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 estimating water flow resistance in a soil-leaf pathway under field conditions. In this model, the change in leaf water content is taken into consideration; the model is based on the assumption that water flow resistance is essentially constant for relatively short periods. Resistance was estimated for three subtropical woody species growing on shallow-soiled ridges. For the estimation, transpiration rate and leaf water potential were measured directly in the field, and leaf water content was estimated based on the relationship between leaf water potential and relative leaf water content as observed in the laboratory. Resistance showed little variation with change in leaf water potential and transpiration rate by day but was particularly high in the evening in all species. The reason for this is not known but was perhaps due to inaccurate measurement for transpiration rate. It was considered to be pertinent to compare daily values of resistance so as to assess plant adaptation to drought. The model was shown to be useful for estimating resistance from conventional measurements in the field.