soil algae and nematodes versus bacteria????

Hello!

I please need a hint. In sample exams the question about soil algae and nematodes comes up repeatedly. Why they occur near the soil surface and why they are smaller than their aboveground and aquatic counterparts. and why this is not the case for bacteria. My apologies, but I just do not get it, neither can I find any notes of mine on this nor valid information in the textbook. This might be very stupid and only my fault but its fact… Thank you very much for any valuable suggestion.

Best regards

hey..you are not alone. I am wondering about the same thing too!

I was part of the group 4 of discussion #2 with the questions... Why are the soil algae usually restricted to the uppermost soil layers? Soil algae are usually smaller than their aquatic counterparts? Explain why this is the case. Explain why this is not true for soil bacteria?

Our answer was:

Soil algae are restricted to the uppermost soil layers because:

• Soil algae require photosynthesis therefore require sunlight (hence being at uppermost layers)

Soil algae smaller than aquatic algae because:

Space:

• -there is more open space in water
• -free floating: can be widespread

Resource availability:

• -maximum sunlight in water
• -water availability in aquatic environment

Why this is not the case for soil bacteria: [Pls note that Maja edited this part of the answer]

Soil bacteria are unicellular organisms, therefore...

• -restrictive space in soils is not an issue for them

Thank you Tanya!

Julia, 1 hint when answering this type of question 1st) define the organism If you understand what algae are, e.g. autotrophs, live in water, have chlorophyll and perform photosynthesis, then you can deduce some of their environmental conditions.

Thank you Sandra! Thank you Tanya!

These are great explanations for algae and bacteria, however why are nematodes found near the surface and why are they smaller than their aquatic counterparts?

I assume that this is because nematodes feed on organic material, helping with decomposition, and most organic material is found on the top layers of soil.

Generally there is more pore space at or close to the soil surface, and (generally) pores became smaller with increasing depth. Nematodes (which are not unicellular organisms like bacteria) require pore space to move around. Hence, abundance of organic matter & presence of larger pores at or close to the soil surface enhance larger number of nematodes at soil surface relative to the deeper depths.

As for why are soil nematodes smaller than nematodes that live in aquatic systems, the explanation is the same as for algae.

If you look at Final exam 2004, Question 4: Soil algae and soil animals (e.g. nematodes) are usually............. I believe nematodes use the same answer as I wrote above...