[Illustrations, footnotes and references available in PDF version]
In atmospheric CO2 enrichment experiments, nearly all plants almost always exhibit increases in photosynthetic rates and biomass production when environmental conditions are optimal for growth. Even when conditions are less than favorable (low soil moisture, poor soil fertility, high soil salinity, high air temperature), many plants still exhibit a CO2-induced growth enhancement; and that relative or percentage enhancement is sometimes (more often than not, in fact) greater than what it is under ideal growing conditions. It is sometimes suggested, however, that results obtained from CO2-enrichment experiments conducted in growth cabinets, greenhouses and other enclosures may not reflect real-world plant responses to atmospheric CO2 enrichment due to perturbations in microclimate caused by the enclosures. Thus, Free-Air CO2 Enrichment or FACE technology was developed as a means to enrich the air with CO2 around vegetation while having minimal effects on the surrounding microclimate; and the following paragraphs of this summary document describe the results of some of those experiments that were conducted on various grassland species, many of which were growing naturally in pastures.