delta C-13 difference between plants and soil organic matter along the eastern slope of Mount Gongga

Carbon isotope ratios (delta C-13) of plants, litter and soil organic matter (0-5 cm, 5-10 cm and 10-20 cm) on the eastern slope of Mount Gongga were measured. The results show that delta C-13 values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e. delta C-13 values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The delta C-13 altitudinal variations are related to the distribution of C-3 and C-4 plants on the eastern slope of Mount Gongga, because C-4 plants are observed to grow only below 2100 m, while C-3 plants occur at all altitudes. There are significantly positive correlations among delta C-13 of vegetation, delta C-13 of litter and delta C-13 of soil organic matter, and litter, 0-5 cm, 5-10 cm and 10-20 cm soil organic matter are 0.56aEuro degrees, 2.87aEuro degrees, 3.04aEuro degrees and 3.49aEuro degrees greater in delta C-13 than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO2 and decreasing delta C-13 of atmospheric CO2 since the industry revolution on delta C-13 of plants, 1.57aEuro degrees is proposed to be the smallest correction value for reconstruction of paleovegetation using delta C-13 of soil organic matter.