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PHYSIOLOGICAL MODELS FOR SCALING PLOT MEASUREMENTS OF CO 2 FLUX ACROSS AN ARCTIC TUNDRA LANDSCAPE
Author(s) -
Vourlitis George L.,
Oechel Walter C.,
Hope Allen,
Stow Doug,
Boynton Bill,
Verfaillie Joseph,
Zulueta Rommel,
Hastings Steven J.
Publication year - 2000
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2000)010[0060:pmfspm]2.0.co;2
Subject(s) - tundra , environmental science , arctic vegetation , arctic , atmospheric sciences , primary production , ecosystem , normalized difference vegetation index , vegetation (pathology) , flux (metallurgy) , climate change , climatology , ecology , geology , biology , medicine , materials science , pathology , metallurgy
Regional estimates of arctic ecosystem CO 2 exchange are required because of the large soil carbon stocks located in arctic regions, the potentially large global‐scale feedbacks associated with climate‐change‐induced alterations in arctic ecosystem C sequestration, and the substantial small‐scale (1–10 m 2 ) heterogeneity of arctic vegetation and hydrology. Because the majority of CO 2 flux data for arctic ecosystems are derived from plot‐scale studies, a scaling routine that can provide reliable estimates of regional CO 2 flux is required. This study combined data collected from chamber measurements of CO 2 exchange, meteorology, hydrology, and surface reflectance with simple physiological models to quantify the diurnal and seasonal dynamics of whole‐ecosystem respiration ( R ), gross primary production (GPP), and net CO 2 exchange ( F ) of wet‐ and moist‐sedge tundra ecosystems of arctic Alaska. Diurnal fluctuations in R were expressed as exponential functions of air temperature, whereas diurnal fluctuations in GPP were described as hyperbolic functions of diurnal photosynthetic photon flux density (PPFD). Daily integrated rates of R were expressed as an exponential function of average daily water table depth and temperature, whereas daily fluctuations in GPP were described as a hyperbolic function of average daily PPFD and a sigmoidal function of the normalized difference vegetation index (NDVI) calculated from satellite imagery. These models described, on average, 75–97% of the variance in diurnal R and GPP, and 78–95% of the variance in total daily R and GPP. Model results suggest that diurnal F can be reliably predicted from meteorology (radiation and temperature), but over seasonal time scales, information on hydrology and phenology is required to constrain the response of GPP and R to variations in temperature and radiation. Using these physiological relationships and information about the spatial variance in surface features across the landscape, measurements of CO 2 exchange in 0.5‐m 2 plots were extrapolated to the hectare scale. Compared to direct measurements of hectare‐scale F made using eddy covariance, the scaled estimate of seasonally integrated F was within 20% of the observed value. With a minimum of input data, these models allowed plot measurements of arctic ecosystem CO 2 exchange to be confidently scaled in space and time.