Here's a problem to solve: Leaves fall from deciduous trees onto the forest floor. These leaves decay slowly and become part of the topsoil. Which change is most likely to have a positive impact on the nutrients available in the topsoil?

Among the 4 following options, which is the correct answer?

- A: a decrease in temperature
 
- B: a decrease in biodiversity
 
- C: an increase in the number of predators
 
- D: an increase in the number of decomposers
 