Do the large termite mounds of Macrotermes concentrate micronutrients in addition to macronutrients in nutrient-poor African savannas?

The influence of soil organisms on the availability of nutrients to other biota within ecosystems can be context-dependent. Fungus-culturing termites, for example, are known to concentrate nutrients by building large mounds in nutrient-poor savannas, but several factors determine the nutritional value of the mounds - whether by geophagy or consumption of forage - for large herbivores. Such factors include the limitations of the local edaphic environment and the degree of nutritional enrichment of plants growing on these mounds. We investigated, in nutrient-poor miombo vegetation in Zimbabwe, how the surrounding soils and maturity of the mounds affected concentrations of macro- and micronutrients in mounds and the woody plant foliage growing on them. All macro- and micronutrients save ammonium, extractable P, Zn and Se were enriched in large mounds relative to matrix soils, but none was significantly enriched in incipient mounds, suggesting that the full nutritional value of mounds is only expressed in large mounds. Concentrations of macronutrients, other than extractable P, in large mounds varied independently of concentrations in the matrix of surrounding topsoils. However, six (Mo, Cu, Fe, Zn, Se and Mn) of the nine micronutrient elements tested showed correlation with surrounding topsoils. Although foliar concentrations of N and P in mound species of woody plants did not differ significantly from those of matrix species, they reached maxima in mound species (5.7% for N and 0.4% for P, exceeding maxima of 4.3% and 0.24% in matrix species). Similarly, foliar concentrations of 75% of the micronutrients tested did not differ between mound and matrix species; but mound species contained maxima for 75% of these elements. Since herbivory is affected by soil nutrients, herbivores might meet their nutrient requirements in this nutrient-poor system by including mound plant species in their diets.