Atmospheric carbon dioxide enrichment effects on ecosystems — experiments and the real world

Abstract

The beneficial effect of atmospheric CO2 on the growth of plants has been known since 1804 (De Sassure 1804; cited in Kimball et al. 1993), and its role as a C source for vegetation was proven by Justus von Liebig 125 years ago. Atmospheric CO2 enrichment has been used to promote the growth of legumes in greenhouse cultures for >50 years. As early as 1961, greenhouses covering >1,600 ha were under enriched CO2 in the Netherlands alone. However, only after atmospheric CO2 concentrations had been recorded from continuous monitoring sites such as the Mauna Loa Observatory at Hawaii, where [CO2] has been recorded since 1958, was there a growing awareness that CO2 enrichment occurs on a global scale and that it affects ecosystems throughout the world. In 2005, the concentration of atmospheric CO2 will be around 380 μmol mol −1; thus already exceeding by ca. 35% the background concentration of ca. 280 μmol mol−1 before the beginning of industrialization. A further increase to at least 550 μmol mol−1 will have occurred by the end of this century (IPCC 2001). Consequently, numerous studies have been performed to test the response of vegetation and ecosystems to CO2 enrichment, and great progress has been made in developing experimental facilities and in our understanding of biosphere–atmosphere interactions with respect to CO2 by means of both experimentation and modelling. CO2 enrichment effects on crops were reviewed as early as the mid 1980s by Cure and Acock (1986) who reported an average increase in C3 crop yield due to CO2 doubling of approximately 41%. A mechanistic understanding of the physiological background for this CO2 fertilization effect in C3 plants that has been widely accepted was provided by von Caemmerer and Farquhar (1981). This CO2 gas exchange model for C3 plants was later extended and modified by Sage (1994) and other authors to explain photosynthetic acclimation to CO2 enrichment. Down-regulation of photosynthesis in C3 plants