Dataset Information

Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga.

ABSTRACT: In freshwaters, algal species are exposed to different inorganic nitrogen (N_i) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium ( NH 4 + )-use, in contrast to nitrate ( NO 3 - )-use, more energy remains for other metabolic processes, especially under CO₂- and phosphorus (P_i) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chlamydomonas acidophila grown on NH 4 + or NO 3 - under covariation of CO₂ and P_i-supply in order to determine limitations, in a full-factorial design. As expected, results revealed higher carbon fixation rates for NH 4 + -grown cells compared to growth with NO 3 - under low CO₂ conditions. NO 3 - -grown cells accumulated more of the nine analyzed amino acids, especially under P_i-limited conditions, compared to cells provided with NH 4 + . This is probably due to a slower protein synthesis in cells provided with NO 3 - . In contrast to our expectations, compared to NH 4 + -grown cells NO 3 - -grown cells had higher photosynthetic efficiency under P_i-limitation. In conclusion, growth on the N_i-source NH 4 + did not result in a clearly enhanced C_i-assimilation, as it was highly dependent on P_i and CO₂ conditions (replete or limited). Results are potentially connected to the fact that C. acidophila is able to use only CO₂ as its inorganic carbon (C_i) source.

SUBMITTER: Lachmann SC

PROVIDER: S-EPMC6374670 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga.

Lachmann Sabrina C SC Mettler-Altmann Tabea T Wacker Alexander A Spijkerman Elly E

Ecology and evolution 20190110 3

In freshwaters, algal species are exposed to different inorganic nitrogen (Ni) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium ( NH 4 + )-use, in contrast to nitrate ( NO 3 - )-use, more energy remains for other metabolic processes, especially under CO2- and phosphorus (Pi) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chla ...[more]

PMID: 30805141

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Project description:Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox), and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. While the effect of N application on BNF is known, little is known about its effect on NO3- partitioning between DNRA, denitrification, and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox, and BNF and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in a glasshouse with N fertilizer (150 kg N ha-1) and without N fertilizer for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone, but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3- reduced by DNRA (0.42 to 0.52 μg g-1 soil day-1 and 45 to 55%, respectively) were similar to or higher than the amount and proportion reduced by denitrification. However, with N the amount of NO3- reduced by DNRA (0.32 to 0.40 μg g-1 soil day-1) was 40 to 50% lower than the amount of NO3- reduced by denitrification. Denitrification loss increased by >20% with N addition and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02 to 0.25 μg N g-1 soil day-1 We found that DNRA plays a significant positive role in paddy soil N retention, as it accounts for up to 55% of the total NO3- reduction, but this is reduced by N application.IMPORTANCE This study provides evidence that nitrogen addition reduces nitrogen retention through DNRA and increases nitrogen loss via denitrification in a paddy soil ecosystem. DNRA is one of the major NO3- reduction processes, and it can outcompete denitrification in NO3- consumption when rice paddies are low in nitrogen. A significant level of DNRA activity in paddy soils indicates that DNRA plays an important role in retaining nitrogen by reducing NO3- availability for denitrification and leaching. Our study shows that by reducing N addition to rice paddies, there is a positive effect from reduced nitrogen loss but, more importantly, from the conversion of NO3- to NH4+, which is the favored form of mineral nitrogen for plant uptake.

Project description:BackgroundIn order to grow, plants rely on soil nutrients which can vary both spatially and temporally depending on the environment, the soil type or the microbial activity. An essential nutrient is nitrogen, which is mainly accessible as nitrate and ammonium. Many studies have investigated transport genes for these ions in Arabidopsis thaliana and recently in crop species, including Maize, Rice and Barley. However, in most crop species, an understanding of the participants in nitrate and ammonium transport across the soil plant continuum remains undefined.ResultsWe have mapped a non-exhaustive set of putative nitrate and ammonium transporters in maize. The selected transporters were defined based on previous studies comparing nitrate transport pathways conserved between Arabidopsis and Zea mays (Plett D et. al, PLOS ONE 5:e15289, 2010). We also selected genes from published studies (Gu R et. al, Plant and Cell Physiology, 54:1515-1524, 2013, Garnett T et. al, New Phytol 198:82-94, 2013, Garnett T et. al, Frontiers in Plant Sci 6, 2015, Dechorgnat J et. al, Front Plant Sci 9:531, 2018). To analyse these genes, the plants were grown in a semi-hydroponic system to carefully control nitrogen delivery and then harvested at both vegetative and reproductive stages. The expression patterns of 26 putative nitrogen transporters were then tested. Six putative genes were found not expressed in our conditions. Transcripts of 20 other genes were detected at both the vegetative and reproductive stages of maize development. We observed the expression of nitrogen transporters in all organs tested: roots, young leaves, old leaves, silks, cobs, tassels and husk leaves. We also followed the gene expression response to nitrogen starvation and resupply and uncovered mainly three expression patterns: (i) genes unresponsiveness to nitrogen supply; (ii) genes showing an increase of expression after nitrogen starvation; (iii) genes showing a decrease of expression after nitrogen starvation.ConclusionsThese data allowed the mapping of putative nitrogen transporters in maize at both the vegetative and reproductive stages of development. No growth-dependent expression was seen in our conditions. We found that nitrogen transporter genes were expressed in all the organs tested and in many cases were regulated by the availability of nitrogen supplied to the plant. The gene expression patterns in relation to organ specificity and nitrogen availability denote a speciality of nitrate and ammonium transporter genes and their probable function depending on the plant organ and the environment.

Dataset Information

Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga.

Publications

Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga.

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