What converts nitrogen into a usable substance during the nitrogen cycle?

a. consumers
b. decomposers
c. leaches
d. nitrogen fixing bacteria

D.Nitrogen fixing bacteria

Explanation:

Fertile soil contains combined nitrogen, mainly in the form of nitrates, nitrites, ammonium or urea salts, CO (NH2) 2. These compounds are absorbed from soil water by plant roots in a process known as nitrogen fixation. A few species of bacteria and cyanobacteria can "fix" atmospheric nitrogen, that is, transform N2 gas into nitrogen compounds; nitrates or ammonium salts. These bacteria can be called nitrogen-fixing bacteria.

The most important genus of these bacteria is Rhizobium. They live in symbiosis in the root nodules of plants of the legume family, for example, peas, beans, clover and alder. Other nitrifying bacteria live free in the soil, for example aerobic bacteria such as Azobacter and Beijerinckia, and anaerobic bacteria such as Clostridium pastorianum. These bacteria require small amounts of certain transition metals like molybdenum, iron, cobalt and copper, as well as boron from the soil.

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