Hydraulic Conductivity Changes in Soybean Plant-Soil System with Decreasing Soil Volumetric Water Content

To avoid dehydration and drought stress, plants must balance transpirational water loss with water transport capacity to replenish water in the leaves. Therefore, changes in hydraulic conductivity (K-total) of the soil-plant system during soil drying may be critical in determining transpiration rates. There has, however, been little study of the changes in Ktotal with respect to decreasing volumetric soil water content. In this study, K-total was measured on pot-grown soybean (Glycine max (Merr.) L.) plants subjected to controlled soil drying across 2 weeks. These results showed that once soil dried to a point when there was a decrease in transpiration rate, there was a coincident decrease in K-total. Further, losses in soil water resulted in further decreases in K-total and transpiration rate. These results showed that the commonly observed pattern of decrease in transpiration rate with decreases in volumetric soil water content is intimately linked to system K-total.