COMPARATIVE WATER-UPTAKE BY ROOTS OF DIFFERENT AGES IN SEEDLINGS OF LOBLOLLY-PINE (PINUS-TAEDA L)

Magnetic resonance (MR) imaging was used to study water absorption from fine, moist sand by the taproot, first-order lateral roots, and fine roots of 9-month-old loblolly pine seedlings. Magnetic resonance imaging provides the opportunity for repeated non-destructive measurements of water uptake by roots growing in a solid medium such as sand. Root systems of container-grown seedlings were pruned to a taproot, one or two first-order laterals and attached fine roots, and were planted in small containers. Reference tubes filled with a mixture of CuSO4/D2O were placed in each container in the field of view. Roots of individual seedlings were repeatedly imaged at approximately 3 h intervals. Water uptake by individual roots was measured and uptake was calculated based on biomass, root length, and surface area. Based on weight and surface area, but not on root length, fine roots were more efficient than the lateral or taproots in water uptake. Measurement of water content in MR images of wet sand was confirmed by the imaging of sand phantoms. These phantoms were tubes filled with fine sand at varied water contents (5-25 %). Additional tubes of CuSO4 with D2O were also imaged. A linear relationship between signal intensity of moist sand (normalized against the CuSO4/D2O) and water content was demonstrated (R2 = 0.97). Fitting the normalized signal intensity of the sand to the calculated linear regression allowed calculation of the water content of the sand.