Water relations of winter wheat triticum aestivum cultivar maris huntsman 4. hydraulic resistance and capacitance in the soil plant system
Wallace, J.S.; Biscoe, P.V.
Journal of Agricultural Science 100(3): 591-600
ISSN/ISBN: 0021-8596 Accession: 006914282
A simple model is presented which can account for the hysteresis observed in the relationship between leaf water potential (.psi.l) and water flow per stem (Q) in winter wheat. Using this model the total hydraulic resistance (R) and capacitance (C) of the soil-plant system were estimated from measured diurnal changes in .psi.l and Q. Daily mean values of R were constant when the soil water potential (.psi.s) was above -0.6 MPa [megapascals], but R increased by about 40% when the soil dried to -1.5 MPa. R also appeared to vary during the day, increasing in the afternoon and evening. The results of experiments on the recovery of .psi.l in plants from which transpiration was prevented suggested that the major resistance to flow was in the soil-root system and that it was an increase in this resistance which gave rise to the overall increase in R as the soil dried. There was substantial variation in the estimates of hydraulic capacitance (C) and no systematic diurnal or seasonal trend was evident. Despite the variation in C the mean value for the season, 8 .times. 10-7 m3/MPa, predicted realistic changes in plant water storage. Estimates of the components of C indicated that the major capacitance was located in the soil-root complex. More information is needed about the components of R and C, particularly those in the soil-root system.