The diagram illustrates a simplified nitrogen cycle. Which row gives the correct labels for P, Q, R and S?
- AP: denitrification by anaerobic bacteria; Q: nitrogen fixation by nitrifying bacteria; R: decay of leaf tissue by saprotrophic bacteria; S: ammonification by saprotrophic fungi
- BP: lightning action on soil nitrates; Q: nitrogen fixation by nitrogen-fixing bacteria; R: decomposition using nitrogenase enzyme; S: decomposition by root nodule bacteria
- CP: nitrification by anaerobic bacteria; Q: nitrification using nitrogenase enzyme; R: decay of leaf tissue by saprotrophic fungi; S: assimilation of organic nitrogen
- DP: reduction by anaerobic bacteria; Q: nitrogen fixation by root nodule bacteria; R: decomposition of organic nitrogen; S: decay of urea by saprotrophic bacteria