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• cation exchange capacity,

• content of potentially mineralizeable N,

• availability of N and P

(Medina 1993). Nutrient categories of savannas depend on the nutrient levels in the soil and the recirculation rates (Table 10.7). Nutritional fertility of savannas may be estimated and ranked by the sum of extractable bases

J2(K+ + Ca2+ + Mg2+ + Na+)[cmol(+)/kg(soil)] , where values lower 5cmol (+) kg-1 mark dystrophic and values higher than 20 cmol (+) kg-1 eutrophic savannas, with mesotrophic savannas in between (Medina 1993). Generally, however, nitrogen and phosphorus are the most strongly limiting elements, although even potassium can become limiting in situations of rapid recirculation. A particular mineral stress factor in savannas is aluminium.

Fig. 10.13A, B Daily courses of potential quantum yield of photosystem II, Fv/Fm, of 12 cerrado tree species as follows: (A) closed circles: Miconia albicans, closed triangles: Miconia ferrugi-nata, closed squares: Roupala montana, open circles: Sclerolobium paniculatum, open triangles: Eryotheca pubescens, open squares: Vochysia eliptica, inverted open triangles: Syagrus comosa (from de Mattos 1998); (B) open squares: Didymopanax macrocarpum, open diamonds: Roupala montana, inverted open triangles: Qualea grandiflora, open triangles: Miconiafallax, open circles: Ouratea hexasperma (from Franco and Luttge 2002)

Fig. 10.13A, B Daily courses of potential quantum yield of photosystem II, Fv/Fm, of 12 cerrado tree species as follows: (A) closed circles: Miconia albicans, closed triangles: Miconia ferrugi-nata, closed squares: Roupala montana, open circles: Sclerolobium paniculatum, open triangles: Eryotheca pubescens, open squares: Vochysia eliptica, inverted open triangles: Syagrus comosa (from de Mattos 1998); (B) open squares: Didymopanax macrocarpum, open diamonds: Roupala montana, inverted open triangles: Qualea grandiflora, open triangles: Miconiafallax, open circles: Ouratea hexasperma (from Franco and Luttge 2002)

Nutrient availability in the various soil horizons of savannas is much lower than in tropical forests (Table 10.8). The height and density of the woody layer in the cerrados (see Table 9.2) depends on the fertility, depth and drainage of the soil and not on rainfall (Eiten 1972,1986).The typical distribution of some mineral elements between the vegetation and the soil in tropical forests and savannas is schematically summarized in Table 10.9. In the savanna most of the K, N, Ca and Mg is in the soil,

Table 10.7 Nutrient categories of savannas. (After Sarmiento 1984)

Table 10.7 Nutrient categories of savannas. (After Sarmiento 1984)

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Renewable Energy 101

Renewable Energy 101

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