Nitrogen and phosphorus retranslocation and N:P ratios of litterfall in three tropical plantations: luxurious N and efficient P use by Acacia mangium

摘要

Some tropical N sub(2)-fixing trees exhibit specific characteristics for phosphorus (P) acquisition and utilisation that contrast with the large nitrogen (N) fluxes in their litterfall. To investigate differences in N and P cycling in N sub(2)-fixing plantations, litterfall and fresh leaf quality of a N sub(2)-fixing Acacia mangium plantation were compared with that of a non-N sub(2)-fixing Swietenia macrophylla plantation and a coniferous Araucaria cunninghamii plantation. The N concentration in the A. mangium litterfall was higher than that in the litterfall of the two other species, whereas the P concentration in the A. mangium leaf litterfall was 0.16mgg super(-1), which was only 12-22% of that of the other species. The P concentration in the reproductive parts of A. mangium was markedly higher (16.1mgg super(-1)) than those in the other fractions. The N:P ratio was higher in the leaf fall (81) compared to the fresh leaves (29) of A. mangium, in contrast to the N:P ratios in the leaf samples of the other two species. An analysis of a global litterfall dataset of tropical plantations indicated that N:P ratios in litterfall were significantly higher in N sub(2)-fixers than in non-N sub(2)-fixers, and those of A. mangium were high among species in the N sub(2)-fixer group. These results indicated that A. mangium efficiently retranslocated P in contrast to very large N cycling, under field conditions. These differences may be related to other physiological characteristics of A. mangium.