What characteristic primarily defines beneficial nematodes?

Beneficial nematodes are primarily defined by their role in decomposing organic material, which includes consuming dead organic matter and fungi. This feeding behavior is vital for nutrient cycling in the ecosystem, as these nematodes break down complex organic materials and help recycle nutrients back into the soil, promoting healthy plant growth.

Their activity in the soil improves soil structure and fertility, making them an important component in the maintenance of turfgrass health. By controlling populations of certain microorganisms and contributing to the breakdown of organic substances, beneficial nematodes play a crucial role in soil health and ecosystem balance. They help create a more hospitable environment for plants by enhancing nutrient availability.

In contrast, the other options describe characteristics that do not align with the defining traits of beneficial nematodes. For instance, feeding on plant roots is characteristic of harmful nematodes that can damage grass and other plants, while living in symbiosis with turf microbes is not a primary feature attributed to nematodes. The creation of air pockets in the soil aligns more closely with the functions of larger soil fauna or earthworms rather than nematodes specifically.