Interactive effects of low pH and high ammonium levels responsible for the decline of Cirsium dissectum (L.) Hill

The decline of Cirsium dissectum in dessicatingwetlands is attributed to acidification and eutrophication. Experimentalevidence was obtained for the first time on ammonium toxicity under low pH. Inahydroculture experiment, interactive effects of nitrogen forms (250mol NH₄ ⁺ or 250molNO₃ ^–) and pH (4, 5 or 6) were studied with regardtothe vitality of C. dissectum seedlings. The results showthat 250 mol l^–1 ammonium as sole nitrogensource only had negative effects on C. dissectum incombination with a low pH. Ammonium uptake at a rhizosphere pH of 4, resultedinlower nitrogen contents of both roots and shoots, lower internal pH of rootsandshoots and increased contents of basic amino-acids, resulting indecreased survival rate and biomass development. At higher pH, or when nitratewas the nitrogen source, these processes do not take place. This phenomenonstresses the importance of periodic influence of base rich groundwater duringthe winter in wet species-rich heathlands and grasslands, necessary torestore the acid neutralising capacity of the soil. Anthropogenic lowering ofthe groundwater table will lead to acidification enabling ammonium to becometoxic to herbaceous plant species such as C. dissectum.     

Influence of ammonium and nitrate supply on growth,nitrate reductase activity and N-use efficiency in a natural hybrid pine and its parents

Aims Selection of tree species with a high capacity to assimilate N and efficiently utilize N resources would facilitate the success of initial tree seedling establishment in infertile soils. The preference for N forms was tested using three pine species (Pinus densata, Pinus tabuliformis and Pinus yunnanensis). Pinus densata is a natural diploid hybrid between P. tabuliformis and P. yunnanensis .Methods Seedlings of three pine species were supplied with nitrate-N, ammonium-N (at two different pH regimes) or combined ammonium and nitrate as a nitrogen source in perlite culture in a controlled environment.Important findings Seedlings of P. densata had higher total biomass and net photosynthesis when supplied with nitrate-N and ammonium nitrate than with ammonium-N. In parental species, total biomass and net photosynthesis for P. yunnanensis seedlings was higher in ammonium-N than in nitrate-N, whereas the other parental species P. tabuliformis had the highest total biomass among species for all treatments except ammonium with CaCO 3. Most morphological traits in P. densata seedlings were intermediate between its two parental species. However, N-use efficiency and photosynthetic N-use efficiency of P. densata significantly exceeded both parents when supplied with nitrate-N and ammonium nitrate. The results suggested that the diploid hybrid tree species P. densata has a preference for nitrate and is not well adapted to ammonium-N as a sole nitrogen source regardless of the growth medium pH. Based on changes in environmental conditions, such as predicted future temperature increases in high altitude areas associated with climate change, P. densata is likely to be increasingly competitive and have wide adaptation in high altitude regions.     

Anion channel SLAH3 functions in nitrate‐dependent alleviation of ammonium toxicity in Arabidopsis

Slow anion channels (SLAC/SLAH) are efflux channels previously shown to be critical for stomatal regulation. However, detailed analysis using the β‐glucuronidase reporter gene showed that members of the SLAC/SLAH gene family are predominantly expressed in roots, in addition to stomatal guard cells, implicating distinct function(s) of SLAC/SLAH in the roots. Comprehensive mutant analyses of all slac/slah mutants indicated that slah3 plants showed a greater growth defect than wild‐type plants when ammonium was supplied as the sole nitrogen source. Ammonium toxicity was mimicked by acidic pH in nitrogen‐free external medium, suggesting that medium acidification by ammonium‐fed plants may underlie ammonium toxicity. Interestingly, such toxicity was more severe in slah3 mutants and, particularly in wild‐type plants, was alleviated by supplementing the media with micromolar levels of nitrate. These data thus provide evidence that SLAH3, a nitrate efflux channel, plays a role in nitrate‐dependent alleviation of ammonium toxicity in plants.     

The effect of glucose and ammonium sulfate on kinetic acidification by heterogeneous mixed culture

Summary The effect of glucose and ammonium sulfate concentration on the kinetics of lactic acid formation by a heterogeneous mixed culture was evaluated by the sole product formation using the Gompertz model, which can be used to define culture media composition taking into account product accumulation and acidification rate constant. A compromise between ionic inhibition and nitrogen limitation was found by using ammonium sulfate as nitrogen source. The sugar tolerance was similar to that in exenic cultures.     

Decline of acid-sensitive plant species in heathland can be attributed to ammonium toxicity in combination with low pH

The effects of increasing ammonium concentrations in combination with different pH levels were studied on five heathland plant species to determine whether their occurrence and decline could be attributed to ammonium toxicity and/or pH levels. Plants were grown in growth media amended with four different ammonium concentrations (10, 100, 500 and 1000 micromol l(-1)) and two pH levels resembling acidified (pH 3.5 or 4) and weakly buffered (pH 5 or 5.5) situations. Survival of Antennaria dioica and Succisa pratensis was reduced by low pH in combination with high ammonium concentrations. Biomass decreased with increased ammonium concentrations and decreasing pH levels. Internal pH of the plants decreased with increasing ammonium concentrations. Survival of Calluna vulgaris, Deschampsia flexuosa and Gentiana pneumonanthe was not affected by ammonium. Moreover, biomass increased with increasing ammonium concentrations. Biomass production of G. pneumonanthe reduced at low pH levels. A decline of acid-sensitive species in heathlands was attributed to ammonium toxicity effects in combination with a low pH.     

Nitrogen nutrition of Douglas-fir (Pseudotsuga menziesii) on strongly acid sandy soil

Through ionic balance calculations, the effect of different sources and levels of nitrogen on nutrient uptake by Douglas-fir was studied. With ammonium as the sole source of N, growth of the plant was very poor. Increasing the levels of ammonium supply strongly decreased the surplus of total inorganic cations (C) over total inorganic anions (A). This decrease in C-A value, corresponding to the level of carboxylates in the plant, implies that in the long term the plant will run out of carboxylates and will then no longer be able to eliminate protons in the cytoplasm, produced during assimilation of ammonium. This can lead to internal acidification of the plant, toxic concentrations of free ammonium and an unbalanced amino acid composition. Values for the ratio of net carboxylate production and organic nitrogen production were in the same range as commonly found for other species. This did not support the theory of a conifer-specific ionic balance regulation as posed by others.     

Heterotrophic production of biomass and lutein by Chlorella protothecoides on various nitrogen sources

The effects of nitrate, ammonium, and urea as nitrogen sources on the heterotrophic growth of Chlorella protothecoides were investigated using flask cultures. No appreciable inhibitory effect on the algal growth was observed over a nitrogen concentration range of 0.85-1.7 g l(-)(1). In contrast, differences in specific growth rate and biomass production were found among the cultures with the various nitrogen compounds. The influence of different nitrogen sources at a concentration equivalent to 1.7 g l(-)(1) nitrogen on the heterotrophic production of biomass and lutein by C. protothecoides was investigated using the culture medium containing 40 g l(-)(1) glucose as the sole carbon and energy source in fermentors. The maximum biomass concentrations in the three cultures with nitrate, ammonium, and urea were 18.4, 18.9, and 19.6 g l(-)(1) dry cells, respectively. The maximum lutein yields in these cultures were between 68.42 and 83.81 mg l(-)(1). The highest yields of both biomass and lutein were achieved in the culture with urea. It was therefore concluded that urea was the best nitrogen source for the production of biomass and lutein. Based on the experimental results, a group of kinetic models describing cell growth, lutein production, and glucose and nitrogen consumption were proposed and a satisfactory fit was found between the experimental results and predicted values. Dynamic analysis of models demonstrated that enhancing initial nitrogen concentration in fermentor cultures, which correspondingly enhances cell growth and lutein formation, may shorten the fermentation cycle by 25-46%.     

Clover and ryegrass are tolerant species to ammonium nutrition

The application of nitrification inhibitors (NIs) together with nitrogen fertilizers in grasslands is an effective alternative to reduce nitrate leaching and nitrogenous gases emissions to the atmosphere. Nevertheless, the use of NIs increases the amount of ammonium available for the plant that, due to its reported toxic effect in plants, can have a direct effect on crop production. Grassland species have traditionally suffered from intensive grazing and urea deposition and, therefore, a tolerance to ammonium nutrition could be expected in these species. Plants of Trifolium repens L. var. huia and Lolium perenne L. var. Herbus were grown under two nitrogen nutrition regimes (nitrate or ammonium) and three different nitrogen concentrations (0.5, 2.5 and 5 mmol/L). The effect of nitrogen form was determined on biomass production parameters, gas-exchange and water relations parameters as well as polyamine (PA) and ion tissue contents. Both grassland species showed tolerance to ammonium nutrition due to their capacity to adjust several metabolic processes in a species-specific way. Gas exchange measurements and biomass production (expressed as dry weight (DW)) were unaffected by the nitrogen form or dose in both species except for a decrease in root total DW in ryegrass plants grown under ammonium nutrition. Hydraulic conductance (L₀) increased in ryegrass with increasing ammonium doses but no change due to the nitrogen source was observed in water potential (Ψ_w) values. Both species, and specially ryegrass, accumulated free ammonium mainly in roots when grown under ammonium nutrition and its translocation to the shoot via xylem was also observed. A clear difference in cations and PAs pattern was observed in each species when comparing both nitrogen nutrition regimes.     

Unusual regulatory nitrate reductase activity in cotyledons of Brassica napus seedlings: enhancement of nitrate reductase activity by ammonium supply

The effect of supplying either nitrate or ammonium on nitrate reductase activity (NRA) was investigated in Brassica napus seedlings. In roots, nitrate reductase activity (NRA) increased as a function of nitrate content in tissues and decreased when ammonium was the sole nitrogen source. Conversely, in the shoots (comprising the cotyledons and hypocotyl), NRA was shown to be independent of nitrate content. Moreover, when ammonium was supplied as the sole nitrogen source, NRA in the shoots was surprisingly higher than under nitrate supply and increased as a function of the tissue ammonium content. Under 15 mM of exogenous ammonium, the NRA was up to 2.5-fold higher than under nitrate supply after 6 d of culture. The NR mRNA accumulation under ammonium nutrition was 2-fold higher than under nitrate supply. The activation state of NR in shoots was especially high compared with roots: from nearly 80% under nitrate supply it reached 94% under ammonium. This high NR activation state under ammonium supply could be the consequence of the slight acidification observed in the shoot tissue. The effect of ammonium on NRA was only observed in cotyledons and when more than 3 mM ammonium was supplied. No such NRA increase was evident in the roots or in foliar discs. Addition of 1 mM nitrate under ammonium nutrition halved NRA and decreased the ammonium content in shoots. Thus, this unusual NRA was restricted to seedling cotyledons when nitrate was lacking in the nitrogen source.     

Root Development and Absorption of Ammonium and Nitrate from the Rhizosphere

Plant roots operate in an environment that is extremely heterogeneous, both spatially and temporally. Nonetheless, under conditions of limited diffusion and against intense competition from soil microorganisms, plant roots locate and acquire vital nitrogen resources. Several factors influence the mechanisms by which roots respond to ammonium and nitrate. Nitrogen that is required for cell division and expansion derives primarily from the apex itself absorbing rhizosphere ammonium and nitrate. Root density and extension are greater in nutrient solutions containing ammonium than in those containing nitrate as the sole nitrogen source. Root nitrogen acquisition alters rhizosphere pH and redox potential, which in turn regulate root cell proliferation and mechanical properties. The net result is that roots proliferate in soil zones rich in nitrogen. Moreover, plants develop thinner and longer roots when ammonium is the primary nitrogen source, an appropriate strategy for a relatively immobile nitrogen form.     

Access to organic and insoluble sources of phosphorus varies among soil Chytridiomycota

The sources of minerals accessed by fungi in the Chytridiomycota (chytrid) in soil are largely unknown. The ability of ten species of soil chytrids to use various sources of phosphorus was examined in vitro. While all grew on orthophosphate, fifty per cent of isolates grew on phytic acid, and one isolate grew on DNA as the sole source of phosphorus. All isolates solubilised and utilised CaHPO₄. Most isolates utilised hydroxyapatite when NH₄⁺ was the nitrogen source. When ammonium was omitted, 50% of isolates solubilised hydroxyapatite. Many soil chytrids may utilise phosphomonoesters as the sole source of phosphorus, and access to DNA appears limited. We suggest that the capacity to use different sources of phosphorus may influence the diversity of chytrids found in Australian soils.     

Nitrogen Forms Influence Microcystin Concentration and Composition via Changes in Cyanobacterial Community Structure

The eutrophication of freshwaters is a global health concern as lakes with excess nutrients are often subject to toxic cyanobacterial blooms. Although phosphorus is considered the main element regulating cyanobacterial biomass, nitrogen (N) concentration and more specifically the availability of different N forms may influence the overall toxicity of blooms. In this study of three eutrophic lakes prone to cyanobacterial blooms, we examined the effects of nitrogen species and concentrations and other environmental factors in influencing cyanobacterial community structure, microcystin (MC) concentrations and MC congener composition. The identification of specific MC congeners was of particular interest as they vary widely in toxicity. Different nitrogen forms appeared to influence cyanobacterial community structure leading to corresponding effects on MC concentrations and composition. Total MC concentrations across the lakes were largely explained by a combination of abiotic factors: dissolved organic nitrogen, water temperature and ammonium, but Microcystis spp. biomass was overall the best predictor of MC concentrations. Environmental factors did not appear to affect MC congener composition directly but there were significant associations between specific MC congeners and particular species. Based on redundancy analyses (RDA), the relative biomass of Microcystis aeruginosa was associated with MC-RR, M. wesenbergii with MC-LA and Aphanizomenon flos-aquae with MC-YR. The latter two species are not generally considered capable of MC production. Total nitrogen, water temperature, ammonium and dissolved organic nitrogen influenced the cyanobacterial community structure, which in turn resulted in differences in the dominant MC congener and the overall toxicity.     

Effect of the air pollution component ammonium sulphate on the VAM infection rate of three heathland species

Three heathand species, Antennaria dioica, Arnica montana and Hieracium pilosella, were artificially rained with ammonium sulphate solutions at increasing concentrations in a greenhouse experiment. The same species were also artificially rained with increasing ammonium sulphate solutions under field conditions. Dry weights of the plants in the field experiments did not change with increasing ammonium sulphate applications. Nor did the dry weights of plants in the greenhouse experiments change with increasing ammonium sulphate concentrations, except for Arnica montana, which showed an increase in dry weight. VAM infection percentage of Antennaria dioica increased in both the greenhouse and the field experiment. The results of the field experiment show that VAM infection rates are reduced after two years of artificial rain in the plant species Arnica montana, which grows naturally under nutrient poor conditions and is presently declining in its natural habitat in the Netherlands. In the greenhouse experiment, VAM infection of Arnica montana did not change with increasing ammonium sulphate concentrations. VAM infection rates of Hieracium pilosella, which presently is not declining, did not change with increasing ammonium sulphate concentrations.     

Isolation and characterization of a bacterium which utilizes polyester polyurethane as a sole carbon and nitrogen source

Abstract Various soil samples were screened for the presence of microorganisms which have the ability to degrade polyurethane compounds. Two strains with good polyurethane degrading activity were isolated. The more active strain was tentatively identified as Comamonas acidovorans . This strain could utilize polyester-type polyurethanes but not the polyether-type polyurethanes as sole carbon and nitrogen sources. Adipic acid and diethylene glycol were probably the main degradation products when polyurethane was supplied as a sole carbon and nitrogen source. When ammonium nitrate was used as nitrogen source, only diethylene glycol was detected after growth on polyurethane.     

Cultivation of Ulva lactuca with manure for simultaneous bioremediation and biomass production

The potential of liquid manure as sole nutrient source for cultivation of Ulva lactuca was investigated with the perspective of utilizing the produced biomass for feed and/or energy. Algae grown with manure demonstrated equal growth rates to algae grown with standard f/2-medium. The optimum manure concentration, expressed as ammonium concentration, was 25?μM. At these conditions, the biomass produced was potentially suitable for anaerobic digestion, due to a relative high carbon/nitrogen ratio (approximately 19). At higher manure concentrations, tissue concentrations of nitrogen, phosphorus, proteins, and amino acids increased, making the biomass less suitable for anaerobic digestion but potentially interesting as a feed supplement. Cultivating U. lactuca with manure as nutrient source has potential in terms of bioremediation as well as production of bioenergy and protein-feed.     

Root Development and Absorption of Ammonium and Nitrate from the Rhizosphere

Plant roots operate in an environment that is extremely heterogeneous, both spatially and temporally. Nonetheless, under conditions of limited diffusion and against intense competition from soil microorganisms, plant roots locate and acquire vital nitrogen resources. Several factors influence the mechanisms by which roots respond to ammonium and nitrate. Nitrogen that is required for cell division and expansion derives primarily from the apex itself absorbing rhizosphere ammonium and nitrate. Root density and extension are greater in nutrient solutions containing ammonium than in those containing nitrate as the sole nitrogen source. Root nitrogen acquisition alters rhizosphere pH and redox potential, which in turn regulate root cell proliferation and mechanical properties. The net result is that roots proliferate in soil zones rich in nitrogen. Moreover, plants develop thinner and longer roots when ammonium is the primary nitrogen source, an appropriate strategy for a relatively immobile nitrogen form. Present address of Alison R. Taylor: The Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK.     

Isolation and characterization of a Pseudomonas sp. strain PH1 utilizing meta-aminophenol

Pseudomonas sp. strain PH1 was isolated from soil contaminated with pharmaceutical and dye industry waste. The isolate PH1 could use m-aminophenol as a sole source of carbon, nitrogen, and energy to support the growth. PH1 could degrade up to 0.32 mM m-aminophenol in 120 h, when provided as nitrogen source at 0.4 mM concentration with citrate (0.5 mM) as a carbon source in the growth medium. The presence of ammonium chloride as an additional nitrogen source repressed the degradation of m-aminophenol by PH1. To identify strain PH1, the 16S rDNA sequence was amplified by PCR using conserved eubacterial primers. The FASTA program was used to analyze the 16S rDNA sequence and the resulting homology patterns suggested that PH1 is a Pseudomonas.     

Simultaneous degradation of acetonitrile and biphenyl by Pseudomonas aeruginosa

A bacterium capable of utilizing either acetonitrile as the sole source of carbon and nitrogen or biphenyl as the sole source of carbon was isolated from soil and identified as Pseudomonas aeruginosa. The bacterium also utilized other nitriles, amides, and polychlorinated biphenyls (PCBs) as growth substrates. Acetonitrile- or biphenyl-grown cells oxidized these substrates without a lag. In studies with [14C]acetonitrile, nearly 74% of the carbon was recovered as 14CO2 and 8% was associated with the biomass. In studies with [14C]biphenyl, nearly 68% of the carbon was recovered as 14CO2 and nearly 6% was associated with the biomass. Although higher concentrations of acetonitrile as the sole sources of nitrogen inhibited the rates of [14C]biphenyl mineralization, lower concentrations (0.05%, w/v) gave a 77% stimulation in 14CO2 recovery. Pseudomonas aeruginosa metabolized acetonitrile to ammonia and acetic acid and biphenyl to benzoic acid. The bacterium also simultaneously utilized biphenyl as the sole carbon source and acetonitrile as the sole nitrogen source. However, biphenyl utilization increased only after the depletion of acetonitrile. Metabolites of the mixed substrate were ammonia and benzoic acid, which completely disappeared in the later stages of incubation. Nitrile hydratase and amidase were responsible for the transformation of acetonitrile to acetic acid and ammonia.     

Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity

Ammonium (NH₄⁺) and nitrate (NO₃⁻) are major inorganic nitrogen (N) sources for plants. When serving as the sole or dominant N supply, NH₄⁺ often causes root inhibition and shoot chlorosis in plants, known as ammonium toxicity. NO₃⁻ usually causes no toxicity and can mitigate ammonium toxicity even at low concentrations, referred to as nitrate-dependent alleviation of ammonium toxicity. Our previous studies indicated a NO₃⁻ efflux channel SLAH3 is involved in this process. However, whether additional components contribute to NO₃⁻-mediated NH₄⁺ detoxification is unknown. Previously, mutations in NO₃⁻ transporter NRT1.1 were shown to cause enhanced resistance to high concentrations of NH₄⁺. Whereas, in this study, we found when the high-NH₄⁺ medium was supplemented with low concentrations of NO₃⁻, nrt1.1 mutant plants showed hyper-sensitive phenotype instead. Furthermore, mutation in NRT1.1 caused enhanced medium acidification under high-NH₄⁺/low-NO₃⁻ condition, suggesting NRT1.1 regulates ammonium toxicity by facilitating H⁺ uptake. Moreover, NRT1.1 was shown to interact with SLAH3 to form a transporter-channel complex. Interestingly, SLAH3 appeared to affect NO₃⁻ influx while NRT1.1 influenced NO₃⁻ efflux, suggesting NRT1.1 and SLAH3 regulate each other at protein and/or gene expression levels. Our study thus revealed NRT1.1 and SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity through regulating NO₃⁻ transport and balancing rhizosphere acidification.