Soil Warming Plus Nitrogen Addition Experiment

• Investigators: Alexandra Contosta, Serita Frey, Melissa Knorr
• Contact: Serita Frey
• Start date: 2006-04-01
• End date: ongoing
• Location: Prospect Hill Tract (Harvard Forest)
• Latitude: +42.54
• Longitude: -72.18
• Elevation: 365
• Taxa:
• Keywords: microbial community, nitrogen additions, soil organic matter, soil respiration, soil warming
• Abstract:

  The purpose of this experiment is to examine the interactive affects of warming and N additions on microbial community dynamics and soil C cycling. The experiment consists of four treatments (control, heated +N, heated -N, +N only) with six replicates per treatment in a completely randomized design. Average soil temperature in the heated plots will be elevated 5 deg C above ambient by the use of buried heating cables placed at 10 cm depth in the soil and spaced 20 cm apart. The heating cables will be controlled by a data logger that monitors thermistors (5 per plot) every 10 min. Plots will automatically turn on and off to maintain a 5 deg C temperature difference between the heated and control plots. The N addition plots (heated +N, +N only) will be fertilized following the protocol of the Chronic Nitrogen Addition Study. An aqueous solution of NH4NO3 will be applied at a rate equivalent to the low N plots at the chronic N study (5 g m-2 yr-1). Fertilizer will be applied in equal monthly doses during the growing season (Apr-Oct). The control plots and unfertilized, heated plots (heated -N) will receive water only.

  We will measure soil CO2 flux following the protocol used at the existing Soil Warming Study. Gas samples will be withdrawn at 0, 5, 10, and 15 min from sealed chambers (4.5 liters) secured at the time of sampling to pre-seated collars. There will be one chamber per plot for a total of 24 chambers. We will sample once per month at dawn (coldest part of day) and in the early afternoon (hottest part of day) to get an estimate for the entire day. Gas samples will be stored in 5 ml vacuumed serum bottles and returned to the lab for analysis on a Licor infrared gas analyzer. We will collect soil samples (O-horizon and 10 cm of mineral soil) four times during the growing season (Apr, Jun, Aug, Oct) for determination of microbial metabolism, community composition, and soil C and N pools. This sampling scheme will provide information on seasonal variability in our measured parameters. At each sampling date we will collect four 2.5 cm diameter soil cores from each plot. The cores from each plot will be bulked for a total of 48 samples (24 O-horizon and 24 mineral soil). Where cores are removed, the hole will be backfilled with soil from outside the plot and a labeled plug will be placed over the hole so that the same spot is not sampled at a later date. The samples will be returned immediately to the lab and stored in an incubator set to the ambient soil temperature measured at the time of sampling. All samples will be analyzed within 5 days of sampling.

• Methods:
• Related datasets: HF005 HF008