Stomatal behaviour, photosynthesis and transpiration under rising CO2

The literature reports enormous variation between species in the extent of stomatal responses to rising CO2. This paper attempts to provide a framewor k within which some of this diversity can be explained. We describe the rol e of stomata in the short-term response of leaf gas exchange to increases i n ambient CO2 concentration by developing the recently proposed stomatal mo del of Jarvis gr Davies (1998). In this model stomatal conductance is corre lated with the functioning of the photosynthetic system so that the effects of increases in CO2 on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way This mod el also allows us to consider the effects of evaporative demand and soil mo isture availability on stomatal responses to photosynthesis and therefore p rovides a means of considering these additional sources of variation. We em phasize that the relationship between the rate of photosynthesis and the in ternal CO2 concentration and also drought will have important effects on th e relative gains to be achieved under rising CO2.