The vast majority of carbon dioxide in the atmosphere, which is responsible for 60% of the total earth warming from greenhouse gases is caused by human activities such as burning fossil fuels and deforestation. Apart from these, organisms are also contributor to this effects, for example, earthworms. Eventhough earthworms are largely beneficial to soil fertility, they also increase net soil greenhouse-gas emissions. Earthworms play an essential part in determining the greenhouse-gas balance of soils worldwide . A study had reveal that earthworms can increase emissions of one greenhouse gas while reducing emissions of the other. Further researches had revealed that earthworms increased the global warming potential of soils by 16%. Earthworms can contribute to global warming by increasing greenhouse gas emissions from the soil, primarily carbon dioxide (CO2) and nitrous oxide (N2O). They do this through several mechanisms:
a. mixing organic matter,
b. enhancing microbial activity,
c. facilitating the release of gases from the soil,
d. and also play a role in carbon sequestration. Earthworms break down organic matter in the soil, a process that releases CO2 as a byproduct. Additionally, they mix organic matter, making it more accessible for decomposition and further boosting CO2 release. Their gut acts as a microbial incubator, boosting the activity of N2O-producing bacteria. Soil worm activity can increase N2O emissions by up to 42%, according to a study published in the journal Nature Communications. Also, earthworm burrows create pathways for greenhouse gases to escape the soil and enter the atmosphere.
IMPORTANCE OF EARTHWORMS. Earthworms are important decomposers in many ecosystems as they help to break down organic matter and release nutrients that can be used by plants and other organisms.
1. They are crucial for the functioning of many ecosystems
2. They play a vital role in supporting soil fertility and plant growth.
3. Their activity can also lead sometimes to the release of greenhouse gases (GHG), such as carbon dioxide (CO2) and nitrous oxide (N2O). According to the latest meta-analysis, earthworms can increase soil CO2 and N2O emissions by 33 and 42%, respectively. This is a great concern to the world as soil play important role in mitigating climate change through carbon (C) sequestration and N2O regulation.
4. Earthworms are referred to as ecosystem engineers due to the fact that they modify soil structure and interact with soil microorganisms and plants through their feeding, burrowing, and casting activities.
5. Earthworms stimulate carbon sequestration in the soil, which helps reduce greenhouse gas emissions.
6. Earthworms contribute to soil formation and nutrient cycling.
7. They regulate soil water pools and fluxes.
8. Earthworms, through physical mechanisms, breakdown silicate grains. Thus, increase exposed surface area and bioturbation, help distribute the silicate amendment in the soil.
9. Earthworms, through chemical mechanisms, stimulate mineral weathering due to
a. low pH environments in the earthworm guts.
b. increase in respiration during earthworm activities and associated increase of soil pCO2 .
c. chemical equilibrium occurence, where a solution lower in a particular dissolved cation promotes weathering of the cation from a solid.
10. Earthworms can excrete solid carbonates from oesophageal (calciferous) glands. Thus, they are refered to as base cation scavengers, .
11. Earthworms have also been shown to produce clay minerals through soil ingestion and excretion. CATEGORIES OF EARTHWORMS
Earthworms can be divided into three ecological categories based on their feeding and burrowing habits:
(1) ANECIC SPECIES : They feed on fresh litter from the soil surface and create mainly permanent burrows, (2) EPIGEIC SPECIES: They live on the soil surface and feed on surface litter without creating permanent burrows, and
(3) ENDOGEIC SPECIES : They live and feed on mineral soil and associated organic matter below the surface, and that create non-permanent burrows without preferential orientation.
The impact of earthworms on greenhouse gas (GHG) emissions is known to vary with the earthworm ecotype, with anecic earthworms stimulating the GHG emissions the most. However, the full understanding of their effect on GHG remains elusive due to multiple contrasting reports published by different researchers. FACTORS THAT AFFECT THE EFFECT OF EARTHWORMS ON GREEN HOUSE GAS EMMISSION
A variety of factors, including the earthworm ecological category, the type of soil, the amount and type of organic matter present etc affect the earthworm’s effects on GHG emissions. Earthworms can affect the soil CO2 emissions directly as a result of breaking down the soil and litter organic matter through digestive processes, releasing CO2 as a by-product, but also indirectly by incorporating plant residues into the soil, modulating the microbial-controlled decomposition of organic matter through changes in soil moisture dynamics, nutrient status, soil aggregation and CO2 diffusivity. In addition to these effects that mainly stimulate the CO2 release from soils, earthworms have also been suggested to induce long-term stabilization of soil C in casts by enhancing the stabilization of C relative to mineralization, but contrasting effects have also been found. Concerning the earthworm impact on the N2O emissions, the proposed mechanisms are both direct, such as the stimulation of denitrifier activity in the earthworm gut due to favorable conditions for denitrifying bacteria such as anaerobic conditions, availability of nitrogen (N) and C at favorable moisture levels, as well as indirect, including the stimulation of denitrifiers communities in the soil (as well as in the burrows, casts and middens) which can be further modulated by earthworms through incorporating plant residues in the soil and enhancing N and C mineralization as well as through burrowing effects on soil water infiltration and gas diffusivity. These later two effects could also reduce N2O emissions if they lead to less anaerobic microsites and increased soil aeration, which is detrimental to denitrifiers.
CONTRIBUTION OF EARTHWORMS TO GREENHOUSE GAS EMMISSION( CO2, N2O ) AND CARBON SEQUESTRATION
A research was carried out by team of scientists on how earthworm contribute to global warming. They found that the presence of earthworms increased nitrous oxide emissions from soil by 42 percent and carbon dioxide emissions from soil by 33 percent. But they found no indications that earthworms affect soil organic carbon stocks — the carbon stored within the soil.The researchers stated that the earthworms contribute to increase in greenhouse gas emissions due to the fact that: organic plant residues where mixed in the soil, which may increase decomposition and carbon dioxide emissions; the earthworm gut acts as a microbial incubator, boosting the activity of nitrous oxide-producing microbes; and the earthworms, by burrowing through the soil, make it easier for greenhouse gases in the soil to escape into the atmosphere.
CONTRIBUTION OF EARTHWORMS TO CO2 EMMISSION
Earthworms contribute to higher atmospheric carbon dioxide levels by stimulating the decomposition of organic matter in the soil. The earthworms ingest soil and organic matter, break it down through digestion and releasing carbon dioxide as a waste product. The released carbon dioxide is a byproduct of the decomposition process. They also increase soil aeration through their burrowing activities. They create channels and pores in the soil, increasing aeration and facilitating the escape of more CO2 from the soil into the atmosphere. In addition, they mix soil through their burrowing activities. They mix soil and organic matter, accelerating decomposition and releasing more CO2 to the atmosphere. Apart from these, they also enhance microbial activity in the soil, including microbes that produce nitrous oxide, a greenhouse gas.
CONTRIBUTION OF EARTHWORMS TO CARBON SEQUESTRATION
Over the past 150 years, the amount of carbon in the atmosphere hasincreased by 30%. Most scientists believe there is a direct relationshipbetween increased levels of carbon dioxide in the atmosphere andrising global temperatures.Most plants especially all green plants, through the process of photosynthesis, assimilate carbon and return some of it to the atmosphere through respiration.The carbon that remains in plant tissue is then consumed by animals or added to thesoil as litter when plants die and decompose. The primary way carbon is stored in the soil is as soil organic matter (SOM). SOM is a complex mixture of carbon compounds, consisting of decomposing plant and animal tissue,microbes (protozoa, nematodes, fungi, andbacteria), and carbon associated with soil minerals. These carbon, when released into the soil can remain stored in soils for millennia, or quickly released back into the atmosphere. Climatic conditions, natural vegetation, soil texture, and drainage etc, all affect the amount and length of the carbon sink in the soil. One important method to reduce atmospheric carbon dioxide is to increase the global storage of carbon in soils through those means that help sequester carbon. An added benefit to this solution is the potential for simultaneous enhancement in agricultural production. With this background knowledge about carbon release and storage, the following questions need to be answered.
1. What exactly is carbon sequestration, and what is its role in the global carbon cycle?
2. How can we manage soils to capitalize on their ability to store carbon? and
3. How is Carbon Sequestered in Soils?
CARBON SEQUESTRATION CARBON SEQUESTRATION IN SOILS
Carbon , a major component in all living organisms and also a major building block for life on Earth exists in many forms, predominately as plant biomass, soil organic matter, and as the gas- carbondioxide (CO2) in the atmosphere and that dissolved in seawater. In agricultural systems, the amount and length of time carbon is stored is determined predominately by how the soil resource is managed. A variety of agricultural practices that can enhance carbon storage include; Panting of crops to increase photosynthetic processes, Application of nitrogen fertilizer to increase soil organic matter, growing plants on semiarid lands etc. All can help increase carbon storage in soils.Plant tissues contain stored carbon. As Nitrogen fertilizers are applied to the soil, it increases carbon storage by increasing SOM. When nitrogen fertilizers are applied to soil, they increase SOM by increasing plant biomass and root development. Nitrogen fertilization can lead to more plant residues returning to the soil. It increases biomass of plants inform of residues (e.g., crop stalks, leaves, roots), which then decompose and contribute to soil organic matter pool. Additionally, nitrogen can influence microbial activity. It can influence microbial communities in the soil. Microbes play a crucial role in the decomposition of organic matter and the cycling of nutrients. It can stimulate microbial activity, leading to faster decomposition of plant residues and potentially increasing the amount of stable organic matter formed. And also, as the microbs die and decompose, the carbon in their tissues is released into the soil. Thus, increasing carbon storage in the soil.In the semi-arid regions, surface and groundwater contain high concentrations of dissolved calcium, and bicarbonate ions which are deposited in the soil, thus, releases CO2 into the atmosphere.Afforestation is another means of increasing carbon sequestration. As forests grow, they store carbon in woody tissues and soil organic matter. The net rate of carbon uptake is greatest when forests are young, and slows with time. Old forests can sequester carbon for a long time but provide essentially no net uptake.When forests are cut, the carbon they contain may be quickly returned to the atmosphere if the woodytissue is burned or converted to products, such as paper, that are short-lived. If the wood is used for construction or furniture, then those products retain carbon during their life-times and act as carbon sinks.
SIGNIFICANT BENEFIT OF ENHANCED CARBON STORAGE IN SOILS
1. Improved soil
2. Improve water quality
3. Decreased nutrient loss
4. Reduced soil erosion
5. Increased water conserva-tion
6. Greater crop production may result from increasing the amount of carbon stored in agriculturalsoils.
ROLE OF EARTHWORM IN CARBON SEQUESTRATION:
Earthworms enhance carbon sequestration by increasing the amount of carbon stored in the soil, primarily by facilitating the formation of stable soil aggregates. They create burrows and casts, formed from compacted soil and organic matter mixtures. These structures, especially macroaggregates (larger than 2 mm), help to protect and stabilize organic matter, thus increasing its persistence in the soil and reducing its decomposition.They also incorporate plant litter into the soil. They ingest and process the plant litter, dragging it deeper into the soil. This process not only returns carbon to the soil but also increases the contact between organic matter and mineral particles, which can improve carbon adsorption and stabilization. They also play a role in the mineralization and stabilization of organic matter, which influences the carbon cycle. They create favorable conditions for microbial growth within their burrows and casts. Microorganisms play a key role in the decomposition and mineralization of organic matter, and earthworms facilitate this process by providing a rich and readily available food source and a stable environment for these microbes. Earthworms also create unequal Amplification of carbon Stabilization. Studies suggest that earthworms may accelerate carbon stabilization more than they enhance carbon mineralization, leading to a net increase in carbon stored in the soil, according to a paper publication. And lastly, earthworms interact with plant species and influence plant productivity, which in turn affects carbon sequestration over longer time scales. For instance, earthworm activity can enhance nutrient cycling, leading to healthier plants that can more effectively capture and store carbon through photosynthesis.
CONTRIBUTION OF EARTHWORMS TO CARBON SEQUESTRATION
Carbon sequestration is the long-term storage of carbon in oceans, soils, vegetation (especially forests), and geologic formations. Among all the bodies on earth, the oceans store most of the Earth’s carbon. Soils contain approximately 75% of the carbon pool on land — three times more than the amount stored in living plants and animals.The anthropogenic emissions of gases like N2O in the post-industrial age is the main contributor to the rising concentration of gases in the atmosphere, and thereby to the greenhouse effect and the depletion of the stratospheric ozone layer .Approximately, one-third of anthropogenic N2O emissions originate from agricultural activities, predominantly through topsoil emissions. These emissions are mainly due to three microbial processes: (i) nitrification, (ii) denitrification; and (iii) nitrifier denitrification.
a. NITRIFICATION PROCESS
Nitrification does not directly cause carbon sequestration, but it can indirectly influence it by affecting soil health and the amount of carbon stored in the soil. Nitrification, the process by which ammonia is converted to nitrate by bacteria,
{Ammonia (NH3) is converted — nitrite (NO2-) is further converted — nitrate (NO3-) (a form of nitrogen that plants can readily absorb).}
can impact soil fertility, which in turn influences plant growth and carbon uptake through photosynthesis. Nitrification also has an indirect impact on carbon sequestration. Eventhough it improves soil health and nutrient availability, it can indirectly support plant growth and biomass production. Plants, through photosynthesis, absorb carbon dioxide from the atmosphere and convert it into organic matter (biomass), which when decompose as litters by the actions of microbes like earthworms, releases its tissue carbon into the soil which is then stored in the soil as organic carbon. A healthier soil, enriched with nutrients from nitrification, can support more robust plant growth and therefore enhance carbon sequestration. For example, in grasslands areas, nitrification can help increase the availability of nitrogen, allowing for more vigorous growth of grasses and root systems. This increased root growth can contribute to storing more carbon in the soil through the production of root biomass and the deposition of organic matter as the roots decay. From the above, nitrification generally supports carbon sequestration, excessive or improper use of nitrogen fertilizers can lead to other issues, such as nitrous oxide (N2O) emissions, a potent greenhouse gas. Another example can be found in the European union where Grasslands are occasionally ploughed and reseeded to maintain productivity, or as part of a rotation involving arable crops and grasses. These grasslands covers approximately 21% of the agricultural land surface and have been reported to be a very important source of N2O, both through emissions from urine and dung patches etc.
b. DENITRIFICATION PROCESSES
Denitrification is a natural process in the nitrogen cycle where bacteria convert nitrate (NO3-) into nitrogen gas (N2). The conversion of the nitrate to nitrogen gas does not directly cause carbon sequestration, but it plays a role in the overall carbon cycle and can indirectly impact carbon storage. It helps to remove nitrate from the soil and water, and return nitrogen to the atmosphere, which can influence other processes that contribute to carbon sequestration. The nitrate can supply nitrogen to plants to build their biomass and photosynthesize. Denitrification is the only process that can reduce the nitrate levels. It can impact plant growth and carbon uptake. It can also lead to emissions of greenhouse gases. The denitrification can also produce nitrous oxide (N2O), a potent greenhouse gas.
c. NITRIFIER DENITRIFICATION
The imbalance between total N inputs and outputs in agricultural systems has being a major concern to scientists and researchers for more than 50 years till date. They have not being able to quantify all sources of N2O, and unclear where all the N produced are going. There is now renewed interest in nitrifier denitrification, as this might, under some conditions, contribute to the loss of N from agricultural systems and be a major source of N2O and NO. Furthermore, interest in nitrifier denitrification is growing in wastewater treatment as new techniques such as OLAND (Oxygen-Limited Autotrophic Nitrification–Denitrification) and ANAMMOX (anaerobic ammonium oxidation) are based on nitrifier denitrification.Nitrifiers are chemoautotrophic microorganisms that utilize the energy from oxidizing ammonia and nitrite to fix carbon dioxide from the environment. This process contributes to the global carbon cycle by dissolved inorganic carbon (DIC) into biomass, and some of this fixed carbon may be released as dissolved organic carbon (DOC). This release can contribute to the overall pool of dissolved organic carbon in the environment. Nitrifier denitrification is a pathway of nitrification involving the oxidation of NH3 to NO2−, followed by the reduction of NO2− to N2O and finally to N2. This sequence of reactions is carried out by only one group of microorganisms, namely autotrophic NH3-oxidizers. Thus, nitrifier denitrification contrasts with coupled nitrification–denitrification, where different groups of coexisting microorganisms can together transform NH3 to finally N2. Earthworms activities of improving soil fertility is a good process, but with the good comes the bad, they also increase greenhouse gas emissions from soils. Thus, stimulate carbon sequestration in the soil. Earthworm Lumbricus terrestris contributes nitrous oxide emission from temperate agricultural soil regardless of applied mineral nitrogen fertilizer doses. Regardless of this, earthworms can contribute to increased N2O emissions from soil. Their activities primarily influences the dynamics within the soil, not necessarily the atmospheric concentration. They increase N2O emissions by mixing organic matter, creating more habitat for N2O-producing microbes in their guts and burrows, and facilitating the release of gases from the soil. In the guts are microbes. The microbes act as a microbial incubator in the guts, boosting the activity of denitrifying bacteria that produce N2O. In addition, earthworms churn and mix soil, exposing more organic matter to decomposition, which can lead to increased CO2 and N2O emissions. Their burrowing also create pathways for gases like N2O to escape the soil, leading to increased emissions.
EFFECT OF EARTHWORMS ON THE EMMISSION OF NITROUS OXIDE GREENHOUSE GAS
Earthworm activity have been reported to lead to increased production of the greenhouse gas nitrous oxide (N2O). This is due to emissions from worms themselves, their casts and drilosphere, as well as to general changes in soil structure. The three microbial processes involved in greenhouse gas emission: nitrification, denitrification; andnitrifier denitrification, result in the emmission of the greenhouse gas N2O.Soil organic matter (SOM), mineralization through ploughing leads directly to elevated CO2 emissions, and indirectly (through mineralization of N and through providing a C source for denitrification) to elevated N2O emissions.Incorporation of crop residues by ploughing also increases N2O emissions, mainly through the input of easily mineralizable N and C compounds.Earthworm activity is an important factor in C and N cycling in the soil, especially under conditions of low or minimum tillage and under grassland, contributing to greenhouse gas emission. Earthworm activity like digestion of soil and plant litters had been reported to lead to elevated N2O emission. The earthworm gut provides an ideal habitat for denitrifying organisms in terms of anaerobicity, mineral N content and available C, leading to N2O emission from the worms themselves. Furthermore, the mixing activity and anaerobic circumstances in the earthworm gut also leads to increased N2O emission and denitrification in fresh earthworm casts and in the drilosphere. Finally, earthworms increase porosity and thereby gas exchange with the atmosphere, possibly decreasing the amount of N2O which is further denitrified to N2 before emission to the atmosphere.
In conclusion, all these increased emissions are a factor in global warming. Apart from this, earthworms also contribute to soil health. The net effect of earthworms on global warming is still under research, and the extent to which their activities contribute to climate change is a complex issue.
