Nitrogen (N) Dynamics in the Mineral Soil of a Central Appalachian Hardwood Forest During a Quarter Century of Whole-Watershed N Additions

Frank S. Gilliam, Christopher A. Walter, Mary Beth Adams, William T. Peterjohn

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25 Scopus citations

Abstract

The structure and function of terrestrial ecosystems are maintained by processes that vary with temporal and spatial scale. This study examined temporal and spatial patterns of net nitrogen (N) mineralization and nitrification in mineral soil of three watersheds at the Fernow Experimental Forest, WV: 2 untreated watersheds and 1 watershed receiving aerial applications of N over a 25-year period. Soil was sampled to 5 cm from each of seven plots per watershed and placed in two polyethylene bags—one bag brought to the laboratory for extraction/analysis, and the other bag incubated in situ at a 5 cm depth monthly during growing seasons of 1993–1995, 2002, 2005, 2007–2014. Spatial patterns of net N mineralization and nitrification changed in all watersheds, but were especially evident in the treated watershed, with spatial variability changing non-monotonically, increasing then decreasing markedly. These results support a prediction of the N homogeneity hypothesis that increasing N loads will increase spatial homogeneity in N processing. Temporal patterns for net N mineralization and nitrification were similar for all watersheds, with rates increasing about 25–30% from 1993 to 1995, decreasing by more than 50% by 2005, and then increasing significantly to 2014. The best predictor of these synchronous temporal patterns across all watersheds was number of degree days below 19°C, a value similar to published temperature maxima for net rates of N mineralization and nitrification for these soils. The lack of persistent, detectable differences in net nitrification between watersheds is surprising because fertilization has maintained higher stream-water nitrate concentrations than in the reference watersheds. Lack of differences in net nitrification among watersheds suggests that N-enhanced stream-water nitrate following N fertilization may be the result of a reduced biotic demand for nitrate following fertilization with ammonium sulfate.

Original languageEnglish (US)
Pages (from-to)1489-1504
Number of pages16
JournalEcosystems
Volume21
Issue number8
DOIs
StatePublished - Dec 1 2018

Bibliographical note

Funding Information:
Research was funded through United States Department of Agriculture (USDA) Forest Service, Fernow Experimental Forest, Timber and Watershed Laboratory, Parsons, W.V., under USDA Forest Service Cooperative Grants 23-165, 23-590, and 23-842. Additional funding for this research was provided by USDA National Research Initiative Competitive Grants (Grant NRICGP #2006-35101-17097) and by the Long Term Research in Environmental Biology (LTREB) program at the National Science Foundation (Grant Nos. DEB-0417678 and DEB-1019522). We are indebted to the following individuals for their excellent assistance in the field: Zach Fowler, Mark Burnham, Nicole Turrill Welch, Brad Yurish, Mark Fisher, and Anne Hockenberry Phillips. Serita Frey provided invaluable conceptual input. The long-term support of the USDA Forest Service in establishing and maintaining the research watersheds is acknowledged. FSG conceived of and designed study, performed research, analyzed data, and wrote the paper; CAW performed research, analyzed data, and wrote the paper; MBA conceived of and designed study, and wrote the paper; WTP performed research and wrote the paper.

Funding Information:
Research was funded through United States Department of Agriculture (USDA) Forest Service, Fernow Experimental Forest, Timber and Watershed Laboratory, Parsons, W.V., under USDA Forest Service Cooperative Grants 23-165, 23-590, and 23-842. Additional funding for this research was provided by USDA National Research Initiative Competitive Grants (Grant NRICGP #2006-35101-17097) and by the Long Term Research in Environmental Biology (LTREB) program at the National Science Foundation (Grant Nos. DEB-0417678 and DEB-1019522). We are indebted to the following individuals for their excellent assistance in the field: Zach Fowler, Mark Burnham, Nicole Turrill Welch, Brad Yurish, Mark Fisher, and Anne Hockenberry Phillips. Serita Frey provided invaluable conceptual input. The long-term support of the USDA Forest Service in establishing and maintaining the research watersheds is acknowledged.

Publisher Copyright:
© 2018, Springer Science+Business Media, LLC, part of Springer Nature.

Keywords

  • N fertilization
  • forest ecosystems
  • forest soils
  • long-term spatial and temporal trends
  • net N mineralization
  • net nitrification
  • nitrogen homogeneity hypothesis
  • nitrogen saturation

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