Stomatal responses to climate change

There remains an ongoing need to make crops more productive in the face of further increases in atmospheric CO2 concentrations as predicted under climate change, along with higher global surface temperatures and more prolonged, severe and frequent periods of drought. With over 90% of water transpired by plants diffusing through their stomata, studying these small, morphologically varied valves in leaf surfaces remains critical to our understanding the consequences of climate change on stomatal responses, and by extension crop productivity. In the short term, stomata adjust their aperture in response to changes in environmental variables affecting carbon assimilation and water loss. In the longer term, adjustments to stomatal density and size may occur, in conjunction with a range of other responses from the plant. While increasing CO2 concentration under climate change had been shown to raise yields and reduce water use by partial stomatal closure, the extent of the fertilisation effect has not been as strong as expected. Meanwhile, higher temperatures and decreasing water availability are likely to have negative yield consequences, with divergent expectations for stomatal aperture and consequently plant water use. However, changes in environmental factors will not occur in isolation and therefore stomatal and plant responses to a combination of these changes will be hierarchical and involve multiple and possibly unique signalling pathways. Predicting stomatal responses to several simultaneous abiotic stresses such as those outlined above adds a layer of complexity, notably where the stresses produce antagonistic responses in the plant. Targeting steady- state stomatal behaviour has been a successful breeding tactic to date, and continues to generate new insights under interacting stresses. Meanwhile, the emerging field of dynamic stomatal responses to environmental stresses offers new phenotypic targets, and the possibility for enhancing water use efficiency by targeting novel signalling and molecular pathways in stomatal responses.