Variations in stable carbon isotopes in different components of aquatic macrophytes from Taihu Lake, China

Understanding the fractionation mechanism and factors controlling carbon isotopes (delta C-13) in macrophytes is significant for studying the biogeochemical carbon cycle and changes in nutrients within lakes. However, whether the environmental implications of delta C-13 are different in the different components (alpha-cellulose, holocellulose and whole sample) of macrophytes is unclear. In this paper, the delta(13)Ccomposition of different macrophytes tissue components in Taihu Lake was analysed on spatial and temporal scales. The effects of aquatic environmental variables on the delta C-13 values of macrophytes were also explored. The results showed that emergent plants have the most negative stable carbon isotope signals, with a mean value (+/- SD) of -27.85 parts per thousand +/- 0.95 parts per thousand. Submerged macrophytes have large variations with significantly more positive delta C-13 values (-15.19 parts per thousand +/- 3.08 parts per thousand). The delta C-13 values of floating-leaved plants (-25.32 parts per thousand +/- 1.02 parts per thousand) fall between those of the two groups above. In the one-way analysis of variance (ANOVA), the different components (alpha-cellulose, holocellulose and whole sample) of delta C-13 exhibited significant differences (p-value < 0.01) among the three groups of macrophytes. However, there was no significant seasonal difference in the delta C-13 of macrophytes. In addition, the delta C-13 of macrophytes in rivers were lighter than those in lakes. Correlation analyses indicated that the water pH was the main factor affecting delta C-13 variability in macrophytes. The delta C-13 values of alpha-cellulose showed stronger sensitivity to environmental variation than did those of the whole samples and holocellulose. Hence, it is necessary to extract alpha-cellulose when using the delta C-13 of aquatic macrophytes to study the changes in lake ecological environments. These results provided a theoretical reference and experimental data support for a modern process of using delta C-13 in macrophytes for palaeoenvironmental changes.