Among the listed plants above, the one that we can expect to grow lowest to the ground would be the hornworts. Hornworts are non-vascular plants which can be found both on water and land. Since these plants do not have a vascular system, it is hard for them to move water internally due to the force of gravity which explains why they cannot grow more above the ground.
The fuel that comes from decayed organisms is petroleum
Soil is dense but not too dense to support the roots and plants, and soil absorbs water and holds it for the plant. and soil also soaks up nutrients for the plant, and also microorganisms in the plants replenish the nutrients constantly in a cycle, so soil is always nutrient rich