Preservation of primary stable isotope signatures of peat-forming plants during early decomposition — observation along an altitudinal transect

Abstract

The preservation of the primary stable isotope compositions of peat-forming plants in peat was tested along a short (< 3.5 km), steep (739–1393 m asl) altitudinal transect. The stable isotope compositions in plant cube samples taken from the surface of mires were compared with the stable isotope compositions in cube samples of the underlying young peat for the following elements: hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS). Electron paramagnetic resonance (EPR) measurements were also compared. Statistically significant correlations (p ≤ 0.03) for the pairs of plant-peat samples among all analyzed elements suggested that the stable isotope compositions of peat are primarily determined by the stable isotope compositions of the peat-forming plants. This implies that preservation of the plants' primary stable isotope variations (e.g., from the time of plant growth) is well preserved in young peat and that the overall decomposition during peat formation has only a secondary influence on the final peat stable isotope composition. We were able to detect relative variations in stable isotope composition between plants growing in different conditions and/or at different times. The EPR results confirmed the more anoxic conditions of decomposition at lower altitudes and more oxic conditions at higher altitudes, which involved an increase in oxygen centered free radicals. The observed correlations between the stable isotope compositions of plants and altitude indicated that the δ 13C value of peat-forming plants is primarily controlled by growing season temperature, while the δ 2H and δ 18O values are controlled by stable isotope composition of surface water. The δ 15N and δ 34S values appear to reflect different distributions and concentrations of anthropogenic pollution at the sites of peat-forming plant growth. A strong and statistically significant correlation between altitude/temperature and δ 13C of plants and peats indicates a good preservation of primary stable carbon isotope composition. Thus, the analysis of peat stable isotope compositions could be useful for paleoclimate and paleoenvironmental evaluations.