Stomatal Density, Anatomy and Nutrient Concentrations of Scots Pine Needles Are Affected by Elevated CO sub(2) and Temperature

Leaf anatomy may be modified by elevated carbon dioxide and temperature conditions predicted under global climate change. Stomatal density, anatomy, and nutrient concentrations in Scots pine needles were studied over 3 yr under elevated CO sub(2), elevated temperature, and combined elevated CO sub(2) and temperature, in closed chambers. Anatomical changes observed included thinner needles, thinner mesophyll in the abaxial side, thinner vascular cylinder, and lower stomatal density in needles of trees grown under elevated CO sub(2) and temperature, compared with those at ambient conditions. Altered anatomy and stomatal density were more distinct at elevated temperatures than at elevated CO sub(2). Both elevated CO sub(2) and temperature induced changes in nutrient concentrations corresponded somewhat to biochemical and photosynthetic alterations as well. Reduced nutrient levels and altered anatomy were transient, and were more evident in needles from the first year of the 3 yr experiment. Specific anatomical changes, stomatal density changes, and nutrient responses are described.