Browsing by Author "McNaughton, S. J."

Now showing 1 - 7 of 7
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    Ecosystem Catalysis: Soil Urease Activity and Grazing in the Serengeti Ecosystem
    (Wiley, 1997) McNaughton, S. J.; Zuniga, Gina; McNaughton, M. M.; Banyikwa, Feetham F.
    The activity of soil ureases was evaluated in the laboratory in soils from three locations in the Serengeti National Park, Tanzania, differing in the grazing intensities that the grasslands there support. Urease activity was assayed by the instantaneous release of NH4 as soon as soils drained to field capacity after application of an aqueous urea solution approximating N concentrations in ungulate urine. The appearance of NO3 and S04 in extracts was used as an index of biological activity and pH changes; neither responded to urea addition. Ammonium appearance in extracts of soils to which water but not urea was applied was low and identical; appearance in extracts where urea had been added was high and differed between sites, increasing with the level of grazer activity at a site. The data document ecologically meaningful levels of soil urease in Serengeti soils and a positive associa- tion of those levels with grazing intensity.
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    Ecosystem Catalysis: Soil Urease Activity and Grazing in the Serengeti Ecosystem
    (1997) McNaughton, S. J.; Zuniga, Gina; McNaughton, M. M.; Banyikwa, Feetham F.
    The activity of soil ureases was evaluated in the laboratory in soils from three locations in the Serengeti National Park, Tanzania, differing in the grazing intensities that the grasslands there support. Urease activity was assayed by the instantaneous release of NH4 as soon as soils drained to field capacity after application of an aqueous urea solution approximating N concentrations in ungulate urine. The appearance of NO3 and SO4 in extracts was used as an index of biological activity and pH changes; neither responded to urea addition. Ammonium appearance in extracts of soils to which water but not urea was applied was low and identical; appearance in extracts where urea had been added was high and differed between sites, increasing with the level of grazer activity at a site. The data document ecologically meaningful levels of soil urease in Serengeti soils and a positive association of those levels with grazing intensity.
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    Plant Communities and Herbivory
    (1995) McNaughton, S. J.; Banyikwa, Feetham F.
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    Promotion of the Cycling of Diet-Enhancing Nutrients by African Grazers
    (1997) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.
    Experiments in Serengeti National Park, Tanzania, provide direct evidence that large, free-ranging mammalian grazers accelerate nutrient cycling in a natural ecosystem in a way that enhances their own carrying capacity. Both nitrogen and sodium were at considerably higher plant-available levels in soils of highly grazed sites than in soils of nearby areas where animal density is sparse. Fencing that uncoupled grazers and soils indicated that the animals promote nitrogen availability on soils of inherently similar fertility and select sites of higher sodium availability as well as enhancing that availability.
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    Promotion of the Cycling of Diet-Enhancing Nutrients by African Grazers
    (1997) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.
    Experiments in Serengeti National Park, Tanzania, provide direct evidence that large, free-ranging mammalian grazers accelerate nutrient cycling in a natural ecosystem in a way that enhances their own carrying capacity. Both nitrogen and sodium were at considerably higher plant-available levels in soils of highly grazed sites than in soils of nearby areas where animal density is sparse. Fencing that uncoupled grazers and soils indicated that the animals promote nitrogen availability on soils of inherently similar fertility and select sites of higher sodium availability as well as enhancing that availability.
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    Root Biomass and Productivity in a Grazing Ecosystem: The Serengeti
    (1998-03) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.
    Does grazing by large wild mammals, an intense form of aboveground herbivory, influence belowground productivity? The vast majority of literature data concentrate on short-term pot studies and indicate that clipping consistently retards root growth. Field studies are few and contradictory, but tend to indicate that grazing has little effect on grassland belowground production. We sampled root-soil cores at 0–10 and 10–20 cm increments, at 11 locations across the Serengeti ecosystem, on 10 dates over an annual cycle, sampling monthly during the rainy and early dry seasons and every 2 mo during peak dry season. Fenced and unfenced plots were replicated (n = 2 or 3) at each location. Live roots, identified visually by brightness and texture, were sorted, washed, dried, and weighed. In addition, profiles were sampled at 10-cm increments to 50 cm in fenced and unfenced plots in short, mid-height, and tall grasslands, representing a gradient of grazing, during the month of peak root biomass. Exclosures erected 22–25 yr previously were similarly sampled in short and tall grasslands to a 30-cm depth. Root biomass reached a pronounced minimum in mid-wet season (February) and a decided maximum at the beginning of the dry season (June). Net productivity, based on maximum–minimum biomass, ranged from 100 to 600 g·m−2·yr−1 to a 20-cm depth, with minima ranging from 40 to 150 g/m2 and maxima from 230 to 700 g/m2, according to location. There was no evidence that grazing reduced root productivity over the annual cycle. Vertical biomass profiles at peak standing crop were similar for short, mid-height, and tall grasslands, with root biomass dropping sharply with depth, except for short grasslands on soils that, atypically, lack a hardpan. In those grasslands, shallow root biomass was lower than in other grasslands, but biomass at depth was distinctly greater. For long-term protected grasslands, root biomasses at peak were identical in short grasslands, whether fenced or unfenced, but fenced tall grasslands had a lower root biomass than grazed plots. We conclude that intense herbivory does not inhibit root biomass or belowground productivity of Serengeti grasslands over either the short or the long term.
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    Root Biomass and Productivity in a Grazing Ecosystem: The Serengeti
    (Wiley, 1998) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.
    Does grazing by large wild mammals, an intense form of aboveground herbivory, influence belowground productivity? The vast majority of literature data concentrate on short-term pot studies and indicate that clipping consistently retards root growth. Field studies are few and contradictory, but tend to indicate that grazing has little effect on grassland belowground production. We sampled root-soil cores at 0–10 and 10–20 cm increments, at 11 locations across the Serengeti ecosystem, on 10 dates over an annual cycle, sampling monthly during the rainy and early dry seasons and every 2 mo during peak dry season. Fenced and unfenced plots were replicated (n = 2 or 3) at each location. Live roots, identified visually by brightness and texture, were sorted, washed, dried, and weighed. In addition, profiles were sampled at 10-cm increments to 50 cm in fenced and unfenced plots in short, mid-height, and tall grasslands, representing a gradient of grazing, during the month of peak root biomass. Exclosures erected 22–25 yr previously were similarly sampled in short and tall grasslands to a 30-cm depth. Root biomass reached a pronounced minimum in mid-wet season (February) and a decided maximum at the beginning of the dry season (June). Net productivity, based on maximum–minimum biomass, ranged from 100 to 600 g·m−2·yr−1 to a 20-cm depth, with minima ranging from 40 to 150 g/m2 and maxima from 230 to 700 g/m2, according to location. There was no evidence that grazing reduced root productivity over the annual cycle. Vertical biomass profiles at peak standing crop were similar for short, mid-height, and tall grasslands, with root biomass dropping sharply with depth, except for short grasslands on soils that, atypically, lack a hardpan. In those grasslands, shallow root biomass was lower than in other grasslands, but biomass at depth was distinctly greater. For long-term protected grasslands, root biomasses at peak were identical in short grasslands, whether fenced or unfenced, but fenced tall grasslands had a lower root biomass than grazed plots. We conclude that intense herbivory does not inhibit root biomass or belowground productivity of Serengeti grasslands over either the short or the long term.