Nitrogen transformations associated with termite biogenic structures in a dry savanna ecosystem

Abstract

Soil structures built by litter-feeding termites are one of the main soil translocation processes in dry tropical savanna. Runways (soil sheeting) made of soil particles cemented with salivary secretions covering the dead plant pieces collected on the ground surface represent the main soil structures. The aim of this study was to determine the impact of this soil engineering activity on the microbially-mediated N transformations (nitrification and denitrification) associated with termite sheeting. We investigated the hypothesis that the physicochemical and microbial properties of termite soil sheeting depend on (i) the termite species and (ii) the type of organic substrate consumed. Soil sheeting built by two of the main savanna species, Macrotermes subhyalinus and Odontotermes nilensis, were sampled on field plots treated with three different types of litter (Acacia leaves, millet straw, both whole and ground (< 500 µm), and cattle manure). The soil's organic C, total N, inorganic N, microbial biomass, potential CO 2 respiration, nitrification and denitrification were measured. For both termite species and all types of litter, the soil sheeting was enriched in organic C and inorganic N, resulting in an increase in soil respiration, whereas the microbial biomass was unchanged with respect to the reference soil. With the exception of the soil nitrification potential, the type of organic substrate did not significantly affect the properties of the soil sheeting measured. However, the nitrogen cycle was affected differently by the two termite species. In O. nilensis sheeting, the denitrification potential was reduced with respect to the reference soil, whereas the nitrification potential was inhibited in M. subhyalinus sheeting. The changes in the nitrogen cycle processes resulted in an increase in NH 4 + and NO 3 − in the termite soil sheeting, increasing the availability of nitrogen to plants. This study reinforces the importance of termites as a keystone savanna group whose building activities have an effect on tropical soil mineralization.

Termites create spatial structure and govern ecosystem function by affecting N2 fixation in an East African savanna

“…Because our measurements are not dynamic we cannot know whether higher mound NO 3 À concentrations reflect enhanced mineralization of a somewhat larger organic N pool, or reduced N loss via leaching and denitrification. Studies of soils associated with termite structures (mounds and sheeting) have reported both higher and lower levels of denitrification (Lensi et al 1992, Ndiaye et al 2004, and this is a subject that warrants further investigation in our study area. Soil N transformations are associated with (sometimes large) isotopic fractionations (Evans 2007) (Ho¨gberg 1997).…”

Impact of termite activity on soil environment: A perspective from their soluble chemical components

“…They generally go through a sequence of actions, from fetching, carrying to cementing mineral particles into mounds by using their salivary secretion (Howse, 1970;Wood, 1988;Donovan et al, 2001;Ndiaye et al, 2004;Vandecasteele et al, 2004;Lopez-Hernandez et al, 2006). For example, it has been shown that termite activity increases the content of organic matter in the soils that they use for the construction of their nests and also modifies the clay mineral composition of these soil materials (Mahaney et al, 1999;Jouquet et al, 2002;Roose Amsaleg et al, 2004).…”

Differences between Bacterial Communities in the Gut of a Soil-Feeding Termite (Cubitermes niokoloensis) and Its Mounds

“…This creates an increased richness in clay (5 times more), minerals (2 to 3 times more P and Ca and up to 50 times more NH 4 [32]), and organic matter (5 to 7 times more C and N [12]) with respect to neighboring soil. The environment for microorganisms derived from soil and feces is modified not just by an increase in available organic compounds but also by a change in their qualities (C/N, humic acid/sugar content [12,36]) and their availability by the formation of stable clay-humus complexes (14).…”