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Root architecture and organic acids

Lap report, Rhizosphere Ecology, WeberV, 24.12.2007

1 Practical Session No 1
lab-report-rhizosphere-ecology_p1.jpg

1.1 Root architecture
The roots of maize, flax and lupin were cut from the shoot and spread on a scanning plate. The roots were separated to achieve minimum root crossing points. Then water with 40°C was added to ensure that no water bobbles develop. Then the plate was scanned and a program computed die length of the roots and the amount of root tips.

1.2 Plant biomass
The roots were cut from the shoot and then the shoots have been weighted. Additionally the shoot high and the length of the root system were recorded.

Questions
How do the different plant species respond to P deficiency?

lab-report-rhizosphere-ecology_p2.jpg

How do they grow under different P supply?
- The table shows, that the response to P deficiency is depending on the plant.
- While maize is really suffering at low P conditions (decrease in biomass and height), flax and especially white lupin can adapt to these deficient conditions. Some parameter do not change (height, root system length) and some are even increased (number of root tips, ratio of root/shoot, total root length)

How do they manage to tolerate deficiency?

  • Generally in low nutrient conditions plants improve root elongation and proliferation of root hairs and enhance formation of fine root
  • The response of Maize to P starvation is the decrease in shoot biomass and root diameter as well as the increase of root biomass and total length
  • White Lupin responds to low P conditions with cluster root formation

How do they respond if there is too much?

  • There is no clear result of this. Maybe we can discuss this again. Or you give me an answer within this lab report

1.3 Composition of root exudates – organic acids

lab-report-rhizosphere-ecology_p3.jpg

100 µl of exudates were diluted with water. The root exudates were measured in a chromatograph which uses an acid with 14 uS as eluend. The chromatograph computes the amount of exudates by measuring the area of the peak over the acid curve. With this citrate, malat, acetate, fumaric acid and succinic acid were measured.

Questions:
Which organic acids are exuded under P deficient conditions (Why)? What are the differences between the different plant species?

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Exudates are released to make P more available. Because organic acids are acid, they can free P from soil particles.
Different plants react differently under P deficiency, what can be observed in different organic acids compositions and amounts. For Lupinus albus thank to cluster roots, leaching carboxylates to the rhizosphere. So Lupin is a very efficient plant in P mobilization and uptake. Additionally it has the highest amount of organic acids present at P deficient conditions as well as to P deficient conditions. Acetate is one of the mostly common metabolit of a plant (e.g. in Krebs cycle). So it could be that the high acetate concentration of maize is a result of damaging the roots at the time of taking probes.

What are the limitations of the data obtained in the hydroponics as compared to soil-based cultivation system?
In the hydroponics a large root growth is induced because there is no resistance of soil to overcome for the roots. With this the exudation rates should be higher than in a soil experiment.

Can you draw a relation between root biomass and root length under the different P supplies? Are there differences between plant species?

lab-report-rhizosphere-ecology_p5.jpg

For maize and lupin the biomass root is increasing with total root length. For flax the root biomass decreases slightly with the total root length.

December 24th, 2007
Topic: Crop Science, Plant nutrition Tags: None

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