Ecological Impact on Nitrogen and Phosphorus Cycling of a Widespread Fast-growing Leguminous Tropical Forest Plantation Tree Species, Acacia mangium

Abstract

Symbiotic nitrogen fixation is one of the major pathways of N input to forest ecosystems, enriching N availability, particularly in lowland tropics. Recently there is growing concern regarding the wide areas of fast-growing leguminous plantations that could alter global N2O emissions. Here, we highlight substantially different N and phosphorus utilization and cycling at a plantation of Acacia mangium, which is N2-fixing and one of the major plantation species in tropical/subtropical Asia. The litterfall, fresh leaf quality and fine-root ingrowth of A. mangium were compared to those of non-N2-fixing Swietenia macrophylla and coniferous Araucaria cunninghamii in wet tropical climates in Borneo, Malaysia. The N and P concentrations of the A. mangium fresh leaves were higher than those of the other two species, whereas the P concentration in the leaf-litterfall of A. mangium was less than half that of the others; in contrast the N concentration was higher. The N:P ratio in the A. mangium leaf was markedly increased from fresh-leaf (29) to leaf-litterfall (81). Although the N flux in the total litterfall at the A. mangium plantation was large, the fine-root ingrowth of A. mangium significantly increased by applying both N and P. In conclusion, large quantities of N were accumulated and returned to the forest floor in A. mangium plantation, while its P resorption capacity was efficient. Such large N cycling and restricted P cycling in wide areas of monoculture A. mangium plantations may alter N and P cycling and their balance in the organic layer and soil on a stand level

Differential Impacts of Acacia Invasion on Nutrient Fluxes in Two Distinct Bornean Lowland Tropical Rain Forests

“…Consistent with other studies on invasive Acacia species [25,41,70], Acacia invasion increased total litterfall production and leaf litterfall production in AMDF. However, a similar increase was not observed for AHF, contrary to our hypothesis.…”

“…Leaf litterfall from both Acacia-invaded habitats recorded higher N and K concentrations and lower Mg concentrations than their intact habitats, indicating greater N and K-return from the plant to the soil [25,26,90]. Symbiotic associations with microorganisms enable N-fixation by Acacia, thus enhancing soil N supply and tissue N concentrations [91].…”

“…However, most Acacia species have the capacity to become invasive when introduced beyond their native ranges [21]. Invasive Acacia species alter nutrient cycling in invaded areas [24,25] and typically produce high total litterfall and nutrient-rich litter, with especially high N concentrations. This nutrient-rich litter increases the concentrations of organic and available nutrients in the soil [24][25][26].…”

“…Invasive Acacia species alter nutrient cycling in invaded areas [24,25] and typically produce high total litterfall and nutrient-rich litter, with especially high N concentrations. This nutrient-rich litter increases the concentrations of organic and available nutrients in the soil [24][25][26]. Increased nutrient cycling rates eventually directly impact native plants that are adapted to a low-nutrient environment [24].…”