Nutrient dynamics (C,N and P) in termite mounds of Nasutitermes ephratae from savannas of the Orinoco Llanos (Venezuela)

Termites play an important role in decomposition processes in savanna and tropical forest ecosystems. In the process of mound building, termites modify the physical, chemical and biochemical characteristics of the soil they use for construction, as well as the soil of nearby areas, so that organic compounds, particularly C and N, and in some cases P, are more abundant in the termite nests than in the surrounding soils. In this study, organic matter and nutrient mineralization in incubation experiments were measured in mounds of Nasutitermes ephratae and associated soils of Orinoco savannas. The mounds of Nasutitermes ephratae contain more C, N and P than adjacent topsoils due to the use of faecal material to build gallery walls. Mounds accumulate 2.25 times more total P than adjacent soils. Available and potentially mineralizable organic P (Po) were significantly higher in Nasutitermes mounds than in adjacent soils. The mound materials significantly stimulated soil microbial metabolism, due to the accumulation of organic carbon (9.30%). The results for nitrogen dynamics emphasise the low ammonification rate in savanna soils. Ammonium production in the savanna soil was very low ranging from 20.4 to 39.9 microgram g(-1), whereas in the mound the value increases to 1528 microgram g(-1), which means that as much as 20% of the total nitrogen was found as inorganic nitrogen within the termitaria. Nitrate production on the other hand was negligible in both soils and mound, so that the nitrification rate seemed to be not limited by ammonium production. The nutrient depleted conditions of this environment together with the important concentrations of C, N and P found within the mounds of Nasutitermes ephratae corroborated the hypothesis that termite mounds can act as 'sinks' in the nutrient economy of well-drained savannas with low productivity.