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Water-use efficiency of forest ecosystems in eastern China and its relations to climatic variables

Yu, Guirui, Song, Xia, Wang, Qiufeng, Liu, Yunfen, Guan, Dexin, Yan, Junhua, Sun, Xiaomin, Zhang, Leiming, Wen, Xuefa
The new phytologist 2008 v.177 no.4 pp. 927-937
Pinus koraiensis, broadleaved evergreen forests, carbon, coniferous forests, eddy covariance, evapotranspiration, forest ecosystems, hydrologic cycle, photosynthesis, plantations, primary productivity, process control, stomatal movement, temperate forests, water use efficiency
Carbon (C) and water cycles of terrestrial ecosystems are two coupled ecological processes controlled partly by stomatal behavior. Water-use efficiency (WUE) reflects the coupling relationship to some extent. At stand and ecosystem levels, the variability of WUE results from the trade-off between water loss and C gain in the process of plant photosynthetic C assimilation. Continuous observations of C, water, and energy fluxes were made at three selected forest sites of ChinaFLUX with eddy covariance systems from 2003 to 2005. WUE at different temporal scales were defined and calculated with different C and water flux components. Variations in WUE were found among three sites. Average annual WUE was 9.43 mg CO₂ g⁻¹ H₂O at Changbaishan temperate broad-leaved Korean pine mixed forest, 9.27 mg CO₂ g⁻¹ H₂O at Qianyanzhou subtropical coniferous plantation, and 6.90 mg CO₂ g⁻¹ H₂O at Dinghushan subtropical evergreen broad-leaved forest. It was also found that temperate and subtropical forest ecosystems had different relationships between gross primary productivity (GPP) and evapotranspiration (ET). Variations in WUE indicated the difference in the coupling between C and water cycles. The asynchronous response of GPP and ET to climatic variables determined the coupling and decoupling between C and water cycles for the two regional forest ecosystems.