PHYSIOLOGICAL RESPONSES OF PLANT POPULATIONS

We explored how responses of two populations variable in grazing tolerance provide feedbacks to nutrient supply by controlling carbon supply to soil heterotrophs. The study fo- cused on differences in production and carbon and nitrogen allocation patterns between the two populations. The grazing-tolerant population, or on-colony population, is found on intensively grazed prairie dog colonies, and a grazing-intolerant population, the off-colony population, is found in uncolonized grasslands. Equations describing the production and allocation responses to defoliation for the two ecotypes described were incorporated into CENTURY, a nutrient- cycling simulation model. Simulations showed an increase in plant production that paralleled increases in net nitrogen mineralization. Production was greater with grazing and was maintained at higher grazing intensities for the on-colony than the off-colony population. Differences be- tween the populations provided important controls over nitrogen losses. Feedbacks between plant responses to grazing and nitrogen cycling accounted for increased nitrogen availability with grazing. These feedbacks were more important determinants of ecosystem function than were fertilization effects of urine and feces deposition. The simulation results suggest that ecosystem function may be sensitive to physiological differences in population responses to periodic disturbances like herbivory.

[1]  F. Stuart Chapin,et al.  Effect of defoliation upon root growth, phosphate absorption and respiration in nutrient-limited tundra graminoids , 2004, Oecologia.

[2]  D. Coleman,et al.  Source-sink carbon relations in two Panicum-coloratum ecotypes in response to herbivory , 1991 .

[3]  E. Holland,et al.  Plant Response to Herbivory and Belowground Nitrogen Cycling , 1990 .

[4]  S. McNaughton,et al.  Large Mammals and Process Dynamics in African EcosystemsHerbivorous mammals affect primary productivity and regulate recycling balances , 1988 .

[5]  V. J. Jaramillo,et al.  Grazing history, defoliation, and competition: effects on shortgrass production and nitrogen accumulation , 1988 .

[6]  W. Parton,et al.  Dynamics of C, N, P and S in grassland soils: a model , 1988 .

[7]  T. Seastedt,et al.  Maximization of Densities of Soil Animals by Foliage Herbivory: Empirical Evidence, Graphical and Conceptual Models , 1988 .

[8]  J. Detling,et al.  Grasslands and savannas: regulation of energy flow and nutrient cycling by herbivores , 1988 .

[9]  W. Parton,et al.  Analysis of factors controlling soil organic matter levels in Great Plains grasslands , 1987 .

[10]  T. Whitham,et al.  Overcompensation in Response to Mammalian Herbivory: The Advantage of Being Eaten , 1987, The American Naturalist.

[11]  K. Krueger.  Feeding Relationships Among Bison, Pronghorn, and Prairie Dogs: An Experimental Analysis , 1986 .

[12]  A. J. Belsky.  Does Herbivory Benefit Plants? A Review of the Evidence , 1986, The American Naturalist.

[13]  W. Parton,et al.  The role of cattle in the volatile loss of nitrogen from a shortgrass steppe , 1986 .

[14]  K. A. Horton,et al.  Soil organic matter dynamics in paired rangeland and cropland toposequences in North Dakota , 1985 .

[15]  M. Caldwell,et al.  Soluble Carbohydrates, Concurrent Photosynthesis and Efficiency in Regrowth Following Defoliation: a Field Study with Agropyron Species , 1985 .

[16]  F. Chapin,et al.  Effects of Phosphorus Nutrition and Defoliation on C4 Graminoids from the Serengeti Plains , 1985 .

[17]  Timothy R. Seastedt,et al.  Maximization of Primary and Secondary Productivity by Grazers , 1985, The American Naturalist.

[18]  Adrian P. Wydeven,et al.  Ungulate Habitat Relationships in Wind Cave National Park , 1985 .

[19]  M. Coughenour.  A mechanistic simulation analysis of water use, leaf angles, and grazing in East African graminoids , 1984 .

[20]  R. Ruess.  Nutrient movement and grazing: experimental effects of clipping and nitrogen source on nutrient uptake in Kyllinga nervosa , 1984 .

[21]  S. McNaughton,et al.  Compensatory Photosynthetic Responses of Three African Graminoids to Different Fertilization, Watering, and Clipping Regimes , 1984, Botanical Gazette.

[22]  S. McNaughton,et al.  Modelling primary production of perennial graminoids 3$̄uniting physiological processes and morphometric traits , 1984 .

[23]  S. McNaughton,et al.  Plant Adaptation in an Ecosystem Context: Effects of Defoliation, Nitrogen, and Water on Growth of an African C4 Sedge , 1983 .

[24]  W. Parton,et al.  Ecosystem Analysis of the Tallgrass Prairie: Nitrogen Cycle , 1982 .

[25]  J. Lacey,et al.  Comparison of herbage production on moderately grazed and ungrazed western ranges. , 1981 .

[26]  S. McNaughton,et al.  Grazing as an Optimization Process: Grass-Ungulate Relationships in the Serengeti , 1979, The American Naturalist.

[27]  D. Anderson.  PROCESSES OF HUMUS FORMATION AND TRANSFORMATION IN SOILS OF THE CANADIAN GREAT PLAINS , 1979 .

[28]  R. G. Woodmansee.  Additions and Losses of Nitrogen in Grassland Ecosystems , 1978 .

[29]  E. Paul,et al.  EFFECTS OF CULTIVATION ON THE ORGANIC MATTER OF GRASSLAND SOILS AS DETERMINED BY FRACTIONATION AND RADIOCARBON DATING , 1974 .

[30]  C. Mcmillan.  Ecotypes and Community Function , 1960, The American Naturalist.