Agriculture Reference
In-Depth Information
3.2.3.1
Chemical quality
For the same reasons, much less information is available on root than on leaf litter
chemical composition and even fewer studies differentiate between coarse and fine roots.
Apart from their mineral nutrient contents, little attention has been paid to the chemical
composition of roots. Nutrient concentrations are often higher in roots than in leaves:
in the strongly nutrient-limited soils of the Amazonian
tierra firme
forests, fine roots
have much higher concentrations of all nutrient elements except calcium (Table I.26)
(Cuevas and Medina, 1988).
In a temperate-climate European deciduous forest, coarse roots generally had lower
concentrations of most nutrient elements than fine roots, except for potassium and sodium
(Table I.27). Dead roots of all sizes had greater concentrations of the nutrient elements
calcium, magnesium, sulphur and aluminium (not a nutrient) with values approximately
twice as high as those of living roots) but only slight differences in potassium, nitrogen
and phosphorus. Finally, comparison of nutrient element concentrations in the fine roots
of Amazonian and temperate climate forests (Tables I.26, I.27, see also Table I.15)
highlights some substantial differences: in the tropical forest, higher concentrations
of potassium (x 15-29), magnesium (x 1.8-2.4) and nitrogen (x 2-2.6), slightly higher
concentrations of phosphorus (x 1.2-1.8), and much lower concentrations of calcium
(x 0.18-0.22) were apparent.
In humid African savannas, roots of the dominant perennial grasses contain more
lignin and cellulose than leaves and are therefore much harder materials. Water-soluble
compounds are present in lower concentrations, although most are only available to
consumers when lipids and waxes have been removed; some appear to contain toxic
compounds (Lavelle
et al.,
1989). Consequently, the overall quality of these roots is
much lower than that of the leaves. This may be interpreted as a defence against soil
herbivores, comparable to those developed against folivores (Table I.28).
