HR: 11:35h
AN: B32B-06    [Abstracts]
TI: The importance of intrinsic factors in driving interannual Net Ecosystem Production (NEP) variability
AU: * Rocha, A V
EM: arocha@uci.edu
AF: UC Irvine, Croul Hall, Irvine, ca 92697, United States
AU: Goulden, M
EM: mgoulden@uci.edu
AF: UC Irvine, Croul Hall, Irvine, ca 92697, United States
AB: Interannual Net Ecosystem Production (NEP) variability is the result of external forcing from the environment (i.e. extrinsic) and internal forcing from biological lags, carryovers, and feedbacks (i.e. intrinsic). Attribution of interannual NEP variability to intrinsic factors has been difficult partly because of the challenge of separating interactions between extrinsic and intrinsic factors from a single measure of ecosystem function. We elucidated the importance of intrinsic controls in driving interannual NEP variations by comparing long term records of eddy covariance data to other independent measures of ecosystem function (i.e. ring width chronologies, remote sensing indices, and biomass harvests) for a late successional Boreal Forest (BF) and also a Temperate Freshwater Marsh (TFM). Analyses indicated that intrinsic controls on NEP were strong in both ecosystems. Carryover effects associated with carbohydrate pools resulted in poor relationships between annual gross carbon uptake (GPP) and ring width at the BF. Feedbacks and carryover effects associated with the accumulation of standing litter and subsequent shading of future plant generations resulted in large interannual differences between remotely sensed vegetation indices, NEP, GPP, and carbon uptake per unit leaf area at the TFM. Small scale manipulations of standing litter coupled with measurements of NEE and surface reflectance further supported the importance of standing litter as an intrinsic control at the TFM. A water table drawdown at the TFM suppressed leaf area production and carbohydrate translocation, and delayed the seasonal cycle of Net Ecosystem Exchange (NEE) in the following year. Our analysis demonstrates that interannual variability in NEP involves both intrinsic and extrinsic factors and that attributing these factors to interannual variability in NEP requires a multifaceted approach.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting