The role of microbiology in regulating climate and underpinning climate-smart agricultural systems

Soils harbour over a quarter of all life on the planet, including a staggering abundance and diversity of microbial life. These micro-organisms are integral to the health and productivity of our farming systems and carry out a range of essential functions. Amongst the most important of these is that of regulating climate, with soil microbes playing a critical role in both generating and mitigating greenhouse gases (GHGs).

Micro-organisms are the engines of nutrient cycles in soils, transforming nutrients from one form to another. These nutrients are the basis of food production, but during these cycles, nutrients can also be lost to the atmosphere as GHGs. Within agricultural soils, the primary GHGs of concern are carbon dioxide (CO₂) and nitrous oxide (N₂O). Soils represent the largest global terrestrial store of carbon (C), holding more C than the atmosphere and plants combined. The net balance of C in and out of soil is therefore crucial to global C cycling. A key focus of international efforts to regulate the climate has been to increase the C sink capacity of soil by enabling conditions where soils sequester more CO₂ than they emit. Fundamental to the success of these efforts is understanding how C is stabilised, with recent evidence suggesting that microbes play a key role by transforming C into more stable forms and that microbial necromass (dead microbial material) may be the most stable component of soil C.

N₂O is a potent GHG with a global warming potential nearly 300 times greater than CO₂. In Ireland, more than 90% of N₂O emissions come from agriculture, largely from microbial transformation of nitrogen (N) in soils by a process known as denitrification. Many soil microbes can transform N in this way and some also have the capacity to mitigate N₂O emissions by transforming it into benign N₂ gas. Whether N₂O is produced or transformed depends on the microbial community composition and environmental conditions. The integral role microbes play in C and N cycles raises the possibility of harnessing knowledge of the soil microbiome to help reduce GHGs in our agricultural systems. As research helps us elucidate the impact of agricultural management (such as liming, crops grown, cultivation methods and fertilisation) on the microbes that orchestrate these processes, there is potential to mitigate GHGs. A further avenue towards reducing GHGs is utilising microbes to facilitate agricultural production in low-input systems that produce fewer emissions.

While microbial processes can contribute to climate change, they are also impacted by the effects of it. Climate change can disrupt the soil microbial communities, affecting how they cycle C and N. Increased frequency and severity of floods and droughts could stress soil microbes to a point where they may not recover from these weather events. How soil microbes respond to such challenges has important consequences for the soil functions we depend on, including food production, C storage and climate regulation. Flood events in grasslands have been found to increase N₂O emissions by orders of magnitude, and droughts can drastically reduce C storage. These events can also disrupt the intimate connection that plants and microbes have, reducing the C exuded via
plant roots, the main source of energy for many microbes. This could also affect the benefits that microbes provide to plants: nutrient uptake, growth promotion and stress reduction.

Research has shown that it is possible to mitigate the negative effects of climate change on soil microbes and their functions which we depend on. First and foremost, we need to address the root of the problem, slowing climate warming by significantly reducing our GHG emissions. Secondly, understanding how climate change affects soil microbes and their interactions with plants could allow us to manage our land in a way to create climate-change resilient soils. This is a daunting task, as there is still so much to learn about the soil microbiome, plant–soil interactions and their responses to climate change. What is known is that conserving soil biodiversity is essential to preserving the ecosystem functions that soils provide. We can do this by diversifying the plant species we grow, reducing over fertilisation, preventing soil physical damage and building soil organic matter. For example, growing mixtures of plant species with diverse characteristics in grasslands or building soil organic matter via cover cropping, diverse crop rotations or including crops with deep, fibrous roots in cropping systems. Essentially, preparing a feast of carbon that satisfies a wide variety of microbial tastes can foster a diverse soil microbial community that performs the functions we depend on.

Fiona Brennan

Department of Environment, Soils and Land-Use, Teagasc (Irish Agriculture and Food Development Authority), Ireland

Natalie Oram

Department of Environment, Soils and Land-Use, Teagasc (Irish Agriculture and Food Development Authority), Ireland; and Department of Ecology, University of Innsbruck, Austria

26th UN Climate Change Conference of the Parties (COP26)

This year, the UK will host the 26th UN Climate Change Conference of the Parties (COP26) in Glasgow, on 1–2 November 2021. At the summit, delegates including heads of state, climate experts and negotiators will come together to agree on coordinated action to tackle climate change.

The UK Presidency provides a platform for the UK to take an international leadership role and champion a green recovery from coronavirus which creates sustainable jobs and addresses the global challenges of public health, climate change and biodiversity loss to safeguard the environment for future generations.

Microbiology can play a leading role in tackling climate change, as micro-organisms and microbial processes can be harnessed into nature-based solutions to mitigate the effects of climate change. Ahead of COP26, there is an opportunity for microbiologists to showcase the important role of microbiology in this global challenge and share knowledge with others on the frontline of climate action.