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Although boron (B) is essential micronutrient, higher soil B concentrations become toxic to the plants in arid and semi-arid regions of the world. Very little is known about the pH related nutrient solubility, including transpiration-mediated B uptake by plants. The effects of high B (200 μM) and low to high pH (3.0–10.0) on B toxicity, transpiration and nutrient uptake by wheat and rapeseed were studied. Plants were grown for 5 weeks under greenhouse conditions and analyzed for elements concentrations. Regardless of high B or not, low pH favored in the higher B accumulation in roots and shoots of both plant species. However, both plant species exhibited a differential B uptake pattern in roots and shoots. Both low and high pH levels in combination with high B decreased the plant biomass, transpiration, N and Mg concentrations, whereas increased the K, Ca, S, Cu, Fe, Mn and Zn concentrations. With the increase in pH 3.0–10.0, excess B decreased the Cl concentrations in wheat and rapeseed. In conclusion, low pH and high B supply enhanced the transpiration-assisted B uptake by plants although pH alone had little effects on B concentrations. Furthermore, nutritional disorder caused by high B in conjunction with low to high pH (3.0–10.0) inhibited the plant growth and transpiration. [ABSTRACT FROM AUTHOR]

Aims: Matching a crop's nitrogen (N) preference with the specific form of N is critical to enhance N recovery efficiency (NRE). Many studies show that maize (Zea mays L.) has a preference for NH4+ uptake over NO3−, but the contribution of this preference to NRE is unclear. This study evaluated the utilization of ammonium (NH4+) and nitrate (NO3−) by maize and its relationship with NRE. Methods: Maize (cv. 'Zhengdan 958') seedlings were grown in a soil culture experiment with 15NH4+ or 15NO3− applied to sterilized or non-sterilized soils, and in a hydroponic experiment supplied with NH4+ or NO3−. We recorded maize root and shoot growth and N uptake, and the distribution of 15N-labeled N in the soil–plant system. Results: Ammonium application enhanced maize root and shoot growth and N uptake compared with those of NO3−-treated plants in both culture systems. This enhancement by NH4+ was further promoted in sterilized soil. More applied N remained in soil supplied with NO3− than with NH4+ after seedling harvest. The NRE of NH4+ in maize was significantly higher than that of NO3−, while a similar proportion of applied N was lost with NH4+ or NO3−supply. Conclusions: Ammonium supply enhances maize growth and NRE compared with NO3− under the present experimental condition, which may be attributable to the superior capability of maize to utilize NH4+. [ABSTRACT FROM AUTHOR]

The phytotoxicity of aluminium ( Al) ions can be alleviated by ammonium ( NH4+) in rice and this effect has been attributed to the decreased Al accumulation in the roots. Here, the effects of different nitrogen forms on cell wall properties were compared in two rice cultivars differing in Al tolerance. An in vitro Al-binding assay revealed that neither NH4+ nor NO3− altered the Al-binding capacity of cell walls, which were extracted from plants not previously exposed to N sources. However, cell walls extracted from NH4+-supplied roots displayed lower Al-binding capacity than those from NO3−-supplied roots when grown in non-buffered solutions. Fourier-transform infrared microspectroscopy analysis revealed that, compared with NO3−-supplied roots, NH4+-supplied roots possessed fewer Al-binding groups (- OH and COO-) and lower contents of pectin and hemicellulose. However, when grown in pH-buffered solutions, these differences in the cell wall properties were not observed. Further analysis showed that the Al-binding capacity and properties of cell walls were also altered by pHs alone. Taken together, our results indicate that the NH4+-reduced Al accumulation was attributed to the altered cell wall properties triggered by pH decrease due to NH4+ uptake rather than direct competition for the cell wall binding sites between Al3+ and NH4+. [ABSTRACT FROM AUTHOR]

The integrated effects of environmental factors on soil nitrification are largely unknown. Here, we performed a microcosm experiment to investigate the interactive effects of pH and NH 4 + on nitrification activity in two acidic soils with different land use patterns (Anhui soil, a forest soil; Jiangxi soil, a brush land soil). Both soils were incubated under native pH and CaCO 3 -manipulated pH in the presence or absence of added ammonium for 60 days. The addition of CaCO 3 alone did not change the nitrification activity of either soil. Ammonium addition stimulated nitrification in Anhui soil, but not in Jiangxi soil, and this stimulation was more pronounced with increased CaCO 3 . The ammonia monooxygenase ( amoA ) gene copy number of both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) was much higher in Anhui soil than in Jiangxi soil. The amoA gene copy number of AOB in Anhui soil was more highly upregulated under CaCO 3 + NH 4 + than NH 4 + during incubation. In Anhui soil, changes in the denaturing gradient gel electrophoresis (DGGE) fingerprint patterns of bacterial amoA genes were parallel to changes in the amoA gene copy number of AOB. In Jiangxi soil, DGGE could not be performed because the PCR for bacterial DGGE did not yield any products, while quantitative PCR revealed that the amoA gene copy number of AOB changed during incubation. These results suggest that AOB plays an important role in CaCO 3 -enhanced nitrification of Anhui soil with ammonium addition. The low nitrification rates of Jiangxi soil regardless of CaCO 3 with or without NH 4 + supply may be ascribed to the lower activity of both AOB and AOA, especially AOA. [ABSTRACT FROM AUTHOR]

Summary: C-type lectin receptors (CLRs) play critical roles as pattern-recognition receptors (PRRs) for sensing Candida albicans infection, which can be life-threatening for immunocompromised individuals. Here we have shown that Dectin-3 (also called CLECSF8, MCL, or Clec4d), a previously uncharacterized CLR, recognized α-mannans on the surfaces of C. albicans hyphae and induced NF-κB activation. Mice with either blockade or genetically deleted Dectin-3 were highly susceptible to C. albicans infection. Dectin-3 constantly formed heterodimers with Dectin-2, a well-characterized CLR, for recognizing C. albicans hyphae. Compared to their respective homodimers, Dectin-3 and Dectin-2 heterodimers bound α-mannans more effectively, leading to potent inflammatory responses against fungal infections. Together, our study demonstrates that Dectin-3 forms a heterodimeric PRR with Dectin-2 for sensing fungal infection and suggests that different CLRs may form different hetero- and homodimers, which provide different sensitivity and diversity for host cells to detect various microbial infections. [ABSTRACT FROM AUTHOR]

Background and Aims Acidic soils are dominated chemically by more ammonium and more available, so more potentially toxic, aluminium compared with neutral to calcareous soils, which are characterized by more nitrate and less available, so less toxic, aluminium. However, it is not known whether aluminium tolerance and nitrogen source preference are linked in plants. Methods This question was investigated by comparing the responses of 30 rice (Oryza sativa) varieties (15 subsp. japonica cultivars and 15 subsp. indica cultivars) to aluminium, various ammonium/nitrate ratios and their combinations under acidic solution conditions. Key Results indica rice plants were generally found to be aluminium-sensitive and nitrate-preferring, while japonica cultivars were aluminium-tolerant and relatively ammonium-preferring. Aluminium tolerance of different rice varieties was significantly negatively correlated with their nitrate preference. Furthermore, aluminium enhanced ammonium-fed rice growth but inhibited nitrate-fed rice growth. Conclusions The results suggest that aluminium tolerance in rice is antagonistic with nitrate preference and synergistic with ammonium preference under acidic solution conditions. A schematic diagram summarizing the interactions of aluminium and nitrogen in soil–plant ecosystems is presented and provides a new basis for the integrated management of acidic soils. [ABSTRACT FROM AUTHOR]

Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability. Rice is the most Al-resistant species among small grain cereal crops and prefers NH4 + as its major inorganic nitrogen source. This study investigates the effects of NH4 + and NO3 − on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH4 + preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH4 + and NO3 − supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH4 +-preferring than Yangdao6. NH4 + alleviated Al toxicity in two cultivars compared with NO3 −. Both NH4 +-Al supply and pretreatment with NH4 + reduced Al accumulation in roots and root tips compared with NO3 −. NH4 + decreased but NO3 − increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO3 − concentration enhanced Al accumulation in root tips but increasing the NH4 + concentration had the opposite effect. These results show NH4 + alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO3 −, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH4 +, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated with the preferred utilization of NH4 + is suggested. [ABSTRACT FROM AUTHOR]

• Ammonium and nitrate reduce only maize rhizospheric bacterial diversity. • Rhizospheric bacterial community varies more significantly than bulk soil. • Maize roots recruit N-form specific bacteria according to soil pH. It is well known that the interactive effect of nitrogen (N) fertilizer and plant root would cause distinct microbial communities and associations between root surface and bulk soil. However, little is known about the continuous changes of these microbial parameters along an increasing distance from roots under different N forms. Ammonium (NH 4 +) and nitrate (NO 3 −) are two major inorganic nitrogen (N) forms available for plant growth, and may have different effects on both plant growth and soil microbiome. Here, a rhizobox containing a root zone (root growing area) and various soil compartments (0–0.5 cm, 0.5–1 cm, 1–2 cm, 2–4 cm, and 4–9 cm from the root zone) was designed to investigate the spatial distribution of soil chemical properties, bacterial diversity, and community structure along a distance from maize (Zea mays L.) roots with the addition of 15N-labeled NH 4 + or NO 3 − in an acidic red soil. Addition of NH 4 + or NO 3 − reduced soil bacterial diversity only in the maize root zone. The structures of soil bacterial communities differed more significantly with addition of NH 4 + or NO 3 − in the root zone and 0.5 cm away from the root zone compared with other soil compartments. Soil pH was the major driver of bacterial community assembly during plant uptake of N. Maize roots recruited acidophilic bacteria (e.g. Acidibacter , Burkholderia, and Catenulispora) under NH 4 + treatment, and recruited bacteria that prefer higher pH (e.g. Sphingomonas , Sphingobium , Azospirillum, and Novosphingobium) under NO 3 − treatment. We concluded that the spatial patterns of soil bacterial communities at different distances from the maize root zone were influenced by the combined effects of the N form and rhizosphere, mainly as a result of changes in soil pH during the uptake of NH 4 + and NO 3 − by maize roots. [ABSTRACT FROM AUTHOR]

Nitrate is a major nitrogen (N) source for most crops. Nitrate uptake by root cells is a key step of nitrogen metabolism and has been widely studied at the physiological and molecular levels. Understanding how nitrate uptake is regulated will help us engineer crops with improved nitrate uptake efficiency. The present study investigated the regulation of the high-affinity nitrate transport system (HATS) by exogenous abscisic acid (ABA) and glutamine (Gln) in wheat ( Triticum aestivum L.) roots. Wheat seedlings grown in nutrient solution containing 2 mmol/L nitrate as the only nitrogen source for 2 weeks were deprived of N for 4 d and were then transferred to nutrient solution containing 50 μmol/L ABA, and 1 mmol/L Gln in the presence or absence of 2 mmol/L nitrate for 0, 0.5, 1, 2, 4, and 8 h. Treated wheat plants were then divided into two groups. One group of plants was used to investigate the mRNA levels of the HATS components NRT2 and NAR2 genes in roots through semi-quantitative RT-PCR approach, and the other set of plants were used to measure high-affinity nitrate influx rates in a nutrient solution containing 0.2 mmol/L 15N-labeled nitrate. The results showed that exogenous ABA induced the expression of the TaNRT2.1, TaNRT2.2, TaNRT2.3, TaNAR2.1, and TaNAR2.2 genes in roots when nitrate was not present in the nutrient solution, but did not further enhance the induction of these genes by nitrate. Glutamine, which has been shown to inhibit the expression of NRT2 genes when nitrate is present in the growth media, did not inhibit this induction. When Gln was supplied to a nitrate-free nutrient solution, the expression of these five genes in roots was induced. These results imply that the inhibition by Gln of NRT2 expression occurs only when nitrate is present in the growth media. Although exogenous ABA and Gln induced HATS genes in the roots of wheat, they did not induce nitrate influx. [ABSTRACT FROM AUTHOR]

Abstract: Glutamine synthetase (GS) and glutamate synthase (GOGAT) serve for primary assimilation of N in higher plants. When NH4 + is the major inorganic N source, rice plants must assimilate NH4 + quickly in roots through the GS/GOGAT cycle to ameliorate the toxic effect of excess NH4 +. The sequence of the rice genome is almost complete, facilitating the identification of the GS and GOGAT gene families in this species. Thus, we investigated the different members of GS and GOGAT genes, and analyzed the pattern of expression of each gene in young rice seedlings by quantitative real-time PCR, revealing a distinct expression pattern for these genes. OsGln1;1 and OsGln1;2 mainly functions in roots, and OsGln2 and OsGlu1 are preferentially expressed in leaves. However, transcriptions of OsGln1;1, OsGln1;2, OsGln2 and OsGlu1 in leaves are all increased by increased N level while those in roots not influenced or even decreased. OsGlt1 and OsGlt2 are expressed primarily in roots when N is limiting, but in leaves when non-limiting. Transcription of OsGlt1 is decreased, but OsGlt2 is increased by increased N level in roots and leaves. When rice roots are exposed to NO3 − and NH4 + for 2h after N-starvation, transcriptions of OsGln1;1, OsGlt1, OsGlt2 and OsGlu1 are all repressed by NO3 − and NH4 +. OsGln1;2 expression shows significant up-regulation by NH4 + and down-regulation by NO3 − while OsGln2 down-regulation by NH4 + and up-regulation by NO3 −. [Copyright &y& Elsevier]

To improve crop nitrogen recovery efficiency (NRE), plants must be supplied with their preferred form of nitrogen (N). However, whether pH affects crop N-form preference remains unclear. Here, we aimed to explore how maize (Zea mays L.) preference for NH4+ and NO3− is affected by pH and to determine the critical pH controlling this preference. Maize plants were grown with NH4+ or NO3− in different soils (pH 4.32–8.14) and nutrient solutions (pH 4.00–8.00). After harvest, plant dry weights, N content, N uptake, NRE, soil pH, and exchangeable aluminum (Al) were measured. Compared with the effect of NO3−, NH4+ decreased maize dry weight, N uptake, and NRE by 28–94% at soil pHs of 4.32 and 4.36 and a solution pH of 4.00, whereas it increased these parameters by 10–88% at soil pHs of 6.52–8.02 and solution pHs of 7.00 and 8.00. NO3− increased soil pH and decreased soil exchangeable Al content at soil pHs of 4.32–6.68. Critical soil and solution pHs for changing plant growth and N uptake preference for NH4+ vs. NO3− ranged from 5.08 to 5.40 and from 5.50 to 6.59, respectively. In conclusion, the preference of maize seedling growth and N uptake for NH4+ vs. NO3− mainly depends on the pH of the growth medium, and maize seedlings generally prefer NO3− in strongly acid soils but NH4+ in neutral to alkaline soils. [ABSTRACT FROM AUTHOR]

• Bacillus pumilus improves tomato growth and N uptake under N fertilization. • B. pumilus does not influence tomato growth or N uptake under no N fertilization. • B. pumilus -induced N 2 fixation contributes to N uptake by tomato. • B. pumilus -induced N 2 fixation is associated with bacterial nifH gene. • Leaf transpiration stream is involved in B. pumilus -enhanced N uptake. Some plant growth-promoting bacteria (PGPB) are capable of fixing atmospheric N 2 and can be used to reduce nitrogen (N) fertilizer application in agriculture. Large amounts of N fertilizers are applied in tomato (Solanum lycopersicum L.). However, less attention has been given to the role of PGPB in the N nutrition of tomato. The present study was carried out under greenhouse conditions to investigate the principal mechanisms underlying PGPB-improved N nutrition in tomato. Tomato plants were grown in pots under –N (native soil N without N fertilization) or + N (supply 150 mg N kg–1 dry soil in the form of urea), with or without Bacillus pumilus (PGPB) inoculation. Nitrogen supply improved the growth of tomato, soil NH 4 + concentration, and plant N uptake. Nitrogen increased the rhizobacterial population, bacterial nifH gene expression, and soil nitrogenase activity only with the inoculation of B. pumilus. B. pumilus inoculation improved the tomato growth, N uptake, soil NH 4 + concentrations, rhizobacterial population levels, soil bacterial gene expression, and soil nitrogenase activity only under + N condition. These results suggest that the inoculation of B. pumilus improves the growth of tomato under the condition of additional fertilizer N supply due to an increase in N uptake by roots from B. pumilus -assisted fixed N in soil. [ABSTRACT FROM AUTHOR]

Background and Aims: Suitable N source supply is critical to improve plant growth and N uptake, but the importance of nitrate (NO3−) for rice (Oryza sativa L.) and microbiota is often neglected in acidic paddy soils where ammonium (NH4+) is dominant. This study aimed to explore the differential effects of NH4+ and NO3− on rice growth, fertilizer nitrogen recovery efficiency (FNRE), and rhizosphere bacterial community in acid soil. Methods: Two rice varieties, Kasalath (Al-sensitive indica) and Koshihikari (Al-tolerant japonica), were exposed to different N sources with or without lime in an acid soil. Results: Liming and NO3− application solely improved the growth and FNRE of the Al-sensitive rice, namely, by increasing soil pH and alleviating Al toxicity. Compared with liming and rice variety, N source had a more pronounced influence on rhizobacterial community composition. Of the two sources, NO3− had a stronger effect on the rhizobacterial community than NH4+. Remarkably, rice plants fed with NH4+ specifically recruited Desulfosporosinus and Desulfitobacterium associated with ferric NH4+ oxidation in the rhizosphere, whereas those exposed to NO3− recruited Alicyclobacillus with NO3−-reducing iron oxidation ability. Three keystone taxa were identified in a rhizobacterial co-occurrence network analysis: Alicyclobacillus, which was positively associated with rice growth and FNRE, and Acidobacteriales and WPS-2, both with negative associations. Conclusion: Compared with NH4+, NO3− enhances the growth and FNRE of Al-sensitive rice and exerts dominant effects on the rhizobacterial community, which indicates the importance of NO3− for rice and has instructive implications for N management in acid soil. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is the primary factor limiting agricultural productivity in acid soils. The cell wall is mainly composed of saccharides and the first barrier for aluminum (Al) to enter plant root cells, but it is unknown whether and how root saccharide components are involved in regulating the Al tolerance of Lespedeza that is well adapted to acid soils. Here, we used Al-tolerant Lespedeza bicolor and Al-sensitive Lespedeza cuneata to examine the association of root saccharide components with Lespedeza Al tolerance through analyzing the saccharide changes of roots exposed to Al toxicity. Al-sensitive Lespedeza accumulated more Al and pectin but less hemicellulose in the root cell walls than Al-tolerant Lespedeza. Al treatment decreased the amounts of total sugar secreted from and within the roots of only Al-tolerant Lespedeza. Al treatment decreased the content of root monosaccharides including glucose and mannose in both Lespedeza species, but increased the xylose contents in only Al-sensitive Lespedeza. Taken together, less cell wall pectin rather than hemicellulose is responsible for less root Al accumulation, and Al-decreased root saccharide contents may enhance root organic-acid secretion to chelate toxic Al, both of which contribute to Lespedeza Al tolerance. [ABSTRACT FROM AUTHOR]

Plant growth promoting rhizobacteria (PGPR) confer plant tolerance to abiotic stresses like salinity and high boron (B) due to limited uptake of toxic ions as well as increased production of antioxidants. The current study was aimed to investigate whether particular PGPR strain is responsible either for the decreased uptake of B together with salt toxic ions or to promote rice growth through an efficient antioxidative system under combined stresses of salinity and high B. Rice seedlings were maintained in pots according to completely randomized design (CRD) and stressed with high B (0.92 mmol L −1 or 10 ppm) and NaCl (150 mmol L −1 or ECw of 14.7 dS m −1 ) for 8 weeks. Half of the pots received Bacillus pumilus -inoculated rice seedlings, whereas the other half received un-inoculated ones. Subsequently, plants were harvested and analyzed for mineral composition and antioxidation activity either using atomic absorption spectrometer (AAS) or spectrophotometer. In the absence of PGPR, NaCl salinity significantly enhanced the leaf B and salt toxic ions concentrations, thereby resulting in the shoot growth reduction when compared with the control. Similarly, combined treatment increased the leaf and xylem sap B as compared to NaCl alone, however, remained insignificant for salt toxic ions. Contrary, NaCl + high B decreased the leaf B concentrations as compared to high B alone. Application of PGPR enhanced the plant growth under individual stresses due to enhanced activity of certain of antioxidative enzymes. In combined treatment, B. pumilus showed a positive potential for limiting the Na + accumulation in rice leaves, but not for leaf B. Moreover, limited uptake of Na + resulted in the decreased plant antioxidation activity irrespective of increasing leaf B concentrations which in turn enhanced the rice tolerance. [ABSTRACT FROM AUTHOR]

Abstract: Rhodotorula taiwanensis RS1 is a high-aluminum (Al)-tolerant yeast that can survive in Al concentrations up to 200mM. The mechanisms for the high Al tolerance of R. taiwanensis RS1 are not well understood. To investigate the molecular mechanisms underlying Al tolerance and toxicity in R. taiwanensis RS1, Al toxicity-induced changes in the total soluble protein profile were analyzed using two-dimensional gel electrophoresis (2-DE) coupled with mass spectrometry. A total of 33 differentially expressed proteins responding to Al stress were identified from approximately 850 reproducibly detected proteins. Among them, the abundance of 29 proteins decreased and 4 increased. In the presence of 100mM Al, the abundance of proteins involved in DNA transcription, protein translation, DNA defense, Golgi functions and glucose metabolism was decreased. By contrast, Al treatment led to increased abundance of malate dehydrogenase, which correlated with increased malate dehydrogenase activity and the accumulation of intracellular citrate, suggesting that Al-induced intracellular citrate could play an important role in detoxification of Al in R. taiwanensis RS1. [Copyright &y& Elsevier]

Aluminum (Al) accumulation and long-distance transport in oil tea (Camellia oleifera Abel.), known to be an Al accumulator, was investigated. The average Al concentration in the embryo of oil tea seeds was 389 mg Al kg−1 dry weight, which was higher than seeds of other Al accumulators. By partially suppressing leaf transpiration in the field, Al accumulation in leaves was depressed, which clarified the importance of xylem transport to Al accumulation in leaves. However, the effects of xylem transport alone could not sufficiently explain the high Al accumulation in the seasons when the leaf transpiration is weak, which hints the necessity of phloem transport working. Aluminum content in phloem exudates of barks provides another evidence of phloem transport. Images from scanning electron microscopy and energy-dispersive analysis also showed that Al was present in the phloem of oil tea petioles. Aluminum in oil tea could also be redistributed: higher concentrations of Al were found in leaves when Al was supplied to a different leaf of the same plant. In addition, Al was present in newly emerging roots of oil tea seedlings in which all original roots were excised prior to treatment, and a positive correlation existed between Al content in the newly formed roots and that in the leaves. The results using the empty seed coat technique showed that Al unloading via the phloem occurred during seed development. In conclusion, the results demonstrated that Al could be redistributed between leaves, from seeds to leaves, leaves to roots and leaves to seeds, which indicates that Al can be transported via the phloem in oil tea. [ABSTRACT FROM AUTHOR]

The glutathione synthetase system (GSS) is an important pathway of glutathione synthesis and plays a key role in heavy metal resistance. In this work, the response of Acidithiobacillus ferrooxidans to extracellular Cd2+ was investigated, and the interplay between Cd2+ resistance and the expression of GSS related-genes was analyzed by reverse-transcription quantitative PCR (RT-PCR). During growth in the presence of 5, 15 and 30 mM Cd2+, the transcript levels of eight GSS pathway genes were affected between 0.81- and 7.12-fold. Increased transcription was also reflected in increased enzyme activities: with those of glutathione reductase (GR) increased by 1.10-, 2.26- and 1.54-fold in the presence of 5, 15 and 30 mM Cd2+, respectively. In contrast, the activities of catalase (CAT) and superoxide dismutase (SOD) were decreased in the presence of Cd2+. At the metabolite level, intracellular methane dicarboxylic aldehyde (MDA) content was increased 1.97-, 3.31- and 1.92-fold in the presence of 5, 15 and 30 mM Cd2+, respectively. These results suggest that Cd2+ directly inhibits the activities of CAT and SOD, breaks the redox balance of the cells, which leads to the activation of the other antioxidant pathway of GSS. Resistance of A. ferrooxidans to Cd2+ may involve modulation of expression levels of glutathione S-transferase (GST), GR, and glutathione synthetase, which may protect against oxidative damage. [ABSTRACT FROM AUTHOR]

Aims: Silicon (Si) as a beneficial element can improve nutrient imbalance, but the molecular mechanism for this effect is poorly understood. The objective of this study is to examine the mechanism underlying Si-induced decrease of phosphorus (P) uptake in rice (Oryza sativa) at adequate/high P supply.Method: A rice mutant (lsi1) defective in Si uptake and its wild type (cv. Oochikara) were used. The P uptake was compared in the presence and absence of Si and the expression of Pi transporter genes was quantified.Results: Si addition in the nutrient solution significantly decreased shoot P concentration and uptake in the WT, but not in lsi1 mutant at two P levels, adequate (90 μM) and high (210 μM). Neither the root-to-shoot translocation of P nor the P distribution in different organs was altered by Si in both WT and lsi1. Heterogeneous expression of Lsi1 in Xenopus oocyte did not show transport activity for Pi. The expression of Pi transporter genes (OsPT1, 2 and 8) in the roots was hardly affected by Si in both WT and lsi1, but that of OsPT6 was down-regulated by Si in the WT roots, but not in the lsi1 roots. Furthermore, a split root experiment showed that Si accumulated in the shoots suppressed the expression of OsPT6. In rice grown in paddy field, lsi1 showed higher P concentration in the straw, husk and brown rice than the WT.Conclusion: Si decreased P uptake through down-regulating the expression of P transporter gene, OsPT6 in rice and Si accumulated in the shoot is required for this down-regulation. [ABSTRACT FROM AUTHOR]

Plant responses to nitrogen (N) and phosphorus (P) deficiencies differ among genotypes. Although the rhizosphere microbiome can serve as an indicator of plant functional traits across different genotypes, whether and how genotypic differences in plant tolerance to N and P deficiencies are associated with the rhizosphere microbiome are unknown. In this study, we carried out a paddy field experiment using five previously screened rice (Oryza sativa L.) varieties and examined crop yield and mineral element concentrations as well as the chemical properties and bacterial community of bulk and rhizosphere soils in response to N and P deficiencies. The three high-yield rice genotypes were found to be tolerant to N and P deficiencies, whereas the two low-yield genotypes were sensitive. Rhizosphere bacterial community compositions under different fertilization treatments were clearly separated into two groups corresponding to tolerant and sensitive rice. Eighteen bacterial keystone taxa were identified across the five rice genotypes under different N and P conditions. Tolerant rice harbored more bacterial keystone taxa in the rhizosphere under N or P deficiency than did sensitive rice. The specific bacterial keystone taxa recruited by tolerant rice were functionally associated with soil N transformation, plant-promoting activity, carbon decomposition, and iron cycling. These results suggest that bacterial community selection in the rhizosphere is dependent on the tolerance of rice genotypes to N and P deficiencies. The findings help explain the intrinsic mechanism that potentially controls the yield gap of rice genotypes through rhizosphere-driven microbial functions under N/P-limited agroecosystem conditions. The identified bacterial keystone taxa, which are potentially useful bio-fertilizer inoculants for agricultural production and possible indicators of rice genotypes for breeding N- and P-efficient rice cultivars, may ultimately contribute to sustainable agricultural development, resulting in high crop yields while minimizing fertilizer input and environmental risks. • Fertilization has a greater effect than rice genotype on the bacterial community. • Bacterial community selection in the rhizosphere is rice-genotype dependent. • Rice tolerance to N/P deficiency drives separation of the bacterial community. • Compared with sensitive rice, tolerant rice harbors more bacterial keystone taxa. • Bacterial keystone taxa are associated with C/N transformation and Fe cycling. [ABSTRACT FROM AUTHOR]

High rates of phosphorus (P) are generally applied to vegetable crops, but this carries a risk of polluting the environment. There has been little research to define optimum soil P levels and strategies to reduce P requirements in the field. We hypothesized that high rates of P fertilization at the seedling stage followed by lower rates later could reduce total P fertilizer use in cucumber ( Cucumis sativus L.). In this study, we explored the optimum P application via pot experiments in which three P levels at the seedling stage (0, 80, and 240 mg P kg −1 soil) were used in factorial combination with three P levels after transplanting (0, 80, and 160 mg P kg −1 soil). Results showed that P applied in the seedling stage was much more effective at maintaining optimal growth than in the field after transplanting. For example, 72 mg P pot −1 applied in the mode 240/0 (P application rates at the seedling vs transplant stages) produced a biomass dry weight (DW) of 17.7 g pot −1 , whereas 360 mg P pot −1 applied in the mode 0/80 produced only 13.8 g pot −1 . An ancillary study measured the depletion of P from solution by cucumber seedlings between 13 and 21 days after sowing. Over this period V max (the maximum uptake velocity) decreased from 1.18 to 0.50 nmol g −1 root dry weight s −1 , while K m (the half-saturation constant where uptake is 50% of V max ) increased from 5.60 to 8.14 μM. That indicates that since cucumber plants have a high capacity to absorb P as seedlings, it would be expected to reduce the P requirement in field soils. There are therefore efficiencies in applying higher P at the seedling stage and lower levels later. [ABSTRACT FROM AUTHOR]

The adaptations of root morphology, physiology, and biochemistry to phosphorus supply have been characterized intensively. However, characterizing these adaptations at molecular level is largely neglected under field conditions. Here, two consecutive field experiments were carried out to investigate the agronomic traits and root traits of wheat (Triticum aestivum L.) at six P-fertilizer rates. Root samples were collected at flowering to investigate root dry weight, root length density, arbusular-mycorrhizal colonization rate, acid phosphatase activity in rhizosphere soil, and expression levels of genes encoding phosphate transporter, phosphatase, ribonucleases, and expansin. These root traits exhibited inducible, inhibitory, or combined responses to P deficiency, and the change point for responses to P supply was at or near the optimal P supply for maximum grain yield. This research improves the understanding of mechanisms of plant adaptation to soil P in intensive agriculture and provides useful information for optimizing P management based on the interactions between soil P dynamics and root processes. [ABSTRACT FROM AUTHOR]

Low soil nutrient availability severely constrains plant growth and productivity in acidic soil ecosystems. Diazotrophs and arbuscular mycorrhizal fungi (AMF) are the important microbial groups that improve the bioavailability of soil nitrogen (N) and phosphorus (P), respectively. Therefore, the objective was to investigate the biogeographic patterns and co-occurrence networks of the diazotrophic and AMF communities in the acidic soil ecosystem. We collected 52 soil samples from four long-term field observation stations with spatial distances of 961.3 km in the acidic soil region of southern China, and analyzed the community composition and biogeographic distributions of the diazotrophs and AMF using high-throughput sequencing of the functional gene amplicons. The variation partition analysis indicated that soil physicochemical factors provided more contributions than geographic distance, sampling stations and land-use types in the assembly of the diazotrophic and AMF community communities. Distance-decay relationships and Mantel tests showed that soil physicochemical factors had remarkable effects on both microbial community structures, whereas geographic distance only significantly affected the diazotrophic community variations. Co-occurrence network analysis revealed that AMF network was more complex and stable than the diazotrophic network. Furthermore, the dominant genera Bradyrhizbium and Glomus might be the more important keystone taxa in the diazotrophic and AMF networks, respectively. These findings suggest that the diazotrophic and AMF communities exhibit different assembly mechanisms and co-occurrence ecological networks in the acidic soil region of southern China, and both community assemblies were mainly driven by soil physicochemical factors. Unlabelled Image • Environmental factors clearly affected the diazotrophic and AMF community structures. • Geographic distance only significantly affected the diazotrophic community variations. • Diazotrophic and AMF communities exhibited different assembly mechanisms. • AMF network was more complex and stable than the diazotrophic network. • Bradyrhizbium and Glomus were the keystone taxa in the diazotrophic and AMF networks. [ABSTRACT FROM AUTHOR]