Belowground carbon cycling in a humid tropical forest decreases with fertilization.
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.
Giardina
Christian P
CP
United States Department of Agriculture-Forest Service, North Central Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA. cgiardina@fs.fed.us
Binkley
Dan
D
Ryan
Michael G
MG
Fownes
James H
JH
Senock
Randy S
RS
D002244:Carbon / Q000502:physiology*; D002247:Carbon Isotopes; D006254:Hawaii; D006813:Humidity; D008954:Models, Biological; D018515:Plant Leaves / Q000737:chemistry; D018521:Plant Physiological Phenomena; D012987:Soil; D014197:Trees / Q000502:physiology*; D014329:Tropical Climate
D002247:Carbon Isotopes; D012987:Soil; D002244:Carbon