Given below are two statements: Statement I: Rhizobium bacteria is responsible for nitrogen fixation in soybean. Statement II: R. japonicum bacteria is found in nodules of soybean.

Correct option is A

The correct answer is (A) Both Statement I and Statement II are correct

Explanation:
• Statement I is correct: Soybean (Glycine max) is a legume that forms a symbiotic relationship with specific bacteria to fix atmospheric nitrogen into a form the plant can use (ammonia). This process reduces the need for synthetic nitrogen fertilizers.
• Statement II is correct: The specific species of Rhizobium that forms nodules and performs nitrogen fixation in soybean is Bradyrhizobium japonicum (formerly referred to as Rhizobium japonicum).
• The bacteria live in specialized structures on the roots called nodules. Inside these nodules, the enzyme nitrogenase converts $N_2$ gas from the soil air into nitrogenous compounds, while the plant provides the bacteria with carbohydrates.

Information Booster:
• Rhizobium species are host-specific: R. meliloti for Lucerne, R. trifolii for Berseem, and R. leguminosarum for Peas/Lentils.
• Leghemoglobin is a pigment found in healthy nodules that regulates oxygen levels to protect the nitrogenase enzyme.
• Biological Nitrogen Fixation (BNF) is a sustainable way to maintain soil fertility.

Additional Knowledge:
• Azotobacter and Azospirillum are examples of free-living or associative nitrogen-fixing bacteria, unlike the symbiotic Rhizobium.
• Inoculating soybean seeds with B. japonicum culture is a common agricultural practice to ensure effective nodulation.