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Hermitage Plant Science Competition

Presentation to CONASTA 69

Canberra 2023

Kerrie Rubie

Simon Hamlet

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Day in the life of soil

Initially saw this resource being deployed by the agronomist David Hardwick at a biodiversity day in Killarney SEQ.

With his permission is has become one of my go to teaching resources.

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“Leonardo da Vinci remarked that we know more about the movement of the celestial bodies than about the soil on our own planet. This remains true today.”

George Monbiot (2022) Regenesis. Allen Lane.

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David Hardwick DILOS with farmers.

Soils | Soil Land Food

Runs for about an hour.

A good revision tool.

Uses lollies not unifix blocks.

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_{Script for set up,}

Hand out the eighteen cards to participants. Not all the cards are needed for the exercise; the essential group is cards 1-8. I also require volunteers to play the roles of the atmospheric carbon pool, the atmospheric nitrogen pool and the rock bound phosphorous pool.

Have participants examine their cards and ask them to stand in groups according to their organism’s characteristics, grouping one feature at a time; eg. kingdom, size, diggers, etc. Facilitate a conversation about diversity in the soil system, and the way in which many of the important components in the soil are not visible to the naked eye.

Point out that only 18 cards are represented in the role play. Can participants think of other organisms which could be on the cards? James Nardi’s book Life in the Soil is an excellent resource to help with this.

Inform participants that at the end of the role play they will be using the cards to construct a soil food web.

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Source: adapted from http://www.engineeringtoolbox.com/air-composition-d_212.html Retrieved Aug 7, 2013

Composition of Dry Air by Volume

Script for drawn from air

This is an optional opening procedure, which focuses on the significance of air to the plant.
Have students blow on their hands ... the reason we can feel the breeze is because air has weight.
Refer to the air density calculator (denysschen.com). This will allow you to customise the air weight for the days presentation. For this exercise I will work through an example which assumes an elevation of 580m and a temperature of 20 °C, at which air has a density of 1.121 kg/m³.

Note that the density of air is influenced by elevation above sea level and temperature and presence of water vapour. The higher the elevation the lower the density and the higher the temperature the lower the density.
For the purpose of this exercise we will consider dry air. The addition of water vapour to air actually decreases the density of air.

Introduce the makeup of Air. The composition is most often conceptualised as proportion by volume. Mostly, N (78%), O (21%), Ar, and CO₂. Show on a pie chart, the fraction of CO₂ is so small it appears as a line, scientists report this as ppmv (parts per million by volume). Due to the difference in the molecular weights of the components which make up air, the proportions by weight are somewhat different (see http://www.engineeringtoolbox.com/air-composition-d_212.html).
Weight of CO₂ in a cubic meter of air = 1,183 * 0.00046 = 0.54 grams of CO₂.
We are interested in Carbon Cycling, 27.3% of the weight of CO₂ is C, so amount of carbon in a cubic metre of air = 0.54 * 0.27 = 0.147 grams of C per cubic metre of air.
Look out the window. 97% of all the weight in all the plants you can see comes from this tiny fraction of CO₂ in air.
Hold up a piece of wood of known weight. For this exercise I will use a block of pine wood weighing 500 grams. A piece of dried pine wood is approximately 50% C.
We may think that we could take a piece of wood like this 500g piece of pine. Divide that by 50% to get 250g. Then Divide 250g by 0.147g to get approx 1,700 m³.
But plants also respire! That amount of air needed is much greater.
When introducing the rhizobia and other nitrogen fixing organisms refer back to point 3 above.

Call out Card 1, ‘the plant’. The plant is the key focus for the agricultural soil system; this is the crop. It is also the only primary source of carbon (C). Plants bring C into the soil via photosynthesis; water plus carbon dioxide in the presence of light (and chlorophyll) produces oxygen plus carbohydrates (which contain C). C is represented by black Unifix blocks. Give a handful of these blocks to the ‘plant’. Stress that this C comes from the air. The vast majority of plant biomass is derived from air.

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Model three nutrients

Carbon
Nitrogen
Phosphorus

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Carbon

Tracking carbon through a system is a proxy for tracking energy.

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Equations for the process of photosynthesis

(Word, unbalanced and balanced)

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Photosynthesis and respiration are the reverse of each other.

Where photosynthesis captures energy as sugars, respiration liberates that energy for cellular processes.

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Element	Chemical Symbol	Concentration in dry matter (ppm by weight)
Nitrogen	N	1.5
Potassium	K	1.0
Calcium	Ca	0.5
Magnesium	Mg	0.2
Phosphorus	P	0.2
Sulphur	S	0.1
Silicon	Si	0.1

Source: Taiz, L. & Zeiger, E. (2006). Plant Physiology, 4th edition. Sinauer & Associates: Massachusetts.

List of Plant Macronutrients

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Proportional Composition of Soil

Source: CMG Garden Notes #211 Introduction to Soils & CMG Garden Notes # 212 The Living Soil. Retreived September 26, 2013 from http://www.ext.colostate.edu/

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Organism	Number
Bacteria	200 Billion
Protozoa	20 Million
Fungal hyphae	100 kilometres
Nematodes	100,000
Arthropods	50,000

Source: Colorado State University (2011) The Living Soil. Retrieved July 16, 2013 from http://www.ext.colostate.edu/mg/gardennotes/212.htm

Number of organisms

in one cup of undisturbed native soil.

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Organism	No per m²	No per gr	kg/HFS
Bacteria	10¹³ - 10¹⁴	10⁸ - 10⁹	450 - 4,500
Actinomycetes	10¹² - 10¹³	10⁷ - 10⁸	450 - 4,500
Fungi	10¹⁰ - 10¹¹	10⁵ - 10⁶	1,120 - 11,200
Algae	10⁹ - 10¹⁰	10⁴ - 10⁵	56 - 560
Protozoa	10⁹ - 10¹⁰	10⁴ - 10⁵	17 - 170
Nematoda	10⁶ - 10⁷	10- 10²	11 - 110
Other fauna	10³ - 10⁵		17 - 170
Earthworms	30 - 300		110 - 1,100

Relative number and biomass of soil biota commonly found in surface soils (to a depth of 15cm with the exception of earthworms which are deeper).

Based on a table in Brady (1990), page 257.

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C. H. O. N. P.

Carbon Hydrogen Oxygen Nitrogen Phosphorus

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Two symbionts, aka mutualists

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Nitrogen

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Importance of Nitrogen (N)

Constituent of amino acids, amides, proteins, nucleic acids, nucleotides, coenzymes, hexoamines, etc.

Simple summary essential nutrient for life.

Source: Taiz, L. & Zeiger, E. (2006).Plant Physiology, 4th edition. Sinauer & Associates: Massachusetts.

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Producing 2.5kg of ammonia fertiliser takes an amount of energy equivalent to burning 1000kg of coal. Even for bacteria that do it naturally, nitrogen fixation requires a great deal of energy.

Spencely et al (2004), p. 208.

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Nitrogen and Energy

Thanks to the Haber – Bosch process “2% of the world’s energy consumption is taken up with the production of nitrogen fertilisers.”

Sutton et al (2013)

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Nitrogen cycle

Fixation
Nitrification
Denitrification

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Phosphorus

Unlike the carbon and the nitrogen which are derived from the air. Phosphorus is derived from rock.

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Importance of Phosphorus (P)

Component of sugar phosphates, nucleic acids, nucleotides, coenzymes, phospholipids, phytic acid, etc. Has a key role in reactions that involve ATP.

Taiz & Zeiger (2006)

Simple summary essential nutrient for life.

Source: Taiz, L. & Zeiger, E. (2006). Plant Physiology, 4th ed. Sinauer & Associates: Massachusetts

The P in rocks is not in a form usable by plants, so plants require the services of other organisms to solubilise the P in the environment. Mycorrhiza do this by excreting acid. 80-90% of plant species have some form of mycorrhizal relationship that assists the plant in many ways, but for the purposes of the role play we are focusing on their ability to solubilise P. P is represented by blue Unifix blocks. Give a handful of these to the ‘mycorrhiza’. You may like to store the blue Unifix blocks in a container with some rocks to show that the P comes from rocks rather than from the air.

Both rhizobia and mycorrhiza live inside the plant roots. The plant exchanges C captured via photosynthesis for the N and the P converted by the symbionts. Encourage the plants and the symbionts to negotiate the value of the N and the P and engage in an exchange. Show that the symbiont makes a direct exchange with the plant ie. injecting into the plant root, not into the soil.

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Root Exudation

The leaking of chemicals into the soil which improves soil structure, has defensive roles and feeds the soil ecosystem.

Cards 4, 5 and 15

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Predator 🡪 Prey

Time to eat.

Time to defecate.

Time to die and decompose.

Let link some cards.

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The Farmer

Time to decide.

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Lesson Planning

Play the game (1-2 lesson)

Consolidate terms, fixation, etc.

Map the food web (1 – 2 lessons )

Focus on diagram literacy.
Explore symbiosis

Student research task (1-2 lessons)

Focus on research strategies, search terms, collecting relevant data and referencing conventions.

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Continued …

Move into nutrient cycles …
Go chasing organisms …

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Diagram literacy

Arrows show movement of energy, i.e. from prey to predator (see chain below)�Bacteria 🡪 Protozoa 🡪 Springtail

Arrows not used in scientific illustration they have specific purposes in specific contexts. This example is food web, but other contexts are ray diagrams, free body diagrams.

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Food web literacy

Predation:

There are over 18 predator – prey relationships in this diagram.

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Research Task (4 slides)

Title
What is [it]?
What is [its] role in the soil?
How is [it] managed?