Give an account of carbon cycle in an ecosystems (long answer)
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INTRODUCTION
Carbon is a constituent of all terrestrial life. Carbon begins its cycle through forest ecosystems when plants assimilate atmospheric CO2 through photosynthesis into reduced sugars (Fig. 3.1). Usually about half the gross photosynthetic products produced (GPP) are expended by plants in autotrophic respiration (Ra) for the synthesis and maintenance of living cells, releasing CO2 back into the atmosphere. The remaining carbon products (GPP − Ra) go into net primary production (NPP): foliage, branches, stems, roots, and plant reproductive organs. As plants shed leaves and roots, or are killed, the dead organic matter forms detritus, a substrate that supports animals and microbes, which through their heterotrophic metabolism (Rh) release CO2 back into the atmosphere. On an annual basis, undisturbed forest ecosystems generally show a small net gain in carbon exchange with the atmosphere. This represents net ecosystem production (NEP). The ecosystem may lose carbon if photosynthesis is suddenly reduced or when organic materials are removed as a result of disturbance (Chapter 6). Soil humus represents the major accumulation of carbon in most ecosystems because it remains unoxidized for centuries. It is the most important long-term carbon storage site in ecosystems. We delay discussion on soil humus until Chapter 4.
Figure 3.1 provides a general framework for modeling carbon flow through ecosystems and is the basis for organizing the material presented in this chapter. All of the environmental variables associated with modeling the water cycle (Chapter 2) are closely linked with the carbon cycle. Atmospheric carbon dioxide concentrations and the availability of soil nitrogen (N) must also be considered when modeling photosynthesis, carbon allocation, and respiration. Confidence in the reliability of models has greatly increased with the development of an eddy correlation technique that uses fast-response sensors to record the net exchange of CO2 and water vapor from forests and other types of terrestrial ecosystems.
As ecosystem scientists, we consider the exchange of carbon into the system through photosynthesis to be a positive flux and respiration to represent a loss to the atmosphere. Atmospheric scientists would consider the signs to be reversed. Net ecosystem exchange (NEE) measured during the daylight hours includes gross photosynthesis (Pg or GPP), photorespiration (Rp), maintenance respiration (Rm), and synthesis (growth) respiration (Rs) of autotrophic plants, as well as heterotrophic respiration (Rh) by animals and microbes:
(3.1)DayNEE=Pg−Rp−Rm−RS−Rh.
At night the photosynthetic terms, Pg and Rp, are absent:
(3.2)NightNEE=−Rm−Rs−Rh=−Re
where Re is total ecosystem respiration, exclusive of Rp. On a given day, Re is largely controlled by temperature, which allows us to make adjustments for its rise during daylight periods from values recorded at lower temperatures during the night. Gross ecosystem production (GEP) includes photorespiration, which is usually small, so GEP is often assumed to approximate Pg:
(3.3)GEP=DayNEE+DayRe=Pg−Rp≈GPP.
To separate the sources of respired CO2, a series of chambers are often installed and CO2 effluxes monitored at frequent intervals from soil, stem, branches, and leaves. Alternatively, respiration sources can be identified by monitoring the isotopic composition of carbon (δ13C) and oxygen (δ18O) in CO2 diffusing into the turbulent transfer steam. The scientific value of full system analyses with eddy correlation techniques has proved immense, particularly when conducted over a series of years (). Eddy-flux installations therefore serve for testing the underlying assumptions and accuracy of stand-level ecosystem models.
Among species (and genetic varieties), important differences exist in the pattern of carbon allocation. These differences affect competitive relationships (Chapter 5), the susceptibility of trees and other plants to various stresses (Chapter 6), as well as the annual carbon balance of a stand. Foresters have developed good empirical models to predict volume growth of trees and whole stands. These are helpful in supporting general assumptions built into stand-level ecosystem models; stem growth, however, is highly dependent on the fraction of NPP allocated to foliage versus roots, and so is difficult to predict as environmental conditions change seasonally and from site to site. Different theories that provide a basis for modeling carbon allocation are presented in this chapter. We will identify general principles governing the way the environment affects carbon allocation seasonally and over the course of a year, and apply these principles in later chapters.
Carbon is a constituent of all terrestrial life. Carbon begins its cycle through forest ecosystems when plants assimilate atmospheric CO2 through photosynthesis into reduced sugars (Fig. 3.1). Usually about half the gross photosynthetic products produced (GPP) are expended by plants in autotrophic respiration (Ra) for the synthesis and maintenance of living cells, releasing CO2 back into the atmosphere. The remaining carbon products (GPP − Ra) go into net primary production (NPP): foliage, branches, stems, roots, and plant reproductive organs. As plants shed leaves and roots, or are killed, the dead organic matter forms detritus, a substrate that supports animals and microbes, which through their heterotrophic metabolism (Rh) release CO2 back into the atmosphere. On an annual basis, undisturbed forest ecosystems generally show a small net gain in carbon exchange with the atmosphere. This represents net ecosystem production (NEP). The ecosystem may lose carbon if photosynthesis is suddenly reduced or when organic materials are removed as a result of disturbance (Chapter 6). Soil humus represents the major accumulation of carbon in most ecosystems because it remains unoxidized for centuries. It is the most important long-term carbon storage site in ecosystems. We delay discussion on soil humus until Chapter 4.
Figure 3.1 provides a general framework for modeling carbon flow through ecosystems and is the basis for organizing the material presented in this chapter. All of the environmental variables associated with modeling the water cycle (Chapter 2) are closely linked with the carbon cycle. Atmospheric carbon dioxide concentrations and the availability of soil nitrogen (N) must also be considered when modeling photosynthesis, carbon allocation, and respiration. Confidence in the reliability of models has greatly increased with the development of an eddy correlation technique that uses fast-response sensors to record the net exchange of CO2 and water vapor from forests and other types of terrestrial ecosystems.
As ecosystem scientists, we consider the exchange of carbon into the system through photosynthesis to be a positive flux and respiration to represent a loss to the atmosphere. Atmospheric scientists would consider the signs to be reversed. Net ecosystem exchange (NEE) measured during the daylight hours includes gross photosynthesis (Pg or GPP), photorespiration (Rp), maintenance respiration (Rm), and synthesis (growth) respiration (Rs) of autotrophic plants, as well as heterotrophic respiration (Rh) by animals and microbes:
(3.1)DayNEE=Pg−Rp−Rm−RS−Rh.
At night the photosynthetic terms, Pg and Rp, are absent:
(3.2)NightNEE=−Rm−Rs−Rh=−Re
where Re is total ecosystem respiration, exclusive of Rp. On a given day, Re is largely controlled by temperature, which allows us to make adjustments for its rise during daylight periods from values recorded at lower temperatures during the night. Gross ecosystem production (GEP) includes photorespiration, which is usually small, so GEP is often assumed to approximate Pg:
(3.3)GEP=DayNEE+DayRe=Pg−Rp≈GPP.
To separate the sources of respired CO2, a series of chambers are often installed and CO2 effluxes monitored at frequent intervals from soil, stem, branches, and leaves. Alternatively, respiration sources can be identified by monitoring the isotopic composition of carbon (δ13C) and oxygen (δ18O) in CO2 diffusing into the turbulent transfer steam. The scientific value of full system analyses with eddy correlation techniques has proved immense, particularly when conducted over a series of years (). Eddy-flux installations therefore serve for testing the underlying assumptions and accuracy of stand-level ecosystem models.
Among species (and genetic varieties), important differences exist in the pattern of carbon allocation. These differences affect competitive relationships (Chapter 5), the susceptibility of trees and other plants to various stresses (Chapter 6), as well as the annual carbon balance of a stand. Foresters have developed good empirical models to predict volume growth of trees and whole stands. These are helpful in supporting general assumptions built into stand-level ecosystem models; stem growth, however, is highly dependent on the fraction of NPP allocated to foliage versus roots, and so is difficult to predict as environmental conditions change seasonally and from site to site. Different theories that provide a basis for modeling carbon allocation are presented in this chapter. We will identify general principles governing the way the environment affects carbon allocation seasonally and over the course of a year, and apply these principles in later chapters.
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Answer:
Give an account of carbon cycle in an ecosystems.
Explanation:
- What is carbon cycle? Carbon cycle is the back bone of the ecosystem. The amount of Carbon which we had earlier on the Earth is same as of now. That means it is not added to taken down.
- When new life is formed carbon molecules like protein and DNA is formed.
- Carbon cycle is way of the nature for using carbon atoms. Most of the carbon atoms are stored in rock and sediments.
- If carbon cycle is being disturbed then there are serious consequences on climate.
- The steps of carbon cycle are- carbon moves from atmosphere to plants, then from plants to animals, then to soil, then it moves from living things to atmosphere, fossil fuels to atmosphere, atmosphere to fossil fuels.
- There are mainly six process in carbon cycle that is-photosynthesis, respiration, exchange, sedimentation, extraction and lastly combustion.
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