2.5.Principal components analysis
Prior to principal components analysis (PCA), all absorbance data were converted into Rsi values. The ratio of the AWCD value per samples and the maximum AWCD value in all samples is regarded the relative ratio of six kinds of carbon sources. The ratio of the AWCD value of the sole carbon source and the AWCD of the 31 carbon source is relative for each carbon source, and make a comparison matrix, which could indicated that the use regularity of strong and weak in sole carbon source.