3.2 Terrestrial Carbon Cycling and Storage
3 min read•july 25, 2024
Carbon cycles through terrestrial ecosystems via and . Plants absorb CO2, converting it to glucose, while respiration breaks down organic matter, releasing CO2. These processes, along with soil carbon dynamics, drive the flow of carbon on land.
Factors like land use, climate change, and ecosystem-specific responses affect carbon storage. Ecosystems can act as carbon sinks or sources, influenced by mechanisms like CO2 fertilization, permafrost thaw, and wildfires. Understanding these dynamics is crucial for managing terrestrial carbon.
Terrestrial Carbon Cycling Processes
Photosynthesis and respiration processes
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- Photosynthesis
- Light-dependent reactions absorb light energy via chlorophyll split water molecules generate ATP and NADPH
- Light-independent reactions (Calvin cycle) fix carbon using RuBisCO enzyme reduce carbon dioxide to glucose
- Net reaction:
- Respiration
- Glycolysis breaks down glucose in cytoplasm produces pyruvate
- Citric acid cycle (Krebs cycle) oxidizes pyruvate in mitochondria generates NADH and FADH2
- Electron transport chain performs oxidative phosphorylation produces ATP
- Net reaction:
Soil carbon in terrestrial cycles
- (SOC) composition includes living dead plant material and humus
- Carbon input mechanisms involve plant litter deposition root exudates and microbial biomass turnover
- Carbon storage forms comprise and
- Soil carbon dynamics encompass processes and stabilization mechanisms (physical protection chemical recalcitrance organo-mineral associations)
- Soil carbon fluxes include CO2 efflux from soil respiration and dissolved organic carbon leaching
Factors Affecting Terrestrial Carbon Storage
Factors affecting carbon storage
- impacts
- reduces aboveground biomass increases soil erosion
- Agricultural conversion alters soil structure through tillage changes soil organic matter content
- Urbanization causes soil sealing and compaction alters hydrological cycles
- Climate change effects
- Temperature increase enhances decomposition rates extends growing seasons
- Precipitation changes alter plant productivity impact soil moisture and microbial activity
- Extreme weather events (droughts floods) release carbon and cause erosion
- Ecosystem-specific responses
- Forest ecosystems experience tree species composition shifts and fire regime alterations
- Grassland ecosystems undergo woody plant encroachment and grazing intensity changes
- Wetland ecosystems face peatland degradation and sea-level rise impacts on coastal areas
Ecosystems as carbon sinks vs sources
- Carbon sink mechanisms
- Enhanced vegetation growth from CO2 fertilization
- Increased nitrogen deposition effects
- Reforestation and afforestation efforts (planting new )
- Carbon source processes
- Thawing permafrost releases methane
- Increased wildfire frequency and intensity
- Accelerated organic matter decomposition
- Ecosystem-specific sink/source potential
- Tropical forests highly productive but vulnerable to deforestation
- Boreal forests store large in soils and biomass
- Temperate have high belowground carbon storage capacity
- accumulate carbon long-term in anaerobic conditions
- Feedback loops
- Positive feedbacks amplify carbon release (melting permafrost releases more greenhouse gases)
- Negative feedbacks stabilize carbon stocks (increased plant growth absorbs more CO2)
- Carbon budget considerations
- Net ecosystem exchange (NEE) measures carbon flux between ecosystem and atmosphere
- Net biome productivity (NBP) accounts for disturbances and lateral carbon fluxes
- Management strategies for enhancing
- Improved agricultural practices (no-till farming cover crops)
- Forest management techniques (selective logging fire management)
- Restoration of degraded ecosystems (wetland restoration reforestation)
Key Terms to Review (20)
Biomass: Biomass refers to the total mass of living organisms in a given area or volume, typically measured in terms of carbon content. It plays a critical role in ecological systems, as it serves as a primary source of energy and nutrients for various organisms, and is a key component in understanding energy flow and matter cycling. The transformation and storage of biomass directly impact carbon cycling and influence the composition and quality of organic matter within ecosystems.
Carbon dioxide exchange: Carbon dioxide exchange refers to the process through which carbon dioxide (CO₂) is absorbed and released by terrestrial ecosystems, primarily through photosynthesis, respiration, and decomposition. This exchange is crucial in regulating atmospheric CO₂ levels, influencing climate change, and maintaining the balance of carbon in the environment. The efficiency of this exchange varies among different ecosystems and plays a significant role in how terrestrial carbon cycling and storage function.
Carbon Sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO2) to mitigate climate change. This process can occur naturally through biological systems or artificially through technology, significantly impacting carbon reservoirs, fluxes, and overall climate dynamics.
Carbon Stocks: Carbon stocks refer to the total amount of carbon stored in different reservoirs, such as forests, soils, and oceans, at a given time. Understanding carbon stocks is essential for evaluating the capacity of terrestrial ecosystems to sequester carbon, influencing global climate regulation and the carbon cycle. These stocks can change over time due to factors like land use, climate change, and natural disturbances, making them a crucial component in assessing carbon cycling and storage.
Decomposition: Decomposition is the biological and chemical process by which organic matter is broken down into simpler organic and inorganic materials, releasing nutrients back into the environment. This process plays a crucial role in nutrient cycling, influencing soil health, carbon storage, and ecosystem productivity.
Deforestation: Deforestation is the large-scale removal of trees from forests or other lands, typically resulting in damage to the quality of the land. This process significantly alters carbon reservoirs, influencing global carbon cycles and impacting various ecosystems, climate regulation, and biogeochemical processes.
Eddy Covariance: Eddy covariance is a method used to measure and analyze the exchange of gases, particularly carbon dioxide, between the atmosphere and terrestrial ecosystems. It involves using instruments to capture rapid fluctuations in wind speed and direction, along with gas concentrations, allowing researchers to quantify how much carbon is being absorbed or released by plants and soils over time. This technique is essential for understanding the dynamics of terrestrial carbon cycling and storage.
Forests: Forests are large areas covered predominantly by trees, which play a critical role in the Earth's ecosystem by acting as significant carbon sinks. They store vast amounts of carbon in their biomass and soils, making them essential for regulating the global carbon cycle and mitigating climate change. The health and structure of forests are influenced by factors such as climate, soil types, and human activities, all of which affect their capacity to sequester carbon over time.
Grasslands: Grasslands are vast, open areas dominated by grasses and occasional shrubs or trees, characterized by low rainfall and distinct seasonal changes. These ecosystems play a vital role in carbon cycling and storage, as they sequester carbon in their rich soil and biomass, impacting global carbon dynamics. They support diverse plant and animal life and are essential for maintaining ecological balance and providing resources for human populations.
Herbert Bormann: Herbert Bormann was an influential ecologist known for his work in forest ecology and biogeochemistry, particularly in understanding carbon cycling in terrestrial ecosystems. His research emphasized the role of forests in sequestering carbon and the impact of human activity on these processes, making significant contributions to our understanding of how carbon is stored and cycled within ecosystems.
James E. Lovelock: James E. Lovelock is a British scientist, environmentalist, and futurist known for proposing the Gaia hypothesis, which suggests that the Earth functions as a self-regulating system that maintains conditions suitable for life. His work has significantly contributed to understanding how different components of the Earth system interact, particularly in relation to carbon cycling and storage in terrestrial ecosystems.
Land use change: Land use change refers to the alteration of the natural landscape as a result of human activities, impacting ecosystems, biodiversity, and biogeochemical processes. These changes often involve converting forests to agriculture, urban development, or infrastructure, significantly affecting carbon cycling, nutrient dynamics, and water cycles. The consequences of land use change are critical in understanding how human actions influence ecological balance and the global environment.
Mineral-Associated Organic Matter: Mineral-associated organic matter refers to the fraction of organic matter in soils that is bound to mineral particles, particularly clay and silt. This association plays a crucial role in the terrestrial carbon cycle, as it stabilizes carbon compounds and influences their availability for microbial degradation. Understanding this relationship is essential for grasping how carbon is stored and cycled within terrestrial ecosystems.
Net Primary Productivity: Net primary productivity (NPP) is the rate at which plants in an ecosystem produce usable energy through photosynthesis, minus the energy they expend for respiration. This measure indicates how much organic matter is available to support herbivores and higher trophic levels, playing a crucial role in carbon cycling. Understanding NPP helps in assessing ecosystem health and functioning, as it reflects both the amount of carbon captured and the efficiency of plants to convert sunlight into biomass.
Particulate Organic Matter: Particulate organic matter (POM) refers to the fraction of organic material that is composed of small particles, typically ranging in size from 1 micrometer to 1 millimeter. This material originates from the decomposition of plant and animal residues, and plays a vital role in terrestrial ecosystems by influencing nutrient cycling, soil structure, and carbon storage. POM acts as a source of energy and nutrients for a variety of organisms within the soil and aquatic environments, contributing significantly to the overall carbon balance in these systems.
Peatlands: Peatlands are wetland ecosystems characterized by the accumulation of peat, a type of soil made up of partially decayed organic matter. These unique environments play a crucial role in carbon storage and are significant for biodiversity, hydrology, and climate regulation due to their ability to sequester carbon dioxide from the atmosphere and store it in the form of peat over thousands of years.
Photosynthesis: Photosynthesis is the biological process through which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This process is essential for producing oxygen and organic compounds that serve as food for various organisms, linking it to vital ecological and biogeochemical cycles.
Respiration: Respiration is a biochemical process in which organisms convert nutrients, primarily glucose, into energy in the form of ATP, while releasing waste products such as carbon dioxide and water. This process is crucial for the survival of living organisms and connects to various cycles and interactions within Earth's systems, affecting everything from energy flow to carbon storage.
Soil Organic Carbon: Soil organic carbon (SOC) refers to the carbon component of organic matter found in the soil, which includes decomposed plant and animal materials, microbial biomass, and various organic compounds. SOC plays a crucial role in terrestrial ecosystems, influencing soil fertility, structure, and the overall carbon cycling processes. It serves as a key indicator of soil health and is significant for understanding how carbon is stored and transformed in terrestrial environments.
Soil Respiration Measurements: Soil respiration measurements refer to the quantification of carbon dioxide (CO₂) emissions from the soil, which results from microbial activity and root respiration. This process is essential for understanding carbon cycling in terrestrial ecosystems, as it indicates the balance between carbon input through organic matter decomposition and carbon output to the atmosphere. Accurate measurements provide insights into soil health, ecosystem productivity, and the potential impacts of climate change on carbon storage in soils.