STOMATAL CHARACTERISTICS OF 4 NATIVE HERBS FOLLOWING EXPOSURE TO ELEVATED CO2

Contrasting effects on the stomatal index (SI), stomatal density, epidermal cell size and number were observed in four chalk grassland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vulneraria L. and Plantago media L.) following exposure to elevated carbon dioxide concentrations (CO2) in controlled environment growth cabinets. SI of S. minor increased for both leaf surfaces, whilst in A. vulneraria and P. media SI decreased on one surface only. In L. corniculatus, no differences in SI were observed as epidermal cell density changed in parallel with stomatal density. In L. corniculatus and S. minor stomatal density increased on both surfaces, whereas in P. media it decreased; in A. vulneraria stomatal density decreased on the abaxial leaf surface alone following exposure to elevated CO2. In the latter three species, SI changed because stomatal density did not change in parallel with epidermal cell density. The results suggest elevated CO2 is either directly or indirectly affecting cell differentiation and thus stomatal initiation in the meristem. In S. minor and P. media leaf growth increased in elevated CO2, because of increased cell expansion of epidermal cells, whereas in L. corniculatus, epidermal cell size decreased and greater leaf growth was because of an increase in epidermal cell divisions. In A. vulneraria, leaf size did not change, but increased cell expansion on the adaxial surface suggests CO2 affects leaf surfaces differently, either directly or indirectly at the cell differentiation stage or as the leaf grows. These results suggest component species of a plant community may differ in their response to elevated CO2. Predicting the effect of environmental change is therefore difficult.