An analysis of the dynamic response of stomatal conductance to a reductionin humidity over leaves of Cedrella odorata

Single leaves of 3-month-old Cedrella odorata seedlings were exposed to a s tep reduction in the ambient dew point, The resultant time series of dynami c variations in leaf surface water vapour concentration, leaf surface wafer vapour concentration gradient, transpiration rate and stomatal conductance to water vapour, are analysed using the data-based mechanistic (DBM) model ling methodology of Young (e.g. Young & Lees 1992; Minchin et al. 1996). It is shown that the identified second-order, dynamic model between transpira tion rate (as the input) and stomatal conductance (as the output) provides an appropriate, physiologically meaningful, description of the system. In p articular, the dynamic relationship between these two variables is remarkab ly linear and can be resolved in terms of two parallel, first-order, subsys tems; a model which complements the results of Cowan (1977) for cotton. The model is also compared with the recently published simulation model of Hae fner, Buckley & Mott (1997).