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Does Chronic N Addition Increase P Limitation in Northeastern U.S. Forest Soils?.

Wednesday, November 6, 2013: 9:05 AM
Marriott Tampa Waterside, Grand Ballroom J, Second Level

Marie-Cecile Gruselle1, Cayce Salvino1, Ivan J. Fernandez2, Kevin Simon3 and Corianne Tartariw4, (1)School of Forest Resources and Climate Change Institute, University of Maine, Orono, ME
(2)Forest Resources and Climate Change Institute, University of Maine, Orono, ME
(3)School of the Environment, The University of Auckland, Auckland, New Zealand
(4)School of Biology and Ecology, University of Maine, Orono, ME
The Bear Brook Watershed in Maine is a paired watershed study composed of an experimentally acidified watershed (West Bear, WB) treated with (NH4)2SO4 (25.2 kg N ha-1 yr-1) for 23+ years and an untreated reference watershed (East Bear, EB). Twenty permanent plots are distributed across the two watersheds and were used to determine if chronic treatments in WB increase P limitations on N dynamics. Within each permanent plot, one subplot was treated in early June 2012 with 100 kg P ha-1, and a second subplot served as reference. Organic (O) and mineral (min) soil samples were collected throughout the 2012 growing season (5 dates) to examine the potential differences in extractable NH4+-N and NO3--N between P-fertilized and non-P fertilized subplots in both the treated and reference watersheds.

Overall, extractable NO3--N concentrations from the O and mineral horizons did not differ between P-fertilized and reference subplots (P = 0.961, 0.200). Extractable O NH4+-N concentrations, however, were higher (P < 0.001) in the reference than in the P-treated subplots, but no difference was detected (P = 0.139) between treatments in the mineral horizon. Sampling time influenced the P treatment effect on inorganic N similarly in both watersheds. Mean O NH4+-N concentrations in the reference subplots ranged from 0.7 to 1.5 (EB), and from 1.5 to 3.2 (WB), times higher than in the P treated subplots. The lowest difference between subplots was found two weeks (mid-June 2012), and highest difference two months (early August 2012), after treatment.

In conclusion, P-enrichment did not increase extractable inorganic N in both horizons at both sites.  These results suggest that acute P additions either suppressed N mineralization, or stimulated alterative soil sinks for mineralized N.  Research on microbial processes and N dynamics is underway to further define responses to P in these long-term experimental watersheds.

See more from this Division: SSSA Division: Forest, Range & Wildland Soils
See more from this Session: General Forest, Range & Wildland Soils: II

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