Carbon Dioxide and Water Vapour Exchange of Leaves on Field-Grown Citrus Trees

Publisher Website
Google Scholar
Abstract
Carbon dioxide and water vapour exchange rates were measured on attached leaves of field-grown citrus trees. The exchange rates were measured continuously during several weeks in the spring of two successive years. These data confirmed the rather low rates of maximum CO2 exchange (6–11 μmol m−2 s−1) by citrus leaves. However, the maximum rate was maintained through the midday period on only about half the days. On the other days, characterized by high temperatures and high atmospheric water vapour pressure deficits, pronounced midday depressions in CO2 exchange rates were observed. Since midday transpiration remained stable at a constant rate even with increasing vapour pressure deficit, these results indicate that stomatal closure was occurring. In fact, the data suggest tfiat specific, maximum transpiration rates were associated with differing rootstocks. Thus, the rate of water supply to the leaves may be an important factor in determining the maximum transpiration rate, and thereby mediating control of stomatal conductance and the resultant midday depression in CO2 exchange rates.