Deep Rooting Characteristics and Water Uptake of Giant Reed

Giant reed (Arundo donax) is a deep rooted crop that can survive prolonged dry periods probably as a consequence of its capacity to uptake water from belowground, but specific information on the functioning and signaling of deep/shallow roots is missing. The objective of this study was to understand the dynamic interrelationship of root water acquisition, canopy water conservation, and hormonal signals (ABA) from both shallow and deep roots in a top-bottom split root system (1-m soil columns). When drought stress was imposed to topsoil layers water uptake from deep soil layers increased gradually up to 2.2 times more than in the control conditions. Whereas when both soil layers (top and bottom) were well-watered the main water source remained the topsoil layer. A gradual increasing difference in surface root length density (SRLD) was also observed between control and treated topsoil layers. Moreover, despite the significant increase in water uptake from deep layers, SRLD of droughted plants was not increased suggesting an increased efficiency in root water uptake. The increased water uptake and water uptake efficiency from deep layers was not enough to sustain photosynthesis and therefore biomass accumulation which was reduced by about 42%. The ABA signal from shallower droughted roots was increased 2.6 times. Such increased signal was closely and positively correlated with the foliar ABA concentration and with sustained leaf water potential. At the same time ABA signal from shallower roots was negatively correlated with the intercellular CO₂ (Ci) and water uptake from top soil layers. In summary, giant reed is able to change its water sources depending on its availability and to maximize its supply efficiency to satisfy the canopy evaporative demands, but when these are not meet, the plant may activate some additional protective mechanisms such as ABA root signallig to enhance stomatal closure.

Acknowledgments: This work was supported by the EU under the 7th Framework Program for Research (FP7-311929, WATBIO)