Stomatal Density Responses of Egyptian Olea europaea L. Leaves to CO₂ Change Since 1327 BC

Abstract

We have attempted to separate the effects of CO₂ and temperature change on stomatal density by examining ancient leaf material of Olea europaea L. The distribution of this species is confined to a Mediterranean type climate, so that O. europaea leaves of different ages will have formed under similar temperatures but different CO₂ levels over the last 3000 years. Stomatal density measurements have been made upon leaves of O. europaea originating from King Tutankhamun's tomb dating from 1327 BC, and have been compared with values obtained from Egyptian O. europaea material dating from pre-332 BC, 1818 and 1978 AD. Together, the four dates provide a record of how the plant has responded to increases in atmospheric CO₂ concentration during that time. The results demonstrate that in accordance with similar studies examining the stomatal density response of plants over three time scales (hundreds, thousands and tens of thousands of years) stomatal density falls as CO₂ levels increase. Since we have examined a natural system with leaves developing under similar environmental temperatures the results confirm observations from experimental studies in which plants were grown under the same temperature but different CO₂ regimes.Copyright 1993, 1999 Academic Press

Olea europaea, stomatal density, atmospheric CO₂, temperature, climate change