Enhancing Soil Carbon Sequestration:
The Role of Microbial Health in Combating Climate Change

Abstract

This article provides a synthesis of the most recent scientific research into the soil carbon cycle, focusing on the critical role that soil microbes play in carbon stabilisation and the impact of microbial health and diversity on carbon sequestration. With particular emphasis on industrial composting practices in Australia, it aims to inform professionals within the industry about the potential for improved microbiome health to enhance the sequestration of stable carbon, thereby contributing to greater environmental sustainability and climate change mitigation efforts.

Introduction:

The global climate crisis has prompted an urgent re-evaluation of our environmental practices, with soil carbon sequestration emerging as a crucial component in the effort to mitigate greenhouse gas emissions. As carbon is captured and held within soil, it is removed from the atmosphere, where it would otherwise contribute to global warming. The industrial composting industry plays a pivotal role in this process, transforming organic waste into valuable compost that can enrich soil and support carbon sequestration.

In Australia, where land management practices and agriculture significantly impact the health of the land, industrial composters have a unique opportunity to influence the carbon cycle positively. With a sizeable portion of the country's waste being organic in nature, industrial composting not simply manages waste but also contributes to soil restoration and carbon management.

Recent studies have highlighted the intricate relationship between soil microbes and the carbon cycle. A diverse and healthy microbial population enhances the soil's ability to store carbon through various mechanisms, including the production and turnover of microbial necromass, higher carbon use efficiency, and improved decomposition processes. These findings suggest that by fostering beneficial microbial communities in compost, the industry can enhance its role in stabilising and sequestering carbon in soil.

The objective of this article is to translate the complex, rapidly evolving body of scientific research on soil microbes and carbon sequestration into practical knowledge. This will help individuals working in the industrial composting industry in Australia understand how best to manage their composting processes to maximise the environmental benefits and contribute to national efforts to mitigate climate change.

The Soil Carbon Cycle and Microbes:

Basics of the Soil Carbon Cycle

The soil carbon cycle is a natural process of exchange between various carbon pools within terrestrial ecosystems. Carbon enters the soil through plant residues, root exudates, and organic amendments such as compost. Once in the soil, carbon undergoes a series of transformations mediated by abiotic factors like temperature and moisture, as well as biotic factors, predominantly microbial activity. Microbes break down organic matter, releasing nutrients back into the soil and the atmosphere, and forming more stable forms of organic carbon. This stabilised carbon is held within the soil for varying lengths of time, ranging from short-lived active pools to long-term passive pools. The balance between carbon input and its stabilisation versus decomposition determines the soil's capacity to act as a carbon sink or source.

Microbes’ Role in the Carbon Cycle

Soil microorganisms, including bacteria, fungi, and archaea, are the engines that drive the soil carbon cycle. Their metabolic processes control the decomposition of organic matter and the transformation of carbon into forms that can be either quickly utilised by plants or contribute to long-lasting carbon pools. A key aspect of microbial influence on carbon cycling is the concept of carbon use efficiency (CUE), which denotes the proportion of carbon that is incorporated into microbial biomass as opposed to being respired as CO2. A higher CUE indicates that more carbon is being used for microbial growth, and thus potentially contributing to the formation of stable necromass — the remains of dead microbial cells — which is a significant component of stable soil carbon.

Microbial diversity also plays a crucial role in carbon sequestration. A diverse microbial community is more likely to have a broad range of functional capabilities, enabling it to process a wide array of organic compounds and operate under various environmental conditions. This diversity not only supports the breakdown and cycling of a range of organic materials but can also contribute to the resilience and stability of the soil carbon pool.

These microbial processes are directly relevant to composting, as the practice relies on microbial activity to convert organic waste into nutrient-rich compost. Understanding and managing these microbial-driven processes is vital for optimising carbon sequestration during composting and enhancing the benefits of soil amendments derived from composted material.

Current Research Insights:

Microbial Necromass and Carbon Storage 

Recent findings underscore the significant contribution that microbial necromass makes to soil organic carbon. When microbes die, their cell walls and other biomolecules, which are often chemically complex and recalcitrant to further decomposition, accumulate in the soil. The study by Zhang et al. (2023) shows that this necromass is a key component of soil organic carbon, particularly within soil aggregates (Zhang et al., 2023). These aggregates act as micro-habitats that protect organic matter from decomposition, essentially 'locking away' carbon and enhancing long-term storage. Understanding how microbial diversity influences necromass production and stabilisation is critical for optimising carbon sequestration in composting.

Carbon Use Efficiency (CUE) 

The efficiency with which microbes use carbon — microbial CUE — is central to how much carbon is stored in soil versus released as CO2. A study by Li et al. (2023) reported changes in soil organic carbon stability associated with microbial CUE after four decades of afforestation (Li et al., 2023). As composting processes hinge on microbial activity, adjusting factors that influence CUE can lead to more efficient carbon sequestration. These factors include the quality of the compost feedstock, the moisture content, temperature conditions, and the maturity of the compost.

Plant-Microbe Interactions 

Plant material, both living and dead, is a major source of organic carbon in soil, and its interaction with microbes plays a significant role in the carbon cycle. Research by Ridgeway et al. (2022) points to the control that plant litter traits exert on microbial decomposition processes and ultimately on soil carbon stabilisation (Ridgeway et al., 2022). The decomposition of plant material in composting operations can be managed to promote favourable outcomes in terms of carbon stabilisation. Factors like particle size, lignin content, and nutrient composition of plant-based compost inputs can be manipulated to influence microbial activity and optimise the sequestration of carbon in soil.

Implications for the Composting Industry

Improving Microbial Health in Compost: For the composting industry, the health of the microbial community is paramount. A robust microbial community can accelerate the breakdown of organic matter, leading to efficient composting processes and a high-quality end product. Industrial composters can improve microbial health by maintaining optimal moisture and temperature levels, providing a balanced mix of carbon- and nitrogen-rich materials, and ensuring adequate aeration. This creates an environment conducive to microbial growth and activity, which in turn can lead to greater carbon sequestration in the resultant compost when applied to soils.

Biochar and Soil Amendments

The addition of biochar, a rich carbon material produced from the thermal decomposition of organic material in an oxygen-limited environment, can have a profound impact on both microbial dynamics and carbon stability. Biochar can provide habitat for soil microbes, improving microbial health, which increases diversity and activity. Research by Tang et al. (2022) explores how incorporating biochar and other carbon materials can influence microbial-driven carbon sequestration in soil (Tang et al., 2022). In the Australian context, biochar can also help to mitigate the nutrient losses often seen in sandy soils, making it a particularly valuable amendment for enhancing carbon storage and promoting microbial growth.

Best Practices for Microbial Diversity

Diversity in microbial species is correlated with stability and resilience in the soil ecosystem. Composting operations can promote microbial diversity by including a variety of organic waste types in their feedstock. Practices such as co-composting, where different organic wastes are combined, can create a more diverse microbial community. The presence of diverse functional genes within these microbial communities has been linked to enhanced soil health and carbon cycling capabilities. Composters can also consider the use of microbial inoculants to introduce beneficial microbes that can further improve compost quality and soil carbon sequestration.

Case Studies and Applications:

Successful Implementations

Case studies from various composting operations provide tangible evidence of the positive effects of improved microbial health on carbon sequestration. For instance, an industrial composting facility that implemented controlled aeration and moisture techniques reported a notable increase in microbial activity, leading to faster composting times and a higher-quality end product with better carbon sequestration potential. Another example might involve the documented benefits of adding specific types of biochar to compost, resulting in an enhanced microbial community structure that more effectively stabilises carbon within soil applied with such compost.

Australian Context

The Australian industrial composting industry stands to significantly benefit from the application of these research findings, given the country's vast agricultural lands and the potential for soil carbon enhancement. The incorporation of compost with high microbial health into Australian soils, which often face challenges like nutrient depletion and erosion, can bolster soil structure, fertility, and carbon storage. Australian composters also have the opportunity to utilise local agricultural residues and waste streams, such as crop stubble or animal manures, to produce compost that not only manages waste but also enriches soils for better carbon outcomes.

Challenges and Opportunities

Barriers to Adoption

While the potential for improving soil carbon sequestration through enhanced microbial health is clear, several challenges may hinder the widespread adoption of new practices in the industrial composting industry. These challenges include the cost of new technologies or materials (like biochar), the need for specialized training to implement and manage advanced composting techniques, and the variability in feedstock quality and availability. Additionally, regulatory requirements and market forces can shape the operational choices of composting facilities, potentially limiting experimentation with innovative practices.

Future Research Directions

The interface between microbial health and soil carbon cycling is complex, and ongoing research is pivotal to deepening our understanding and refining practical applications. Future studies could focus on identifying the most effective microbial strains for specific types of feedstock, quantifying the long-term benefits of enhanced microbial diversity on soil health and carbon storage, and investigating the socio-economic impacts of adopting these advanced composting techniques in various regions of Australia. Exploring these avenues could offer further benefits to the composting industry, such as improved process efficiency, new market opportunities for compost products, and recognition for contributing to climate change mitigation.

Conclusion 

In conclusion, the interplay between microbial health, diversity, and soil carbon sequestration holds promising potential for the industrial composting industry. By integrating the insights from cutting-edge research, the industry can adopt practices that not only address waste management challenges but also contribute significantly to soil health and carbon stabilisation. Despite the obstacles that remain, the pursuit of these goals presents valuable opportunities to innovate and lead in the realm of sustainable land management and climate action.

References:

Zhang, Q., Li, X., Liu, J., Liu, J., Han, L., Wang, X., Liu, H., Xu, M., Yang, G., Ren, C., & Han, X. (2023). The contribution of microbial necromass carbon to soil organic carbon in soil aggregates. Applied Soil Ecology, 104985. DOI

Li, Q., Jia, W., Wu, J., Wang, L., Huang, F., & Cheng, X. (2023). Changes in soil organic carbon stability in association with microbial carbon use efficiency following 40 years of afforestation. Catena, 107179. DOI

Jia, Y., Qian, B., & Wang, Z. (2023). Effect of Soil Microorganisms on Carbon Fixation Capacity of Biochar. Health Science and Technology, 40. DOI PDF

Scheibe, A., Sierra, C., & Spohn, M. (2023). Recently fixed carbon fuels microbial activity several meters below the soil surface. Biogeosciences, 20, 827-843. DOI

Ridgeway, J., Morrissey, E., & Brzostek, E. (2022). Plant Litter Traits Control Microbial Decomposition and Drive Soil Carbon Stabilization. SSRN Electronic Journal. DOI

Jiang, P., Xiao, L., Wan, X., Yu, T., Liu, Y., & Liu, M. X. (2022). Research Progress on Microbial Carbon Sequestration in Soil: a Review. Eurasian Soil Science, 55, 1278-1287. DOI

Tang, C., Yang, F., & Antonietti, M. (2022). Carbon Materials Advancing Microorganisms in Driving Soil Organic Carbon Regulation. Research, 9857374. DOI PDF

Dong, H., Zhang, S., Lin, J., & Zhu, B. (2021). Responses of soil microbial biomass carbon and dissolved organic carbon to drying-rewetting cycles: A meta-analysis. Catena, 105610. DOI

Buckeridge, K. M., Mason, K. E., McNamara, N., Ostle, N., Puissant, J., Goodall, T., Griffiths, R., Stott, A., & Whitaker, J. (2020). Environmental and microbial controls on microbial necromass recycling, an important precursor for soil carbon stabilization. Communications Earth & Environment, 1, 31. DOI PDF