if the earth only have plants, what would it be ?

Answer 1

In the literal sense this is impossible. The world needs micro organisms for the ecological cycles to work.
If you simply meant "no animals" that was once the case and the ecological cycles certainly do not rely on animals. Specialized plants that rely on animal pollinators could not exist of course, otherwise not much would change. The equilibrium levels of CO2 and O2 are dependent on plants not animals. CO2 is returned to the air as dead plants rot. Most of this ecological cycling takes place in the oceans with algae being the main guys. The nitrogen cycle requires bacteria at both ends. The phosphorus cycle requires birds but is fairly inefficient at best. Many plants avoid phosphorus.
So yeah no sweat, different but would still work OK.

Answer 2

It could still be the earth with plants but many plants. The carrying capacity and otherwise the law of nature will control the number-those plants species that could not withstand competition will perish and those that could withstand competition and are strong will survive. The carbon dioxide and oxygen in the air is enough to make the plants continue to grow.

Answer 3

The reason there are animals and plants on the earth is because each uses what the other discards. Before there were animals on the earth, plants were giving off oxygen (which is a poison to plants) and nothing was using up the oxygen (except the occasional fire). Animals came about because there was an abundance of oxygen and they gave off carbon di-oxide.

To answer your question, there would be nothing, because the plants would die.

Answer 4

Dead of oxygen poisoning, just as an Earth with only animals would die of CO2 poisoning.

Answer 5

Kudzu

Answer 6

It would still be Earth.

Answer 7

it will still be calle earth.

Answer 8

"Could only have" or "had". Use the force, Luke.