Paleovegetation reconstruction using δ13C of Soil Organic Matter

The relative contributions of C-3 and C-4 plants to vegetation at a given locality may be estimated by means of delta C-13 of soil organic matter. This approach holds a great potential for paleoecological reconstruction using paleosols. However, two main uncertainties exist, which limits the accuracy of this application. One is C-13-enrichment as the plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on delta C-13 of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated delta C-13 variations of 557 C-3 and 136 C-4 plants along a precipitation gradient in North China. A strong negative correlation is found between the delta C-13 value of C-3 plants averaged for each site and the annual precipitation with a coefficient of -0.40 parts per thousand/100mm, while no significant coefficients were found for C-4 plants. Second, we measured delta C-13 of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8 parts per thousand for the surface soil and 2.8 parts per thousand for the soil at the bottom of soil profiles. We conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glacial (LG), and conclude that, without corrections for C-13-enrichment by decomposition, the C-4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.