Which of the following statements about the nitrogen cycle are false? 1. Rhizobium and Frankia cause nitrogen fixation in their independent free-living stage. 2. Azotobacter and Anabaena are anaerobic, symbiotic as well as free-living, nitrogen fixers. 3. Rhodospirillum is an aerobic, nitrogen-fixing microbe found in the root nodules of legumes. 4. Nitrobacter oxidises nitrites to nitrates.