Wheat plant hydraulic properties under prolonged experimental drought:: Stronger decline in root-system conductance than in leaf area

Wheat plants (Triticum aestivum var. INTA 'Cinco Cerros') were grown in pots with fine sand under a rain-out shelter to assess their response to a water shortage spanning most of the growth cycle. Three watering treatments, based on different thresholds of plant-available water, were started 8 weeks after sowing and maintained for 10 weeks. After allowing recovery from any short-term embolism, stem-segment and root-system hydraulic conductances were then measured by standard low-pressure methods. Stress treatments reduced, as compared to controls, tiller number (by 31% and 41% for moderate and intense drought, respectively), total plant biomass (by 21% and 52%) and total plant leaf area (43% and 68%). The capacity of stems to transport water was reduced only by the most intense treatment (and then by no more than 50%), but root-system hydraulic conductance (k(R)) was strongly reduced by both treatments (37% and 80%, respectively). The transport capacity of belowground structures decreased not only on an absolute basis (k(R)), but also per unit root mass (K-RS: 51% and 83%) and per unit of leaf area (K-RL: 23% and 73%). Simulation of maximum transpiration under different soil and plant water conditions indicate that these changes in plant hydraulics had a significant impact on either transpiration at the leaf level or leaf water status for a given transpiration rate.