Mycorrhiza (AMF)

400-360 mya Late Devonian

Plants Animals Springtails Arachnids Greening

Mycorrhiza

Fungi clearly existed before this period, but they were free standing or growing on stems. Now some were developing relations with roots. Generally we call these mycor (fungal) rhizas (roots) . These early fungal forms (2 sorts) are called endomycorrhiza because they live inside roots. These fungi penetrate the cells of the roots of vascular plant roots. This was a monumental step in soil evolution.

Another group of mycorrhiza living on outside of the roots and called ectomychorrhiza do not appear for another three hundred million years. Evolution of Mycorrhiza determined by genome sequencing

2 Sorts

There are two main types pf endomycorrhiza.

Arum-type endomycorrhiza: In this type, the fungal partner belongs to the Glomeromycota phylum, specifically within the genus Glomus. Arum-type endomycorrhiza is characterized by the presence of highly branched structures called arbuscules within the plant root cells. These arbuscules facilitate nutrient exchange between the fungus and the plant.

Paris-type endomycorrhiza: Paris-type endomycorrhiza also involves fungi from the Glomeromycota phylum, but typically involves fungal species from the genus Rhizophagus (formerly known as Glomus). In this type, the fungal hyphae penetrate the root cells of the host plant but do not form prominent arbuscules. Instead, the fungal colonization occurs intercellularly, forming a dense network known as the Hartig net.[CH12]

Morphologies and rooting depths of rooting systems and mycorrhiza through the Devonian (420-360mya) . Envisaged and drawn by Algeo and Scheckler 1998) prog-arc = Archaeopterid. Note the increased depth during late Devonian - Famenian and Tournasian @Royal Society

Which roots?

These fungi form symbiotic relationships with a wide range of plants, including many agricultural crops, grasses, and some trees, estimated to be on 80% of all plant species. Not all plant species form mycorrhizal associations, and the extent of association can vary even within a single plant species. Some trees commonly associated with arbuscular mycorrhizal fungi (AMF):

Fruit trees such as apple (Malus domestica) and citrus trees (Citrus spp.).
Crop trees like avocado (Persea americana) and olive (Olea europaea).
Some tropical trees such as coconut palms (Cocos nucifera) and banana trees (Musa spp.).

Nowadays, 80-90% of all plants living have root-fungal relations Around 200,000 species of plants have fungal relations called AM. Ecto(outside) mycorrhiza (EcM), emerged 300 million years later, and developed relationship with broadleaved trees like beech birch and oak as late as 50mya. We will also meet, also much later, two further mycorrhiza, for heathers and orchids.

"The evolution of fungal symbiosis probably has an ancient origin. It might date back to a common ancestor that evolved a strategy with factors for recognising autotrophic organisms and structures for infecting them (Tehler et al., 2000). Such an event would make a synapomorphic feature for a group of chitinous fungi, including all Dikaryomycota and the Glomeromycota, informally referred as ‘Symbiomycota’ by Tehler et al. (2003). Palaeontogical evidence supports the hypothesis that fungi developed symbiosis with photoautotrophs long before the evolution of land plants (Yuan, Xiao & Taylor, 2005)". (Santos-Gonzales 2007)

AMF

AMF stands for Arbuscular Mycorrhizal Fungi which inhabit around 80% of all plants. AMF is used to describe the symbiotic relation between roots and these endomycorrhiza. The fungi belong to a clade (meaning they all have the same ancestor) called Glomeromycetes. The 'Arbusular' refers to the formations created by the plant in response to the fungus and have been found over 410mya.

Increasingly we are hearing - in regenerative circles- that AMF is the 'Secret Soil Powerhouse'. Many studies have quantified AM effects on soil aggregation, and the relationship between AMF and healthy soil is an axiom of regenerative farming.

Living Fossils

AMF are ancient and fossil evidence suggests that AMF existed in this period, around 400 million years ago. They may have existed earlier. The ancient AMF are considered to be ancestral to both sorts of endomycorrhiza, but the specific order of evolution between the two is still a subject of ongoing research and scientific debate.

"AM fungi are considered to be 'living fossils' and 'ancient asexuals', because structurally identical fungi were detected in association with the oldest land plant fossils and sexual stages or mechanisms are unknown." (Parniske 2008)

Signal Process

"A class of terpenoids, strigolactones, signal the symbiosis, acting like endogenous plant hormones, by inducing a signal transduction process in root cells that overlaps with the root-nodule symbiosis. Seven plant genes are required for these signalling processes in AM and root-nodule symbiosis. Plant cells respond to fungal signals by forming a tunnel-like structure in anticipation and preparation for penetration by fungal hyphae. Transport through the coenocytic mycelium uses cargo packages for carbon, phosphate and nitrogen transport that can be actively moved by the cytoplasm and includes lipid droplets, glycogen and polyphosphate granules." (Parniske 2008)

Arbuscule

Formations made by the roots in response to the fungal growth inside the cells are: branching (arbuscules)

balloon-like (vesicles)

or hyphae forming spores

or crushed spores

AM are mycorrhizas whose hyphae penetrate plant cells, producing structures that are a means of nutrient exchange. The hyphae of arbuscular mycorrhizal fungi (AMF) form bushy structures after making contact with the plasma membrane of a root cell. "AM endosymbiosis involves intracellular accommodation of the microbial partner in the cells of the plant host. Since plant cells are surrounded by sturdy cell walls, root penetration and cell invasion requires mechanisms to overcome this barrier while maintaining the cytoplasm of the two partners separate during development of the symbiotic association". (Rich et al 2014)

The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.

"From the outset, symbiotic associations with fungi were important (Taylor et al., 2004; Strullu-Derrien and Strullu, 2007; Bonfante and Genre, 2008), and it is clear that mycorrhizae and plant roots have coevolved in many different ways (Brundrett, 2002; Wang and Qiu, 2006; Taylor et al., 2009b; Strullu-Derrien et al., 2014). Roots and Rhizoid-based Rooting Systems can be observed in many geological contexts". Kenrick et al 2014

Fossil roots

There were structures resembling vesicles and spores of the fungus Glomus species – still found today. Colonized fossil roots have been observed in spore bearing Aglaophyton and Rhynia – small plants less than 20cm high.

The two earliest mycorrhiza groups are Mucoromycotina and Glomeromycotina, both had internal symbiotic bacteria living in them, developed in small rootless vascular plants (Aglaophyton, Horneophyon), when soil depths were of the order of millimetres to centimetres. By 385 mya, tree‐like growth forms (c. 8 m tall) evolved in the fern stem group (Cladoxylales) and 370 Mya tree like characters had evolved in several groups, including Archaeopteris, > 30 m tall, when soil depths were of the order of decimetres to a metre.

These ancient plants possess characteristics of vascular plants and mosses and liverworts and have rhizomes – which are essentially underground modified stems. Fungi commonly colonize rhizomes of vascular plants and the ribbons attached to substratum (thalli) of early-diverging land plants, likely liverworts and hornworts (Strullu-Derrien et al 2018]. So mycorrhiza preceded true roots. These early fungal associations are sometimes called mycorrhiza-like or ‘para’ mycorrhizas because the early plants had no true roots, but the general consensus is now that they are the first mycorrhiza.

While explaining when mycorrhiza arrived, this graphic Is one of the best graphics showing soil formation, but lacks much explanation as to how..

Root colonisation by endomycorrhizas was by fungi which previously colonised aerial parts. It all points to fungi previously feeding on dead stuff on stems becoming symbiotic fungi of roots. This occurred during declining levels of atmospheric CO2 and increasing O2 levels that probably enhanced respiration in soils. The surface layers could breathe. All the biochemical processes driving soil formation at this period are aerobic – ie requiring oxygen

Symbiosis

The mycorrhizal relationships would have greatly increased the water and mineral absorbing capabilities of plants. We often use this relationship as the prime example of ‘symbiosis’ – where two organisms live together and the presence of each benefits the other.
The plant makes organic molecules such as sugars by photosynthesis which travel down the stem to the roots and supplies them to the fungus with the energy. The fungus supplies to the plant water and mineral nutrients, such as phosphorus, taken from the soil.

Metabolism.

The plant -AMF interaction is probably the most important symbiotic relationship in the living kingdom, and has been crucial in evolution for 400 million years. We are beginning to appreciate this relationship more and more. “During initial colonization, plant–AMF interaction is facilitated through the regulation of signaling and carotenoid pathways. After the establishment, the AMF symbiotic association influences the primary metabolism of the plant, thus facilitating the sharing of photosynthates with the AMF. The carbon supply to AMF leads to the transport of a significant amount of sugars to the roots, and also alters the tricarboxylic acid cycle. Apart from the nutrient exchange, the AMF imparts abiotic stress tolerance in host plants by increasing the abundance of several primary metabolites. Although AMF initially suppresses the defense response of the host, it later primes the host for better defense against biotic and abiotic stresses by reprogramming the biosynthesis of secondary metabolites.”(Kaur & Suseela 2020)

Bacteria

"Soil-dwelling Bacillus velezensis migrates along the hyphal network of the AM fungus Rhizophagus irregularis, forming biofilms and inducing cytoplasmic flow in the AM fungus that contributes to host plant root colonisation by the bacterium. During hyphosphere colonisation, R. irregularis modulates the biosynthesis of specialised metabolites in B. velezensis to ensure stable coexistence and as a mechanism to ward off mycoparasitic fungi and bacteria. ..The lipopeptide surfactin plays key roles in the chemical ecology of the interaction " (Anckaert et al 2024)

Physical

Another part of the symbiosis must have been the physical impacts. If roots were holding particles when water being washed over them, gradually building sediment, the fungal hyphae would be making more of a mat to trap more.

“Despite an increasing global understanding of the arbuscular mycorrhizal (AM) fungal diversity, distribution and prevalence in different biomes, we have largely ignored the main dispersal mechanisms of these organisms”.(Paz et al 2021) Looking at available studies, the main distributors appear to be small mammals, soil invertebrates, small birds, wind, and water. Perhaps the most significant are springtails

Stress

There is a growing body of research demonstrating how AMF can protect host plants from biotic and abiotic stress, including increased pathogen resistance, chemical tolerance, heavy metal protection, and mediation of salinity. “An important process for the development of this association is the exchange of chemical signals between the symbionts and the accommodation of AMF inside the plant roots, for which the root cells undergo dramatic developmental changes”(Das & Gutjahr 2019)

There is increasing concern that this important symbiotic relation may be affected by increasing climatic events, like flooding.(Padje et al 2021)

More on AMF in plants and the role of phytohormones

Phosphates

There may well be close relations between mycorrhizal fungi and phosphate-solubising bacteria (Nacoon et al 2020), that we bumped into earlier. AM and phosphate solubilising bacteria (PSB) could interact synergistically because PSB solubilize sparingly available phosphorous compounds into orthophosphate that AM can absorb and transport to the host plant. It seems that the relationship is not multiplier but only ‘additive’.

Key Role

The key role for AMF in soil–plant processes is in unlocking the limiting nutrient phosphorus in soil. The fungi use C a‐phosphate dissolution mineral weathering to have further impacts (Morris et al 2015). The co‐evolution of roots and symbiotic fungi could well have triggered positive feedbacks on weathering rates whereby root–fungal P release supports higher biomass forested ecosystems. There is uncertainty in this around: (1) limited fossil record documenting the origin and timeline of the evolution of tree‐sized plants through the Devonian; and (2) the effects of the evolutionary advance of trees and their in-situ rooting structures on palaeosol geochemistry..

Mycorrhizal roots play a pivotal role in the plant’s phosphate transport system. And phosphates are needed to build the AMF. There are two transport routes - the direct phosphate pathway and the mycorrhizal pathway. They are not simply additive, but we are trying to understand better the mechanism that balances the contribution of these two pathways. We need to learn much more about AMF and phosphates

Other fungi, like Penicillium and Aspergillus, and actinomycetes, can also solubise phosphates

Orthophosphates

AMF don’t just rely on extending the reach of the plant’s root system. They also actively mobilize phosphorus by altering its chemical form in the soil with:

- Release of organic acids: AMF secrete organic acids (such as citric acid and oxalic acid), which can dissolve or break down phosphate-containing minerals in the soil. These acids help release bound phosphates from insoluble compounds, converting them into more plant-available forms like orthophosphates (H₂PO₄⁻ and HPO₄²⁻).
- Release of enzymes: Mycorrhizal fungi also produce enzymes like phosphatases. These enzymes break down organic phosphorus compounds (such as those found in decomposing organic matter), releasing inorganic phosphate that plants can absorb.
- Chelation of cations: In acidic soils, phosphates often bind with iron (Fe) and aluminum (Al), making them insoluble. Mycorrhizal fungi can release compounds that chelate (bind) these cations, freeing up phosphate ions and making them available to plants.

While mycorrhizae are not directly transforming all phosphate forms into orthophosphate themselves, they create conditions that favour the release of phosphate from insoluble or bound forms in the soil. By solubilising phosphorus, they increase the pool of available orthophosphates that roots can absorb, thereby enhancing the plant's access to this critical nutrient. While bacteria also 'solubise phosphates' releasing them into soil, these may be leached away. Whereas when these fungi solubise the phosphates they are already on their way to the roots.

Electrons

When phosphates - from rocks - are released, much of this is adsorbed (adsorbed NOT absorbed) by the soil. This is adsorption is due to lots of electrons moving about

Phosphates come as ‘negative’ particles (with extra electron), called ‘anions’ which are attracted to the positively charged (lacking an electron) ions called ‘cations’ - like calcium, aluminium and iron. In turn these are fixed to the negatively charged clay particles. Calcareous cations are found in chalk and metal ones in more acid soils.(Kalayu 2019) Insoluble phosphates of calcium or hydrous oxides of iron and aluminium cannot be taken up by plants.

PSBs

We have seen that bacteria called Phosphate Solubsing Bacteria (PSBs) were around half a billion years ago They make the surroundings around phosphates more acidic and then ‘chelate’ (make a ring round) those cations, making the phosphate soluble. These bacteria secrete organic acids like citric, oxalic, succinic, tartaric, and malic acids in the soil rhizosphere, and thus ‘chelate the cations’ - ie create complex (but soluble) compounds consisting of a central metal atom attached to a large molecule, releasing the phosphate as soluble orthophosphate.

Various free-living bacteria can ‘solubise’ phosphates, including Bacillus, Pseudomonas, Rhizobium, Micrococcus,Aspergillus,&Fusarium . It was probably around 400mya these PSBs came into their own, creating the chemical pathways to help soil develop and still present to this day. Bacteria fossils discovered in rocks date from around 400mya.

Consortia of PSBs

Recently, it has been found that ‘–e.g.consortium of four bacterial taxa Enterobacter, Citrobacter, Pseudomonas and Comamonas – work much better than individual PSB and improve yields and blooming to levels equivalent to artificial fertilisers (Bass et al 2016).

Bacteria have thus had plenty of time to adapt to their environments and to have given rise to numerous descendant forms, which may evolve increasing the availability of phosphorus in the soil rhizosphere.

The other form of phosphates found in soil is ‘organic’ and is there because of phosphates in animal dung and phytates, the principal storage form of phosphorus in many plant tissues. More than half of soil phosphate comes from this organic matter, which must be ‘mineralised’ (or mobilised’) to become available for plants. Most of the mobilising bacteria are also solubising bacteria. (Samanthi 2021)

There is also a vital relation between AMFs and those PSBs. We have seen that PSBs had been around for around four hundred millions of years. PSBs have been found to enhance metabolically active mycorrhizal colonisation, measured as percentage root length colonized by AMF. It has been found that AMF did not aid plant phosphate uptake when there was only insoluble, rock phosphate, but did when PSBs were added.

Glomalin

The AMF produce a compound called Glomalin. Glomalin is a glycoprotein only discovered at the end of the 20th century (Irving et al 2021). The name comes from Glomales an order of fungi.

One of the key substances said to improve aggregate formation is glomalin. It is a glycoprotein produced by root fungi, and only ‘discovered’ in the mid-1990s..Glomalin acts like little globs of chewing gum on strings or strands of plant roots and the fungal hyphae. Into this sticky “string bag” fall the sand, silt and clay particles that make up soil, along with plant debris and other carbon-containing organic matter.

Glomalin is produced, not by roots like a root exudate, but only by AMF. It is produced aerobically, meaning that the function involved relies on oxygen. There is oxygen in the atmosphere, and this would be available too in any shallow soil formation. It would be a crucial element in soil development. Aerobic functions can now go on that are vital for chemical transfers.

Glomalin occurs in very large amounts in soil, typically in the range of several to 10 mg g−1 soil, representing a – if not the – major contribution to Soil Organic Matter (SOM) Glomalin decomposes slower than the AMF hyphae producing it, and the estimated turnover time for glomalin in soil is on the order of several decades..

Onychiurid springtail

The glomalin glycoprotein has 3-10 sugar molecules and is insoluble and water resistant and provides the sheath over filaments. The pathway of release of glomalin into soil is not clear. Glomalin could be actively secreted at the hyphal tip, or it could be sloughed off hyphae as they grow through soil. I've seen springtails - onychiurid - nibbling these hyphae. They contain a lot of energy trapped as sugars, as well as glomalin. As a plant grows, the fungi move down the root and form new hyphae to colonize the growing roots. When hyphae higher up on the roots stop transporting nutrients, their protective glomalin sloughs off into the soil, providing an incredible food source

Glomalin is being seen as 'the glue' of the soil. Glomalin is very strong and found throughout the world with the most in soils in Hawaii and Japan. "Anything present in these amounts has to be considered in any studies of plant-soil interactions," Wright says. "There may be implications beyond the carbon storage and soil quality issues—such as whether the large amounts of iron in glomalin mean that it could be protecting plants from pathogens."

This sticky protein may become the unsung hero of carbon capture. One study showed that glomalin accounts for 27 % of carbon in soil and is a major component of soil organic matter, previously discounted when calculating ‘humus’ content. Thus, glomalin must provide food for many creatures, as we will see when looking at springtails, which also explains about GRSPs.

Glomalin eluded detection until soil scientist Sara F Wright,in 1996, boiled some up in a bath of citrate to 250 F (121 C) for at least an hour. “No other soil glue found to date required anything as drastic as this,” says Sara Wright.

GRSPs

Since the turn of the century, research efforts have concentrated not on glomalin itself, but have switched to the snappy-sounding ‘Glomalin Related Soil Protein’ (GRSP). It is not clear from many studies whether Glomalin and GRSPs are different names for the same thing. I think not, but that glomalin is a resistant glycoprotein, but is broken down to GRSPs found widely.

"GRSP is a mixture of compounds that contains humic, lipid, inorganic materials, etc. (Gillespie et al., 2011). It is estimated that the organic C in GRSP accounts for 4–15% of SOC (Rillig et al., 2001, Singh et al., 2016, Wang et al., 2020a), and its residence time in soil is around 35 years (Harner et al., 2004)." (Yang et al 2024)

The link between glomalin and various protein fractions in the soil is not yet clearly defined, so the term glomalin-related soil protein (GRSP) was coined by Rilling (2004) and is now used to describe glomalin's existence in natural organic matter (NOM) (Schinder et al 2007) GRSP is increasingly being quoted as the important active soil ingredient, often described as a ‘microbial by-product’, which plays a key role in soil aggregation, flocculation and metal holding (Wang et al 2021) and more generally good soil health (Galazka et al 2020).

There are debates about GRSP, about the veracity of the testing and measuring methods and whether it is mixed with humic substances.

How does glomalin become GRSPs? This is up for debate. I believe the role of springtails should be explored. What if they chewed the heavy-duty glomalin, and with the help of the bacteria in their guts, turned it into GRSPs? But we need proof.

See 'Don't pooh-pooh humus'

Research

The most recent review of GRSPs says the research "could be divided into the initial stage (1999–2009), the steady stage (2010–2018), and the explosive stage (2019–2022). The Chinese Academy of Sciences is the organization with the most publications, and the United States, China, and India are the three leading nations in the C field of GRSP." (Deng et al 2023)

Deng et al (2023) go on "AMF, the producer of GRSP, can combine microaggregates into macroaggregates. Hence, AMF stabilize soil aggregates to increase the residence time of organic C in soil.....Studies have revealed a significantly positive correlation between GRSP levels and SOC concentrations , because GRSP contain organic C. Therefore, different land use patterns and climate conditions will lead to dynamic changes in C ."

See Glomalisation for more on my original contribution to science

But how does the AMF stabilise soil? It is not explained. Along with many others Dung et al conflate 'glomalin' and 'GRSPs'. But they are not the same - glomalin is hard to isolate and break down while all the smaller RSPs are going round reacting. Dung et all identify the elements in both, but not their chemical structures. Much more needs to be done on this, as it is obvious there is a lot of interest, as they visiulaised the changes in hot research topics...

Glue

AMF are widely considered to stabilise soil aggregates. But how?, We know mycelium and GRSP of AMF have a positive correlation with soil aggregate stability in natural systems. Yet note, it is the GRSPs which have the association not glomalin itself - a stable compound, insoluble in water and resistant to heat degradation, and not isolated till mid 1990s.

I propose that it is the breakdown products of glomalin - GRSPs - which are so sticky to make aggregates

"GRSPs stabilise the macro aggregates (> 0.25 mm) to improve soil structure through their glue function and the function is more significant under drought stress than under salt stress". Eramma et al 2021
"Our results firstly demonstrated the positive contribution of exogenous EE-GRSP to soil aggregation, relevant rhizospheric enzyme activities and/or plant growth, which has important implications for exploring GRSP in enhancing soil structure and/or plant performance" Wang 2015

This 'primary article aggregation mechanism' would have been essential in the creation of soil at the water's edge all those years ago. For complete explanation of my hypothesis called 'glomalisation'

"Based on its solubility characteristics, glomalin would be a component of the humin fraction, but if it exists as a glycoprotein, it would need to be sorbed onto soil mineral colloids (crystalline layer silicate clays, noncrystalline layer silicate clays, and non-silicate clays) or refractory organic substances". (Hayes et al 2017).

So if glomalin is not part of humification, but exists as a glycoprotein, it (or rather GRSPs) could have created better soil particles all those years ago, by mixing with clay colloids and organic remains.

GRSPs & Clay

An investigate into the sorption of phenanthrene (as a model polycyclic aromatic hydrocarbon PAH) by metal cation-modified montmorillonites in the presence of GRSP, "highlighted the vital contribution of GRSP to this sorption. GRSP, as a glue-like protein, could bind or sequestrate large amounts of phenanthrene. The sorption experiments showed that the sorption amounts of phenanthrene on montmorillonites significantly increased with the introduction of T-GRSP and EE-GRSP, i.e., GRSP-bound montmorillonite samples exhibited higher phenanthrene sorption capacities. (Chen et al 2019)

Improved sorption of polycyclic aromatic hydrocarbons (PAHs) by clays has significant implications for the rest of the soil and the broader environment. PAHs are a group of organic pollutants that are typically hydrophobic, meaning they don't dissolve easily in water and can persist in the environment. Clays, due to their high surface area and chemical properties, can adsorb (or bind) these PAHs more effectively.

This improved sorption means for the rest of the soil: Clays that have
enhanced sorption capacity can:

1. Trap PAHs more effectively, reducing their mobility in the soil. This limits the migration of PAHs to deeper soil layers or into groundwater, thereby containing any pollution and preventing its spread. This is especially important for protecting water supplies and ecosystems that could be harmed by PAH contamination.

2. Enhance soil's ability to act as a filter, helping to remediate PAH-contaminated sites. When PAHs are strongly adsorbed onto clay particles, they are less bioavailable, meaning they become less likely to be absorbed by plants, soil organisms, or enter the food chain. This could improve the overall health of the ecosystem in contaminated areas.

3. alter the physical and chemical properties of the soil. For example, increased PAH binding can change the surface chemistry of clay particles, potentially affecting how nutrients or water move through the soil. This could influence plant growth and soil fertility, especially in soils with high clay content. Additionally, as clays adsorb more PAHs, the soil structure might become more compacted or less permeable, affecting root growth and water retention.

Influence on Soil Microbial Activity

The bioavailability of PAHs influences microbial activity. If clays adsorb PAHs too effectively, this might reduce the availability of these hydrocarbons for degradation by microbes that can break them down (biodegradation). As a result, while improved sorption can stabilize PAHs and reduce their toxic effects, it might also slow the natural breakdown of these pollutants by microorganisms.

Protection of Plants and Soil Organisms

By trapping PAHs, clays can reduce the exposure of plants and soil organisms to these harmful pollutants. This can help mitigate toxic effects such as stunted plant growth, reduced microbial diversity, and toxicity to soil invertebrates, all of which are crucial for maintaining a healthy and functioning ecosystem.

In summary, improved sorption of PAHs by clays generally means better containment and stabilization of organic pollutants in soil, protecting groundwater, plants, and organisms. However, it also raises concerns about the long-term fate of PAHs in the environment and their potential effects on soil fertility and microbial degradation processes.

The role of GRSPs in increasing PAH sorption adds an extra layer of defense against soil and water contamination, further immobilizing PAHs and protecting the ecosystem. While this could reduce the availability of PAHs to cause harm, it might also slow down natural biodegradation.
This insight could lead to innovative soil remediation strategies, especially for regenerative agriculture, that involve boosting mycorrhizal fungi and GRSP production to enhance soil's natural capacity to deal with PAH contamination. This has been added to the Glomalin Research Gaps

The fact that Glomalin Related Soil Proteins (GRSP) increase the sorption of polycyclic aromatic hydrocarbons (PAHs) by clays adds another layer of complexity to how these pollutants interact with the soil environment.

Here's how GRSPs may affect the sorption of PAHs and what it means for the soil:

1. Increased Sorption Capacity

GRSPs likely enhance the binding of PAHs to clays by increasing the overall surface area or providing additional binding sites for these hydrophobic compounds. This could mean that soils with higher GRSP levels can trap more PAHs, further immobilizing these pollutants and preventing their movement through the soil and into water systems.

2. Enhanced Soil Structure and Aggregation

GRSPs are known to promote soil aggregation by binding soil particles together. This improved aggregation could have a dual effect:

It may reduce the mobility of PAHs, as these pollutants can become trapped within the stable soil aggregates.
It could also reduce erosion, thereby preventing the spread of PAHs to other parts of the ecosystem via water or wind.

3. Synergistic Effect with Clay

Clays already have a high sorption capacity for PAHs, and the presence of GRSPs may amplify this by creating a synergistic effect. GRSPs can coat the clay particles, potentially altering their chemical properties in a way that makes them even more effective at capturing PAHs. This could be particularly useful in soils with high clay and GRSP content, effectively locking down PAHs and reducing their availability in the environment.

4. Reduced Bioavailability of PAHs

With GRSPs helping to enhance the sorption of PAHs, this might further reduce the bioavailability of these contaminants. This is important for reducing the toxic effects of PAHs on plants, microorganisms, and animals in the soil ecosystem. However, as with improved sorption by clays alone, this could also slow down the natural biodegradation of PAHs because they are less accessible to microorganisms that break them down.

5. Potential Impacts on Soil Microbial Communities

GRSPs themselves are a byproduct of microbial activity (from mycorrhizal fungi), and their role in PAH sorption could also influence the broader soil microbial community. By trapping PAHs more effectively, GRSPs could protect the microbial populations that are sensitive to PAH toxicity, allowing more balanced and diverse microbial ecosystems to thrive in contaminated soils.

However, there could also be a downside: if PAHs are sorbed too strongly, some microbes that rely on them as a carbon source (for biodegradation) might have less access, which could slow down the natural cleanup process. This raises interesting questions about the balance between reducing toxicity and allowing natural degradation to occur.

6. Implications for Soil Remediation

The involvement of GRSPs in increasing PAH sorption could be harnessed for bioremediation purposes. Soils enriched with mycorrhizal fungi and GRSPs may be more effective at trapping PAHs and other hydrophobic pollutants, potentially offering a natural or enhanced method for cleaning up contaminated soils. By promoting fungal growth or adding organic matter that encourages GRSP production, soil remediation strategies could improve.

7. Long-Term Stability of PAHs

While GRSP-enhanced sorption could immobilize PAHs in the short term, the long-term stability of these complexes is still uncertain. Changes in environmental conditions (such as soil moisture, temperature, or pH) might affect the ability of GRSPs to keep PAHs locked away. Over time, GRSPs can degrade, which might release previously bound PAHs back into the soil. This means that while GRSPs enhance sorption, they might not be a permanent solution unless the soil environment remains stable and conducive to the continued production of GRSPs.

8. Broader Soil Health Implications

Since GRSPs are critical for soil aggregation and health, their role in PAH sorption ties into the larger picture of soil quality. Healthier soils with higher GRSP levels are likely to be more resilient to pollution and better able to protect plants and soil organisms from PAHs. This also emphasizes the importance of maintaining practices that encourage mycorrhizal fungi, such as minimizing soil disturbance (like tilling) and avoiding excessive chemical inputs that harm beneficial fungi.

PAHs

We primarily encounter PAHs as pollutants resulting from the incomplete combustion of organic matter (fossil fuels, biomass, etc.). However, their cosmic and geological history reveals that they were forming billions of years ago, as their presence in meteorites and space dust tells us.

Clay Flocculation

This is the process when clay mineral platelets which are physically dispersed, form edge to face electrostatically attracted (+edges to -faces) attachments, which eventually 'clump' enough to form 'flocs'
The clay then aggregates and precipitates out of the suspension due to gravity and settles to the bottom, removing algae and various minerals from the water along the way. It is hard to underestimate the importance of GRSPs and clay minerals in the creation of sediments that would lead to soil formation...as Wang says..

Bioflocculent

"We found that GRSP fraction (gravimetric mass of extracted GRSP, 5.1–24.3 mg g−1) was a globally relevant novel bioflocculant and that protein (linked to Bradford protein assay, 1.64–4.37 mg g−1) was the active flocculant constituent.....The analysis of particle aggregation mechanism and its metal adsorption capacity is of great significance to elucidate the role of GRSP fraction in coastal environment improvement. (Wang et al 2021).

This is likely to have gone on in the presence of bacteria which could make larger masses, as several of them (like Bacillus nitratireducens & velezensis) are bioflocculents in their own right.

Bioflocculants are a promising alternative to synthetic organic and inorganic flocculants in wastewater treatment because they are biodegradable, safe and often cheaper. They can be produced from a wide range of microorganisms, and now seemingly GRSPs, and are composed of glycoproteins, protein, or polysaccharides

The difference between flocculated (aggregated) and dispersed soil structure. Flocculation (right) is important because water moves through large pores and plant roots grow mainly in pore space. Dispersed clays (left) plug soil pores and impede water movement and soil drainage (Choudhary & Kharche, 2018)

EcM 200- 145 mya

EcM do not appear for another 200my. Trees associated with ectomycorrhizal fungi (EcM):

Conifers
Broadleaf trees like oaks (
Some tropical trees like Dipterocarpaceae in tropical rainforests
Oaks (Quercus spp.):
Beeches (Fagus spp.):
Birches (Betula spp.):.

Fungi 500mya

Glomalisation

Plants

Springtails

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