title: Foliar and ecosystem respiration in an old-growth tropical rain forest.
abstract: Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 +/- 0.2 micromol CO2 m(-2) s(-1), and ecosystem respiration was 9.4 +/- 0.5 micromol CO2 m(-2) s(-1)[soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error.
authors.affiliation: Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA. mollycavaleri@gmail.com
authors.forename: Molly A
authors.initials: MA
authors.lastname: Cavaleri
authors.forename: Steven F
authors.initials: SF
authors.lastname: Oberbauer
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ryan
mesh_terms: D019069:Cell Respiration / Q000502:physiology*; D003364:Costa Rica; D017753:Ecosystem; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism*; D012987:Soil; D014197:Trees / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D012987:Soil