Modeling to discern nitrogen fertilization impacts on carbon sequestration in a Pacific Northwest Douglas‐fir forest in the first‐postfertilization year |
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Authors: | BAOZHANG CHEN NICHOLAS C COOPS T ANDY BLACK RACHHPAL S JASSAL JING M CHEN MARK JOHNSON |
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Institution: | 1. LREIS Institute of Geographic Sciences & Nature Resources Research, Chinese Academy of Sciences, Beijing 100101, China;2. Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;3. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;4. Department of Geography and Program in Planning, University of Toronto, 100 St. George St., Room 5047, Toronto, Ontario, Canada M5S 3G3;5. Department of Earth and Ocean Sciences, Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 |
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Abstract: | This study investigated how nitrogen (N) fertilization with 200 kg N ha?1 of urea affected ecosystem carbon (C) sequestration in the first‐postfertilization year in a Pacific Northwest Douglas‐fir (Pseudotsuga menziesii) stand on the basis of multiyear eddy‐covariance (EC) and soil‐chamber measurements before and after fertilization in combination with ecosystem modeling. The approach uses a data‐model fusion technique which encompasses both model parameter optimization and data assimilation and minimizes the effects of interannual climatic perturbations and focuses on the biotic and abiotic factors controlling seasonal C fluxes using a prefertilization 9‐year‐long time series of EC data (1998–2006). A process‐based ecosystem model was optimized using the half‐hourly data measured during 1998–2005, and the optimized model was validated using measurements made in 2006 and further applied to predict C fluxes for 2007 assuming the stand was not fertilized. The N fertilization effects on C sequestration were then obtained as differences between modeled (unfertilized stand) and EC or soil‐chamber measured (fertilized stand) C component fluxes. Results indicate that annual net ecosystem productivity in the first‐post‐N fertilization year increased by~83%, from 302 ± 19 to 552 ± 36 g m?2 yr?1, which resulted primarily from an increase in annual gross primary productivity of~8%, from 1938 ± 22 to 2095 ± 29 g m?2 yr?1 concurrent with a decrease in annual ecosystem respiration (Re) of~5.7%, from 1636 ± 17 to 1543 ± 31 g m?2 yr?1. Moreover, with respect to respiration, model results showed that the fertilizer‐induced reduction in Re (~93 g m?2 yr?1) principally resulted from the decrease in soil respiration Rs (~62 g m?2 yr?1). |
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Keywords: | Douglas‐fir ecological modeling ecosystem respiration net ecosystem productivity nitrogen fertilization photosynthesis |
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