A Model for Estimation of Water Flow Resistance in Soil-Leaf Pathway under Dynamic Conditions

The present study was carried out to establish a model for estimatingwater flow resistance in a soil-leaf pathway under field conditions.In this model, the change in leaf water content is taken intoconsideration; the model is based on the assumption that waterflow resistance is essentially constant for relatively shortperiods. Resistance was estimated for three subtropical woodyspecies growing on shallow-soiled ridges. For the estimation,transpiration rate and leaf water potential were measured directlyin the field, and leaf water content was estimated based onthe relationship between leaf water potential and relative leafwater content as observed in the laboratory. Resistance showedlittle variation with change in leaf water potential and transpirationrate by day but was particularly high in the evening in allspecies. The reason for this is not known but was perhaps dueto inaccurate measurement for transpiration rate. It was consideredto be pertinent to compare daily values of resistance so asto assess plant adaptation to drought. The model was shown tobe useful for estimating resistance from conventional measurementsin the field. Key words: Leaf water content, leaf water potential, transpiration rate, water flow resistance