STOMATAL CONTROL OF PHOTOSYNTHESIS AND TRANSPIRATION

The stomata occupy a central position in the pathways for both the los s of water from plants and the exchange of CO2. It is commonly assumed that they therefore provide the main short-term control of both trans piration and photosynthesis, though the detailed control criteria on w hich their movements are based are not well understood and are likely to depend on the particular ecological situation. This paper first rev iews the main methods available for quantifying the control exerted by stomata over transpiration and photosynthesis in the absence of feedb acks between gas-exchange and stomatal function. The discussion is the n extended by using very simple models to investigate the role of stom ata in the control of gas exchange in the presence of hydraulic feedba cks and to clarify the nature of causality in such systems. Comparison of a limited number of different mechanistic models of stomatal funct ion is used to investigate likely mechanisms underlying stomatal respo nses to environment.