A COMBINATION MODEL FOR ESTIMATING STOMATAL CONDUCTANCE OF MAIZE (ZEA-MAYS L.) LEAVES OVER A LONG-TERM

In this study, an environmental variable model for estimating stomatal conductance of maize (Zea mays L.) leaves over a long term is develop ed, based on research results concerning responses of stomatal conduct ance to environmental variables. This model is actually a combination of optimized formulae for potential stomatal conductance during daytim e, PSC, and for the relative degree of stomatal opening during daytime , RDO, with a basic form expressed as a multiplication of inter-day an d intra-day factors. We call this environmental variable model as the combination model. Compared with other models presented in the past, t his combination model is convenient in practical use because it can es timate not only maximum and average values but also instantaneous valu es of stomatal conductance during daytime. Also, the theoretical descr iption of this model has been clarified by introducing into it the con cept of environmental stress. As compared with Jarvis-type multiplicat ion environmental variable models, we think this combination model is a refinement and development of the Jarvis-type models. (C) 1998 Elsev ier Science B.V. All rights reserved.