Fine-root production in response to nutrient application at three forest plantations in Sabah, Malaysia: higher nitrogen and phosphorus demand by Acacia mangium

We measured fine-root production at Acacia mangium (AM), Swietenia macrophylla (SM), and Araucaria cunninghamii (AC) sites in response to nitrogen (N) and phosphorus (P) application using the root-ingrowth core method for a period of 5 months in Sabah, Malaysia. Root growth increased significantly using a combined N and P application at the AM site, whereas it did not increase at the SM and AC sites. The number of nodules at the AM site increased significantly following N application and the combined application of N and P. Root production was not significantly enhanced by nutrient application at the SM and AC sites. At the AM site, both P and N were in high demand despite a larger N pool compared with at the SM and AC sites. These results can be explained by the larger nutrient demand by legumes. We conclude that both N and P is limiting for AM plantations under natural conditions and that N fertilization may be more effective than expected, depending on the site conditions.