SCE 3108

Subject :
Ecosystem and Biodiversity (SCE3108)

Topic :
Soil ecosystems (Soil Biota and Food Webs)

Objectives :
1. To enable students to identify and differentiate diversity of macro fauna from different types of soils.
2. As a platform to students to gain experience with techniques for extraction of soil organisms
3. To gain the ability to recognize characteristic traits of the major groups of soil dwelling organisms
4. To enable students o practice basic microscopy skills
5. To increase students’ understanding about the food web involved and the functions of soil biota.

Introduction:
Everything in the natural world is connected. Anecosystem is a community of living and non-living things that work together. Ecosystems have no particular size. An ecosystem can be as large as a desert or a lake or as small as a tree or a puddle. If you have a terrarium, that is an artificial ecosystem. The water, water temperature, plants, animals, air, light and soil all work together. If there isn't enough light or water or if the soil doesn't have the right nutrients, the plants will die. If the plants die, animals that depend on them will die. If the animals that depend on the plants die, any animals that depends on those animals will die. Ecosystems in nature work the same way. All the parts work together to make a balanced system.
Soil is a critical part of an ecosystem. It provides important nutrients for the plants in an ecosystem. It helps anchor the plants to keep them in place. Soil absorbs and holds water for plants and animals to use and provides a home for lots of living organisms.
A healthy ecosystem has lots of species diversity and is less likely to be seriously damaged by human interaction, natural disasters and climate changes. Every species has a niche in its ecosystem that helps keep the system healthy. We are learning about new species every day, and we are just figuring out the roles they play in the natural world. By studying and maintaining biodiversity, we help keep our planet healthy.
The atmosphere provides oxygen and carbon dioxide for the plants and animals in an ecosystem. The atmosphere is also part of the water cycle. Without the complex interactions and elements in the atmosphere, there would be no life at all.
The heat and light from the sun are critical parts of an ecosystem. The sun's heat helps water evaporate and return to the atmosphere where it is cycled back into water. The heat also keeps plants and animals warm. Without light from the sun there would be no photosynthesis and plants wouldn't have the energy they need to make food.
Apparatus:
1. Plastic bags
2. Retort stand
3. Petri dish
4. Torch light
5. Piece of cloth
6. Hand lens
7. Container
8. Measuring scale
9. Measuring cylinder
10. Forceps



Procedure A: Identification of macrofauna
1. A measured volume of the leaf litter and topsoil are examined using a hand lens.
2. Any fauna found is removed to a clean petri dish for identification according to different groups ( with legs and no legs).
3. The number of each group is counted and results are tabulated. (refer table 2 and 3 in results section)
4. The results from both tables are counted and calculated regarding the number of Orders or groups per liter of soil and leaf litter. (refer table 4 in results section

Procedure B : Identification of Microfauna
1. A sample of leaf litter ( O Horizon) and topsoil (A Horizon) which is not deeper than 3cm is collected from two different locations. It was choose from lawn, native vegetation, garden bed, under species of trees or other distintive area.
2. The sample was placed in plastic bags, sealed and was labelled with group name and collection location.
3. Both sites characteristics were tabulated in table 1. ( refer Table 1 in Result section)
4. In the lab, the soil and leaf litter sample from the same location were mix thoroughly.
5. About 100g of both samples were placed in two different Tulgren funnel.
6. Leave the sample for two days.
7. After two days, the preserving jar containing ethanol is removed and the lid is screwed.



Results:
Sites characteristics

Site characteristics Site 1 Site 2
Type of vegetation Lawn Garden bed
Level of shade Low High
Soil dryness/dampness Very dry Wet
Soil pH - -
Soil compactness Hard Loose
Soil texture Sandy Soggy

Table 1
Identification of Macrofauna
a) Macrofauna
Macrofauna Order or group Number at site 1
Soil volume = 1000 g/cm3 Number at site 2
Soil volume = 1000 g/cm3
Group A – without legs Earthworm (1)
Insect larvae (1) Earthworm (3)
Insect larvae (1)
Group B – with legs Ants (10) Termites (4)
Ants (13)
Spider (2)
Millipede (3)
Beetle (1)
Centipede (1)
Snail (1)
Total 12 29
Table 2

b) Microfauna
Microfauna Order or group Number at site 1
Soil volume = 1000 g/cm3 Number at site 2
Soil volume = 1000 g/cm3
Group A – without legs No result found No result found
Group B – with legs No result found No result found
Table 3

The number of Orders or groups per liter of soil and leaf litter
Macrofauna Site 1 Site 2
Number of orders or group per cm3 soil/litter 12/1000 = 0.012 unit per g 29/1000 = 0.029 unit per g
No. individuals of group A per cm 3 soil/litter (without leg) 2/1000 = 0.002 unit per g 4/1000 = 0.004 unit per g
No. individuals of group B per cm3 soil/litter (with leg) 10/1000 = 0.001 unit per g 25/1000 = 0.025 unit per g
Table 4






Questions :
1. How did the biodiversity of macrofauna from the soils from the two locations differ? Can you suggest why there might be differences? What soil parameter could you has measured which may help explain the differences?
The biodiversity of macrofauna from the soils depend of type of vegetation and soil hardness. This is because, lawn and garden bed have different texture of soils which enable macrofauna to live in. for example, if the soil is quite hard and dry, less species will make it their habitat due to lack of food, shelter and not all macrofauna able to penetrate the hardness of the soils. This is different with garden bed which prepared enough leaves litter and suitable environment for them.
2. Explain the role of macrofauna in the soil.
Macrofauna play big roles to mixing and redistributing organic materials, enhances soil physical properties, neutralize soil pH, Increase the availability of many nutrients, stimulate microbial populations and may reduce levels of harmful nematodes
3. On the food web diagram provided, label the type of biota, what do they do, and describe which way the energy flows. What will happens to the enrgy and nutrients when the organisms ath the top of the food chain die?

If the organism at the top of the food chain die, the remaining below will face a drastic increase and it will lead into higher compettition to get the food. This may also lead to lack of consumer.
4. What group of organisms make up the mesofauna? What groups make up the microfauna? What are the main functions of these two main groups?
Soil Mesofauna: Nematodes
1. Microscopic non-segmented roundworms
2. Ecologically diverse
3. Overall, 10-20 million/m-sq are found
4. Major consumer group
5. Both free-living and parasitic groups exist
Soil Microfauna: Protozoa
1. Important in mineralization and immobilization of N, P, and S
2. Most numerous soil fauna
3. Prey on microbes (especially bacteria)
4. Enhance nitrification rates
5. Suppress bacterial and fungal pathogens

6. Food webs can indicate the biological complexity, and therefore the health, of the soil. Explain how our land managemant practices alter soil health.

They ensure that soil pH is at stable level which is not too acidic and not too alkaline. This is where they are using macrofauna as natural stabilizer to neutralize the soil pH and make it healthy.

7. Explain how the soil biota contribute to the functioning of the soil ecosystem. What ecosystem services do they regulate?

If harnessed properly, soil biota helps maintaining the circulation of organic materials besides ensure the stability of the soils. They provide a consumer, predator and other function to natural interaction in the ecosystem.









Discussion:
1. Energy and nutrients are passed as one group of organisms feeds on another.
2. At the bottom level of the food web is the decaying organic matter in the soil that ultimately came from plants. Roots are a source of nourishment for some organisms.
3. Feeding on the organic matter are bacteria, fungi, root-feeding nematodes, microscopic round worms and other organisms.
4. Feeding on them are the first-level predators such as protozoa one-celled organisms like amoebae, some species of nematodes and arthropods such as bugs with jointed legs like mites and insects.
5. Bacteria are small bundles of protein with a high percentage of nitrogen. If the nutrients they need are at the precise site of the bacterium, then bacterial metabolic rate is unequaled. But everything has to be present, just like the coal and oil at a power plant.
6. Soil food web is a basis for life on the land. It breaks down dead plants and animals and recycles nutrients. Numbers and varieties of organisms are staggering. Reproduction rates are high especially bacteria, and populations tend to boom and bust with different levels of oxygen, nutrients, heat, pH and water. It’s a complex ecological relationships.
7. Soil food web is composed of several classes of organisms.
o Plants - roots and organic matter from plants.
o Bacteria and fungi - many varieties and functions. Most are decomposers, while many others are mutualists.
o Other members of the food web - protozoa, nematodes, arthropods, earthworms and higher predators.
o Predators eat other organisms and make nutrients available.
8. Soil food web is important for plant growth. It builds soil structure and stores nutrients and releases them in forms plants can use. It also protects plants against diseases and pests.