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INTRODUCTION

INTRODUCTION

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INTRODUCTION

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  1. INFLUENCE OF TERMITES ON STABILITY AND REACTIVITY OF PHOSPHORUS IN EAST AFRICAN SAVANNA 1 2 Lucy Ngatia1, A. E. Normand1, B.L. Turner2, P.W. Inglett1 and K. R. Reddy1 1 Wetland Biogeochemistry Laboratory, Soil and Water Science Department, University of Florida 2 Smithsonian Tropical Research Institute 3 (a) 4 5 • INTRODUCTION • Termites are major ecosystem engineers in African savanna creating soil heterogeneity and nutrient hotspots in the form of mounds. • Plant productivity in African savanna is limited by cycling of phosphorus (P) and nitrogen (N). • However, little is known about the influence of termite mounds on P reactivity and stability. • Objective: To determine the influence of termite mounds on soil P distribution and reactivity. • Hypothesis: The termites increase the phosphorus availability on the termite mounds. RESULTS (b) 6 Termite mound A (Center) B (Edge) Termite • MATERIALS AND METHODS • Study site • Mpala Research Centre (MRC) and associated Mpala Ranch which encompasses 190 km2 of semi arid savanna within the Laikipia District of Rift Valley Province, Kenya. • Laikipia District is a semi arid Acacia savanna that boasts the largest population of wildlife in Kenya’s non protected areas. • Livestock and wildlife co-exist and depend on natural vegetation including Acacia drepanolobium(overstory) and grass (understory)for feed. • Methods • 42 soil composite samples from the centre, edge and 5m away from the termite mound were collected up to 10 cm depth (Fig 2), air dried for 12 days and analyzed for select chemical parameters . • Soil phosphorus forms were determined on alkali extracts using 31P nuclear magnetic resonance (NMR) spectroscopy. • Isotope signature δ13C and δ15N were determined. • Total P was determined using ashing method. • Available P determined using Mehlich-1 method. • Statistical analysis was done using JMP 8.0 software program and results were considered significantly different at p<0.05 level. • Study site 5m Fig 5. Relationship between (a) δ15N vs TP and (b) δ15N vs N:P ratio within and around the termite mound Orthophosphate C (5 m away) Phosphomonoesters Table 2. Soil nutrient concentration as influenced by termite mound Phosphodiesters/DNA Fig 2. Termite mound, termite on a hand help chunk of soil and sampling points A, B, C. Fig 3. Source of soil organic matter as indicated by isotope signatures Pyrophosphate Acacia leaves Grass vegetation Center of mound Edge of mound 5m away from mound Africa Off mound soil Kenya Mpala Research Centre • The ∂13C(Fig. 3; -15.2 to -17.3‰) indicated that grass was the main source of soil organic matter. • Total P and available P were three and two times higher, respectively, at the center of the termite mound (0.37±0.06 g kg-1 and 11±1 mg kg-1) compared to off termite mound soils (0.14±0.01 g kg-1 and 6±1 mg kg-1) (Table 2) indicating that termite activities promote P accumulation. • NMR results indicated that at all sites near the termite mound soil P was dominated by orthophosphate, phosphomonoesters, phosphodiester (DNA) and pyrophosphate while in contrast, off mound soil P was dominated by orthophosphate and phosphodiesters. This indicate that termite promote both P availability and stability (Fig. 4;Table 1). • ∂15N was negatively correlated with soil P and positively with N:P ratio potentially suggesting N2 fixation by termites (Fig 5a,b). • Total P, Ca, and Al were significantly higher at the center of the termite mound while K and Mg were higher off the termite mound (Table 2), suggesting that termites could be pumping P, Ca and Al from the deeper soil horizons to upper horizon. • The presence of termite mounds in the savanna is important because they promote short term availability of P to plants through orthophosphate as well as long term P availability through pyrophosphate. • P heterogeneity created by termite mound potentially influences plant productivity and feed quality to livestock and wild animals. • Nitrogen fixation by the termites in the savanna is likely to reduce N limitation to plant productivity. DISCUSSION AND CONCLUSIONS Fig 4. 31P spectra with functional groups referenced using 85% phosphoric acid Table 1. Recovered P fractions in alkali extracts using 31P nuclear magnetic resonance (NMR) spectroscopy. Fig 1. Study site and typical/Model P functional groups in 31P NMR spectrum (Cheesman et al.) STRI and NCCR is hereby acknowledged for providing the necessary funding for carrying out this research. Corresponding author: Lucy Ngatia, Soil and Water Sciences Dept., 2181 McCarty Hall A. PO Box 110290, Gainesville, FL 32611-0290. lucyngatia@ufl.edu