Which process directly involves the transformation of ammonia?

The transformation of ammonia is directly involved in the process of nitrification. Nitrification is a crucial step in the nitrogen cycle where ammonia, produced from organic matter decomposition or from excretion, is converted into nitrite and subsequently into nitrate by specific bacteria. This process has two main stages: the first stage is the oxidation of ammonia to nitrite, carried out by ammonia-oxidizing bacteria, and the second stage is the oxidation of nitrite to nitrate, performed by nitrite-oxidizing bacteria.

Nitrification is essential for making nitrogen available to plants in a form they can absorb and use for growth. This transformation is vital for soil fertility and overall ecosystem health. Thus, the correct answer highlights the significant role of nitrification in the nitrogen cycle, focusing specifically on how ammonia is processed within that context.