Shrubs root depths

There are many types of roots, including thick fibrous, deep tap, shallow, and tubers, all in one plant community. Some roots explore the soil to significant depth (i.e., as much as 250 cm deep), while others are shallow (i.e., only 25 cm deep). Different rooting depths are found in all plant types grasses, legumes, shrubs, and trees. Each root type will contribute its own unique exudates and characteristics to its unique volume of soil and the associated soil solution. 

Mobilization of water from the soil is closely related to root depth and root density in each layer of soil. Fine roots of active B. brizantha pastures, established in deeply weathered clayey soils in eastern Amazonia, reach depths of 8 m or more (Nepstad et al. 1994). In abandoned pastures (50% B. humidicola and P. maximum cover and 50% invading shrubs and small trees), fine roots ( < 1 mm in diameter) were found at depths of 12 m (Nepstad et al. 1994). Fine-root biomass in the superficial soil layers of an active pasture in Paragominas, eastern Amazonia, was 3 times higher than that found in an adjacent primary forest area. Fine root biomass in the active pasture decreased by a factor of 100 between the surface and 6 m depth. In an abandoned pasture area, the distribution pattern of fine-root biomass was similar to that observed in the deeper soil layers of the forest ecosystem. This pattern is associated with the fine roots of the existing dicotyledonous invading species. 

In the collection areas tragacanth is produced by a process of regular, systematic, artificial incisions which is called tapping. Tapping must be done carefully to avoid possible injurious effects that may lessen the productivity of the shrubs. Each plant can be tapped in its first year and alternate years thereafter, but will not yield good gum in two successive years (S). Usually the root is exposed to a depth of 2 inches, incision is made with a sharp knife, and a small wedge is then forced into the wound to allow more rapid extrusion. Sometimes the plants are burned at the top after incisions are made. This is supposed to increase the yield, but such gum is a very inferior grade of a dirty reddish color. 

How and what to sample Plant samples are generally taken from the branches of the largest tree or shrub that is available for maximum depth of root penetration. To minimize seasonal variations in the metal composition of plant tissue twig material of at least a few years in age is recommended. 

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