Human Impacts on Earth’s Systems
Lesson 4: Mycorrhizal Fungi
No organism exist by itself, but is dependent on others to survive. Organisms have relationships with others that can be beneficial or detrimental (mutualistic or parasitic) depending on what is happening in the environment. In this lesson, students will be encouraged to predict patterns of interactions within and across ecosystems.
Mycorrhizal fungi, symbiotic relationship, nitrogen, phosphorus, nutrients
Prior to starting the lesson please make 60 cards; 20 nitrogen, 20 phosphorus and 20 water cards. These cards can be as big or small as you like, just make sure they are color coordinated into the three types listed above. You will also need a projector or some sort of similar device to project the video and pictures (see supplementary materials section).
Captivate & Collaborate:
A tree root’s job is to find nutrients and water in the soil. Compared to the millions of microscopic organisms in the soil, roots are very big structures, lumbering their way through the underground world. The roots of Joshua Trees form a symbiotic relationship with tiny fungi that live in the soil, which allows the tree to get more nutrients and water that it uses to make plant sugars which is how the plant grows and functions. In exchange, the plant produces sugars and passes them to the fungi. These mycorrhizal fungi (myco-rye-zal, meaning fungus root) help the Joshua tree to survive in the desert where it can be hard to find soil nutrients and water. This is a symbiotic relationship, and can be mutualistic (both partners are benefitting) or parasitic (one partner takes more than it shares).
We are going to play a game called Soil Symbiosis.
1.For round one, the teacher will assign four students to be Joshua Trees (Jt), and scatter nutrient and water cards around the trees and across the room. The teacher will scatter 20 phosphorus cards (red), 20 nitrogen cards (yellow), and 20 water cards (blue). In the first round, the Joshua trees will try and collect as many of the cards as their “roots” (reaching out with their legs and dragging a card in) can reach - but they cannot leave their spot because they are trees and can’t move, so they can only get the cards closest to them (teacher should make sure that students can reach some cards, but that many are out of reach - see supplementary materials).
In order for the Joshua Trees to get one point, they must acquire 2 N cards, 1 P, and 2 H2O cards. (2N +1P 2H2O = 1 plant sugar)
2.For round two, choose 3 different students to be new Joshua trees - these trees will form symbiotic relationships with mycorrhizal fungi. Put the same number of N, P, and H2O cards in the same places as you did before, only now break up the remaining number of students into mycorrhizal fungi (MF) and place the fungi students around the classroom (see supplementary materials) letting them know which tree they will be partnering with. Let students know that the fungi will also be able to collect the cards and can pass them into the trees but that it will cost the trees a sugar payment for their help. For every 4 sugars you make, you have to pay the group of fungi you associate with, 1 sugar.
Before collecting nutrients make a group hypothesis (educated guess) to predict if the trees will be able to collect more nutrients, and end up with more sugar overall by forming partnerships with the fungi.
3.Begin round two, and the trees can collect nutrients and water with their roots and also by partnering with the fungi. The fungi can collect cards and pass them directly to a tree (fungi should always pass to their same tree), or pass to another fungus that is closer who then passes to the tree. (this is because fungi form networks throughout the soil and can pass between each other).
Record round two results in a data table.
1.Under these normal climate conditions, (when water, plants, and sun are in equilibrium) how much water are the plants able to catch?
2.How much water, phosphorus, and nitrogen was caught? Record round one results in a data table.
3.Will the trees be able to get more nutrients and water the second round with the help of the fungi?
1.create class data table (see materials section)
3.Hypothesis: The trees will make more plant sugar by partnering with the fungi then they would without fungal partnerships.
The teacher will help students create the data table and create data plots under the two different scenarios.
4.Discuss the graphs and hypothesis. Please see the example graph in the supplementary materials section.
4.Now we are going to display the results of our activity on a bar graph. What do you think is the best way to display our finding? How many sugars did each tree make in each scenario? How much did it cost to associate with the fungi?
4.A bar graph is the best way to display our findings. In the first scenario, the tree was able to make ____ sugars and ____ sugars in the second scenario. It cost ______ when the fungi was involved.
5.In regards to the graphs, what situation was the Joshua Tree most successful? And why?
5.The Joshua Tree was most successful when it had the mycorrhizal fungi because the partnership allowed the Joshua Tree to get more nutrients.
6.Watch the short stop-motion animation about current research on Joshua trees and their symbiotic partners.
Have students think about this animation and discuss the open questions with a partner. Each student must then write up their answers to each question and turn them in.
6.Imagine playing the game again but with limitless soil nutrients that the tree roots can absorb. Makeup data sheets and draw new graphs for round 1 and round 2 and explain how the symbiosis could be different.
If the soils were very rich with nutrients and the trees didn’t have a problem getting all of the nutrients they needed. Is it still a good idea to partner with and pay the mycorrhizal fungi?
As the climate changes, the soil is dryer and the soil becomes less nutrient rich. How does this change the relationship of symbiosis?
6.No because the fungi will be taking some of the trees’ nutrients. If the soil is nutrient rich then it would be more efficient for the tree to depend solely on itself.
See Powerpoint “Lesson 4 - Mycorrhizal fungi” for Visual Example of the Activity (Round 1 & 2) and Printable Data Recording Sheet: