delta super(13)C variation of C sub(3) and C sub(4) plants across an Asian monsoon rainfall gradient in arid northwestern China

摘要

We have investigated carbon isotopic compositions of four plant genus-species, Bothriochloa ischaemum (C sub(4)), Stipa bungeana (C sub(3)), Lespedeza sp. (C sub(3)) and Heteropappus less (C sub(3)), along a precipitation gradient in northwest China in order to assess the impact of water availability on the carbon isotopic discrimination against super(13)C during carbon assimilation in this area. This information is necessary for reconstruction of paleovegetation, particularly paleo-C sub(3)-C sub(4) plant ratios using delta super(13)C value of organic matter in loess and paleosols in the Chinese Loess Plateau. The delta super(13)C of C sub(3) plants, as a group, exhibits a negative correlation with the annual precipitation amount with a total change and sensitivity of 5ppt and -1.1ppt-100 mm, respectively, for the precipitation range from 200 to 700 mm. The C sub(4) grass, B. ischaemum responds to aridity by decreasing 1.7ppt for over the precipitation range from 350 to 700 mm; the plant delta super(13)C is significantly correlated with annual precipitation with a slope -0.61ppt-100 mm. This result implies that without considering the effect of water availability on the plant delta super(13)C values, reconstruction of percent C sub(4) vegetation during the last glaciation can be overestimated by about a factor of two.