Isotopic fractionation during cellulose synthesis in two mangrove species: Salinity effects

Abstract

Carbon, non-exchangeable hydrogen, and oxygen isotope ratios of cellulose of Avicennia germinans and Rhizophora mangle plants hydroponically grown under different salinities (0, 18, 45% sea water, but with irrigation waters having the same isotopic ratios) were measured to determine the possibility of using isotopic ratios of plant tissues as biological recorders of sea level rise. There was a large variability in the δD values of leaf nitrated cellulose between different treatments and even within a single treatment for both A. germinans and R. mangle. Thus, δD values of non-exchangeable hydrogens of cellulose cannot be used as a historical tracer for utilization of ocean water or freshwater by mangroves. In contrast, δ 18O values of cellulose were not significantly different between different salinity treatments for both mangroves, indicating that δ 18O of cellulose can be used as a sea water tracer. δ 13C values of cellulose did not vary directly with salinity as has been observed with other plants. δ 13C values of cellulose from A. germinans were the lowest for plants growing at 18% sea water, with cellulose from plants growing in 0 and 45% sea water having significantly higher δ 13C values. δ 13C values of cellulose from R. mangle were the highest for plants grown in 45% sea water, with plants grown in 0 and 18% sea water having equally lower δ 13C values.