It converts atmospheric nitrogen into compounds of nitrogen in the soil.
Explanation
The Nitrogen Cycle is a biogeochemical process through which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. Nitrogen fixation is the primary step wherein atmospheric nitrogen ($N_2$), which is relatively inert, is converted into reactive compounds like ammonia or nitrates that living organisms can utilize.
Analysis of the Role of Lightning:
- Atmospheric Nitrogen Fixation: Lightning plays a crucial role in the natural fixation of nitrogen. The high temperature and pressure generated during lightning strikes provide the energy required to break the strong triple bonds of atmospheric nitrogen molecules ($N_2$).
- Chemical Conversion: Once the bonds are broken, nitrogen atoms react with oxygen to form oxides of nitrogen (such as $NO$ and $NO_2$).
- Deposition in Soil: These nitrogen oxides dissolve in rainwater to form dilute nitric and nitrous acids, which fall to the ground. In the soil, these acids react with alkali to form nitrates, which are soluble and easily absorbed by plants.
Evaluation of Options:
- It destroys nitrogen in the atmosphere. is incorrect: Lightning does not destroy nitrogen; it transforms it from an elemental gaseous state into a compound form.
- It converts atmospheric nitrogen into compounds of nitrogen in the soil. is correct: It accurately describes the process of converting atmospheric nitrogen into soil-based nitrogen compounds (nitrates).
- It releases nitrogen gas from the soil back to the atmosphere. is incorrect: The release of nitrogen gas from the soil back to the atmosphere is called denitrification, which is carried out by denitrifying bacteria (e.g., Pseudomonas), not lightning.
- It prevents plants from absorbing nitrogen. is incorrect: By converting inert nitrogen into nitrates, lightning actually facilitates the availability of nitrogen for plant absorption.
Key Takeaway:
Lightning facilitates atmospheric nitrogen fixation by converting inert nitrogen gas into nitrogen oxides, which eventually reach the soil as nitrates usable by plants.