The delta C-13 changes in four plant species of the Loess Plateau over the last 70 years

The relative abundance of carbon isotope (delta C-13) was measured in four C-3 species (Sophora viccifolia. Quercus liaotungensis. Ostryopsis davidiana and Zizyphus jujuba var. spinosa) of the Loess Plateau in China from the 1930's to 2002. The results showed that the delta C-13 values in the four species varied from -25.05 parts per thousand to -29.75 parts per thousand with their average at -27.04 parts per thousand. A decrease in the delta C-13 value with time was found in all the four species, which indicating that the water use efficiencies (WUEs) of all the measured species declined during 70 years. However. the decrease in delta C-13 value differed among the four species with its significant decreases measured in two of the species, Sophora viciifolia and Quercus liaotungensis, its relatively significant decrease found in Ostryopsis davidiana, and its slight decrease appearing in Zizyphus,jujuba var. spinosa. in the delta C-13 values in the four species decreased by 14.65 parts per thousand, 14.46 parts per thousand, 11.99 parts per thousand and 2.44 parts per thousand, respectively. The different species were shown to have different sensitivities to climatic change, and Zizyphus jujuba var. spinosa was found to be the most drought-tolerant species of the four, which had a high WUE.