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PLANT & MYCORRHIZA ROOT LENGTHS
In greenhouse experiments where all of the roots of an experimental plant can be collected and manipulated, then the grid-line intersect method (Giovannetti and Mosse, 1980) can be used to measure two important variables:
1. Mycorrhizal root length -- an estimate of the length of roots colonized by mycorrhizal fungi (convertable to percentage colonization when divided by plant root length).
2. Plant root length -- an estimate of the total length of roots produced by the plant.
| Several small samples are removed from the main root mass after blotting, pooled, and fresh weight is measured (FW1). Total mass should be no more than 0.1-0.2 grams (varying with abundance of fine and coarse roots). |
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The remaining roots of the sample are weighed quickly (weight will decline rapidly as water evaporates) to obtain a measurement of fresh weight (FW1). |
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| Stain root sample in 0.05% direct blue or other acidic stain.
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Place in paper envelopes and dry for at least 48 hr at 62oC.
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| Spread roots in plastic petri dish in which a grid with 0.5 x 0.5 squares is affixed to the base. Collect the following data:
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Measure
dry weight of large sample (DW1) |
EXAMPLE: In the illustration at right, R1 (root length) is 40 cm: 21 intersects (horizontal lines) + 19 intersects (vertical lines) |
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EXAMPLE: In the illustration at left, R2 (mycorrhizal root length) is 21 cm: Intersects designated by red circles: 11 (horizontal) + 10 (vertical) also: 21/40 = 53% colonization |
THE DATA ABOVE IS USED TO CALCULATE PLANT ROOT LENGTH AND MYCORRHIZAL ROOT LENGTH OF THE TOTAL SAMPLE:
| 1. Calculate the dry weight of the small root sample used to measure mycorrhizal colonization (DW2): | ||
| First determine % weight of large sample remaining after drying (P1): DW1/FW1 | ||
| then: DW2 = FW2 x P1 | ||
| 2. Calculate the dry weight of total root sample (DW3): | ||
| DW3 = DW1 + DW2 | ||
| 3. Calculate the total root length of sample (R3): | ||
| First determine conversion factor based on proportion of dry weight of small sample relative to that of the large sample (P2): DW3/DW2 | ||
| then: R3 = P2 x R1 | ||
| 4. Calculate the total mycorrhizal root length of sample (R4): | ||
| R4 = P2 x R2 | ||