Alteration of transpiration rate, by changing air vapour pressure deficit,influences leaf extension rate transiently in Miscanthus

A controlled environment chamber for whole plants is described in which vap our pressure deficit (VPD) and temperature can be controlled independently. Plant responses to changes in VPD at constant temperature were measured in terms of leaf extension and plant transpiration rates. Manipulation of VPD independently of temperature was shown to be capable of altering the leaf extension rates of the C-4 grass Miscanthus x giganteus grown in hydroponic s. The effects of VPD on leaf extension are attributed to changes in transp iration rate and hence leaf water status. It was found that, at a temperatu re of 20 degrees C, the influence of a fixed change in VPD was proportional ly less than those observed at temperatures which are close to the threshol d for growth (between 6 and 10 degrees C), These responses are discussed in relation to our current understanding of the mechanisms of cell growth. Th e fact that the VPD effects on leaf expansion rates were largely transient suggest that sample models driven by temperature alone are adequate to pred ict leaf expansion within the temperature range 6-20 degrees C, for this ge notype of Miscanthus, in the field.