Results

1. 31P NMR Analysis of African Tropical Savanna Herbivore Manure Anna E. Normand1, L. Ngatia1, B.L. Turner2, and K.R. Reddy1 1 Wetland Biogeochemistry Laboratory, Soil and Water Science Department, University of Florida 2 Smithsonian Tropical Research Institute δ15N δ13C INTRODUCTION In Africa tropical savanna large herbivores are a major ecosystem driver. Plant primary productivity is dependent on nutrient availability.  Phosphorus (P) is one the major limiting nutrients in this ecosystem, which limits plant productivity and influences the availability and quality of forage for herbivores.  Herbivore grazing accelerates P cycling through the deposition of organic P in manure thus promoting soil fertility and plant productivity. Little is known about the forms and stability of the organic P in manure which likely regulates plant available P.  Objective: The objective was to determine the forms and stability of organic P in manure deposited by herbivores with different grazing habits. Hypothesis: The forms of faecal organic P depends on herbivores feeding habits (grazers vs. browsers) and digestive system efficiency (ruminant vs. non ruminant). HERBIVORES b) a) e) c) d) f) Figure 3. African tropical savanna herbivores: browsers - a) camel and b) giraffe; mixed feeders - c) elephant (non ruminant) and d) impala - grazers: e) cattle and f) zebra (non ruminant) • 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 – Acacia (overstory) and grass (understory) – for feed. • Methods • Fresh vegetation and manure were sampled at MRC during the dry season. Vegetation included Acacia and grass. Herbivores included browsers (giraffe, Giraffa camelopardalis; camel, Camelus dromedaries), mixed feeders (elephant, Loxodonta africana; impala, Aepyceros melampus and grazers (cattle, Bos indicus; zebra, Equus  burchellii). • Orthophosphate and organic P were determined from an NaOH extract using 31P nuclear magnetic resonance (NMR). • Stable isotope ratios (δ13C and δ15N) were determined. • Total P was determined using ashing method. • Statistical analysis was done using JMP 8.0 software program and results were considered significantly different at p<0.05 level. • Study site Results Orthophosphate Pyrophosphate Phosphomonoesters Phosphodiesters DNA Acacia Grass Africa Kenya Mpala Research Centre Figure 5. Vegetation and manure bivariate fit of δ15N by δ13C. Samples denoted by ●- acacia leaves, ■-grass, ∆-camel, X- cattle, Y-elephant, +-giraffe, ○-impala, Z-zebra. Ngatia et al., 2013 (in review) Camel Table 2. Total concentrations of C and N, and C;P ratio from manure. Giraffe Elephant Impala • Manure δ13C data supported the expectation that cattle and zebra grazed while camel and giraffe browsed. Mixed feeders are expected to browse during the dry season. Manure δ13C data confirmed that elephant predominately browsed, but impala primarily grazed as a selective feeder (Figure 5). • The organic P forms of manure are similar for all of the animals regardless of the source of forage or digestion process (Figure 4). • The decrease in NMR signal corresponds to a decrease of manure TP (Table 1). • The manure NMR spectra are dominated by an orthophosphate signal. Forms of organic P are phosphomonoester > pyrophosphate > DNA (Figure 4). • All forms of organic P compounds in the manure are labile in respect to P cycling. • Acacia and grass have similar functional groups to the manure; however, pyrophosphate is absent from Acacia and constitutes a small percentage of P in grass (Figure 4). • Digestion of forage by browsers may form pyrophosphate in manure or the browsers may be feeding on parts of Acacia that have pyrophosphate. • C:P ratios from manure are <200 which infers that P is mineralized from manure deposited on soil (Table 2). • Manure may have a critical role in P cycling. • High TP values, low C:P ratios, dominance of orthophosphate, and presence of labile organic P compounds provide short term P availability to plants. Zebra DISCUSSION AND CONCLUSIONS Figure 1. Study site: Mpala Research Centre (MRC), the Laikipia District of Rift Valley Province, Kenya Cattle Figure 4. 31P NMR spectra of vegetation and herbivore manure with functional groups labeled. Table 1. Total P concentration of manure and percent recovery of vegetation and manure TP from NaOH extraction. Percent of TP accounting for each functional group from 31P NMR spectra. Figure 2. Model P functional groups in 31P NMR spectrum (Cheesman et al.) STRI, NCCR, NHMFL, and NSF is hereby acknowledged for providing the necessary funding for carrying out this research. Special thanks to Dr. Jim Rocca. Corresponding author: Anna E. Normand, Soil and Water Sciences Dept., 2181 McCarty Hall A. PO Box 110290, Gainesville, FL 32611-0290. evangeline@ufl.edu