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The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.
A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high discharge. The soils usually consist of clays, silts, sands, and gravels deposited during floods.
A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica and are found in most ecoregions of the Earth. Furthermore, grasslands are one of the largest biomes on Earth and dominate the landscape worldwide. There are different types of grasslands: natural grasslands, semi-natural grasslands, and agricultural grasslands. They cover 31–69% of the Earth's land area.
The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.
Ecosystem ecology is the integrated study of living (biotic) and non-living (abiotic) components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals.
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Human impact on the nitrogen cycle is diverse. Agricultural and industrial nitrogen (N) inputs to the environment currently exceed inputs from natural N fixation. As a consequence of anthropogenic inputs, the global nitrogen cycle (Fig. 1) has been significantly altered over the past century. Global atmospheric nitrous oxide (N2O) mole fractions have increased from a pre-industrial value of ~270 nmol/mol to ~319 nmol/mol in 2005. Human activities account for over one-third of N2O emissions, most of which are due to the agricultural sector. This article is intended to give a brief review of the history of anthropogenic N inputs, and reported impacts of nitrogen inputs on selected terrestrial and aquatic ecosystems.
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The fungal loop hypothesis suggests that soil fungi in arid ecosystems connect the metabolic activity of plants and biological soil crusts which respond to different soil moisture levels. Compiling diverse evidence such as limited accumulation of soil organic matter, high phenol oxidative and proteolytic enzyme potentials due to microbial activity, and symbioses between plants and fungi, the fungal loop hypothesis suggests that carbon and nutrients are cycled in biotic pools rather than leached or effluxed to the atmosphere during and between pulses of precipitation.
Whendee Silver is an American ecosystem ecologist and biogeochemist.
Pamela H. Templer is an ecosystem ecologist and professor at Boston University who focuses on plant-microbial interaction and their effect on carbon exchange and nutrient cycling. She is also interested in examining how urban ecosystems function, how human actions influence nutrient cycling, atmosphere-biosphere interactions, and other ecosystem processes.
Elizabeth T. Borer is an American ecologist and a professor of ecology in the College of Biological Sciences at the University of Minnesota.
Ingrid C. "Indy" Burke is the Carl W. Knobloch, Jr. Dean at the Yale School of Forestry & Environmental Studies. She is the first female dean in the school's 116 year history. Her area of research is ecosystem ecology with a primary focus on carbon cycling and nitrogen cycling in semi-arid rangeland ecosystems. She teaches on subjects relating to ecosystem ecology, and biogeochemistry.
Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential, although some of them, such as silicon (Si), have been shown to improve nutrent availability, hence the use of stinging nettle and horsetail macerations in Biodynamic agriculture. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.
Kate Lajtha is an ecologist known for her use of stable isotopes to examine biogeochemical cycling in soils.
Bridget Emmett is a British ecologist, Professor and Science Area Head for the UK Centre for Ecology & Hydrology. She is the President of British Ecological Society from 2024.
References
- ↑ Stevens, Carly (2004). Ecosystem properties of acid grasslands along a gradient of nitrogen deposition. The Open University - PhD thesis. Retrieved 30 December 2020.
- ↑ "Carly Joanne Stevens". UK Research and Innovation. Retrieved 30 December 2020.
- ↑ Stevens, Carly J.; Dise, Nancy B.; Mountford, J. Owen; Gowing, David J. (2004). "Impact of nitrogen deposition on the species richness of grasslands". Science. 303 (5665): 1876–9. Bibcode:2004Sci...303.1876S. doi:10.1126/science.1094678. PMID 15031507. S2CID 37690774.
- ↑ "Report: CIEEM air pollution and biodiversity conference". Air Quality News. Retrieved 1 May 2021.
- ↑ Stokstad, Erik (2011). "Open-Source Ecology Takes Root Across the World". Science. 334 (6054): 308–309. Bibcode:2011Sci...334..308S. doi:10.1126/science.334.6054.308. PMID 22021835 . Retrieved 30 December 2020.
- ↑ "Nutrient Network: A Global Research Cooperative". The Nutrient Network. Retrieved 30 December 2020.
- ↑ "Professor Carly Stevens". University of Lancaster. Retrieved 29 December 2020.
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