Plant responses to low [CO2] of the past


Author for correspondence:
Joy K. Ward
Tel: +1 785 8645218



II.The case for low-[CO2] studies675
III.Experimental approaches for reducing [CO2]677
IV.Early low-[CO2] studies679
V.Low-[CO2] effects on the individual plant680
VI.Low [CO2] and plant evolution683
VII.Interactions of low [CO2] with other factors687
VIII.Low-[CO2] effects on community composition689
IX.Low-[CO2] effects on the ecosystem689
X.Low-[CO2] effects on early human societies690


During the Last Glacial Maximum (LGM; 18 000–20 000 yr ago) and previous glacial periods, atmospheric [CO2] dropped to 180–190 ppm, which is among the lowest concentrations that occurred during the evolution of land plants. Modern atmospheric CO2 concentrations ([CO2]) are more than twice those of the LGM and 45% higher than pre-industrial concentrations. Since CO2 is the carbon source for photosynthesis, lower carbon availability during glacial periods likely had a major impact on plant productivity and evolution. From the studies highlighted here, it is clear that the influence of low [CO2] transcends several scales, ranging from physiological effects on individual plants to changes in ecosystem functioning, and may have even influenced the development of early human cultures (via the timing of agriculture). Through low-[CO2] studies, we have determined a baseline for plant response to minimal [CO2] that occurred during the evolution of land plants. Moreover, an increased understanding of plant responses to low [CO2] contributes to our knowledge of how natural global change factors in the past may continue to influence plant responses to future anthropogenic changes. Future work, however, should focus more on the evolutionary responses of plants to changing [CO2] in order to account for the potentially large effects of genetic change.