干旱区生态环境知识资源中心

Stable carbon isotopes of soil organic matter from 12 sites in the southern Chinese Loess Plateau are reviewed to examine spatial and temporal patterns of C-3 and C-4 plants in the arid to semiarid monsoonal region during three key periods - last glacial maximum, mid-Holocene, and modern. We have tentatively corrected the effects of atmospheric CO2 concentrations and precipitation amounts on the delta C-13 endmembers for C-3 plants to reconstruct the relative proportion of C-4 plants because the delta C-13 values of C-3 plants are variable under different CO2 and climate conditions. The results indicate that C-4 grasses increase from northwest to southeast spatially, which is consistent with present-day increasing precipitation and temperature patterns. This suggests that for a monsoon-dominant arid to semiarid region, such as the Loess Plateau, warm-season rainfall is a primary factor limiting C-4 plants growth, and thus C-4 grasses have been outcompeted by C-3 grasses/shrubs under cold-dry climate conditions. However, temporal fluctuations in atmospheric CO2 concentration may also affect plant growth through altering water-use efficiency (WUE). Enhanced drought caused by decreased WUE due to low atmospheric CO2 concentrations during glacial periods, combined with a cold-dry climate, leads to a decline in C-4 grasses, canceling out any advantages gained from lowered atmospheric CO2 concentrations. To reconstruct accurately the abundance of C-3 and C-4 plants in an ecosystem and explore their controlling factors, process-based vegetation models integrating CO2 and climatic parameters interactive with plant physiology are necessary. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.