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SOIL NITRATE AND AMMONIUM THROUGH 2 YEARS OF SELECTIVE HERBIVORY AND CHRONIC NITROGEN ENRICHMENT
Citation:
Jorgensen*, E E., A. West, D. M. Engle, AND S. J. Tunnell. SOIL NITRATE AND AMMONIUM THROUGH 2 YEARS OF SELECTIVE HERBIVORY AND CHRONIC NITROGEN ENRICHMENT. Presented at Ecological Society of America Annual Meeting, Madison, WI, August 2001.
Description:
-The effects of increased amounts and flux of bioavailable nitrogenous compounds in the ecosystem is of great interest to ecological researchers and longstanding concern to land-managers. Excess nitrogen in the environment is associated with many large-scale environmental concerns, including; eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, and global warming. Since 1999, we have investigated changes to soil nitrate and ammonium concentrations in sixteen 40x40-m research plots in south-central Oklahoma that selectively manipulate herbivory with fencing and availability of nitrate with fertilizer. Initially, through spring and summer, nitrate concentrations remained uniformly low; concentrations increased over 300% during the first winter and early spring of the second year on fertilized plots whereas a notably smaller increase on fertilizer control plots was observed. Following a short period during which nitrate concentrations returned to low levels, during the late spring of the second year nitrate concentrations increased again by 100-200% even on plots that manipulated herbivory whereas nitrate concentrations did not change on control plots. Ammonium levels increased seasonally by 300% during winter on fertilized plots, but no effects attributable to herbivory are apparent. We tentatively conclude that at least in some instances, our hypothesis that effects associated with herbivory mimic effects associated with fertilization is supported. These effects point to the potential importance of herbivore management when land managers contemplate interventions designed to reduce nitrogen loading to water. The views expressed are those of the author and do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency (EPA).