PARENT SESSION
Poster Session #11: Elevated CO₂.
Monday, August 6, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Effects of a 4-year exposure to pre-industrial and elevated CO₂ on stomatal characters of C₃ and C₄ species.

REID, CHANTAL¹, MAHERALI, HAFIZ¹, JACKSON, ROB¹, JOHNSON, HYRUM², POLLEY, WAYNE², ^{1 2}

ABSTRACT- Most studies examining effects of pre-industrial atmospheric CO₂ on stomatal density (SD) report a negative relationship between SD and [CO₂]. However, many of these studies are based on paleofossils or herbarium specimens where other environmental factors may affect stomatal distribution. To understand the effect of CO₂ on stomatal distribution, we examined 9 grassland species grown for 4 years in the field under an experimental gradient of CO₂ ranging from pre-industrial to elevated concentrations (200 to 550 mol CO₂ mol^-1). In the field, casts were made on leaves of C₃ and C₄ annual and perennial grasses and forbs. Leaf impressions were made from the casts and SD, stomatal index (SI), and stomatal aperture length (SAL) were measured. The C₄ grasses showed no strong negative linear relationship between SD and [CO₂] (e.g., r²=0.31 for Bothriochloa ischaemum), SI and [CO₂] (e.g., r²=0.33 for B ischaemum) or SAL and [CO₂] (e.g., r²=0.17 for B ischaemum). In contrast, C₃ annuals showed strong positive linear relationships between SD and [CO₂] (e.g., r²=0.96 for Bromus japonicus [C₃ grass], r²=0.47 for Euphorbia bicolor) or SI and [CO₂] (e.g. r²=0.79 for B. japonicus, r²=0.89 for E. bicolor). These stomatal parameters show no effect of CO₂ on C₄ grasses but different responses on C₃ species, suggesting limited use of preserved material as [CO₂] proxy. Also, C₃ plants respond to CO₂ by adjusting stomatal cell initiation, epidermal cell expansion, or both.

KEY WORDS: stomatal index, C₄ and C₃ grasses, stomatal density, stomatal aperture length