Correction: Biophysical Controls on Light Response of Net CO2 Exchange in a Winter Wheat Field in the North China Plain

For each year, NEEs was calculated at the same PAR using Eq. (3) and the light response parameters in Table 6. The mean values were obtained for two sky conditions and total standard error was computed using Eq. (4). The meanings of Pmax, a and Rd were the same as Tables 1. Significance of the difference was ‘‘’’ for P,0.05 if the absolute difference between two sky conditions was greater than the total standard error. doi:10.1371/journal.pone.0089469.t007