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

Abstract

Understanding the fractionation mechanism and factors controlling carbon isotopes (δ13C) in macrophytes is significant for studying the biogeochemical carbon cycle and changes in nutrients within lakes. However, whether the environmental implications of δ13C are different in the different components (α-cellulose, holocellulose and whole sample) of macrophytes is unclear. In this paper, the δ13C composition of different macrophytes tissue components in Taihu Lake was analysed on spatial and temporal scales. The effects of aquatic environmental variables on the δ13C 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‰ ± 0.95‰. Submerged macrophytes have large variations with significantly more positive δ13C values (−15.19‰ ± 3.08‰). The δ13C values of floating-leaved plants (−25.32‰ ± 1.02‰) fall between those of the two groups above. In the one-way analysis of variance (ANOVA), the different components (α-cellulose, holocellulose and whole sample) of δ13C exhibited significant differences (p-value <0.01) among the three groups of macrophytes. However, there was no significant seasonal difference in the δ13C of macrophytes. In addition, the δ13C of macrophytes in rivers were lighter than those in lakes. Correlation analyses indicated that the water pH was the main factor affecting δ13C variability in macrophytes. The δ13C values of α-cellulose showed stronger sensitivity to environmental variation than did those of the whole samples and holocellulose. Hence, it is necessary to extract α-cellulose when using the δ13C 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 δ13C in macrophytes for palaeoenvironmental changes.