Stomatal behaviour, photosynthesis and transpiration under rising CO2

Definitions of the variables used and the units are given in Table 1 The literature reports enormous variation between species in the extent of stomatal responses to rising CO 2 . This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short‐term response of leaf gas exchange to increases in ambient CO 2 concentration by developing the recently proposed stomatal model of Jarvis & Davies (1998 ). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO 2 on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way. This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO 2 concentration and also drought will have important effects on the relative gains to be achieved under rising CO 2 . . Abbreviations image