Terrestrial biological carbon cycle

Last updated April 24, 2024

The carbon cycle is an essential part of life on Earth. About half the dry weight of most living organisms is carbon.^{[ citation needed ]} It plays an important role in the structure, biochemistry, and nutrition of all living cells. Living biomass holds about 550 gigatons of carbon,^[1] most of which is made of terrestrial plants (wood), while some 1,200 gigatons of carbon are stored in the terrestrial biosphere as dead biomass.^[2]

Carbon is cycled through the terrestrial biosphere with varying speeds, depending on what form it is stored in and under which circumstances.^[3] It is exchanged most quickly with the atmosphere, although small amounts of carbon leave the terrestrial biosphere and enter the oceans as dissolved organic carbon (DOC).

Movement of carbon in the terrestrial biosphere

Most carbon in the terrestrial biosphere is stored in forests: they hold 86% of the planet's terrestrial above-ground carbon and forest soils also hold 73% of the planet's soil carbon.^[4] Carbon stored inside plants can be transferred into other organisms during plant consumption. When animals eat plants, for example, the organic carbon stored in the plants is converted into other forms and utilized inside the animals. The same is true for bacteria and other heterotrophs. Dead plant material in or above soils remains there for some time before being respired by heterotrophs. Thus carbon is transferred in every step of the food chain from one organism to another.

Carbon exchange between the terrestrial biosphere and other systems

Atmosphere

Autotrophs, such as trees and other green plants, use photosynthesis to convert carbon dioxide during primary production, releasing oxygen in the process. This process occurs most quickly in ecosystems with high amounts of growth, such as in young forests. Because carbon is consumed in the process of autotrophic growth, more carbon is consumed in spring and summer during daytime than in winter and at night, when photosynthesis no longer takes place in most plants. Carbon storage in the biosphere is influenced by a number of processes on different time-scales: while carbon uptake through autotrophic respiration follows a diurnal and seasonal cycle, carbon can be stored in the terrestrial biosphere for up to several centuries, e.g. in wood or soil.

Most carbon leaves the terrestrial biosphere through respiration. When oxygen is present, aerobic respiration occurs, producing carbon dioxide. If oxygen is not present, e.g. as is the case in marshes or in animals' digestive tracts, anaerobic respiration can occur, which produces methane. About half of the gross primary production is respired by plants directly back into the atmosphere. Part of the net primary production, or the remaining carbon absorbed by the biosphere, is emitted back into the atmosphere through fires and heterotrophic respiration. The rest is converted into soil organic carbon, which is released more slowly, or "inert" dissolved carbon, which can remain in the biosphere for an unknown period of time.^[3]

This can be a very vital aspect to have in life as it will work to promote all kinds of living things to co-exist within an ecosystem. The role of Carbon within a Terrestrial Ecosystem consists of Carbon being stored within plants which will eventually be deposited in other forms for other organisms to absorb and consume.

Geosphere

Carbon in the terrestrial biosphere enters the geosphere only through highly specialized processes. When anaerobic decomposition converts organic material into hydrocarbon rich materials and is then deposited as sediment, the carbon can enter the geosphere through tectonic processes and remain there for several million years. This process can lead to the creation of fossil fuels.

Anthropogenic influences

Human activity has large effects on the terrestrial biosphere, changing the way that it acts as a carbon reservoir. Anthropogenically caused fires release large amounts of carbon as CO₂ directly into the atmosphere. More significantly, however, humans modify land cover. Land cover change greatly decreases the amount of carbon uptake in the terrestrial biosphere. It modifies the local ecosystem, often replacing carbon-rich forest with agricultural or urban land use. This releases the carbon stored in the former land cover type and simultaneously decreases the biosphere's ability to absorb carbon from the atmosphere.

Indirectly, human-induced changes in the global climate cause widespread modifications to the terrestrial ecosystem's function in the carbon cycle. As local climates transition, locations that have long been conducive to one type of ecosystem can become more favorable for other ecosystem types. For example, warming in the Arctic has caused stress in North American boreal forests,^[5] thus decreasing primary production and carbon uptake, while the same warmer temperatures have led to increased shrub growth in the same areas,^[6] producing an opposite effect. Changes in weather patterns can also affect animals. For example, changed weather patterns may create favorable conditions for pine beetles, leading to large beetle outbreaks and forest destruction.^[7] Modified precipitation patterns can also lead to droughts or extreme precipitation events, causing additional stress for ecosystems and more erosion. Not only do such influences on the terrestrial ecosystem modify its carbon exchange with the atmosphere - they also can lead to increased outwashing of carbon into the oceans through the transport of organic material in rivers. These widespread changes in land cover also causes changes to the planetary albedo, inducing complex feedbacks in the Earth's planetary radiation budget.

Higher CO₂ levels in the atmosphere can cause photosynthesis to take place more efficiently, thus increasing plant growth and primary production. This could lead to the biosphere extracting more carbon dioxide from the atmosphere. How long this carbon would remain sequestered in the terrestrial biosphere before being rereleased into the atmosphere is unclear, however, and it is likely that other limiting factors (e.g. nitrogen availability, moisture, etc.) would prevent CO₂ fertilization from significantly increasing primary production.

Related Research Articles

A carbon sink is a natural or artificial process that "removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere". These sinks form an important part of the natural carbon cycle. An overarching term is carbon pool, which is all the places where carbon on Earth can be, i.e. the atmosphere, oceans, soil, plants, and so forth. A carbon sink is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.

An ecosystem is a system that environments and their organisms form through their interaction. The biotic and abiotic components are linked together through nutrient cycles and energy flows.

The carbon cycle is that part of the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycle. Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. The carbon cycle comprises a sequence of events that are key to making Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration (storage) to and release from carbon sinks.

In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

Energy flow is the flow of energy through living things within an ecosystem. All living organisms can be organized into producers and consumers, and those producers and consumers can further be organized into a food chain. Each of the levels within the food chain is a trophic level. In order to more efficiently show the quantity of organisms at each trophic level, these food chains are then organized into trophic pyramids. The arrows in the food chain show that the energy flow is unidirectional, with the head of an arrow indicating the direction of energy flow; energy is lost as heat at each step along the way.

A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is transformed and cycled by living organisms and through various geological forms and reservoirs, including the atmosphere, the soil and the oceans. It can be thought of as the pathway by which a chemical substance cycles the biotic compartment and the abiotic compartments of Earth. The biotic compartment is the biosphere and the abiotic compartments are the atmosphere, lithosphere and hydrosphere.

<span class="mw-page-title-main">Ecosystem ecology</span> Study of living and non-living components of ecosystems and their interactions

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.

Carbon sequestration is the process of storing carbon in a carbon pool. It plays a crucial role in mitigating climate change by reducing the amount of carbon dioxide in the atmosphere. There are two main types of carbon sequestration: biologic and geologic. Biologic carbon sequestration is a naturally occurring process as part of the carbon cycle. Humans can enhance it through deliberate actions and use of technology. Carbon dioxide is naturally captured from the atmosphere through biological, chemical, and physical processes. These processes can be accelerated for example through changes in land use and agricultural practices, called carbon farming. Artificial processes have also been devised to produce similar effects. This approach is called carbon capture and storage. It involves using technology to capture and sequester (store) CO^₂ that is produced from human activities underground or under the sea bed.

In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of carbon dioxide (CO₂) in the atmosphere is 421 ppm as of May 2022 (0.04%). This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity. Burning fossil fuels is the main cause of these increased CO₂ concentrations and also the main cause of climate change. Other large sources of CO₂ from human activities include cement production, deforestation, and biomass burning.

Soil respiration refers to the production of carbon dioxide when soil organisms respire. This includes respiration of plant roots, the rhizosphere, microbes and fauna.

Soil carbon is the solid carbon stored in global soils. This includes both soil organic matter and inorganic carbon as carbonate minerals. It is vital to the soil capacity in our ecosystem. Soil carbon is a carbon sink in regard to the global carbon cycle, playing a role in biogeochemistry, climate change mitigation, and constructing global climate models. Natural variation such as organisms and time has affected the management of carbon in the soils. The major influence has been that of human activities which has caused a massive loss of soil organic carbon. An example of human activity includes fire which destroys the top layer of the soil and the soil therefore get exposed to excessive oxidation.

This is a glossary of environmental science.

The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.

Carbon dioxide removal (CDR) is a process in which carbon dioxide is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in products. This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated into climate policy, as an element of climate change mitigation strategies. Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then—in addition—the use of CDR. In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.

Ecosystem respiration is the sum of all respiration occurring by the living organisms in a specific ecosystem. The two main processes that contribute to ecosystem respiration are photosynthesis and cellular respiration. Photosynthesis uses carbon-dioxide and water, in the presence of sunlight to produce glucose and oxygen whereas cellular respiration uses glucose and oxygen to produce carbon-dioxide, water, and energy. The coordination of inputs and outputs of these two processes creates a completely interconnected system, constituting the underlying functioning of the ecosystems overall respiration.

In ecology, the term productivity refers to the rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume per unit of time, such as grams per square metre per day. The unit of mass can relate to dry matter or to the mass of generated carbon. The productivity of autotrophs, such as plants, is called primary productivity, while the productivity of heterotrophs, such as animals, is called secondary productivity.

The atmospheric carbon cycle accounts for the exchange of gaseous carbon compounds, primarily carbon dioxide, between Earth's atmosphere, the oceans, and the terrestrial biosphere. It is one of the faster components of the planet's overall carbon cycle, supporting the exchange of more than 200 billion tons of carbon in and out of the atmosphere throughout the course of each year. Atmospheric concentrations of CO₂ remain stable over longer timescales only when there exists a balance between these two flows. Methane, Carbon monoxide (CO), and other human-made compounds are present in smaller concentrations and are also part of the atmospheric carbon cycle.

<span class="mw-page-title-main">Oceanic carbon cycle</span> Ocean/atmosphere carbon exchange process

The oceanic carbon cycle is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both inorganic carbon and organic carbon. Part of the marine carbon cycle transforms carbon between non-living and living matter.

Lake metabolism represents a lake's balance between carbon fixation and biological carbon oxidation. Whole-lake metabolism includes the carbon fixation and oxidation from all organism within the lake, from bacteria to fishes, and is typically estimated by measuring changes in dissolved oxygen or carbon dioxide throughout the day.

Net ecosystem production (NEP) in ecology, limnology, and oceanography, is the difference between gross primary production (GPP) and net ecosystem respiration. Net ecosystem production represents all the carbon produced by plants in water through photosynthesis that does not get respired by animals, other heterotrophs, or the plants themselves.

References

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