The Nitrogen Cycle: The Nitrogen Cycle

TABLE OF CONTENTS

Introduction

Nitrogen is essential to all living systems, which makes the nitrogen cycle one of Earth's most important nutrient cycles. Atoms of nitrogen don't just stay in one place. They move slowly between living things, dead things, the air, soil and water. These movements are called the nitrogen cycle. The nitrogen cycle is one of the biogeochemical cycles and is very important for ecosystems. Nitrogen moves slowly through the cycle and is stored in reservoirs such as the atmosphere, living organisms, and soils. Approximately 80% of the molecules in Earth's atmosphere are made of two nitrogen atoms bonded

Among the main processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification.

Nitrogen is present in the environment in chemical forms such as organic nitrogen, ammonium, nitrite, nitrate, nitrous oxide, or inorganic nitrogen gas. Organic nitrogen may be in the form of a living organism, humus or in the intermediate products of organic matter decomposition. The processes of the nitrogen cycle are carried out by microbes.

Nitrogen Fixation

Nitrogen fixation is the conversion of nitrogen into nitrates and nitrites through atmospheric, industrial and biological processes. Atmospheric nitrogen must be processed in a usable form to be taken up by plants. Atmospheric nitrogen are fixed by lightning strikes, but most fixation is done by free-living or symbiotic bacteria known as diazotrophs. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which is converted by the bacteria into other organic compounds. Most biological nitrogen fixation occurs by the activity of Mo-nitrogenase, found in a wide variety of bacteria and some