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SCI论文目录 |
Climate impact on net ecosystem productivity of a semi-arid natural grassland: modeling and measurement |
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| 出 版 社：Agricultural and forest meteorology |
| 发表时间：2004, Vol.126: 99-116 |
| 台 站：
沙坡头沙漠试验研究站
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| 作 者：Tao Li1, Robert F. Grant1, Lawrence B. Flananan2 |
| 点 击 率：6365 |
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| 摘 要： Models used to estimate net ecosystem productivity (NEP) during climate change should first be shown to simulate the effects on NEP of interannual variability in current climates. Energy andCO2 fluxes simulated by the ecosystem model ecosys were compared with those measured by eddy covariance over a semi-arid ungrazed grassland near Lethbridge, Alberta to improve confidence in model projections of grassland NEP. Differences between simulated and measured fluxes of CO2 and energy were within the range of uncertainty in measured fluxes during 3 years with declining precipitation (466, 363, and 276 mm in 1998, 1999, and 2000, respectively). Standard differences between modelled versus measured CO2 and LE over 3 years were 1.0 μmol m-2 s-1 and 22W m-2 which were comparable to standard errors estimated from eddy covariance measurements. However, further research is needed to reconcile differences in modelled vs. measured ecosystem respiration. Annual modelled NEP of the semi-arid ungrazed grassland was +59gC m-2 in 1998, +5gC m-2 in 1999, and -33gC m-2 in 2000. Long-term modelled rate of C accumulation in this grassland under current climate was 26g C m-2 y-1 which is consistent with C accumulation in semiarid grasslands estimated from measurements and models elsewhere. Under climate change projected by the Canadian Regional Climate Model II from theIS92a emissions scenario, increases in transpiration caused by rising temperatures were fully offset by decreases in transpiration caused by rising CO2, thereby alleviating water deficits and lengthening growing seasons. The consequent rise in grassland net primary productivity was largely offset by a rise in heterotrophic respiration, so that C sequestration by the semi-arid ungrazed grassland rose by less than 2 g C m-2 y-1 under climate change.
Key words: ecosystem modeling; energy exchange; latent heat flux; CO2 flux
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