title: Nutrient additions to a tropical rain forest drive substantial soil carbon dioxide losses to the atmosphere.
abstract: Terrestrial biosphere-atmosphere carbon dioxide (CO(2)) exchange is dominated by tropical forests, where photosynthetic carbon (C) uptake is thought to be phosphorus (P)-limited. In P-poor tropical forests, P may also limit organic matter decomposition and soil C losses. We conducted a field-fertilization experiment to show that P fertilization stimulates soil respiration in a lowland tropical rain forest in Costa Rica. In the early wet season, when soluble organic matter inputs to soil are high, P fertilization drove large increases in soil respiration. Although the P-stimulated increase in soil respiration was largely confined to the dry-to-wet season transition, the seasonal increase was sufficient to drive an 18% annual increase in CO(2) efflux from the P-fertilized plots. Nitrogen (N) fertilization caused similar responses, and the net increases in soil respiration in response to the additions of N and P approached annual soil C fluxes in mid-latitude forests. Human activities are altering natural patterns of tropical soil N and P availability by land conversion and enhanced atmospheric deposition. Although our data suggest that the mechanisms driving the observed respiratory responses to increased N and P may be different, the large CO(2) losses stimulated by N and P fertilization suggest that knowledge of such patterns and their effects on soil CO(2) efflux is critical for understanding the role of tropical forests in a rapidly changing global C cycle.
authors.affiliation: *Institute of Arctic and Alpine Research, Campus Box 450, and cory.cleveland@colorado.edu.
authors.forename: Cory C
authors.initials: CC
authors.lastname: Cleveland
authors.affiliation: *Institute of Arctic and Alpine Research, Campus Box 450, and.|Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Townsend
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism*; D005308:Fertilizers; D006813:Humidity; D009747:Nutritional Physiological Phenomena; D018517:Plant Roots; D012621:Seasons; D012987:Soil / Q000032:analysis*; D013696:Temperature; D014197:Trees; D014329:Tropical Climate
chemical_list: D005308:Fertilizers; D012987:Soil; D002245:Carbon Dioxide