Stomatal index responses of Agrostis canina to CO2 and sulphur dioxide: implications for palaeo-[CO2] using the stomatal proxy.
• Stomatal index values of fossil plants are widely used in reconstructing palaeo-[CO(2)]. This depends upon the assumption that the stomatal index is determined by the atmospheric concentration of CO(2) ([CO(2)]). This study investigates whether fumigation with, and resistance to, sulphur dioxide (SO(2)) induces a reduction in the stomatal index that may affect stomatal reconstructions of palaeo-[CO(2)] coinciding with episodes of global-scale volcanism. • Agrostis canina from Mefite di Ansanto, Italy, grow in atmospheres of elevated-[CO(2)], SO(2) and hydrogen sulphide (H(2)S). Mefite A. canina were compared with a control population in a 'common-garden' experiment and a controlled-environment study under elevated-[CO(2)] and SO(2) fumigation. • In A. canina, resistance to toxic volcanic gases is not associated with reduced stomatal index, and fumigation with SO(2) does not cause a decrease in stomatal initiation. The two populations of A. canina analyzed in this study exhibit different stomatal index-[CO(2)] 'responses', with control plants showing a reduction in stomatal index and Mefite plants showing no response. • Stomatal reconstructions of palaeo-[CO(2)] during past episodes of global-scale volcanism probably reflect atmospheric [CO(2)] and not [SO(2)]. The lack of a reduction in the stomatal index in response to elevated [CO(2)] in the Mefite plants, suggests that resistance to toxic gases and/or long-term growth at high [CO(2)] reduces, or negates, sensitivity of the stomatal index-[CO(2)] relationship, or that stomatal index-[CO(2)] in the Mefite plants is attuned to [CO(2)] fluctuations at much higher concentrations.
Haworth
Matthew
M
School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland. matthew.haworth@ucd.ie
Gallagher
Angela
A
Elliott-Kingston
Caroline
C
Raschi
Antonio
A
Marandola
Danilo
D
McElwain
Jennifer C
JC
D031703:Agrostis / Q000033:anatomy & histology*; D002245:Carbon Dioxide / Q000032:analysis / Q000494:pharmacology*; D005651:Fumigation; D049690:History, Ancient; D006862:Hydrogen Sulfide / Q000032:analysis / Q000494:pharmacology*; D007558:Italy; D054046:Plant Stomata / Q000187:drug effects; D013458:Sulfur Dioxide / Q000032:analysis / Q000494:pharmacology*; D018707:Volcanic Eruptions / Q000032:analysis*
D013458:Sulfur Dioxide; D002245:Carbon Dioxide; D006862:Hydrogen Sulfide