Monitoring environmental features using leaf stomatal characteristics

Abstract

It is recognised that atmospheric CO(_2) concentrations are increasing, with concerns raised as to the global impact continued rises may have. Plant stomatal parameters have been suggested as a means of monitoring changing CO(_2) levels. In order to assess their suitability for use, a thorough examination of leaf characteristics within a variety of surroundings was undertaken. Environments examined included both natural variations in CO(_2), which incorporated a variety of environmental influences and artificially enhanced ones where it was possible to monitor specific responses to variable CO(_2) levels. A short term study of Ranunculus ficaria, Sambucus nigra and Hedera helix revealed considerable variation in stomatal parameters, with inconsistent responses observed between and within species. These variations could not be attributed to CO(_2) changes and were assigned to a combination of other factors. R. ficaria grown in an artificial environment at ambient and elevated CO(_2) produced significant and consistent changes in stomatal parameters. Stomatal density and index were found to be reduced at elevated CO(_2) concentrations, with a decrease in guard cell dimensions. Salix herbacea, growing along a naturally reduced CO(_2) partial pressure gradient further highlighted the extent of variation in stomatal parameters in extant material within a species. No consistent stomatal trends associated with changing CO(_2) levels were observed. This inherent variation must be considered before any conclusions can be made regarding stomatal parameters obtained from fossil material. The novel application of molecular biology techniques to identify S. herbacea leaves was partially successful. However, identification of leaf macrofossils was not possible, due to the inferior preservation of DNA. However, the technique will provide a useful tool for identification if suitably preserved macrofossil fragments were available. S. herbacea leaf macrofossils revealed no consistent correlation to past changes in CO(_2) levels. The use of as an additional tool with which to monitor environmental change once again showed variation, and was not associated closely with changes in CO(_2) levels or stomatal parameters. In light of this work it would appear that the use of stomatal parameters is of limited value as a model to monitor environmental change, in the absence of information concerning other variables, and as such must be treated with caution.