Late-Quaternary variation in C3 and C4 grass abundance in southeastern Australia as inferred from δ13C analysis: Assessing the roles of climate, pCO2, and fire

QUATERNARY SCIENCE REVIEWS

卷:139

Review

Nelson, David M.¹  Urban, Michael A.²  Kershaw, A. Peter³  Hu, Feng Sheng^2,4,5 

[1] Univ Maryland, Ctr Environm Sci, Appalachian Lab, Frostburg, MD 21532 USA

[2] Univ Illinois, Program Ecol Evolut & Conservat Biol, Urbana, IL 61801 USA

[3] Monash Univ, Sch Earth Atmosphere & Environm, Melbourne, Vic 3800, Australia

[4] Univ Illinois, Dept Plant Biol, Urbana, IL 61801 USA

[5] Univ Illinois, Dept Geol, Urbana, IL 61801 USA

关键词: Australia;    Atmospheric CO2;    C-3 grasses;    C-4 grasses;    Carbon isotopes;    Climate change;    Fire;   

DOI  :  10.1016/j.quascirev.2016.03.006

来源: Elsevier

【 摘 要 】

Climate, atmospheric pCO(2), and fire all may exert major influences on the relative abundance of C-3 and C-4 grasses in the present-day vegetation. However, the relative role of these factors in driving variation in C-3 and C-4 grass abundances in the paleorecord is uncertain, and C-4 abundance is often interpreted narrowly as a proxy indicator of aridity or pCO(2). We measured delta C-13 values of individual grains of grass (Poaceae) pollen in the sediments of two sites in southeastern Australia to assess changes in the proportions of C-3 and C-4 grasses during the past 25,000 years. These data were compared with shifts in pCO(2), temperature, moisture balance, and fire to assess how these factors were related to long-term variation of C-4 grass abundance during the late Quaternary. At Caledonia Fen, a high-elevation site in the Snowy Mountains, C-4 grass abundance decreased from an average of 66% during the glacial period to 11% during the Holocene, primarily in response to increased pCO(2) and temperature. In contrast, this pattern did not exist in low-elevation savannah woodlands around tower Hill Northwest Crater, where C-4 grass abundance instead varied in response to shifts in regional aridity. Fire did not appear to have strongly influenced the proportions of C-3 and C-4 grasses on the landscape at millennial timescales at either site. These patterns are similar to those of a recent study in East Africa, suggesting that elevation-related climatic differences influence how the abundance of C-3 and C-4 grasses responds to shifts in climate and pCO(2). These results caution against using C-4 plant abundance as a proxy indicator of either climate or pCO(2) without an adequate understanding of key controlling factors. (C) 2016 Elsevier Ltd. All rights reserved.

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