Soil Biota & Global Warming

Soil & Global Warming

Surface Carbon Water Temperature Climate

Biotic Climate

I saw James Lovelock answer a question at the Hay Book Festival, when asked about the reliability of present-day models of global warming , he said they were predominantly chemical and physical, and needed to factor in the biology. Most of that biological interchange will be at the soil surface.

Others have highlighted “episodes of climate change that have disrupted ecosystems and trophic interactions over time scales ranging from years to millennia" (Blois et al 2013) We have noted how soil has evolved through these millennia and wonder the relation of soil and climate change during the last half billion years to see what we can learn.

Lovelock @ 100yrs old

Throughout this site, we have carefully studied the evolution of soil over the past ½ billion years, which may offer lots of insights to help with the present.. In particular we’ve seen the relationship between fungi, bacteria, mosses, lichens, springtails, mites, roundworms, and then earthworms. The insects took off later, and the flowers emerged giving rise later to grasses and legumes. As life grew, carbon in the atmosphere got down to 100ppm -300mya, compared to 7,000ppm 200 million years earlier. We are now concerned as it goes past 400ppm.

We’ve already just seen how trees are probably the main biotic contribution to global warming, in terms of water movement and temperature. But let’s dig down into the rhizosphere , that we first came across 350mya. There we need to try and work out the role of the root exudates, microbes, mycorrhiza, the worms and the small soil arthropods. This rhizosphere may provide us with a better understanding of the gas exchanges going on the soil surface.

How do we add 'biotic'?

We need to get ‘biotic’ into climate change . The ‘Biotic Climate’ concept adds the role of living organisms in the soil to regulate the Earth's climate. In an attempt to include the biotic “a new framework, the Biotic Impacts of Climate Change Core Concepts (BIC⁴), which provides context for addressing understanding of how climate change will impact the living environment. The BIC⁴ consists of 7 Core Concepts" (Dunk et al 2022)

Many biological processes and interactions within the soil ecosystems play a significant role in sequestering carbon dioxide (CO2) from the atmosphere. In order to work out how these interactions work we need to look at all the organisms and how they relate with each. We saw 3 - 4 hundred millions of years ago, that mites and springtails would have bacteria in their guts. Trees and plants absorb CO2 during photosynthesis and store it as biomass, much going into the soil. This helps nutrient cycling, and overall soil ecosystem resilience. When promoting biodiversity and restoring natural capital, we should pay more attention to what goes on in the soil.

We must include biodiversity. Biodiversity is not an add-on. Increasingly we are realising its importance in all walks of life, including the soil. We saw in the soil biome how E.O.Wilson campaigned for an International Panel on Biodiversity - like the International Panel on Climate Change, and that top of the list to be protected for biodiversity were oribatid mites.

Arrows indicate CO2 flow; solid arrows represent net input, and dashed arrows represent net output, with arrow thickness proportional to flow. Circles show different species in a simplified soil food web. The unperturbed system prior to the onset of a chronic global change driver (A) gives way to a long-term response (B) (Pugnaire et al 2019)

Some are beginning to work out “biodiversity responses to anthropogenic climate change by rethinking climate context dependencies in biological terms" (Lenoir 2020)

Microbes

The microbes fart out some end products like carbon dioxide and methane both with GHG potential. While evolution is normally thought of as occurring over millions of years, researchers have discovered that bacteria can evolve in response to climate change in 18 months which is one way that soil microbes might deal with global warming.

Over the last couple of decades, new techniques for measuring microbes have developed. Soil microbes are very difficult to culture in the lab, so ‘metagenomics’ is proving a useful tool. In measuring bacterial DNA, “High throughput sequencing studies have succeeded in illuminating the previously unknown compositions and diversities of soil microbial communities across a variety of soil habitats" (Janssan & Hofmockel 2018) . However, while it provides an overview, it cannot tell the state that the DNA is in- it could be dead, alive, dormant or trapped, or in the guts of small animals, or free living. A rough figure is that about half the DNA found in soil is dead.

Microorganisms can improve water retention in soil as a drought mitigation strategy For example, through production of extracellular polymeric substances (EPS) to plug soil pores as a strategy for retaining soil water under dry conditions. Soil microorganisms can serve as a plant carbon sink through microbial uptake of carbon exported from plant roots that is subsequently stored as cellular biomass or transformed to stable metabolites. Carbon can be sequestered in soil as dead microbial biomass (necromass). Plant growth-promoting microorganisms can be used to enhance plant production in soils that are negatively impacted by climate change. Examples include increasing the provision of nutrients such as N2 through symbiotic or associative nitrogen-fixing bacteria, enhancing nutrient uptake through mycorrhizal fungi and the production of microbial plant (Janssan & Hofmockel 2018)

But general thinking at present sees the microbiome more of a ‘mush’. Many believe that as temperatures rise, microbial activity in the soil increases, accelerating the decomposition of organic matter. This releases carbon dioxide into the atmosphere, contributing to the greenhouse effect. But as microbiologists will tell you, there is a lot more to the soil metaphene. We’ll take a closer look at the way global warming disrupts soil ecosystems by altering the composition, activity and diversity of those roots, bacteria, fungi and arthropods. Some species may become more abundant, while others may decline.

Soil microbial responses to 'climate change'. A soil microbial community of bacteria, archaea (red & blue) and fungal hyphae (green). The centre depicts the absence of climate change pressures. The periphery shows 'climate change' pressures, where the cell colour changes to orange, green or purple indicate a community shift.

Fungi

Underground fungi absorb up to a third of our fossil fuel emissions. Researchers estimate that plants transfer more than 13 gigatonnes of carbon dioxide each year to mycorrhizal fungi, which we have seen over the last 400m years grow around their roots. Despite the interest in nature-based solutions to global warming, fungi have been largely overlooked.

Heidi-Jayne Hawkins at the University of Cape Town, South Africa and her colleagues set out to calculate just how much carbon plants might be transferring to these fungi. (Hawkins et al 2023). By scouring data from dozens of scientific studies on the relationships between plants and fungi, the researchers estimated that between 3 and 13 per cent of the carbon dioxide that plants pull out of the atmosphere ends up in the fungal tissue. Yet, we saw around 400 mya, this symbiotic relationship is actually 3-way as this carbon is then eaten by springtails and the like, who in turn disperse the fungal spores. This vital tri-symbiotic relationship is perhaps coming into its own - again . They say what is not clear is how long that carbon remains. If they look at the animals, then - as we saw with the woodlice - they keep that carbon cycle turning.

We have seen throughout this site the important role of mycorrhizal fungi, first AMF around 400mya, then EcM two hundred million years later, and another 50 million years after heather and orchid mycorriza. However the role of mycorrhizal fungi in transporting carbon into soil systems on a global scale remains under-explored. Now an analysis of nearly 200 datasets has provided the first global quantitative estimates of ‘carbon allocation’ from plants to the ’mycelium’ of mycorrhizal fungi. They estimated that global plant communities allocate 3.93 Gt CO2e per year to arbuscular mycorrhizal (AM) fungi, 9.07 Gt CO2e per year to ’ectomycorrhizal’ (EcM) fungi, and 0.12 Gt CO2e per year to ’ericoid’ mycorrhizal fungi. “Based on this estimate, 13.12 Gt of CO2e fixed by terrestrial plants is, at least temporarily, allocated to the underground mycelium of mycorrhizal fungi per year, equating to ∼36% of current annual CO2 emissions from fossil fuels." (Hawkins et al 2023) We have seen throughout this site how this carbon is then eaten, from living fungi by springtails, and cycled through the soil so that 75% of terrestrial carbon is stored belowground.

Illustration of how the evolution of the plant–fungal symbiosis coincided with plant radiation and a ∼10-fold reduction in atmospheric CO2 levels during the Paleozoic Era and beyond. (Hawkins et al 2023)

Earthworms

We have a dilemma with worms. “The phrase ‘earthworm dilemma’ captures the intricate role of earthworms in the GHG balance of soils. It is analogous to the ‘soil C dilemma’, explained in 2006 by Henry Janzen: “can we both conserve organic matter and at the same time profit from its decay?”(Shall we hoard it or use it? Janzen 2016) ). The inherent paradox of aiming to increase soil C stocks lies in the fact that the benefits from soil C arise not from its accumulation, but from its decay. After all, decay of soil C feeds the soil food web and improves soil fertility through mineralization of nutrients. A similar paradox is found in the functioning of earthworms in soil ecosystems — their ability to increase soil fertility as well as C stabilization lies primarily in their ability to accelerate decomposition and increase soil aggregation. In turn, these capacities may, however, cause an increase in net soil GHG emissions" (Lubbers et al 2013)

There is much more about earthworms than their relation with carbon..

The idea that earthworms 'increase soil aggregation' is generally accepted, and, along with the 'conceptual model of C-dynamics' (above), fits with my hypothesis that macro-aggregates became widespread worldwide when the earthworms did - less than 200mya.

Nitrous oxides

We saw around 200 mya that worms provide hotspots of microbial activity We have known for around 20 years that earthworm gut provides ideal conditions for denitrifying bacteria to live (Drake & Horn 2006). Denitrifying bacteria convert nitrates and nitrites into nitrogen gas, which is released into the atmosphere, and is a potent GHG. The nitrous oxide-produced permeates into the soil, so that in earthworm casts, with mucus and burrow walls, there can be up to three times greater nitrous oxides than from bulk soil (Elliot, Knight & Anderson 1991).

Shakoor et al 2020

Over the last few years, we have been getting a lot better at seeing soil as more than a lump of carbon. We now see a wider variety of mechanisms by which earthworms regulate soil C dynamics: they are summarised right. Over the short term, earthworms cause an increase in C mineralisation, while over the long term they induce the stabilisation of C within macroaggregates formed as a result of its feeding and casting activities

Earthworms and Soil C 'complex'

"In view of the collected data, it can be concluded that the effect of earthworms on soil C dynamics is quite complex and depends mainly on several factors viz. (i) the incubation period (ii) the quantity, as well as the quality of OM, amended (iii) the earthworm species present and (iv) the physicochemical and biological properties of the parent soil" (Thomas et al 2020)

Dung Beetles

We need to look much more at these interactions between soil organisms, and we have many more to look at. What if we could do the same sort of trial and include dung beetles, springtails and all those other creatures in the litter layer? How much do they contribute to reducing the 'land carbon–climate feedback' as it is known? After all this is the place where there is massive surface areas for exchange of chemicals and of life.

One study assessed GHG emissions related to dung beetles at three scales: the dung pat, pasture ecosystem and whole lifecycle of milk or beef production. “At the first two levels, dung beetles reduced GHG emissions by up to 7% and 12% respectively, mainly through large reductions in methane (CH4) emissions. However, at the lifecycle level, dung beetles accounted for only a 0.05–0.13% reduction of overall GHG emissions" (Slade et al 2016)

While these may look like insignificant bugs and microbes, their numbers mean these reactions add up across the world. Is there any way of quantifying this?

"Here reveal a potential impact of dung beetles on gas fluxes realized at a small spatial scale, and thereby suggest that arthropods may have an overall effect on gas fluxes from agriculture" (Penttila et al 2013).

IPCC (The UN’s Intergovernmental Panel on Climate Change)

The UN’s Intergovernmental Panel on Climate Change (IPCC) projections factor the land into their calculations and they are predominantly physically and chemically based. They say "There is unanimous agreement among the models that future climate change will reduce the efficiency of the land and ocean carbon cycle to absorb anthropogenic (made by humans) CO2" in particular carbon dioxide and methane. They believe that increased global temperatures will lead to more carbon dioxide and methane gases released from the soils. As recently as 2019 they said: “warming of soils and increased litter inputs will accelerate carbon losses through microbial respiration (high confidence)" (p134)

They also mention that “new evidence suggests ..

They also mention that “new evidence suggests that ecosystem adaptation through plant-microbe symbioses could alleviate some nitrogen limitation (medium evidence, high agreement).”
But there is very little more biology, there is a special sub head “Biophysical and biogeochemical land forcing and feedbacks to the climate system. The nearest is p201 And “Soil carbon and microbial processes, which interact with plant responses to climate, represent another large source of uncertainty in model projections (medium confidence)” They seem to think that microbes are the only living organisms, when there are quadrillions more legging it about and trillions more moving around as they have been for over 350m years.

The IPCC recognise that ‘climate change and biodiversity are inextricably linked’ and helped sponsor a workshop to that effect They recognised that “Maintaining or enhancing the sinks (CO2 emissions get, physically and biologically, absorbed in land and oceans)and ensuring long-term carbon storage in biomass, soils or sediments is an important aspect of climate change mitigation, and in avoiding exacerbating climate change…The large historic loss of soil carbon (about 20% to over 60%) implies that agricultural soils, appropriately managed, have a significant future capacity to take up CO2 from the atmosphere (e.g., 0.4-8.6 Gt CO2 a-1)and to store it in the form of soil carbon, potentially with a wide range of co-benefits in addition to climate change mitigation”. (IPBES-IPCC)

Yet, it would seem the microbial dynamics in soil is more complicated in that “climate warming could alter the decay dynamics of more stable organic matter compounds, thereby having a positive feedback to climate that is attenuated by a shift towards a more efficient microbial community in the longer term" (Frey et al 2013) The way IPCC sees soil is a fine example of the traps you can run into if you think the soil is just a lump of carbon or a microbial mush and do not look at the whole soil structure. They see carbon as carbon dioxide released from bacteria, not running round in tiny animals making aggregates, like they have been for the past 350 million years. There is a massive body of research needed on how global warming takes in the biology.

But if instead of this going to air, the microbes are eaten, then the carbon saved. Instead of going into the air, it is now running round in the soil. It is the next stage in the feeding levels that other predators benefit from , and enable the world to go round, as we shall see when we meet the woodlice below.

Woodlice

An international collaboration between researchers, from Yale, Helsinki, New Hampshire and the Czech Republic, designed a trail to shed light on the issue of increased microbial decomposition. (Crowther et al 2015). They found: "In disturbed environments, where soil animals are not present, the feedback between climate change and microbial carbon production was strong, yet, when the soil community is healthy and diverse, we saw that animals feed on the microorganisms, limiting the feedback effects." The soil animals they studies were Isopods, we know better as 'woodlice'. You may see these woodlice under piles of stones and they feed on fungal remains and other microbes.

They checked out the role of the grazing animals - woodlice, by setting out plots with various combinations of warmth, nitrate and isopods.

The woodlice running around. keep the carbon where it is most useful, in their skeletons. When they die something else will eat them. In this graph, the cords with no isopods were much taller in N and W&N than those with cords and their predatory isopods (lightest grey). This means that soils with woodlice do not send so much carbon gas into the air.

This long-term study showed that small soil surface animals can limit the effects of global warming. Those woodlice may look insignificant, yet may be one of the most important aspects to factor into Global Warming calculations. In future, when you lift a stone or bit of dead wood, thank those little creatures running away.

They found that when the soil is warmer and has nitrate feed, the isopods were very successful at keeping the microbes, measured as ’fungal cords’ (aggregations of hyphae), under control and showed how microbes are an example of "the ability to self-regulate critical systems"

The role of soil animals seems v important in global warming, but virtually unrecognized. One of the authors said. "As a result of climate change, there's going to be more nitrogen deposition, it's going to be warmer -- many of the things that limit fungal growth are going to be alleviated…And by stimulating microbial activity it will trigger higher carbon emissions. So when those 'bottom up' limitations are gone, the grazing animals become even more important."

Do you remember the arrival of woodlice - less than 150mya?They may have been the first true terrestrialilsers..ie walked out the sea on to land

Their contribution to our survival may belie their commonplace appearance.

The IPCC now say: “The study highlights the importance of understanding biological processes if scientists are going to be able to predict the consequences of climate change. Our current understanding of carbon cycle feedbacks to climate change stem mostly from the physical sciences; this study shows that precise global predictions can be achieved only if we understand the interactions between organisms"

Living Entity

By including life in the equation, it raise doubts with the use of 'Soil Organic Matter' (SOM ) as our preferred measure of soil activity. Quite simply, SOM is dead matter. Yet, the ‘woodlouse’ study showed the importance of factoring in live animals. In future when we read about soil carbon, remember most of that will be running round in organisms and creatures, and that is good for the soil. Some people look for ‘stable soil carbon’, whereas here we look for ‘moving' soil carbon.

We have to reassert that soil is a distinct entity. We saw, at the outset, that soil scientists broke barriers when they first considered that soil was a distinct entity in the 19th century. They were challenging the idea that soil was just weathered rock. Now we are challenging that soil is just carbon, as it has its own characteristics quite distinct from anything else. We are still learning about many of them - all about those aggregates and animals mixing with the microbes and minerals to make this unique entity. Can all their chewin’, pooin’ and gluein’ hold the earth together? We’ve seen what woodlice can do in relation to the microbiome, but there are also the trillions of springtails, mites and worms to make the soil control the water cycle and help cool the earth.

"Invertebrates and microorganisms can regulate much larger fluxes than their direct effects on soil processes. The mechanisms often involve the formation of durable artefacts, such as stabilised aggregates, burrows, or buried organic matter, which continue to function in the absence of the organisms creating them The effects of these artefacts, most notably those created by earthworms and termites, are cumulative and can therefore be manifested in macroscale measurements. However, the net effects of these activities may not be detectable on larger areas, or over longer time periods, because sink/source processes operate within patches at the scale, or domain, at which the species populations function "

While soil may look immovable, it is moving all the time. The future is about diversity and dynamics. The soil animals are constantly moving as are the bacteria, fungal spores, chemicals, ions, water and air inside the soil. That living entity, still largely unexplored, could offer an insight as to how we can use soil services to help us deal with global warming. This thin skin which has helped the planet through five previous extinctions, may just help us with the 6th possible extinction.

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