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Activity 3
Activity 3
In Groups, Choose one of the 3 functions, Decomposing (drilosphere), Growing plants (porosphere) OR Building Aggregates aggrugatesphere
Make a poster explaing that particular function (in the relevant 'sphere') as if to group of 6th formers. Use the links (including Digging Deeper) to collect pictures/videos of the key characteristics and make into a collage.
Either print out physically or 'Whats App/Instagram/send' poster and we'll add them here...
Overall function
Overall function
All living things are divided into five kingdoms: animal, plant, fungi, protist and monera and they are ALL found in soil. The microrganisms - bacteria and fungi in particular, perform a range of important processes, both in aerobic and anaerobic conditions, thereby giving the soil resilience. There are small soil creatures which feed, walk and spread the microorganisms and a lot of poo. This helps bind the soil particles together to make aggregates, the key soil component. Aggregated soil particles, with pores between them , help support plants and animals with their breathing and nutritional needs.
"Soil functions are flows and transformations of mass, energy, and genetic information that connect soil to the wider critical zone"
3 main Functions
3 main Functions
There are three main functions carried in soils, each involving similar amounts of energy and making up about 90% of soil life.
Decomposing dead debris
Helping grow plants
Building aggregates
Click Life IN Earth Soil 1 Functions
NOTE!!! When we talk about soil life, you will here about the soil web, often described as the body of worms,fungi and microorganisms. Here we include also sorts of other small soil creatures - called arthropods (jointed legs) - that run round connecting up all the other components. They have bacteria in their guts and spread various spores around as they travel, thus distributing the microorganisms and giving thema safer place to live.
We hear a lot about soil carbon, but this does not come as a lump of carbon. It comes in the form of various organic compounds, many running round in the bodies of these arthropods. This may be as skin (cuticle) or inside body, particularly their organs and the metabolism they support. As a result of these 3 functions, soil performs another vital function - water holding - which we will see may be the most important function/feature.
CC How our soil works (or click image)
- Decomposing dead debris
This is the function most people know about, and many consider that this is the sole function of soil. Yet it is relatively recent function, in geological time.
Basically the worms are the great earth engineers turning over the soil mixing it up and excreting the mixture with mucous . This is called 'Bioturbation'. There are 3 main groups fo earthworms - epigeic, endogeic and anecic (like Lumbicus terrestris)
The mucous attracts other small creatures - predominantly mites, whose guts are full of bacteria. These break down big molecules like lignin and chitin to small carbohydrates that are now food for others and plants. This is called 'Humification', and the end product is humus, which helps build aggregates - see below.
More on Humification & Decomposition
More on Humification & Decomposition
Humus is created through anaerobic fermentation, while compost is the result of aerobic decomposition.
Composting
Composting
Two hardest compound to break down are lignin and chitin. Lignin is chemical that makes plants strong enough to hold water that makes strong skeleton for plants to grow up - hence ‘vascular’ plants.
The converse is lignin is hard to breakdown. White rot fungi (aerobic) use strong enzymes, proteins that speed up chemical reactions. These enzymes split many of lignin's chemical bonds, turning it into simple sugars and releasing carbon dioxide into the air. White rot is better at rending lignin than any other type of fungus First discovered early 1930s. More on decomposition
But this is much more extensive
Humification
Humification
Oribatids chew up that harder to digest stuff – the wood with lignin. Breakdown by bacteria (anaerobic) can occur in soil and In the bodies of mites. They can break down lignin and other hard to digest substances, with various bacteria carrying out different chemical reaction. This leads to a substance we call ‘humus’ - a complex, reactive but stable ‘sludge’, consisting of ‘Humic Substances’. This process is all about breaking down complex bits of organic matter into simpler chemicals. The Humus Substances are attracted electrostatically to colloid particles like clay, and thus help to build aggregates! More on humification
So humus may have provided the next step in the evolution of soil..
More in the drilosphere
2. Helping grow plants
2. Helping grow plants
Various creatures keep the root sof plants healthy, so that they can better supply the necessary water and nutrients to the main part of the plant. To help do this, most plants have relations with fungi - called mycorrhiza - that extends the spread of the roots thus absorbing much more than they could on their own. Their filaments absorb nutrients for plants, and can collect water from further afield, and in return plants provide the fungi with energy. They produce glomalin - accounting for around 1/4 of all carbon in soil.
Springtails nibble the roots and eat the dead fungi. They poo out glomalin related products that help make soil aggregates.
More on plant growing
More on plant growing
The area around roots is called the 'rhizosphere'.
Mycorrhiza have evolved in four different forms over the years - the first over 350 million years ago. Living between the roots and fungi are one of the main groups of soil animals - springtails - which also go back nearly 400 million years. They and eat the fungal glomalin, dead debris on the roots and dead bits of fungi too. In the process they accidentally pass on the fungal spores to the roots, thus acting like 'bees of the soil'.
Click image See how springtails jump and lay eggs and how some mites (tr)eat them
More in the porosphere
3. Building aggregates
3. Building aggregates
The property of soil that distinguishes it from silt, sludge, mud and dirt is that the soil consists of many structures of different shapes and sizes, and it is these that house the creatures and organisms, providing them stable living place - otherwise they would soon be washed away. These aggregates are called 'peds' which give the name to soil science - pedology. These aggregates start as (microaggregates) coating on clay particles, that stick together catching other bits of debris. Subtle science of soil aggregates
More on Aggegates
More on Aggegates
Soil animals have an important role in the formation of soil structure. Soil animals improve soil structure by forming - along with roots, worms and fungi - channels and pores.
Soil animals also do a lot of chewin and pooin'. The poo from springtails has the catchy name Glomalin Related Soil Protein'. (GRSP) and it is very sticky helping to make aggregates. Mites chew , and thanks to the bacteria in their guts, poo with humic-like substances. They too provide coatings to for aggregate formation. This is a crucial soil characteristic where concentrating fine soil particles together into aggregates, by fragmenting and mixing organic matter through soil. Between aggregates are pores, providing a living atmosphere and accounting for much of soil.
Carbon
"Plant-stimulated soil pore formation appears to be a major, hitherto unrecognised, determinant of whether new C inputs are stored or lost to the atmosphere. Unlike monocultures, diverse plant communities favour the development of 30–150 µm pores." Nature provides "novel evidence that development of pores of certain sizes can have a controlling effect on C accrual"
More on soil structure and in the Aggregatusohere
The biology is soils involves many biochemical reactions, most involving electrons, that are either aerobic or anaerobic. Both can work closely alongside each other.
"The Science Behind Healthy Soil: NRCS' Soil Health Literature Review Project" Webinar Slides
Nutrient Cycling Elaine Morgan
Sustainable Soils Alliance Monthly Blog BSSS
Most soil reactions involve the transfer of electrons
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