Cerling T E, Ehleringer J R, Harris J M
Department of Geology and Geophysics, University of Utah, Salt Lake City 84112, USA.
Philos Trans R Soc Lond B Biol Sci. 1998 Jan 29;353(1365):159-70; discussion 170-1. doi: 10.1098/rstb.1998.0198.
The decline of atmospheric CO2 over the last 65 million years (Ma) resulted in the 'CO2-starvation' of terrestrial ecosystems and led to the widespread distribution of C4 plants, which are less sensitive to CO2 levels than are C3 plants. Global expansion of C4 biomass is recorded in the diets of mammals from Asia, Africa, North America, and South America during the interval from about 8 to 5 Ma. This was accompanied by the most significant Cenozoic faunal turnover on each of these continents, indicating that ecological changes at this time were an important factor in mammalian extinction. Further expansion of tropical C4 biomass in Africa also occurred during the last glacial interval confirming the link between atmospheric CO2 levels and C4 biomass response. Changes in fauna and flora at the end of the Miocene, and between the last glacial and interglacial, have previously been attributed to changes in aridity; however, an alternative explanation for a global expansion of C4 biomass is CO2 starvation of C3 plants when atmospheric CO2 levels dropped below a threshold significant to C3 plants. Aridity may also have been a factor in the expansion of C4 ecosystems but one that was secondary to, and perhaps because of, gradually decreasing CO2 concentrations in the atmosphere. Mammalian evolution in the late Neogene, then, may be related to the CO2 starvation of C3 ecosystems.
在过去6500万年里，大气中二氧化碳含量的下降导致陆地生态系统“二氧化碳饥饿”，并使得C4植物广泛分布，C4植物对二氧化碳水平的敏感度低于C3植物。在约800万至500万年前的这段时期内，亚洲、非洲、北美洲和南美洲哺乳动物的饮食记录显示C4生物量在全球范围内有所增加。这一时期，这些大陆上都出现了新生代最显著的动物群更替，表明此时的生态变化是哺乳动物灭绝的一个重要因素。在末次冰期期间，非洲热带地区的C4生物量也进一步增加，这证实了大气二氧化碳水平与C4生物量响应之间的联系。此前，中新世末期以及末次冰期与间冰期之间的动植物变化一直被归因于干旱程度的变化；然而，C4生物量全球扩张的另一种解释是，当大气二氧化碳水平降至对C3植物至关重要的阈值以下时，C3植物出现了二氧化碳饥饿现象。干旱可能也是C4生态系统扩张的一个因素，但它是次要因素，或许是大气中二氧化碳浓度逐渐降低的结果。因此，晚新近纪的哺乳动物进化可能与C3生态系统的二氧化碳饥饿有关。
