the lighter isotopes whereas older leaves and the total roots were simultaneously depleted in light iron isotopes. Oat plants were also enriched in the light iron isotopes but during growth the initial isotope ratio maintained in all organs at all growth stages.

Conclusions

We conclude that isotope fractionation in bean as a representative of strategy I plants is a result of translocation or re-translocation processes. Furthermore we assume that both uptake and translocation of Fe in oat maintains the irons’ ferric state, or that Fe is always bound to high-mass ligands, so that isotope fractionation is virtually absent in these plants. However, in contrast to our previous study in which strategy II plants were grown on soil substrate, oat plants grown on Fe(III)-EDTA contain iron that enriches ⁵⁴Fe by 0.5 permil over ⁵⁶Fe. A possible explanation for the enrichment is the prevalence of a constitutive reductive uptake mechanism of iron in the nutrient solution used which is non-deficient in iron.     

Energy-dispersive X-ray fluorescence analysis of zinc and iron concentration in rice and pearl millet grain

Background and aims

Rice (Oryza sativa L.) and pearl millet (Pennisetum glaucum L.) biofortification breeding programs require accurate and convenient methods to identify nutrient dense genotypes. The aim of this study was to investigate energy-dispersive X-ray fluorescence spectrometry (EDXRF) for the measurement of zinc (Zn) and iron (Fe) concentration in whole grain rice and pearl millet.

Methods

Grain samples were obtained from existing biofortification breeding programs. Reference Zn and Fe concentrations obtained by inductively-coupled plasma-optical emission spectroscopy (ICP-OES) were used to calibrate the EDXRF instrument. Calibration was performed with 24 samples and separate calibrations were developed for rice and pearl millet. To validate calibrations, EDXRF analyses were conducted on an additional 40 samples of each species.

Results

EDXRF results were highly correlated with ICP-OES values for both Zn and Fe in both species (r²?=?0.79 to 0.98). EDXRF predicted Zn and Fe in rice to within 1.9 and 1.6?mg?kg^?1 of ICP-OES values, and Zn and Fe in pearl millet to within 7.6 and 12.5?mg?kg^?1 of ICP-OES values, at a 95% confidence level.

Conclusion

EDXRF offers a convenient, economical tool for screening Zn and Fe concentration in rice and pearl millet biofortification breeding programs.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

Identification of hot pepper cultivars containing low Cd levels after growing on contaminated soil: uptake and redistribution to the edible plant parts

Aims

This study aimed to screen and identify low-cadmium (Cd) hot pepper (Capsicum annuum L.) cultivars and to clarify the mechanisms of low Cd accumulation in fruits.

Methods

A pot experiment was conducted to investigate the variations of fruit Cd concentration among 30 hot pepper cultivars and to determine the differences in uptake and translocation of Cd between low- and high-Cd cultivars in the control and two Cd treatments.

Results

There are significant differences among the cultivars in their ability to accumulate Cd in fruits. Fruit Cd concentrations are positively and significantly correlated with the translocation of Cd from roots to aboveground parts and the Cd concentrations of leaves and stems. However, no correlation was observed between the fruit’s Cd concentration and the root’s Cd uptake ability.

Conclusions

Two hot pepper cultivars, Yeshengchaotianjiao (No. 16) and Heilameixiaojianjiao (No. 23), were identified as low-Cd cultivars, and two, Jinfuzaohuangjiao (No. 13) and Shuduhong (No. 18), were treated as high-Cd cultivars. The difference in fruit Cd concentrations between low- and high-Cd cultivars is attributable to the difference in Cd translocation from roots to aboveground parts and from leaves and stems to fruits, rather than to the root’s Cd uptake ability.     

Variation in cadmium accumulation and translocation among peanut cultivars as affected by iron deficiency

Purpose

The current study aimed to test the hypothesis that the variations in shoot Cd accumulation among peanut cultivars was ascribed to the difference in capacity of competition with Fe transport, xylem loading and transpiration.

Methods

A hydroponics experiment was conducted to determine the plant biomass, gas exchange, and Cd accumulation in Fe-sufficient or -deficient plants of 12 peanut cultivars, at low Cd level (0.2 μM CdCl₂).

Results

Peanut varied among cultivars in morpho-physiological response to Cd stress as well as Cd accumulation, translocation and distribution. Qishan 208 and Xvhua 13 showed a higher capacity for accumulating Cd in their shoots. Fe deficiency increased the concentration and amount of Cd in plant organs, but decreased TF _{root to shoot} and TF _{root to stem}, while TF _{stem to leaf} remained unaffected. Fe deficiency-induced increase rates of Cd concentration and total Cd amount in roots and leaves were negatively correlated with the values in Fe-sufficient plants. Transpiration rate was positively correlated with leaf Cd concentration, TF _{root to shoot}, TF _{root to stem} and TF _{stem to leaf}.

Conclusions

The difference in shoot Cd concentration among peanut cultivars was mainly ascribed to the difference in Fe transport system, xylem loading capacity and transpiration.     

Occluded C in rice phytoliths: implications to biogeochemical carbon sequestration

Aims

Carbon (C) bio-sequestration within the phytoliths of plants, a mechanism of long-term biogeochemical C sequestration, may play a major role in the global C cycle and climate change. In this study, we explored the potential of C bio-sequestration within phytoliths produced in cultivated rice (Oryza sativa), a well known silicon accumulator.

Methods

The rice phytolith extraction was undertaken with microwave digestion procedures and the determination of occluded C in phytoliths was based on dissolution methods of phytolith-Si.

Results

Chemical analysis indicates that the phytolith-occluded C (PhytOC) contents of the different organs (leaf, stem, sheath and grains) on a dry weight basis in 5 rice cultivars range from 0.4 mg?g^?1 to 2.8 mg?g^?1, and the C content of phytoliths from grains is much lower than that of leaf, stem and sheath. The data also show that the PhytOC content of rice depends on both the content of phytoliths and the efficiency of C occlusion within phytoliths during rice growth. The biogeochemical C sequestration flux of phytoliths in 5 rice cultivars is approximately 0.03–0.13 Mg of carbon dioxide (CO₂) equivalents (Mg-e-CO₂) ha^?1?year^?1. From 1950 to 2010, about 2.37?×?10⁸?Mg of CO₂ equivalents might have been sequestrated within the rice phytoliths in China. Assuming a maximum phytoliths C bio-sequestration flux of 0.13 Mg-e-CO₂ ha^?1?year^?1, the global annual potential rate of CO₂ sequestrated in rice phytoliths would approximately be 1.94?×?10⁷?Mg.

Conclusions

Therefore rice crops may play a significant role in long-term C sequestration through the formation of PhytOC.     

Field performance of STG06L-35-061, a new genetic resource developed from crosses between weed-suppressive indica rice and commercial southern U.S. long-grains

Aims

Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations including Echinochloa crus-galli (L.) Beauv. Indica rice cultivars can produce high yields and suppress barnyardgrass, but have not been commercially acceptable in the U.S. due to inferior agronomic traits and grain quality. Our objectives were to combine high yield and weed-suppressive characteristics from indica cultivars with commercially acceptable grain quality and plant types from long-grain cultivars grown in the southern U.S.

Methods

Crosses between indica and commercial tropical japonica (cv. Katy, and cv. Drew) rice were evaluated for weed suppression and agronomic traits in a breeding program.

Results

In some tests, the selection STG06L-35-061 was nearly as weed suppressive as PI 312777, the suppressive parent, and more suppressive than its tropical japonica parents. Its main crop yield is commercially acceptable, and intermediate between PI 312777 and Katy. Its milling quality and cooking quality are similar to long-grain commercial cultivars, and it has resistance to rice blast disease. Marker analyses identified introgressions from the indica parents on chromosomes 1 and 3 of STG06L-35-061 that require further analysis as possible sources of weed suppressive traits.

Conclusions

STG06L-35-061 might be suitable for organic rice or reduced input conventional systems.     

Peanut as a potential crop for bioenergy production via Cd-phytoextraction: A life-cycle pot experiment

Aims

The current study aimed to assess the potential of peanut (Arachis hypogaea L.) for bioenergy production via phytoextraction in cadmium (Cd) -contaminated soils and screen appropriate cultivars for this approach.

Methods

A life-cycle pot experiment was conducted to determine the biomass, seed yield, oil content and Cd accumulation of seven peanut cultivars under Cd concentration gradients of 0, 2, and 4 mg kg^?1.

Results

Peanut exhibits genotypic variations in Cd tolerance, seed production, oil content, and Cd accumulation. Exposure of plants to 2 and 4 mg kg^?1 Cd did not inhibit shoot biomass, seed yield, and oil content for most of the cultivars tested. There are large amounts of Cd accumulated in the shoots. Although the seed Cd concentration of peanut was relatively high, the Cd concentration in seed oils was very low (0.04-0.08 mg kg^?1). Among the cultivars, Qishan 208 showed significant Cd tolerance, high shoot biomass, high pod and seed yield, high seed oil content, considerable shoot Cd concentration, and the largest translocation factor and total Cd in shoots.

Conclusions

The cultivation of peanut in Cd-contaminated farmland was confirmed to be feasible for bioenergy production via phytoextraction, and Qishan 208 is a good candidate for this approach.     

Root porosity, radial oxygen loss and iron plaque on roots of wetland plants in relation to zinc tolerance and accumulation

Background and aims

Wetland plants have been widely used in constructed wetlands for the clean-up of metal-contaminated waters. This study investigated the relationship between rate of radial oxygen loss (ROL), root porosity, Zn uptake and tolerance, Fe plaque formation in wetland plants.

Methods

A hydroponic experiment and a pot trial with Zn-contaminated soil were conducted to apply different Zn level treatments to various emergent wetland plants.

Results

Significant differences were found between plants in their root porosities, rates of ROL, Zn uptake and Zn tolerance indices in the hydroponic experiment, and concentrations of Fe and Mn on roots and in the rhizosphere in the pot trial. There were significant positive correlations between root porosities, ROL rates, Zn tolerance, Zn, Fe and Mn concentrations on roots and in the rhizosphere. Wetland plants with higher root porosities and ROL tended to have more Fe plaque, higher Zn concentrations on roots and in their rhizospheres, and were more tolerant of Zn toxicity.

Conclusions

Our results suggest that ROL and root porosity play very important roles in Fe plaque formation, Zn uptake and tolerance, and are useful criteria for selecting wetland plants for the phytoremediation of Zn-contaminated waters and soils/sediments.     

Silicon-mediated amelioration of zinc toxicity in rice (Oryza sativa L.) seedlings

Background and aims

Silicon (Si) was suggested to enhance plant resistance to toxic elements, and its beneficial role was mainly based on external and internal plant mechanisms. This work aimed at investigating the internal effect of Si on zinc (Zn) detoxification to rice (Oryza sativa L., cv. Tian You 116) seedlings.

Methods

In a hydroponic experiment, we examined the uptake, xylem loading and localization of Zn in rice seedlings under the condition of 200?μM Zn contamination with the additional silicate supply at three levels ( 0, 0.5 and 1.8?mM).

Results

The silicate addition significantly increased the seedling biomass, and decreased Zn concentration in both root and shoot of seedlings and in xylem sap flow. Zinpyr-1 fluorescence test and Energy-dispersive X-ray spectroscopy analysis showed the concentration of biologically active Zn²⁺ decreased, and Zn and Si co-localized in the cell wall of metabolically less active tissues, especially in sclerenchyma of root. The fractionation analysis further supported silicate supply increased about 10% the cell wall bound fraction of Zn.

Conclusions

This study suggests the Si-assisted Zn tolerance of rice is mainly due to the reduction of uptake and translocation of excess Zn, and a stronger binding of Zn in the cell wall of less bioactive tissues might also contribute to some degree.     

Differential toxicity and accumulation of inorganic and methylated arsenic in rice

Background and aims

Efficient accumulation of arsenic (As) in rice (Oryza sativa L.) poses a potential health risk to rice consumers. The aim of this study was to investigate the mechanisms of uptake, transport and distribution of inorganic arsenic (As_i) and dimethylarsinic acid (DMA) in rice plants.

Methods

Rice was exposed to As_i (As(V)) and DMA in hydroponics. High-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and synchrotron X-ray fluorescence (SXRF) microprobe were used to determine As concentration and the in situ As distribution.

Results

DMA induced abnormal florets before flowering and caused a sharp decline in the seed setting rate after flowering compared to As_i. Rice grains accumulated 2-fold higher DMA than As_i. The distribution of As_i concentration (root?>?leaf?>?husk?>?caryopsis) in As(V) treatments was different from that of the DMA concentration (caryopsis?>?husk?>?root?≥?leaf) in DMA treatments. SXRF showed that As_i mainly accumulated in the vascular trace of caryopsis with limited distribution to the endosperm, whereas DMA was observed in both tissues.

Conclusions

DMA tended to accumulate in caryopsis and induced higher toxicity to the reproductive tissues resulting in markedly reduced grain yield, whereas As_i mainly remained in the vegetative tissues and had no significant effect on yield. DMA is more toxic than As_i to the reproductive tissues when both of them are at similar concentrations in nutrient solution.     

Phosphorus accumulation in grains of japonica rice as affected by nitrogen fertilizer

Background and aims

This study aims to investigate the effect of nitrogen (N) on grain phosphorus (P) accumulation in japonica rice.

Methods

Six cultivars with contrasting agronomic traits were grown for 3 years (from 2008 to 2010) of field experiments under seven N treatments and 1 year (in 2010) of pot experiments with five N treatments to study the effect of N on grain phosphorus accumulation and to explore its physiological foundation.

Results

Grain total P and phytic acid concentration showed a clearly decreasing trend as N rate increased for both field and pot experiments. Pot experiment revealed that application of N increase plant biomass, but tended to lower plant P uptake, especially for the split topdressing treatments. Both harvest index (HI) and P harvest index (PHI) increased with N rate, but PHI was consistently higher than HI, indicating the larger proportion of P translocation to grain than that of dry matter by N. Further, ratio of PHI/HI differed significantly among genotypes, but was stable across contrasting N treatments.

Conclusions

The combination of decreased plant P uptake and dilution effect of increased grain yield by N is proposed as underlying mechanism of the decreased grain P concentration by high N.