**2. CO2 balance in soils**

The technique of increasing soil carbon storage by reducing net CO2 emissions in agricultural soils is known as carbon sequestration. Soil carbon sequestration (SCS) is the process of absorbing C-containing compounds from the atmosphere and storing them in soil C pools. Variations in the ability to store carbon in soils have been linked to the activity of the soil microbial community (SMC). The turnover and supply of nutrients, as well as the rate of decomposition of SOM, are all influenced by the structure and activity of the SMC, which is crucial for the maintenance of soil ecosystem

#### *Regenerating Soil Microbiome: Balancing Microbial CO2 Sequestration and Emission DOI: http://dx.doi.org/10.5772/intechopen.104740*

services. As a result, the influence of farming activities on SMC and SCS should be quantified as part of any soil management practice's sustainability evaluation.

Because a big fraction of the biomass is produced in agricultural systems cycles *via* the soil decomposer community, the quantity of gross CO2 fluxes between agricultural soils and the atmosphere is significant. The difference between photosynthetically fixed CO2 entering the soil as plant wastes and CO2 exhaled during decomposition, on the other hand, is far smaller. This distinction determines whether the ecosystem is a CO2 source or sink in terms of its net carbon balance.

Raising the C content of agricultural soils is a well-known technique. The equilibrium between C inputs from plant residues and C losses, primarily through decomposition, determines the soil C levels. The increasing residue inputs and/or delaying breakdown rates (i.e., heterotrophic soil respiration) also govern the C level in soils. The relationship between C inputs and SOC levels could be straightforward; in which many agricultural soils' steady-state C contents have been shown to be linearly related to C input levels, that is compatible with the current SOM dynamics theory [14]. This may not be the case in soils with exceptionally high quantities of carbon, which may exhibit "saturation" behavior.

The following factors must be considered when developing soil carbon sequestration management practices and policies: Soils have a finite capacity to store carbon, gains in soil carbon can be reversed if proper management is not maintained, and fossil fuel inputs for various management practices must be factored into the total agricultural CO2 balance [15].

The interaction of numerous ecosystem activities, the most important of which are photosynthesis, respiration, and decomposition, results in the SOC level. Photosynthesis is the process of converting atmospheric CO2 into plant biomass. The root biomass of a plant determines the majority of SOC ingestion rates, however, litter deposited by plant shoots also plays a role. The growth and death of plant roots, as well as the transfer of carbon-rich molecules from roots to soil microbes, produce carbon in the soil both directly and indirectly.

Decomposition of biomass by soil microbes leads to carbon loss as CO2 as a result of microbial respiration. Through the formation of humus, a material that gives carbon-rich soils their unique black hue, a small fraction of the original carbon is kept in the soil (**Figure 1**). These various forms of SOC differ in their recalcitrance, or resistance to decomposition. Humus is a recalcitrant plant that takes a long time to degrade, resulting in a long period of time spent in the soil. Plant waste is less abrasive; therefore, it stays in the soil for a shorter period of time. When carbon imports and outputs are in equilibrium, there is no net change in SOC levels. When carbon inputs from photosynthesis exceed carbon losses, SOC levels rise over time.

#### **2.1 Impact of climate change on soils carbon**

The effects of climate change on soil functions, including soil carbon, is a complex subject since numerous direct and indirect factors are involved. For instance, the atmospheric temperature may affect the rate of SOM decomposition, a process that could release greenhouse gases that contribute to climate change [16]. The effects of moisture and temperature due to climate change will be highlighted as key parameters since soil humidity and temperature are among the most important variables in determining microbial activity and therefore SOC [17].

One of the most critical effects of climate change on soil is the alteration of rainfall patterns, resulting in intense rain and drought. These phenomena may be beneficial

#### **Figure 1.**

*Carbon inputs from photosynthesis and carbon losses from respiration govern the carbon balance within the soil. Humus, long-lived storage of SOC, is formed through the decomposition of roots and root products by soil bacteria. Created with BioRender.com.*

or detrimental according to the agricultural activities and climatic requirements, but they present economic challenges nonetheless [18]. The selective migration of soil particles, where fine particles and micro-aggregates are transported *via* erosion while macroaggregates are left *in situ* resulted in different carbon mineralization patterns. These lateral redistributions of sediments create (i) eroded environments dominated by large particles exhibiting increased porosity and permeability but decreased waterholding capacity, and (ii) deposited environments where enrichment of fine particles enhances the water holding capacity [17]. Similar to water erosion induced by water runoff, wind erosion induced by drought also redistributes a large amount of SOC as well as soil inorganic carbon (SIC). In addition to soil particles, the net effects of these soil C redistribution on the soil as a C source or sink also depend on site-specific topography (such as slope gradient and location), distribution distance, and duration [19]. Some of these interacting factors are outlined in **Figure 2**.

Among the most consistent narrative of climate change is climate warming as a result of rising temperature [20]. Climate warming has been associated mainly with SOC decomposition due to the effects of temperature on soil microbial community and their enzymatic and metabolic activities. Unlike the effects of moisture, however, the

*Regenerating Soil Microbiome: Balancing Microbial CO2 Sequestration and Emission DOI: http://dx.doi.org/10.5772/intechopen.104740*

#### **Figure 2.**

*Interaction of diverse factors affecting soil as C source or sink.*

dynamic relationship between temperature and soil C is less certain and more constrained. In general, elevated atmospheric temperature could also elevate soil temperature, which would subsequently elevate microbial processes and SOC decomposition rate [21]. This is not always the case due to the difference in temperature sensitivity of soil biota, especially the microbial community, where the higher-temperature sensitivity such as in colder regions exhibited more enhanced soil respiration, potentially resulting in a net efflux of C toward increased atmospheric CO2 in comparison with those inhabiting soils in hotter regions [22]. In contrast, a higher rate of microbial OM decomposition was reported in hotter regions, suggesting other environmental factors that may affect the SOC, including topography, soil texture, and pH. Ultimately, climate warming leads to decreased SOC input and increased SOC output [23].
