Biological Nitrogen Fixation: Perspectives and Limitations

Mini Case Study
>PBL
Perspectives and Limitations of
Biological Nitrogen Fixation
Learning objective
 Elaborate and expound the chances of increasing nitrogen fixation through working on the plant host,
regulation of various agronomic methods as well as microbial symbiont
Background
Nitrogen is one of the most important nutrients of a plant. The sustainability of the earth has greatly been
influenced by the ever increasing population of human beings and the advancements in agricultural
productivity. The sharp increase in the use of nitrogen fertilizer that was experienced between the period 1960
and 2000 through elaborate agricultural practice have resulted into numerous environmental issues. Since
nitrogen normally limits the primary limits of most of the ecosystems, great variations in nitrogen availability
may result in numerous alterations of the nitrogen cycle not only in the aquatic but also terrestrial ecosystems
(Heilmann‐Clausen et al., 2015). KIMSA has developed interest in improving nitrogen fixation through the use
of natural biological processes.
Fig. 1(a): Biological Nitrogen Fixation process Fig. 1(b): Nitrogen over use effect: Eutrophication: Extracted
from https://www.nature.com/articles/srep02579
Nitrogen fixation is one of the most important processes in the nitrogen cycle. Chemical nitrogen fixation is one
of the greatest industries that at the moment generate to the tune of more than 85 million metric tonnes of fixed
nitrogen around the globe. Industrial fixation of nitrogen gas exponentially enhanced since the 1940s and the
activity of human beings has led to a lest double the amount of global nitrogen fixations to meets the human
needs for fibre, food energy among other products (Montañez, 2000). Chemical nitrogen fixation leads to
devastating impacts on the ecosystems, situation that calls for an alternative to the situation to check on the
amount of nitrogen in the atmosphere.
 1. Which of the following bacteria is not a nitrogen-fixing bacterium? (1 mark)
A. Cyanobacteria
B. Clostridium
C. Streptococcus
D. Azotobacter
 2. Looking at the graph below is there a significant greater height and root diameter of plant that is treated
with N fertilizer in comparison with that which is not treated? Explain. What is the effect of treating the
plant with both P and N? (3 marks)
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Figure 2: Combined and individual effect of NP on the height and collar diameter of Acer mono seedling: Extracted from
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0171321
 3. A study was carried out to by farmers to gain an understanding of the need of N by plants and the role N
plays in plants as shown in the diagram below. Looking at figure 3, do you think N is a necessity for growth of
plants? (2 marks)
Figure 3: Nitrogen deficiency in plants: Extracted from: http://www.knowledgebank.irri.org/training/fact-sheets/nutrient-
management/deficiencies-and-toxicities-fact-sheet/item/nitrogen-deficiency
 4. Nitrogen is often available to the plants in the form of nitrates, ammonia in the form of ammonium ion as
well as in the form of nitrogen gas. Nitrate and ammonia are often available to the plants form the soil whereas
nitrogen gas is often available only after reduction. Which organisms reduce nitrogen gas to a form that is
available to plants? What makes it difficult to break the N-N bonds? (Paul, 2014)
 5 There is a close linkage between carbon dioxide assimilation and nitrate assimilation in the various plants
with photosynthesis that offers the backbones of carbon that we used in the synthesis of carbon as well as the
assimilation of nitrogen which is provides the required nitrogen (Peng et al., 2018). How are carbon and
nitrogen assimilation linked? (2 marks)
Figure 4: Schematic diagram of nitrate assimilation: Extracted from
https://academic.oup.com/jxb/article/53/370/905/537240
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