Northeast Forestry University, China (People's Republic)
Background/Question/Methods:
Xylem positive pressure―root pressure―has gained new interests after a long period of underestimation, because it is important to restore tissue moisture, maintain function and interconnection of plant hydraulic system, and contribute to cells and tissues growth. In this paper, hydroponic lucky bamboo (Dracaena sanderiana Sander) in the height 60-80 cm was used to study the circadian variation of root pressure and its influencing factors in order to reveal the role that root pressure plays in the upward transport of water across xylem. Root pressure was measured with pressure sensors (PX26-100GV) which were connected to the top of the stems after cutting off all leaves. The experiments were conducted in a laboratory in a building in summer in Harbin, China.
Results/Conclusions:
The results showed that: (1) The positive root pressure of D. sanderiana existed throughout the day, and the maximum value obtained was 103 kPa, with a rhythm of high root pressure at daytime and low at night. (2) Root pressure decreased as water temperature declined, and at 0℃, root pressure reduced to nearly zero and the circadian rhythm was altered too; (3) The different concentrations of nitrate (KNO3) addition all increased root pressure, and the circadian rhythm was not altered; (4) Root pressure of stems with tillers was smaller but also positive than that of stems without tillers; (5) After completely cutting off the fibrous roots, root pressure quickly decreased to negative. In summary, compared with plant height, the positive root pressure of most of the hydroponic lucky bamboos can fully provide the force needed to transport transpiration water upwards throughout the day, and the effect of transpirational pull can be excluded. At the same time, the root pressure showed a relatively stable rhythm, that is, high at the day and low at night. Temperature, mineral elements, tillering and root removing all had significant effects on root pressure.
