Answer:
The A horizon will be relative large with a high content of sand.
Step-by-step explanation:
A desert, as it is, is covered with very fine sediments in most cases, ranging from medium and small rocks to fine sand. If the climate conditions were to change where there is a desert and the climate became more temperate, the soil will change as well relatively quickly. What is actually now the surface of the deserts will become the new soil's A horizon while on top of it a 0 horizon will form.
The A horizon in a former desert will become very fertile and it will be able to support lush vegetation. This will be the case because it will have a very high content of sand, thus it will be very airy and soft. The newly formed O horizon made out of biomass on top of it will wash away to the A horizon, increasing its fertility further by adding a big amount of decomposed biomass to it.