Migration and transformation of cadmium in rice - soil under different nitrogen sources in polymetallic sulfide mining areas.
ABSTRACT: We conducted pot experiments to assess the bioavailability of cadmium (Cd) in contaminated rhizosphere soil and accumulation in rice organs in response to nitrogen (N) supply ((NH4)2SO4, NH4NO3, NH4Cl). The results showed that the concentration of bioavailable Cd in rice rhizosphere soil was (NH4)2SO4 treatment?>?NH4Cl treatment?>?NH4NO3 treatment at the same level of N application and growth period; the Cd concentration in rice roots was (NH4)2SO4 treatment?>?NH4NO3 treatment?>?NH4Cl treatment; and the Cd concentration in rice straw was NH4NO3 treatment?>?NH4Cl. The Cd concentration in rice roots, straws, and seeds at the maturity stage was (NH4)2SO4 treatment?>?NH4Cl treatment. With the same N fertilizer, excessive N promoted Cd accumulation in rice at later growth stages. This suggested that sulfate (SO42-) influenced Cd concentration in rice. NH4Cl application maintained a low Cd level in different rice organs with the same N level. This confirmed that NH4Cl is a safe N source for rice planting in polymetallic sulfide mining areas. The study concludes that appropriate NH4Cl levels for Cd-contaminated paddy soil with high-S-content could obtain rice grains with Cd concentrations below the food safety standards (0.2 or 0.4?mg·kg-1).
Project description:Enhanced nitrogen (N) availability is one of the main drivers of biodiversity loss and degradation of ecosystem functions. However, in very nutrient-poor ecosystems, enhanced N input can, in the short-term, promote diversity. Mediterranean Basin ecosystems are nutrient-limited biodiversity hotspots, but no information is available on their medium- or long-term responses to enhanced N input. Since 2007, we have been manipulating the form and dose of available N in a Mediterranean Basin maquis in south-western Europe that has low ambient N deposition (<4 kg N ha(-1) yr(-1)) and low soil N content (0.1%). N availability was modified by the addition of 40 kg N ha(-1) yr(-1) as a 1?1 NH4Cl to (NH4)2SO4 mixture, and 40 and 80 kg N ha(-1) yr(-1) as NH4NO3. Over the following 5 years, the impacts on plant composition and diversity (richness and evenness) and some ecosystem characteristics (soil extractable N and organic matter, aboveground biomass and % of bare soil) were assessed. Plant species richness increased with enhanced N input and was more related to ammonium than to nitrate. Exposure to 40 kg NH4+-N ha(-1) yr(-1) (alone and with nitrate) enhanced plant richness, but did not increase aboveground biomass; soil extractable N even increased under 80 kg NH4NO3-N ha(-1) yr(-1) and the % of bare soil increased under 40 kg NH4+-N ha(-1) yr(-1). The treatment containing less ammonium, 40 kg NH4NO3-N ha(-1) yr(-1), did not enhance plant diversity but promoted aboveground biomass and reduced the % of bare soil. Data suggest that enhanced NHy availability affects the structure of the maquis, which may promote soil erosion and N leakage, whereas enhanced NOx availability leads to biomass accumulation which may increase the fire risk. These observations are relevant for land use management in biodiverse and fragmented ecosystems such as the maquis, especially in conservation areas.
Project description:Azospirillum sp. B510, a free-living nitrogen-fixing bacterium isolated from the stems of rice (Oryza sativa cv. Nipponbare), was investigated to establish effective conditions for the colonization of rice plants. We analyzed the effects of the nitrogen sources KNO3, NH4Cl, urea (CO[NH2]2), and NH4NO3 at different concentrations (0.01-10 mM) on this colonization. Nitrogen promoted plant growth in a concentration-dependent manner, with minor differences being observed among the different nitrogen sources. Bacterial colonization was markedly suppressed on media containing NH4+ concentrations higher than 1 mM. Since concentrations of up to and including 10 mM NH4+ did not exhibit any antibacterial activity, we analyzed several factors affecting the NH4+-dependent inhibition of endophytic colonization, including the accumulation of the reactive oxygen species H2O2 and the secretion of the chemotactic substrate malic acid. The accumulation of H2O2 was increased in rice roots grown on 1 mM NH4Cl. The amounts of malic acid secreted from NH4-grown rice plants were lower than those secreted from plants grown without nitrogen or with KNO3. Although the bacterium exhibited chemotactic activity, moving towards root exudates from plants grown without nitrogen and KNO3-grown plants, this activity was not observed with root exudates from NH4+-grown plants. NH4+, but not NO3-, caused the acidification of growth media, which inhibited plant bacterial colonization. These NH4+-dependent phenomena were markedly suppressed by the stabilization of medium pH using a buffer. These results demonstrate that the type and concentration of nitrogen fertilizer affects the colonization of rice plants by Azospirillum sp. B510.
Project description:Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.
Project description:Few studies have quantified the effects of different levels and forms of nitrogen (N) deposition on soil nitrous oxide (N2O) emissions from temperate forest soils. A 5-year field experiment was conducted to investigate the effects of multiple forms and levels of N additions on soil N2O emissions, by using the static closed chamber method at Xi Mountain Experimental Forest Station in northern China. The experiment included a control (no N added), and additions of NH4NO3, NaNO3, and (NH4)2SO4 that each had two levels: 50 kg N ha-1 yr-1 and 150 kg N ha-1 yr-1. All plots were treated to simulate increased N deposition on a monthly schedule during the annual growing season (March to October) and soil N2O emissions were measured monthly from March 2011 to February 2016. Simultaneously, the temperature, moisture, and inorganic N contents of soil were also measured to explore how the main factors may have affected soil N2O emission. The results showed that the types and levels of N addition significantly increased soil inorganic N contents, and the accumulation of soil NO3--N was significantly higher than that of soil NH4+-N due to N addition. The three N forms significantly increased the average N2O emissions (P < 0.05) in the order of NH4NO3 > (NH4)2SO4 > NaNO3 by 355.95%, 266.35%, and 187.71%, respectively, compared with control. The promotion of N2O emission via the NH4+-N addition was significantly more than that via the NO3--N addition, while N addition at a high level exerted a stronger effect than at the low-level. N addition exerted significantly stronger effects on cumulative N2O emissions in the initial years, especially the third year when the increased cumulative N2O emission reached their maximum. In the later years, the increases persisted but were weakened. Increasing inorganic N concentration could change soil from being N-limited to N-rich, and then N-saturated, and so the promotion on soil available N effect increased and then decreased. Moreover, the soil NH4+-N, NO3--N, temperature, and water-filled pore space were all positively correlated with soil N2O emissions. These findings suggest that atmospheric N deposition can significantly promote soil N2O emission, and that exogenous NH4+-N and NO3--N inputs into temperate forests can have synergic effects on soil N2O emission. In future research, both aspects should be better distinguished in the N cycle and balance of terrestrial ecosystems by using 15N tracer methods.
Project description:In wetland soils, changes in oxygen (O2) level in the rhizosphere are believed to influence the behaviour of nutrients and their usage by plants. However, the effect of aeration on nitrogen (N) acquisition under different N supply conditions remains largely unknown. In this study, the rice cultivars Yangdao 6 (YD6, with higher root aerenchyma abundance) and Nongken 57 (NK57, with lower root aerenchyma abundance) were used to evaluate the effects of aeration on rice growth and N accumulation. Our results showed that the number of adventitious roots and the root surface area increased significantly, and ethylene production and aerenchyma formation decreased in both cultivars after external aeration (EA). Five N treatments, including no N (-N), 0.125 mM NH4NO3 (LN), 1.25 mM Ca(NO3)2 (NO3-N), 1.25 mM (NH4)2SO4 (NH4-N) and 1.25 mM NH4NO3 (N/N), were applied to YD6 and NK57 for 2 days under internal aeration or EA conditions. External aeration increased the root biomass in both cultivars and the shoot biomass in NK57 by 18-50 %. The total N concentrations in roots of YD6 grown under -N and LN and of NK57 grown under NO3-N were increased by EA. Expression of OsPAD4, one of four putative genes regulating aerenchyma formation, showed a similar pattern alongside changes in the ethylene level in the EA-treated rice irrespective of the N treatments. Furthermore, expression of the high-affinity nitrate transporter gene OsNRT2.1 was increased by EA under -N, LN and NO3-N conditions. Our data provide evidence of an interaction between O2 and the supply of N in ethylene production, aerenchyma formation and N nutrition through modification of the expression of OsPAD4 and OsNRT2.1.
Project description:Salt-enhanced cultivation as a morphology engineering tool for the filamentous actinomycete Actinomadura namibiensis was evaluated in 500-mL shaking flasks (working volume 100 mL) with the aim of increasing the concentration of the pharmaceutically interesting peptide labyrinthopeptin A1. Among the inorganic salts added to a complex production medium, the addition of (NH4)2SO4 led to the highest amount of labyrinthopeptin A1 production. By using 50 mM (NH4)2SO4, the labyrinthopeptin A1 concentration increased up to sevenfold compared to the non-supplemented control, resulting in 325 mg L-1 labyrinthopeptin A1 after 10 days of cultivation. The performance of other ammonium- and sulfate-containing salts (e.g., NH4Cl, K2SO4) was much lower than the performance of (NH4)2SO4. A positive correlation between the uptake of glycerol as one of the main carbon sources and nongrowth-associated labyrinthopeptin productivity was found. The change in the cell morphology of A. namibiensis in conjunction with increased osmolality by the addition of 50 mM (NH4)2SO4, was quantified by image analysis. A. namibiensis always developed a heterogeneous morphology with pellets and loose mycelia present simultaneously. In contrast to the non-supplemented control, the morphology of (NH4)2SO4-supplemented cultures was characterized by smaller and circular pellets that were more stable against disintegration in the stationary production phase.
Project description:Transcriptomic profiling was carried out for leaves of Lotus japonicus plants grown with different mineral nitrogen sources (NO3-, NH4+ or NH4NO3) or under conditions of biological nitrogen fixation (Nod). Nodulated plants were inoculated with Mesorhizobium loti and watered with nitrogen-free “Hornum” medium supplemented with 3 mM KCl. Plants under different nitrogen nutritions were watered with “Hornum” nutrient solution containing 10 mM KNO3 (NO3- plants) or with 10 mM NH4Cl supplemented with 3 mM KCl (NH4+ plants) or with 5 mM NH4NO3 supplemented with 3 mM KNO3 (NH4NO3 plants). After all the plants reached the size of 7 trifoils, leaf tissue was harvested. Every harvest involved at least three independent biological replicates for each treatment.
Project description:Slag-based silicate fertilizer has been widely used to improve soil silicon- availability and crop productivity. A consecutive early rice-late rice rotation experiment was conducted to test the impacts of steel slag on soil pH, silicon availability, rice growth and metals-immobilization in paddy soil. Our results show that application of slag at a rate above higher or equal to 1 600 mg plant-available SiO2 per kg soil increased soil pH, dry weight of rice straw and grain, plant-available Si concentration and Si concentration in rice shoots compared with the control treatment. No significant accumulation of total cadmium (Cd) and lead (Pb) was noted in soil; rather, the exchangeable fraction of Cd significantly decreased. The cadmium concentrations in rice grains decreased significantly compared with the control treatment. In conclusion, application of steel slag reduced soil acidity, increased plant-availability of silicon, promoted rice growth and inhibited Cd transport to rice grain in the soil-plant system.
Project description:The objective of this study was to explore the effect of heavy metal-resistant bacteria and biochar (BC) on reducing heavy metal accumulation in vegetables and the underlying mechanism. We tested Bacillus thuringiensis HC-2, BC, and BC+HC-2 for their ability to immobilize Cd and Pb in culture solution. We also studied the effects of these treatments on the dry weight and Cd and Pb uptake of radish in metal-contaminated soils under field conditions and the underlying mechanism. Treatment with HC-2, BC, and BC+HC-2 significantly reduced the water-soluble Cd (34-56%) and Pb (31-54%) concentrations and increased the pH and NH4+ concentration in solution compared with their vales in a control. These treatments significantly increased the dry weight of radish roots (18.4-22.8%) and leaves (37.8-39.9%) and decreased Cd (28-94%) and Pb (22-63%) content in the radish roots compared with the control. Treatment with HC-2, BC, and BC+HC-2 also significantly increased the pH, organic matter content, NH4+ content, and NH4+/NO3- ratio of rhizosphere soils, and decreased the DTPA-extractable Cd (37-58%) and Pb (26-42%) contents in rhizosphere soils of radish. Furthermore, BC+HC-2 had higher ability than the other two treatments to protect radish against Cd and Pb toxicity and increased radish biomass. Therefore, Bacillus thuringiensis HC-2 combined with biochar can ensure vegetable safety in situ for the bioremediation of heavy metal-polluted farmland.
Project description:Cadmium (Cd) and arsenic (As) accumulation in rice grains is a great threat to its productivity, grain quality, and thus human health. Pot and field studies were carried out to unravel the effect of different water management practices (aerobic, aerobic-flooded, and flooded) on Cd and As accumulation in rice grains of two different varieties. In pot experiment, Cd or As was also added into the soil as treatment. Pots without Cd or As addition were maintained as control. Results indicated that water management practices significantly influenced the Cd and As concentration in rice grains and aerobic cultivation of rice furnished less As concentration in its grains. Nonetheless, Cd concentration in this treatment was higher than the grains of flooded rice. Likewise, in field study, aerobic and flooded rice cultivation recorded higher Cd and As concentration, respectively. However, growing of rice in aerobic-flooded conditions decreased the Cd concentration by 9.38 times on average basis as compared to aerobic rice. Furthermore, this treatment showed 28% less As concentration than that recorded in flooded rice cultivation. The results suggested that aerobic-flooded cultivation may be a promising strategy to reduce the Cd and As accumulations in rice grains simultaneously.