Utilization Of Organic Nitrogen Research Articles

The Difference in Shoot Metabolite Profiles of a Wild and a Cultivated Barley Genotype in Response to Four Nitrogen Forms

Plants can utilize different N forms, including organic and inorganic N resources, and show great differences in the utilization efficiency of each N form among species and genotypes within a species. Previously, we found that the Tibetan wild barley genotype (XZ16) was better in the utilization of organic nitrogen in comparison with the cultivated barley genotype (Hua30). In this study, the metabolite profiles of the two barley genotypes were comprehensively compared in their response to four N forms, including nitrate (NO3−), ammonium (NH4+), urea, and glycine. The macro and micro nutrient concentrations in shoots were mostly found to be higher in the nitrate and urea treatments than in ammonium and glycine in both the genotypes. XZ16 had higher concentrations of nutrient ions in the glycine treatment, but Hua30 accumulated more nutrients in the ammonium treatment. Among a total of 163 differentially regulated metabolites, the highest up-regulation and highest down-regulation values were found in XZ16 in the glycine and urea treatments, respectively. Some important metabolites, such as proline, glutamine, serine, asparagine, L-homoserine, aspartic acid, putrescine, ornithine, and 4-aminobutyrate, were up-regulated in the glycine treatment in both the genotypes with a higher fold change in XZ16 than that in Hua30. Similarly, fructose-6-PO4, aconitic acid, and isocitrate were only up-regulated in XZ16 in the glycine treatment. Here, we concluded that the genotype XZ16 exhibited a better response to the glycine treatment, while Hua30 showed a better response to the NH4+ treatment, which is attributed to the better utilization of glycine-N and NH4+-N, respectively.

Single-cell isotope tracing reveals functional guilds of bacteria associated with the diatom Phaeodactylum tricornutum

Bacterial remineralization of algal organic matter fuels algal growth but is rarely quantified. Consequently, we cannot currently predict whether some bacterial taxa may provide more remineralized nutrients to algae than others. Here, we quantified bacterial incorporation of algal-derived complex dissolved organic carbon and nitrogen and algal incorporation of remineralized carbon and nitrogen in fifteen bacterial co-cultures growing with the diatom Phaeodactylum tricornutum at the single-cell level using isotope tracing and nanoSIMS. We found unexpected strain-to-strain and cell-to-cell variability in net carbon and nitrogen incorporation, including non-ubiquitous complex organic nitrogen utilization and remineralization. We used these data to identify three distinct functional guilds of metabolic interactions, which we termed macromolecule remineralizers, macromolecule users, and small-molecule users, the latter exhibiting efficient growth under low carbon availability. The functional guilds were not linked to phylogeny and could not be elucidated strictly from metabolic capacity as predicted by comparative genomics, highlighting the need for direct activity-based measurements in ecological studies of microbial metabolic interactions.

Multiple facets of cutting-edge mycorrhizal research: 11th International Conference on Mycorrhiza (ICOM 11), Beijing, China, August 2022: 11th International Conference on Mycorrhiza (ICOM 11), Beijing, China, 1-5 August 2022.

Multiple facets of cutting-edge mycorrhizal research: 11th International Conference on Mycorrhiza (ICOM 11), Beijing, China, August 2022: 11th International Conference on Mycorrhiza (ICOM 11), Beijing, China, 1-5 August 2022.

Expression of AtAAP Gene Family and Endosperm-Specific Expression of AtAAP1 Gene Promotes Amino Acid Absorption in Arabidopsis thaliana and Maize

The amino acid permease (AAP) is an important transmembrane protein that is involved in the absorption and transport of amino acids in plants. We investigated the expression patterns of AtAAP genes in Arabidopsis thaliana, based on quantitative real-time PCR. The results revealed differential expression patterns of eight AtAAP genes in different tissues, with five genes (AtAAP1, AtAAP2, AtAAP6, AtAAP7, and AtAAP8) expressed at relatively high levels in both flowers and siliques, suggesting their shared functions in the accumulation of amino acids. In transgenic plants, with endosperm-specific overexpression of AtAAP1, both AtAAP1 and AtAAP6 were up-regulated in both the roots and siliques, while AtAAP2, AtAAP3, AtAAP4, and AtAAP5 showed similar expression levels in the stems and siliques, whereas AtAAP7 and AtAAP8 were expressed at their highest levels in the stems and roots. The results of the amino acid affinity experiments revealed varied absorption capacities for different amino acids, by AtAAP1, and increased acid amino contents in the reproductive organs. These results were verified in transgenic maize plants, with the overexpression of AtAAP1, revealing higher amino acid contents in the reproductive organs than those of the vegetative organs. Our study clearly demonstrated that the endosperm-specific promoter increased the amino acid contents in the reproductive organs and improved the effective utilization of organic nitrogen in plants.

Direct Utilization of Organic Nitrogen by Phytoplankton and Its Role in Nitrogen Cycling Within the Southern California Bight.

The new production model attempts to quantify the amount of organic material exported from surface waters based on the form of nitrogen (N) being utilized. Dissolved organic N (DON) is rarely assessed during such investigations and even less is understood about the organisms involved in these different transformations within the complex N cycle. Stable isotope probing (SIP) and uptake activity measurements were combined to investigate the dynamics of new and regenerated production during the spring within the Southern California Bight (SCB). We examined the uptake and assimilation of several nitrogenous substrates at several depths to quantify these processes and identify the active communities across all three domains of life that are driving each transformation. Several reoccurring members closely related to the eukaryotic diatom Chaetoceros, dominated assimilation of NO3- and urea through the water column, and contributed greatly to the overall production. Prokaryotic growth was predominantly carried out through NH4+ assimilation with transitions from Flavobacteria to Rhodobacteraceae and Marine Group II Euryarchaeota to Marine Group I Thaumarchaeota with increasing depth for bacterial and archaeal clades, respectively. Only urea uptake and SIP activity correlated with each other, likely demonstrating that cellular transport and incorporation of urea were coupled. SIP was therefore able to identify the organisms primarily responsible for urea cycling at each depth during this investigation. The role of diatoms within high nutrient areas are well defined but their part in DON cycling in highly stratified regimes is less well understood. Here we demonstrate their ability to efficiently scavenge urea in situ, allowing certain diatoms to outcompete the rest of the community. This diversion of DON away from the trophically inefficient microbial loop directly back into the larger, particle forming populations would alter the current view of microbial food webs. This proposed “phytoplankton shunt” of organic material could potentially enhance the biological pump by mitigating losses due to trophic transfers while increasing DON flux due to ballasting. Our results provide unique biogeochemical and ecological insight into the dynamics and diversity of N cycling and the organisms involved within the surface waters of the SCB.

Utilization of organic nitrogen by arbuscular mycorrhizal fungi-is there a specific role for protists and ammonia oxidizers?

Arbuscular mycorrhizal (AM) fungi can significantly contribute to plant nitrogen (N) uptake from complex organic sources, most likely in concert with activity of soil saprotrophs and other microbes releasing and transforming the N bound in organic forms. Here, we tested whether AM fungus (Rhizophagus irregularis) extraradical hyphal networks showed any preferences towards certain forms of organic N (chitin of fungal or crustacean origin, DNA, clover biomass, or albumin) administered in spatially discrete patches, and how the presence of AM fungal hyphae affected other microbes. By direct 15N labeling, we also quantified the flux of N to the plants (Andropogon gerardii) through the AM fungal hyphae from fungal chitin and from clover biomass. The AM fungal hyphae colonized patches supplemented with organic N sources significantly more than those receiving only mineral nutrients, organic carbon in form of cellulose, or nothing. Mycorrhizal plants grew 6.4-fold larger and accumulated, on average, 20.3-fold more 15N originating from the labeled organic sources than their nonmycorrhizal counterparts. Whereas the abundance of microbes (bacteria, fungi, or Acanthamoeba sp.) in the different patches was primarily driven by patch quality, we noted a consistent suppression of the microbial abundances by the presence of AM fungal hyphae. This suppression was particularly strong for ammonia oxidizing bacteria. Our results indicate that AM fungi successfully competed with the other microbes for free ammonium ions and suggest an important role for the notoriously understudied soil protists to play in recycling organic N from soil to plants via AM fungal hyphae.

Oxygen, carbon, and nutrients in the oligotrophic eastern subtropical North Atlantic

Abstract. The Beta Triangle, a region of the oligotrophic subtropical eastern North Atlantic Ocean, is notorious for its enigmatic oxygen, carbon, and nitrogen balances, in which nutrient supply is said to explain only a fraction of production necessary for estimated carbon export. Rates of dissolved organic carbon accumulation and dissolved organic nitrogen utilization in surface water and an assessment of oxygen utilized, organic matter consumed, and nitrate and phosphate regenerated in subsurface water, show that conventional production estimates miss substantial shares of biotic production. The shallow export of total organic carbon, predominantly dissolved (DOC), by subduction is responsible for about 50–70% of apparent oxygen utilization in subsurface water between the base of the surface layer at ca. 140 m and ca. 195 m depth, but it is insignificant below. Additionally, there is an estimated accumulation of 1.0 to 1.75 mol DOC m−2 a−1 in surface water. Including DOC dynamics in its carbon balance reveals the surface of this ultra-oligotrophic part of the ocean to be net autotrophic. Increasing subsurface values of excess nitrogen (DINxs) imply the export of nitrogen from surface water stemming from production not exclusively fuelled by new nitrate supplied from below. Total organic nitrogen (almost exclusively dissolved, DON) is consumed in the surface layer at a rate estimated at 0.13 to 0.23 mol m−2 a−1. There is no variation in dissolved organic phosphorus (DOP) in the same direction. DON utilization thus contributes to the pronounced subsurface DINxs signature. DOC export and accumulation are important in the carbon balance in surface and near-surface water. DON utilization and, probably, N2 fixation contribute significant amounts to the nitrogen supply of surface water. These processes can close part of the enigmatic carbon and nitrogen balances in the Beta Triangle. There are, however, no comparable processes which can explain the equally enigmatic situation concerning phosphorus supply in this area.

Effects of Nitrogen Forms on Carbon and Nitrogen Accumulation in Tomato Seedling

Utilization of organic nitrogen (N) is an important aspect of plant N assimilation and has potential application in sustainable agriculture. The aim of this study was to investigate the plant growth, C and N accumulation in leaves and roots of tomato seedlings in response to inorganic (NH 4 +-N, NO 3 −-N) and organic nitrogen (Gly-N). Different forms of nitrogen (NH 4 +-N, NO 3 −-N, Gly-N) were supplied to two tomato cultivars (Shenfen 918 and Huying 932) using a hydroponics system. The plant dry biomass, chlorophyll content, root activity, total carbon and nitrogen content in roots and leaves, and total N absorption, etc. were assayed during the cultivation. Our results showed that no significant differences in plant height, dry biomass, and total N content were found within the first 16 d among three treatments; however, significant differences in treatments on 24 d and 32 d were observed, and the order was NO 3 −-N > Gly-N > NH 4 +-N. Significant differences were also observed between the two tomato cultivars. Chlorophyll contents in the two cultivars were significantly increased by the Gly-N treatment, and root activity showed a significant decrease in NH 4 +-N treatment. Tomato leaf total carbon content was slightly affected by different N forms; however, total carbon in root and total nitrogen in root and leaf were promoted significantly by inorganic and organic N. Among the applied N forms, the increasing effects of the NH 4 +-N treatment were larger than that of the Gly-N. In a word, different N resources resulted in different physiological effects in tomatoes. Organic nitrogen (e.g., Gly-N) can be a proper resource of plant N nutrition. Tomatoes of different genotypes had different responses under organic nitrogen (e.g., Gly-N) supplies.

Foliar uptake of atmospheric organic nitrates

Increasing nitrogen deposition to forests can impact the balance between the carbon and nitrogen cycles. This nitrogen source, if taken up and used by forests, can increase growth and carbon storage. While previous findings have suggested that nitrogen deposition is not an important source of nitrogen for a forest ecosystem, the possibility of canopy uptake was not considered. Foliar uptake and utilization of inorganic nitrogen, such as NO2 and NH3, has been shown to occur, but utilization of organic nitrogen has not been demonstrated directly. Here we show for the first time that atmospheric organic nitrates (RONO2), one form of organic nitrogen, can be taken up by foliage and incorporated into the leaf amino acids, and we discuss possible uptake mechanisms.

Role ofptsP,orfT, andsssRecombinase Genes in Root Colonization byPseudomonas fluorescensQ8r1-96

Pseudomonas fluorescens Q8r1-96 produces 2,4-diacetylphloroglucinol (2,4-DAPG), a polyketide antibiotic that suppresses a wide variety of soilborne fungal pathogens, including Gaeumannomyces graminis var. tritici, which causes take-all disease of wheat. Strain Q8r1-96 is representative of the D-genotype of 2,4-DAPG producers, which are exceptional because of their ability to aggressively colonize and maintain large populations on the roots of host plants, including wheat, pea, and sugar beet. In this study, three genes, an sss recombinase gene, ptsP, and orfT, which are important in the interaction of Pseudomonas spp. with various hosts, were investigated to determine their contributions to the unusual colonization properties of strain Q8r1-96. The sss recombinase and ptsP genes influence global processes, including phenotypic plasticity and organic nitrogen utilization, respectively. The orfT gene contributes to the pathogenicity of Pseudomonas aeruginosa in plants and animals and is conserved among saprophytic rhizosphere pseudomonads, but its function is unknown. Clones containing these genes were identified in a Q8r1-96 genomic library, sequenced, and used to construct gene replacement mutants of Q8r1-96. Mutants were characterized to determine their 2,4-DAPG production, motility, fluorescence, colony morphology, exoprotease and hydrogen cyanide (HCN) production, carbon and nitrogen utilization, and ability to colonize the rhizosphere of wheat grown in natural soil. The ptsP mutant was impaired in wheat root colonization, whereas mutants with mutations in the sss recombinase gene and orfT were not. However, all three mutants were less competitive than wild-type P. fluorescens Q8r1-96 in the wheat rhizosphere when they were introduced into the soil by paired inoculation with the parental strain.

Utilization of organic nitrogen at two different substrate pH by different ectomycorrhizal fungi growing in symbiosis with Pinus sylvestris seedlings

The aim of this study was to test the potential of four isolates of ectomycorrhizal (EM) fungi to utilize organic nitrogen (N) at two different substrate pHs. The organic N source ((1)5N labelled lyophilised fungal mycelium) was mixed with either untreated peat/sand mixture (pH 4.9) or peat/sand mixture limed to a pH of 5.9 and put in cylindrical containers added to each pot. The content of the containers was separated from the roots of Pinus sylvestris seedlings by a nylon mesh and a 2 mm air gap to reduce diffusion of labelled N to the roots. The mycorrhizal plants (except those colonized by Suillus variegatus 2) took up significantly more (1)5N from the labelled mycelium than uncolonized seedlings. Liming significantly reduced the uptake of (1)5N by one of the EM fungi (unidentified) but not the other tested species (Paxillus involutus and two isolates of S. variegatus). The EM fungal isolates differed in their influence on the bacterial activity of the soil. This was reduced with P. involutus at both pH levels and increased with one of the two S. variegatus isolates at the high pH and with the other S. variegatus isolate at the low pH level. Liming the soil generally increased bacterial activity. The influence of liming on the proportion of organic N uptake in relation to inorganic N uptake by ectomycorrhizal trees is discussed. (Less)

Utilization of organic nitrogen by ectomycorrhizal fungi ( Hebeloma spp.) of arctic and temperate origin

Arctic and temperate strains of Hebeloma spp. were grown in axenic culture on glutamic acid, alanine, lysine and NH4+ as sole sources of nitrogen (N), with excess carbon (C) or deficient C (supplied as glucose). Their ability to utilize seed protein as a natural N source was also assessed. All strains tested had the capacity to assimilate amino acids and generally utilized alanine and glutamic acid more readily than NH4+. Some strains were able to utilize amino C when starved of glucose C, and could mineralize amino-N to NH3-N. Arctic strains, in particular, appeared to be pre-adapted to the utilization of seed protein N and glutamic acid N, which is often liberated in high concentrations after soil freezing. The results are discussed in relation to their possible ecological importance.

Organic nitrogen utilization by an unidentified mycobiont isolated from mycorrhizas of Pisonia grandis

The ability of an unidentified mycobiont from Pisonia grandis mycorrhizas to utilize organic nitrogen and phosphorus sources was determined in axenic liquid cultures. The fungus utilized inorganic phosphate and both freely- and poorly-soluble salts of inositol hexaphosphate as sole phosphorus sources. With the exception of uric acid which did not support growth, the yield of the mycobiont on all organic nitrogen sources tested was significantly greater than the yield on either NH4+ or NO3−. It is suggested that the major ecological role of the Pisonia mycobiont in stands of P. grandis on coral cays may be rapid absorption of allantoin and urea produced during degradation of uric acid by the spil microflora. This may be important in retaining nitrogen in the soil: plant system prior to loss from the coral cay by further degradation, volatilization and/or leaching.

The utilization of organic nitrogen for growth of algae: physiological aspects

AbstractThe ability of 27 algae belonging to 11 taxonomic divisions to grow at the expense of organic nitrogen was tested in axenic culture. Experiments were carried out in buffered media: morpholine propanesulphonic acid (MOPS) was used successfully for all fresh water strains except diatoms. It was not used as a nitrogen source by any strain examined but served as a good source of sulphur for four strains. The range of substrates used was extensive and included amino acids, urea, acetamide, urate and some nucleosides. Growth rates varied widely but growth yields were generally comparable to those attained with nitrate or ammonia except for substrates containing more than one utilizable nitrogen atom. Limited experiments were carried out in the dark, and it was found that a given substrate was equally suitable for both dark heterotrophic and photolithotrophic growth. Levels of chlorophyll a were measured during growth of two algae with nitrate, glycine and urate. With nitrate, levels of specific chlorophyll a declined some ten‐fold during growth: with poor substrates supporting only slow growth, levels were more uniform but were only 10–15% of those attained during growth with good substrates. One strain grown with MOPS as sole source of sulphur produced cultures with levels of chlorophyll a about half those found in sulphate‐grown cultures. Tolerance of sodium chloride was examined in a few strains and even putatively fresh water strains were found to be appreciably tolerant.

A Physiological Comparison of the Symbiotic AlgaPlatymonas Convolutaeand its Free-Living Relatives

Platymonas convolutaeParke et Manton is the natural algal partner of the symbiotic wormConvoluta roscoffensisGraff (Parke & Manton 1967). Recent work by Provasoli, Yamasu & Manton (1968) has shown that although several algae can form a symbiotic relationship with the worm if supplied in unialgal culture, the natural symbiont is the most effective and is able to eliminate competitors. The alga can be cultured in a denned medium away from its partner, and this paper presents some physiological characteristics of the alga in pure culture in comparison with some of its free-living relatives, in particular the type species of the genusPlatymonas, P. tetratheleG. S. West. The present investigation has been concerned mainly with the uptake of carbohydrates and the utilization of organic nitrogen. Other aspects that are included are the excretion of metabolites into the medium and the soluble carbohydrates found within the algae. In addition, culturing the algae has revealed a difference in behaviour of possible relevance to the symbiotic relationship.