Carbon isotope ratios (δ^(13)C) of 89 C_4 plant samples were determined fromthe loess area in North China. δ^(13)C values vary between -10.5per thousand and -14.6per thousandwith a mean of -12.6per thousand. Along a precipitation gradient from the semi-moist area to thesemiarid area, then to the arid area, the δ^(13)C values of C_4 plants show a slight decreasingtrend. The δ^(13)C values of C_4 plants in the dry season are found lower than those in the wetseason. These trends are opposite to those observed for C_3 species.
WANG Guoan1,2,3, HAN Jiamao 2, ZHOU Liping3, XIONG Xiaogang4, TAN Ming2, WU Zhenhai5 & PENG Jun6 1. Department of Plant Nutrition, China Agricultural University, Beijing 100094, China
13C of 367 C3 herbaceous plants was measured in loess area in northern China. Their δ13C values vary between ?21.7%. and ?30.0%., with a mean of ?26.7%.. In the center of Loess Plateau (semimoist area) with annual precipitation of 400–600 mm, the δ13 C values of C3 herbaceous plants range from ?24.4%. to ?28.5%., with a mean of ?27.5%.. In the west of Loess Plateau (semiarid and arid area) with annual precipitation less than 400 mm, they range between ?21.7%. and ?30.0%., with a mean of ?26.2%.. Annual precipitation is the main factor that makes δ13C values of C3 herbaceous plants in the west greater than those in the central Loess Plateau. The composition of δ13C in C3 plants increases with deceasing annual precipitation, and the mean change is ?49%./100 mm.
