Mature second leaves of Lolium perenne L. cv. Vigor, were sampled in a spring and summer regrowth period. Effects of CO 2 enrichment and increased air temperature on stomatal density, stomatal index, guard cell length, epidermal cell density, epidermal cell length and mesophyll cell area were examined for different positions on the leaf and seasons of growth.
Leaf stomatal density was smaller in spring but greater in summer in elevated CO 2 and higher in both seasons in elevated temperature and in elevated CO 2 ×temperature relative to the respective controls. In spring, leaf stomatal index was reduced in elevated CO 2 but in summer it varied with position on the leaf. In elevated temperature, stomatal index in both seasons was lower at the tip/middle of the leaf but slightly higher at the base. In elevated CO 2 ×temperature, stomatal index varied with position on the leaf and between seasons. Leaf epidermal cell density was higher in all treatments relative to controls except in elevated CO 2 (spring) and elevated CO 2 ×temperature (summer), it was reduced at the leaf base. In all treatments, stomatal density and epidermal cell density declined from leaf tip to base, whilst guard cell length showed an inverse relationship, increasing towards the base. Leaf epidermal cell length and mesophyll cell area increased in elevated CO 2 in spring and decreased in summer. In elevated CO 2 ×temperature leaf epidermal cell length remained unaltered in spring compared to the control but decreased in summer. Stomatal conductance was lower in all treatments except in summer in elevated CO 2 it was higher than in the ambient CO 2 .
These contrasting responses in anatomy to elevated CO 2 and temperature provide information that might account for differences in seasonal leaf area development observed in L. perenne under the same conditions.
November 27, 1995 ; May 1, 1996
For correspondence at: Plant Environment Laboratory, Department of Agriculture, The University of Reading, Cutbush Lane, Shinfield, Reading, RG2 9AD UK.