Chin J Plan Ecolo ›› 2017, Vol. 41 ›› Issue (3): 369-377.doi: 10.17521/cjpe.2016.0098

• Research Articles • Previous Articles     Next Articles

Circadian rhythm of root pressure in popular and its driving factors

Jian-Rong GUO, Xian-Chong WAN*()   

  1. Institute of New Forestry Technology, Chinese Academy of Forestry, Beijing 100091, China
  • Online:2017-04-12 Published:2017-03-10
  • Contact: Xian-Chong WAN
  • About author:

    KANG Jing-yao(1991-), E-mail:


Aims Our main purposes were to investigate root pressure and its circadian rhythm of excised roots in ‘84K’ popular (Populus alba × P. glandulosa) cultured in soil and solution, to explore the influencing factors and their relationships with root pressure systematically and to understand the generation and rhythm regulation of root pressure. Methods We investigated the root pressure of excised roots in ‘84K’ popular using the method of digital pressure transducer. The diurnal rhythm of excised roots was conducted through different experimental treatments including sampling in different time, defoliation and girdling, together with ambient condition like soil temperature, differential or consistant temperature during day and night. Then we discussed the effects of root respiration and hydraulic conductivity on root pressure by further using chemical inhibitor. Furthermore, diurnal variation of osmotic potential and ions content as well as soluble sugar content of exudation was determined in order to explore their relationships with root pressure rhythm. Important findings Root pressure of excised roots in popular had diurnal rhythm which was higher during daytime and lower overnight. It reached its peak value in the morning to noon and valley value at 20:00. Root pressure of excised roots sampled at different time and cultured in different medium had influence on the rhythm of root pressure to some degrees, but did not the general rhythm of high in daytime and low overnight. Defoliation, girdling and the inhibitors for root respiration or cytomembrane hydraulic conductivity could affect the maximum value of root pressure while have no significant influence on the daily rhythm. Defoliation, girdling and respiration inhibitor reduced the maximum value of root pressure, whereas the hydraulic conductivity inhibitor had little influence on root pressure. The maximum value of root pressure declined with the decrease in soil temperature which could change the rhythm of root pressure. The synchronous change in the maximum value of root pressure and root respiration rate with temperature indicated that root respiration contributed to the change of root pressure along with temperature. Osmotic potential of root exudation was higher during the daytime and lower at night. Diurnal variations of ions and soluble sugar content of exudation were consistant with that of osmotic potential. The peak of root pressure measured under the condition of differential temperature during day and night was significant higher than that measured under constant temperature. In conclusion, root pressure of the poplar ‘84K’ showed significant diurnal rhythm, i.e. higher during the daytime and lower at night. The maximum value of root pressure was mainly regulated by root respiration metabolism. The factors such as respiration inhibitor, respiration substrate and temperature influence the value of the maximum root pressure of poplar ‘84K’. Root hydraulic conductivity had no significant influence on root pressure.

Key words: root pressure, excised roots, diurnal rhythm, influencing factors

Fig. 1

The circadian rhythm of root pressure measured at different time of a day."

Fig. 2

The root pressure measured under different soil temperatures."

Fig. 3

The maximum of root pressure and respiration rate measured under different soil temperatures (mean ± SD, n = 6)."

Fig. 4

The root pressure under constant temperature during day and night (25 °C/25 °C) and different temperature during day and night (25 °C /19 °C)."

Fig. 5

Effects of defoliation and girdling on root pressure."

Fig. 6

Effects of inhibitors on root pressure."

Fig. 7

Effects of inhibitors on the maximum of root pressure (mean ± SD, n = 3-6, α = 0.05. CK, Control; T1, treatment 1, 0.1 mmol·L-1 HgCl2; T2, treatment 2, 1.0 mmol·L-1 NaN3; T3, treatment 3, 1.0 mmol·L-1 NaN3 + 0.1 mmol·L-1 HgCl2)."

Table 1

Effects of inhibitors on root respiration rate and hydraulic conductivity (mean ± SD)"

Dispose dose
Inhibition percentage of root respiration (%)
Inhibition percentage of root hydraulic conductance (%)
1.0 mmol·L-1 NaN3 44.07 ± 15.35a 41.66 ± 14.83a
0.1 mmol·L-1 HgCl2 23.16 ± 0.01b 50.94 ± 31.37a
1.0 mmol·L-1 NaN3 +
0.1 mmol·L-1 HgCl2
50.00 ± 4.55a 44.04 ± 21.49a

Fig. 8

Diurnal variation of osmotic potential of root exudation (mean ± SD, n = 6)."

Fig. 9

Diurnal variation of ions and sugar in the exudation (mean ± SD, n = 6)."

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