THE IMPORTANCE OF SOIL CARBON AND THE ASSOCIATED MICRO-BIOME

Soil carbon is the primary measure of soil organic matter (SOM) and is a key indicator of soil health and quality. A high level of soil carbon implicates a stable and healthy soil, where a healthy soil is being described as the soil’s capacity as a ‘’living ecosystem’’ to support productivity, filter water and maintaining dynamic biological functions through its individual components – physical structure and porosity, chemical (nutrients, pH) and biological (microbes, earthworms, dung beetles), connected in the organic matter.

The microbial component, or micro-biome, of the soil is of special interest, yet still inadequately studied. It reflects exceptional biodiversity and is the largest source of microbial populations any where on earth, about 60% of all. The Enchytraeidae have the greatest percentage of species in soil (98.6%), followed by fungi (90%), Plantae (85.5%), and Isoptera (84.2%). From a soil health and quality perspective, the soil should be rich in fauna(earth worms, dung beetles, other invertebrates), microbial phyla (major ones are Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes)and the mycorrhizal fungi, especially the arbuscular group (arbuscular refers to the tree-like highly branched feeding structures of the fungus inside the plant root cortical cells).

Soil micro-biome work in recent international research has focussed much on the mycorrhizal fungi. Mycorrhizal mycelium is the vast, underground network of fungal threads (hyphae) that forms a crucial symbiotic partnership with plant roots, exchanging vital water and nutrients (P, N) for plant sugars (carbon). However, its functions go much further: (a) Fungal mycelium extends far beyond root systems, as it can gather water and minerals from the soil elsewhere and delivers them to the plants in return for energy-rich sugars from photosynthesis; (b) They also connect trees and plants, enabling them to share resources and even send distress signals to support ecosystem health; (c) Their sticky nature helps to bind soil particles, thereby forming stable aggregates that improve soil structure and water retention; (d) Mycorrhizal (fungus-root) fungi are significant in the global carbon cycle, as they move substantial amounts of carbon from plants into soil for stable storage. One estimate shows 13+ Gt of CO₂e fixed by terrestrial plants is, at least temporarily, allocated to the underground mycelium of mycorrhizal fungi per year, equating to about 36% of current annual CO₂ emissions from fossil fuels. It is evident that Mycorrhizal mycelium is an essential component of terrestrial ecosystems, which is vital for plant survival, forest health, nutrient cycling and soil stability, and by supporting a huge portion of the Earth’s biodiversity.

Observation: Measurement of soil carbon as a prime indicator of soil health of dairy pastures is crucial moving forward, but we need to go even further, by measuring soil micro diversity. In this, the Mycorrhizal mycelium with its vast functions is crucial. The methods in some instances require sophisticated measurements, but we need to create the capacity. Soil microbial count and diversity can be determined by two types of amplicon sequencing: (a) 16S rRNA gene metagenomics sequencing and (b) ITS metagenomics sequencing to understand the diversity of the bacterial and fungal community, whereas Mycorrhizal mycelium analyses include direct microscopy after physical soil sampling and molecular techniques (real-time PCR [qPCR]).