University of Minnesota
University of Minnesota
College of Biological Sciences

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Methods for Experiment 145h -

Fertilization method

Half (six) of the plots in each site are fertilized 3 times/ yr (May, July, October) with aqueous NH4NO3 to receive an annual total of 100 kg N/ha y

Litter Nitrogen Content

Litter nitrogen concentration was measured on all harvested litter using near-infrared reflectance spectroscopy (Foss NIRSystems/Tecator, Silver Springs, MD). For each harvest, one of the eight sites was randomly chosen to generate separate calibrations for each harvest. Harvested litter from calibration sites was analyzed for N by combustion-GC on an ECS 4010 element analyzer (Costech Analytical, Valencia, CA).

Plot Description

Plots are 2.5 x 2.5m, located in each of 8 sites defined by dominant plant cover. Sites and plots were established in 1999. Within each site, each of twelve 2.5 m x 2.5 m plots received either a control treatment (water only) or a fertilization treatment consisting of 10g N/m2/yr of aqueous NH4NO3 (n = 6) in three applications per year starting in 1999

cze145h - Extracellular enzyme

Sampling for Extracellular enzyme data

We collected soil and litter samples from all eight study sites in May, July, and September of 2005. Randomly located soil samples were collected using a 2 cm diameter x 10 cm deep soil corer. The litter layer (O horizon) overlying each soil core was collected from within a 20 cm x 20 cm sampling frame centered over each soil core. Four litter and four soil samples were collected and composited per plot. Soil samples were mixed and passed through a 2mm sieve and litter samples were homogenized by mixing and shredding litter by hand prior to subsampling and analysis. Samples for enzyme assays were frozen at -10 ?C for 2-12 months until time of analysis.

Results from these data are published in:
Keeler, Bonnie L; Hobbie, Sarah E.; Kellogg, Laurie E.; Effects of Long-Term Nitrogen Addition on Microbial Enzyme Activity in Eight Forested and Grassland Sites: Implications for Litter and Soil Organic Matter Decomposition. Ecosystems. 12:1-15 2009

ldnde145h - Litter Decomposition and Nitrogen Dynamics


Decomposition was assessed using 400 cm2 litter bags containing one of 8 substrates. Bags were constructed of .3 mm mesh nylon tent netting tops