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

Abstract

temperatures. In the field, crops experience both diurnal and seasonal changes in temperature and humidity and A controlled environment chamber for whole plants is leaf growth has been demonstrated to be very sensitive described in which vapour pressure deficit (VPD) and to both these environmental variables (Gallagher and temperature can be controlled independently. Plant Biscoe, 1979; Parsons and Robson, 1980; Ben Haj Salah responses to changes in VPD at constant temperature and Tardieu, 1996). The rate of canopy development in were measured in terms of leaf extension and plant spring is important in determining the quantity of raditranspiration rates. Manipulation of VPD independently ation intercepted by a crop and, consequently, the final of temperature was shown to be capable of alter- yield (Monteith and Elston, 1972; Van der Werf et al., ing the leaf extension rates of the C 4 grass 1993). Simple models developed to predict canopy closure Miscanthus◊giganteus grown in hydroponics. The often use an empirical relation between accumulated effects of VPD on leaf extension are attributed to temperature above a threshold (e.g. degree days) and leaf changes in transpiration rate and hence leaf water expansion rate when a healthy crop is receiving adequate status. It was found that, at a temperature of 20°C, supplies of water ( Van der Werf et al., 1995). This the influence of a fixed change in VPD was proportion- approach assumes a linear relationship between temperally less than those observed at temperatures which ature and the rate of leaf expansion, and a lack of are close to the threshold for growth (between 6 and significant influence of other correlated variables such as 10°C). These responses are discussed in relation to humidity and light. our current understanding of the mechanisms of cell It has recently been shown that there was considerable growth. The fact that the VPD effects on leaf expansion variation in the leaf expansion rate of diVerent Miscanthus rates were largely transient suggest that simple genotypes over a range of temperatures between 5°C and models driven by temperature alone are adequate to 20°C and that this could influence final yield of the predict leaf expansion within the temperature range genotypes significantly (Clifton-Brown and Jones, 1997). 6‐20°C, for this genotype of Miscanthus, in the field. Miscanthus is a grass genus with C 4 photosynthesis with origins in eastern Asia. The genotype M.◊giganteus