Which of the following processes contributes to the transformation of nitrogen in the soil?

Nitrification is a crucial microbial process that contributes to the transformation of nitrogen in the soil, making it accessible for plant uptake. During nitrification, ammonia (NH3) is first oxidized to nitrites (NO2-) by specialized bacteria, and then nitrites are further oxidized to nitrates (NO3-). These nitrates are a vital source of nitrogen, which plants can readily absorb and utilize for growth.

Given the other processes listed, they do not directly contribute to nitrogen transformation in the soil. Photosynthesis involves the conversion of light energy into chemical energy in plants, transpiration refers to the movement of water evaporating from plant leaves, and respiration is the process where living organisms convert oxygen and glucose into energy, releasing carbon dioxide. None of these processes directly involve the transformation of nitrogen into forms that plants can use as significantly as nitrification does.