English  Sprachen Icon  |  Gebärdensprache  |  Leichte Sprache  |  Kontakt


Is organic Nitrogen uptake a relevant source for agricultural plants?

By Daniel Moran Zuloaga (12.03.2013)

Nitrogen (N) is an essential nutrient for plants but its availability is certainly limited in most of the ecosystems. Since the past century, many studies have been focused on the organic nitrogen uptake with the study of Low Molecular Weight Organic Substance (LMWOS) by forest in certain ecosystems. In recent years many studies have been focused on plants; particularly by using uniform labelling. In this research, we focused on the use of position-specific labelling as a new technique to help us with a better understanding of plant uptake and provided more precise data regarding intact uptake of organic N in plants.

The objective of this study is to understand the uptake of organic N by three agricultural species: chicory (Cichorium intybus L), white lupine (Lupinus alba L) and maize (Zea mays L). Our LMWOS were acetic acid and alanine; in which 15N and 14C alanine (position-specific and uniform labelled) were injected into the rhizosphere of these plants presented on figure 1.

[Bildunterschrift / Subline]: Figure 1. Diagram of the experimental design

As control, N-free LMWOS acetic acid and inorganic N sources (15NH4+ and 15NO3-) were used as seen in figure 2.

[Bildunterschrift / Subline]: Figure 2. Low Molecular Weight Organic Substances LMWOS used in this study and its position-specific tracer 14C and 15N respectively

Six hours after labelling, we measured 14C and 15N content of the soil, CO2 efflux of the soil and 15N and 14C incorporation in shoot and roots. Therefore, our results showed that LMWOS can be taken up by plants, irrespective whether they contain N or not. On a position-specific level plants showed a higher uptake of C1 than C2, whereas it was vice versa for alanine (C3>C2>C1). Either for acetic acid and alanine indicated that microbial processes dominate the fate of LMWOS in soils and that plants utilized a small proportion of LMWOS (< 13%) as seen in table 1.

[Bildunterschrift / Subline]: Table 1. Intact uptake of alanine for chicory, lupine and maize and total nutrition with respect to the other inorganic sources

The ratio of C to N uptake from alanine revealed from the 13% of alanine-N was incorporated into plant biomass, and only a range from 7 to 13% were taken up as intact alanine. Consequently, the majority of N was already mineralized after 6h. Differences among species were found concerning the relevance of this N source compared to mineral nitrogen as well as the allocation of LMWOS uptake within the plants. Lupine showed highest intact uptake of alanine with 3.5% of the N nutrition, additionally, this alanine was first metabolized in the root and then allocated into the shoot. We found that C3 position occurred preferentially. On the other hand, maize mainly took up split fragments of alanine from the soil. Besides, we found no clear pattern in chicory.

[Bildunterschrift / Subline]: Figure 3. Percentage of 15N in root and shoot of alanine, ammonia (NH4+) and nitrate (NO3-) uptake by chicory, lupine and maize

In summary, the metabolization and allocation of LMWOS showed the high competition of microorganisms concerning LMWOS. Regarding the organic nitrogen, we found that ammonium and nitrate are not the only sources of N uptake but LMWOS uptake in a minor scale are also taken up. However, the percentage of plant nutrition was the highest in lupine followed by maize and chicory in which we found relative lower values. Therefore, we concluded that position-specific labelling is a unique tool to investigate soil transformation as well as a precise method for understand plant LMWOS uptake.

Daniel Moran Zuloaga
*01.06.1979 in Guayaquil

Scientific Career

Internships and International Schools
  • 2012
  • Biogéochimie et écologie des milieux continentaux (BioEMco) Université Pierre Marie Curie. Procope programme supervised by Guido Wiesenberg and Sylvie Derenne
  • 2011
  • Winter School “Science meet practice” sponsored by the Competence Centre Environmental and Sustainability CCES. Zurich
  • 2011
  • Summer School “Species distribution modelling” sponsored by Grand Paradiso National Park and the University of Pavia
  • 2010
  • Max Planck Institut für Chemie in Mainz. Reactive Nitrogen Species Group supervised by Dr Ivonne Trebs