Spatial and temporal variations of C 3/C 4 relative abundance in global terrestrial ecosystem since the Last Glacial and its possible driving mechanisms

Abstract

The primary factor controlling C 3/C 4 relative abundance in terrestrial ecosystem since the Last Glacial has been widely debated. Now more and more researchers recognize that climate, rather than atmospheric CO 2 concentration, is the dominant factor. However, for a specific area, conflicting viewpoints regarding the more influential one between temperature and precipitation still exist. As temperature and precipitation in a specific area usually not only vary within limited ranges, but also covary with each other, it is difficult to get a clear understanding of the mechanism driving C 3/C 4 relative abundance. Therefore, systematic analysis on greater spatial scales may promote our understanding of the driving force. In this paper, records of C 3/C 4 relative abundance since the Last Glacial on a global scale have been reviewed, and we conclude that: except the Mediterranean climate zone, C 3 plants predominated the high latitudes during both the Last Glacial and the Holocene; from the Last Glacial to the Holocene, C 4 relative abundances increased in the middle latitudes, but decreased in the low latitudes. Combining with studies of modern process, we propose a simplified model to explain the variations of C 3/C 4 relative abundance in global ecosystem since the Last Glacial. On the background of atmospheric CO 2 concentration since the Last Glacial, temperature is the primary factor controlling C 3/C 4 relative abundance; when temperature is high enough, precipitation then exerts more influence. In detail, in low latitudes, temperature was high enough for the growth of C 4 plants during both the Last Glacial and the Holocene; but increased precipitation in the Holocene inhibited the growth of C 4 plants. In middle latitudes, rising temperature in the Holocene promoted the C 4 expansion. In high latitudes, temperature was too low to favor the growth of C 4 plants and the biomass was predominated by C 3 plants since the Last Glacial. Our review would benefit interpretation of newly gained records of C 3/C 4 relative abundance from different areas and different periods, and has its significance in the understanding of the driving mechanisms of C 3/C 4 variations on longer timescales (e. g., since the late Miocene) with reliable records of temperature and atmospheric CO 2 concentration. © 2012 The Author(s).