Chronic Nitrogen Ammendment Experiment
HF008 Overview Data EML Archive- Investigators: John Aber, Serita Frey, Alison Magill, Scott Ollinger
- Contact: Serita Frey
- Start date: 1988-01-01
- End date: ongoing
- Location: Prospect Hill Tract (Harvard Forest)
- Latitude: +42.54
- Longitude: -72.18
- Elevation: 385 meters
- Taxa: Acer rubrum (red maple), Betula lenta (black birch), Fagus grandifolia (american beech), Pinus resinosa (red pine), Quercus rubra (red oak), Quercus velutina (black oak)
- Keywords: ammonium nitrate, foliar chemistry, litterfall biomass, microbial biomass, microbial community composition, mycorrhiza, nitrogen, soil CN, soil solution chemistry, tree biomass
- Abstract:
The purpose of this study is to increase our understanding of ecosystem nitrogen dynamics in response to elevated nitrogen inputs. With atmospheric nitrogen deposition in the Northeastern United States currently at 10 to 20 times above historic background levels, it is possible that excessive nitrogen inputs could saturate the retention capacity of a forest ecosystem. Potential effects of nitrogen saturation include increased nitrate leaching and simultaneous base cation losses, soil acidification, altered fluxes of trace gases and forest decline. Two adjacent stands were chosen for the study: an even-aged red pine (Pinus resinosa Ait.) stand planted in 1926 and a 50-year-old mixed hardwood stand that had regenerated naturally after clearcutting in approximately 1945. The hardwood stand is dominated by black and red oak (Quercus velutina Lam.; Q. rubra L.) with significant amounts of black birch (Betula lenta L.), red maple (Acer rubrum L.) and american beech (Fagus grandifolia Ehrh.). The dominant soil types are stony- to sandy-loams formed from glacial till, and are classified as Typic Dystrochrepts of the Canton or Montauk series. Four treated plots were established within each stand: control, low N, low N plus sulfur (N+S) and high N. Each plot measures 30 x 30 meters (0.09 ha) and is divided into thirty-six 5 x 5 m subplots.
- Methods:
Fertilization: Fertilizer additions of NH4NO3 and Na2SO4 began in 1988 as six equal applications over the growing season (May - Sept). Fertilizer is weighed, mixed with 20 liters of water (equivalent to 0.002 cm rainfall) and applied using a backpack sprayer. Na2SO4 applications were discontinued after the 1998 growing season.
Soil Mineralization: In situ buried bags were used to measure net mineralization, net nitrification and extractable NH4 and NO3 concentrations. Samples were extracted in 1 N KCl, filtered and analysed on a Bran+Luebbe Traacs Autoanalyser using the Berthelot Reaction (NH4-N) or hydrazine reduction (NO3-N) chemistry.
Soil CN: Soils were split into organic and mineral horizons, dried, ground and measured for total carbon and nitrogen content using either a Perkin Elmer or Carlo Erba CHN analyzer.
Litterfall: Total litter mass was measured by collecting annual litterfall in baskets, sorting into species, drying and weighing. Samples were then ground and scanned for percent nitrogen, lignin and cellulose using an NIRSystems near infrared spectrometer.
Green Foliage: Samples collected, dried, ground and scanned for percent nitrogen, lignin and cellulose using an NIRSystems near infrared spectrometer. Samples were digested and digestate measured for base cations using either ICP (1999, 2002) or DCP (1997 and earlier).
B horizon lysimeters: Tension of 50psi was drawn for 24 hours. Soil water samples were collected, filtered and frozen prior to analysis. NH4 and NO3 were measured using the Traacs Autoanalyser (see soil mineralization for methods) and for DOC using a Shimadzu TOC-5000 Total Organic Carbon Analyser with a NDIR detector. TDN was measured using the TOC-5000 with an Antek chemiluminecent detector. Base cations were measured using either ICP (1998 and later) or DCP (1997 and earlier).
O horizon lysimeters (ztl's): ZTL's are gravity fed gravel and glass bead filled collection units (0.3 to 1.5cm) located beneath the organic horizon with a tube draining approximately 154 cm2 into a 1 liter bottle. Samples were collected within 1 week following a rain event, weighed, filtered through a 0.7um filter and frozen prior to analysis. N and C were measured in the same manner as B horizon lysimeters. Base cations were measured using either ICP (1998 and later) or DCP (1997 and earlier).
Fine Roots: Fine root cores were taken, roots hand picked, washed, dried, weighed and ground for CHN analysis. Separation by size class and core size/depth were not consistent across years.
Tree DBH: All trees above 5cm DBH were numbered and measured in 1988. In 1996, trees previously too small in 1988 were tagged and measured. DBH measurements were converted to aboveground biomass using published allometric equations.
Microbial community characterization: Samples (O-horizon and mineral soil) were collected to a depth of 10 cm in four subplots within each treatment plot. Bacterial and fungal biomass was determined by direct microscopy and substrate-induced respiration with selective inhibitors. Microbial community composition was determined by phospholipid fatty acid (PLFA) analysis.
Some measurements are made annually. Most data sets are collected on a 3-year cycle (considered an "intensive sampling year") beginning in 1996.
- Related datasets: