Percent carbon, percent nitrogen, del13C and del15N were measured from above ground plant and belowground stem biomass samples from experimental plots in moist acidic and moist non-acidic tundra. Biomass data are in 2000lgshttbm.dat.
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Plots at the acidic site (MAT) were set up in July 1996 on extra 5 x 20 meters plots within the four block design of the 1989 LTER acidic tussock experimental plots. On each plot a 5x10 meter section was fenced with large mesh (4-inch square mesh) and within this fence a 5x5-meter plot was fenced with a small mesh (1/2-inch square mesh). In each block two fenced plots were setup: a plot with no fertilizer and a plot with annual fertilization (NP) treatments of 10 g/m2 Nitrogen (as NH4NO3) and 5 g/m2 Phosphorous (as triple superphosphate). In this biomass harvest only the control unfenced (NFCT) and NP unfenced (NFNP) treatments were sampled.
Plots at the non-acidic site (MNT) were setup in July 1997. Three replicate blocks were established with the following annual treatments in 5 x 20 m plots: control, nitrogen added (N), phosphorus added (P) and N and P (NP) in the same amounts as described for the MAT site. Two replicate blocks were established with a greenhouse treatment (GHCT) and a greenhouse fertilized treatment (GHNP). Greenhouses are annually set up in late May or early June and removed in the end of August or early September.
Calculations: All isotope values are in per mil (o/oo) and are calculated as 13C or 15N (o/oo) = [(R sample/R standard)-1] x 1000, where R is (15N/14N) or (13C/12C). Results are reported versus atmospheric nitrogen or PDB as standards.
Reference Citations: Gough, L. and S.E. Hobbie. 2003. Responses of moist non-acidic arctic tundra to altered environment: productivity, biomass, and species richness. Oikos 103:204-216.
Biomass quadrats, size 20x20 cm, were taken from each site. Four quadrats were randomly located along line transects in each of the replicate blocks of each treatment. Aboveground biomass is considered "within" the quadrat if it is associated with a meristem that is within the quadrat. Quadrats were sorted within 24 hours into species and then into tissue type. The samples were dried at 50-70 degrees C in a drying oven and after several days weighed to nearest milligram. Details are given in Shaver and Chapin (Ecological Monographs, 61(1), 1991, pg. 1.) Samples were lumped by block and shipped to the Stable Isotope Mass Spectrometry Laboratory, Division of Biology, Kansas State University, Manhattn, Kansas. Samples were then coarsely ground in a Wiley mill and finely ground in a Wig-L-Bug grinder before being analyzed for %C, %N, del13C and del15N with a ThermoFinnigan Delta Plus mass spectrometer coupled to a CE 1110 elemental analyzer.
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