The carbon isotope composition of C3 herbaceous plants in loess area of northern China

delta(13)C of 367 C-3 herbaceous plants was measured in loess area in northern China. Their delta(13)C values vary between -21.7parts per thousand and -30.0parts per thousand, with a mean of -26.7parts per thousand. In the center of Loess Plateau (semimoist area) with annual precipitation of 400-600 mm, the delta(13)C values Of C3 herbaceous plants range from -24.4parts per thousand to -28.5parts per thousand, with a mean of -27.5parts per thousand. In the west of Loess Plateau (semiarid and arid area) with annual precipitation less than 400 mm, they range between -21.7parts per thousand and -30.0parts per thousand, with a mean of -26.2parts per thousand. Annual precipitation is the main factor that makes delta(13)C values of C-3 herbaceous plants in the west greater than those in the central Loess Plateau. The composition of delta(13)C in C-3 plants increases with deceasing annual precipitation, and the mean change is -0.49parts per thousand/100 mm.