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Oecologia. 2004 May;139(4):545-50. Epub 2004 Apr 8.

Belowground carbon cycling in a humid tropical forest decreases with fertilization.

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  • 1United States Department of Agriculture-Forest Service, North Central Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA.


Only a small fraction of the carbon (C) allocated belowground by trees is retained by soils in long-lived, decay-resistant forms, yet because of the large magnitude of terrestrial primary productivity, even small changes in C allocation or retention can alter terrestrial C storage. The humid tropics exert a disproportionately large influence over terrestrial C storage, but C allocation and belowground retention in these ecosystems remain poorly quantified. Using mass balance and 13C isotope methods, we examined the effects of afforestation and fertilization, two land-use changes of large-scale importance, on belowground C cycling at a humid tropical site in Hawaii. Here we report that in unfertilized plots, 80% of the C allocated belowground by trees to roots and mycorrhizae was returned to the atmosphere within 1 year; 9% of the belowground C flux was retained in coarse roots and 11% was retained as new soil C. The gains in new soil C were offset entirely by losses of old soil C. Further, while fertilization early in stand development increased C storage in the litter layer and in coarse roots, it reduced by 22% the flux of C moving through roots and mycorrhizae into mineral soils. Because soil C formation rates related strongly to rhizosphere C flux, fertilization may reduce an already limited capacity of these forests to sequester decay-resistant soil C.

Copyright 2004 Springer-Verlag

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