What Role Do Bacteria Play In The Nitrogen Cycle – Effect of forage plant mixture and use of biostimulants on yield, changes in botanical composition and microbiological soil activity

The effect of biochar-based organic amendments on the structure of soil bacterial communities and yield of maize (Zea mays L.)

What Role Do Bacteria Play In The Nitrogen Cycle

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What Are Soil Microbes & Why Do They Matter?

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Nitrogen Cycle In Aquariums: Timeline & Cycling

By Aleksandra Grzyb Aleksandra Grzyb Scilit Preprints.org Google Scholar View Publications , Agnieszka Wolna-Maruwka Agnieszka Wolna-Maruwka Scilit Preprints.org Google Scholar View Publications * and Alicja Niewiadomska Alicja Niewiadomska Scilit Preprints.org Google Scholar View Publications

Received: 18 June 2021 / Revised: 12 July 2021 / Accepted: 13 July 2021 / Published: 15 July 2021

Nitrogen (N) is widely distributed in the lithosphere, hydrosphere, atmosphere and biosphere. It is a fundamental component of every plant cell as well as microorganisms, as a component of proteins, nucleic acids and chlorophyll. It enters the soil with organic and mineral fertilizers, plant and animal residues and biological nitrogen fixation. There are different forms of nitrogen in the soil, and this element is usually converted by microorganisms. The conversion of nitrogen compounds (ammonification, nitrification and immobilization) is significantly influenced by climatic conditions and the physico-chemical properties of the soil. Microbial mineralization of organic nitrogenous matter results in the enrichment of the soil with this element, which is necessary to generate a yield. The amount of nitrogen that enters the soil through mineralization of crop residues varies from 15 to 45 kg N/ha in cereal residues and from 80 to 144 kg N/ha in winter rape residues. Biological nitrogen fixation can increase the nitrogen content in the soil by 30-50 kg/ha/year. In recent decades, poor management of mineral fertilizers has drastically changed the natural balance of the nitrogen cycle. Every year, huge amounts of nitrogen compounds enter the aquatic ecosystems and cause their eutrophication. Therefore, it is important to have sufficient knowledge about sustainable fertilization in order to practice integrated crop management.

In the natural environment, nitrogen is distributed between the atmosphere, the soil and the biomass of microorganisms. The total nitrogen content of mineral soils usually varies from 0.02% to 0.3%, which corresponds to about 600–9000 kg N/ha in the topsoil. Only a small part of the total nitrogen content in the soil, i.e. less than 5%, is directly available to plants [1]. The largest amount of this element in mineral soil can be found at humus horizons. After that, the content drops rapidly into deeper layers in the soil profile. In general, about 90% of the nitrogen in arable soils is combined with organic matter in the form of amino acids (about 60%), amino sugars (5%-15%), amide nitrogen (up to 15%) and non-hydrolysable nitrogen (up to 30% ). The remaining 10% of the nitrogen content is in mineral forms [2, 3]. Dinitrogen is a gas that makes up 79% of the Earth’s atmosphere, and it is by far the most abundant form of nitrogen in the biosphere. However, most organisms, including plants, cannot absorb nitrogen in this form. It can only be absorbed after soil microorganisms have converted it to NH

Bacteria And Humans

Nitrogen is a fundamental element in every living cell because it is a component of nucleic acids (DNA, RNA), proteins, membrane lipids, ATP, NADH, NADPH and photosynthetic pigments. According to Kopcewicz et al. [5] and Zboińska [6], it is also a component of acyl residues (coenzyme A), cytochromes, cytokinins and some vitamins, as well as secondary plant metabolites, such as alkaloids, betalains, mustard oils and cyanogenic glycosides.

Nitrogen enters the soil through mineral and organic fertilizers (manure, crop residues) and as a result of biological fixation of elemental nitrogen by symbiotic and free-living bacteria [7, 8]. Plants absorb two forms of nitrogen: ammonium (NH

). The absorption also depends on the plant’s development phase and temperature. In early stages of development and lower temperatures, plants take up mainly ammonium nitrogen. In acidic soils, the nitrate form is absorbed better, whereas the ammonium form in neutral soil. No other element necessary for life has as many forms in the soil as nitrogen and is transformed by microorganisms [9]. According to Lamb et al. [10], the circulation of nitrogen in the environment involves six microbiological processes, viz. atmospheric nitrogen fixation, mineralisation, immobilisation, nitrification, denitrification and anaerobic ammonium oxidation (anammox), which are significantly influenced by the soil’s physico-chemical properties and climatic conditions. . Soil microorganisms are very sensitive to changes in environmental conditions, such as soil water content and pH, temperature, plant cover type, and soil type, and their activity also depends on agricultural management practices [ 11 , 12 , 13 ].

Microorganisms play a key role in the nitrogen transformation cycle because they have genes encoding enzymes involved in nitrogen metabolism, which are used as indicators of the potential of this cycle [14]. The following microbial marker genes that affect the conversion rate of nitrogen compounds have been studied most often: nifH (encodes nitrogenase reductase), amoA (encodes ammonia monooxygenase), nirK and nirS (encodes nitrite reductase) and nosZ (encodes nitrous oxide [which encodes for nitric oxide reductase) 15, 16, 17]. According to Levy-Booth [18], the characterization of functional genes involved in the biogeochemical cycle of nitrogen helps to relate groups of microorganisms directly to the transformation processes of this element. According to Geisseler et al. [19], the understanding of microbial nitrogen transformations is necessary to find the right nitrogen management methods and to understand their influence on ecosystem productivity.

Understanding The Microbiome

Since plants have a very high demand for nitrogen, the availability of this element is often the most important factor limiting their growth and development. Therefore, more than 110 million tonnes of nitrogen are added to agricultural land around the world every year, including 15 million tonnes in Europe. Globally, wheat and corn consume 32%, while oil plants consume 10% of nitrogen. The annual nitrogen consumption in Poland is 70 kg/ha, which gives a grain yield of 4.2 t/ha [20, 21, 22, 23].

An incorrect balance of nutrients can have negative effects on plants, because neither nitrogen deficiency nor its excess is good for them. An insufficient supply of nitrogen results in stunted growth of plants that are poorly branched and have a low root-to-shoot ratio. Their leaves are small and thin, with signs of chlorosis. The first symptoms of nitrogen deficiency appear on older leaves and they gradually spread to higher leaves on the shoot. Furthermore, a nitrogen deficiency results in fewer flowering shoots (spikes), limited flower bud production and faster flowering, which results in fewer flowers (caryopses per spike). Consequently, there is lower seed weight, lower protein content in seeds and lower useful yield. An excess of nitrogen also negatively affects the yield and quality of crops. Excessive fertilization causes delayed and irregular flowering of plants. The shoots are thick and finish their growth late, delaying harvest time. The leaves are large, thick, dark green and susceptible to many fungal diseases, and they are willingly inhabited by pests. Cereals, corn and canola are susceptible to lodging. Excessive nitrogen fertilization of canola results in an overgrowth of vegetative organs, such as stems and leaves, and a decrease in the number of generative organs, ie. siliquae. In addition, excessive nitrogen fertilization of winter canola in the fall reduces its winter hardiness. Too high doses of nitrogen stimulate the rapid growth and development of new organs in plants. The process involves consumption of sugars that should be stored for winter. As a result, canola plants are poorly hardened, wilting and over-hydrated, increasing their sensitivity to frost. Excess nitrogen also contributes to the accumulation of harmful nitrates in root vegetables (carrot, beet, radish, celery, etc.) and leafy vegetables (lettuce, cabbage, spinach, parsley, etc.). Extremely large amounts of nitrogen fertilizer cause the shoot tips and youngest leaves to dry out. As a result, the useful yield of crops decreases [24, 25, 26, 27, 28].

The natural nitrogen cycle is disturbed by man-made factors, such as the use of nitrogen-containing mineral fertilizers,

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