title: Belowground carbon cycling in a humid tropical forest decreases with fertilization.
abstract: 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.
authors.affiliation: United States Department of Agriculture-Forest Service, North Central Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA. cgiardina@fs.fed.us
authors.forename: Christian P
authors.initials: CP
authors.lastname: Giardina
authors.forename: Dan
authors.initials: D
authors.lastname: Binkley
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ryan
authors.forename: James H
authors.initials: JH
authors.lastname: Fownes
authors.forename: Randy S
authors.initials: RS
authors.lastname: Senock
mesh_terms: 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
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D002244:Carbon