Release of major ions and nutrients by decomposing leaves of Pseudobombax munguba, a common tree in the Amazonian floodplain

Summary

Fresh leaves of Pseudobombax munguba, a common tree in the inundation forest of the Amazonian floodplain (várzea), were submerged in a waterfilled tank, for decomposition studies. Changes in dry weight and water chemistry were followed for about four months.

Relatively high leaf decomposition rates, with dry weight losses of 15% after two weeks and 50% after twelve weeks, are accompanied by drastic changes in the solute content of the water. Oxygen depletion is rapid and anaerobic conditions occur during the subsequent ten weeks. Remarkable quantities of solutes, especially of C, N, P, K, Ca and Mg, are released from decomposing leaf material.

A rise in pH during leaf decomposition can be explained mainly by a considerable increase in HCO₃ concentration, associated with CO₂ depletion. Thus the water has changed from acidic, unbuffered and electrolyte-poor to neutral, well-buffered and electrolyte-rich.