Why do tropical rain forest and marshes have high NPP?

The mechanism that allows rain forests and marshes to have high NPP differs. For tropical rain forests, the long growing season allows plants to photosynthesize and grow throughout the year, and their high leaf area allows for high rates of gross carbon uptake. For marshes, they have plenty of nutrients for growth, but lower leaf areas, lower annual gross carbon uptake and shorter growing seasons. Marshes, thus, take up less carbon from the atmosphere, but use this carbon much more efficiently for growing plant tissues than tropical rain forests (see Rocha and Goulden 2009 Why is marsh NPP so high? Agricultural and Forest Met.)