title: Biophysical controls on light response of net CO2 exchange in a winter wheat field in the North China Plain.
abstract: To investigate the impacts of biophysical factors on light response of net ecosystem exchange (NEE), CO2 flux was measured using the eddy covariance technique in a winter wheat field in the North China Plain from 2003 to 2006. A rectangular hyperbolic function was used to describe NEE light response. Maximum photosynthetic capacity (P max) was 46.6 ± 4.0 µmol CO2 m(-2) s(-1) and initial light use efficiency (α) 0.059 ± 0.006 µmol µmol(-1) in April-May, two or three times as high as those in March. Stepwise multiple linear regressions showed that P max increased with the increase in leaf area index (LAI), canopy conductance (g c) and air temperature (T a) but declined with increasing vapor pressure deficit (VPD) (P<0.001). The factors influencing P max were sorted as LAI, g c, T a and VPD. α was proportional to ln(LAI), g c, T a and VPD (P<0.001). The effects of LAI, g c and T a on α were larger than that of VPD. When T a>25°C or VPD>1.1-1.3 kPa, NEE residual increased with the increase in T a and VPD (P<0.001), indicating that temperature and water stress occurred. When g c was more than 14 mm s(-1) in March and May and 26 mm s(-1) in April, the NEE residuals decline disappeared, or even turned into an increase in g c (P<0.01), implying shifts from stomatal limitation to non-stomatal limitation on NEE. Although the differences between sunny and cloudy sky conditions were unremarkable for light response parameters, simulated net CO2 uptake under the same radiation intensity averaged 18% higher in cloudy days than in sunny days during the year 2003-2006. It is necessary to include these effects in relevant carbon cycle models to improve our estimation of carbon balance at regional and global scales.
authors.affiliation: College of Forestry, Beijing Forestry University, Beijing, China.
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Tong
authors.affiliation: Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology, Sydney, Australia ; Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Yu
authors.affiliation: Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Zhonghui
authors.initials: Z
authors.lastname: Lin
mesh_terms: D055592:Biophysical Phenomena / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D002681:China; D017753:Ecosystem; D008027:Light; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D012621:Seasons; D014908:Triticum / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D002245:Carbon Dioxide