Nitrogen-fixing trees boost carbon sequestration

The research found that on a eucalyptus plantation in Hawaii, areas interplanted with mimosa trees (Albizia falcataria) were able to sequester more carbon than areas where eucalyptus trees were planted as a monoculture. The researchers suggest that nitrogen which is added to the soil by the mimosas may be inhibiting the decomposition of carbon in the soil.

“Carbon sequestration is the balance of inputs and outputs from a system,” said Jason Kaye, one of the researchers from Colorado State University. “What we’ve shown here is that carbon outputs from soil are lower in stands that have more nitrogen-fixing trees. If decomposition is inhibited because of nitrogen inputs, then increased biological nitrogen fixation, nitrogen fertilisation and nitrogen deposition may promote carbon sequestration.” However, the mechanisms at work are still poorly understood, say the researchers.

Though the mimosa is not a cash crop like eucalyptus, the trees’ positive effect on soil quality in areas where nutrient levels are often limited has prompted some farmers to test the potential benefits of interplanting the two species.

“Changes in the composition of tree species which result from land use or climate changes may have important feedbacks to terrestrial carbon sequestration,” said Kaye. “We still need to learn more about how species composition may be affecting the soil of these and other forests in order to fully understand their ability to act as carbon sinks.”