Abstract
Seedlings of lupin (Lupinus angustifolius cv. 75A-258) were grown in cores of sandy loam which was compacted to bulk densities of 1.6 and 1.8 Mg m-3 . There was a substantial decrease in root elongation rate at the higher bulk density. After 4-7 d, roots were rinsed free of soil and clamped loosely in a Perspex block for measurement of turgor pressure (P) using a pressure probe. Measurements were made at 3-4 positions on each root, each estimation taking 2 min. Turgor pressures in the terminal 15 mm of the axes ranged between 0.213 and 0.530 at 1.6 Mg m-3 and 0.210 and 0.570 MPa at 1.8 Mg m-3; mean P values were 0.365 and 0.351 MPa in roots growing at 1.6 and 1.8 Mg m-3, respectively. These measurements were made on roots removed from the soil; P could have been greater in roots still growing in compact soil. Anatomical studies showed that the distal boundary of the zone of cell expansion was 2-4 mm nearer the apex in roots growing at 1.8 than at 1.6 Mg m-3. Using this information, we showed that the mean P of expanding tissue was the same in roots of the two treatments. The apparent rise in P near the apex of roots at 1.8 Mg m-3 was not statistically significant. Primary roots growing against high mechanical impedance had a 34% lower rate of elongation and a 22% greater diameter, resulting in nearly identical rates of volume expansion (35.1 and 34.9 mm3 d-1 at 1.6 and 1.8 Mg m-3 respectively). Furthermore, the rate of O2 uptake was the same in 10 mm root apices from both treatments so that there was no evidence that the carbohydrate requirement for respiration was enhanced by high soil strength. Moreover, while mechanical impedance decreased root elongation, it did not significantly affect our estimate of P. We believe that P in lupin roots changes in response to mechanical impedance only when volume expansion or utilization of solutes are affected.
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Claims 11
Claim · model-written summary
Higher bulk density reduced lupin root elongation rate.
LupinusNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There was a substantial decrease in root elongation rate at the higher bulk density.”
t0“Lupin Roots”
Claim · model-written summary
Mean root turgor pressure was 0.365 MPa at 1.6 Mg m-3 and 0.351 MPa at 1.8 Mg m-3.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mean P values were 0.365 and 0.351 MPa in roots growing at 1.6 and 1.8 Mg m-3, respectively”
t0“Lupin Roots”
Claim · model-written summary
The distal boundary of root cell expansion was 2-4 mm nearer the apex at 1.8 than 1.6 Mg m-3.
- Treatment
- 1.8e0
- Outcome
- distal boundary of the zone of cell expansione0
- Direction
- nearere0
- Value
- 2-4 mme0
- Comparator
- 1.6 Mg m-3e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the distal boundary of the zone of cell expansion was 2-4 mm nearer the apex in roots growing at 1.8 than at 1.6 Mg m-3”
t0“Lupin Roots”
Claim · model-written summary
Mean turgor pressure of expanding tissue was the same under both compaction treatments.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the mean P of expanding tissue was the same in roots of the two treatments”
t0“Lupin Roots”
Claim · model-written summary
The apparent apical rise in turgor at 1.8 Mg m-3 was not statistically significant.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The apparent rise in P near the apex of roots at 1.8 Mg m-3 was not statistically significant”
t0“Lupin Roots”
Claim · model-written summary
High mechanical impedance lowered primary-root elongation rate by 34%.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Primary roots growing against high mechanical impedance had a 34% lower rate of elongation”
t0“Lupin Roots”
Claim · model-written summary
High mechanical impedance increased primary-root diameter by 22%.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Primary roots growing against high mechanical impedance had a 34% lower rate of elongation and a 22% greater diameter”
t0“Lupin Roots”
Claim · model-written summary
Primary-root volume expansion rates were nearly identical at the two soil densities.
- Treatment
- 1.8 Mg m-3e0
- Outcome
- rates of volume expansione0
- Direction
- nearly identicale0
- Value
- 35.1 and 34.9 mm3 d-1e0
- Comparator
- 1.6e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nearly identical rates of volume expansion (35.1 and 34.9 mm3 d-1 at 1.6 and 1.8 Mg m-3 respectively)”
t0“Lupin Roots”
Claim · model-written summary
Oxygen uptake in 10 mm root apices was the same across treatments.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the rate of O2 uptake was the same in 10 mm root apices from both treatments”
t0“Lupin Roots”
Claim · model-written summary
Mechanical impedance did not significantly affect estimated turgor pressure.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mechanical impedance decreased root elongation, it did not significantly affect our estimate of P”
t0“Lupin Roots”
Claim · model-written summary
The authors infer that root turgor changes under impedance only when volume expansion or solute use changes.
- Treatment
- mechanical impedancee0
- Outcome
- P in lupin rootse0
- Qualifier
- only when volume expansion or utilization of solutes are affectede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“P in lupin roots changes in response to mechanical impedance only when volume expansion or utilization of solutes are affected”