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Spatial and temporal variations in C3 and C4 plant abundance over the Chinese Loess Plateau since the last glacial maximum |
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| Authors: | Z Yao H WuM Liang X Shi |
| Institution: | a Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China b Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China c Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China d Three Gorges Research Center for Geo-hazard, Ministry of Education, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China |
| Abstract: | 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 C3 and C4 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 δ13C endmembers for C3 plants to reconstruct the relative proportion of C4 plants because the δ13C values of C3 plants are variable under different CO2 and climate conditions. The results indicate that C4 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 C4 plants growth, and thus C4 grasses have been outcompeted by C3 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 C4 grasses, canceling out any advantages gained from lowered atmospheric CO2 concentrations. To reconstruct accurately the abundance of C3 and C4 plants in an ecosystem and explore their controlling factors, process-based vegetation models integrating CO2 and climatic parameters interactive with plant physiology are necessary. |
| Keywords: | Monsoon Vegetation Semiarid region Stable carbon isotope |
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