Increased nutrient inputs is one of many global change factors predicted to affect the composition and ecosystem function of plant communities. In general, nitrogen deposition decreases diversity and increases productivity. The effects of phosphorus addition have received less attention, however, and the interactive effect of both nutrients is likely to exacerbate diversity loss over time. Here we addressed whether chronic nutrient additions changed community structure and ecosystem productivity of a native tallgrass prairie. This study took place in an ungrazed watershed that is burned every two years. Two N treatments, 0 and 10 g m-2, and four P treatments, 0, 2.5, 5 and 10 g m-2 were crossed in a fully factorial experimental design. The experiment was initiated in 2002 and starting in 2003 nutrients were added at the beginning of each growing season. Plant species composition was surveyed both in the spring and late summer each year, and aboveground biomass was harvested at the end of each summer to estimate aboveground net primary productivity (ANPP).
In 2002, a 30 × 40 m area was divided into 5 × 5 m plots arrayed in a contiguous 6 × 8 plot grid. Starting in 2003, 2 nitrogen (0 and 10 g m-2) and 4 phosphorus (0, 2.5, 5, and 10 g m-2) treatments were applied to the plots in a fully factorial design (8 treatment combinations). There were 6 replicates of each treatment combination resulting a total of 48 plots. Nutrients were added by hand in an even distribution in early June. Nitrogen was added as ammonium nitrate, and phosphorus as superphosphate.
The site is ungrazed by bison and is burned in odd years (2003, 2005, 2007, ect.)
Treatment codes are as follows:
N1P0 - N0-P0,
N1P1 - N0-P2.5,
N1P2 - N0-P5,
N1P3 - N0-P10,
N2P0 - N10-P0,
N2P1 - N10-P2.5,
N2P2 - N10-P5,
N2P3 - N10-P10
Plant community composition:
Within each plot, permanent species composition plots were designated. Species composition plots were 0.5 × 2 m long and were divided into 4, 0.5 × 0.5 m subplots. In each subplot, percent aerial cover was estimated to the nearest 1% for each species that was rooted in the plot in early June and late August. Maximum cover estimates for each species were averaged across the four quadrats for each plot, which is the data here.
Each September, above-ground biomass was clipped to ground level within 2 20 × 50 cm quadrats randomly located in each plot and sorted into graminoids (grasses and sedges), non-graminoid forbs, woody plants, and previous year’s dead (in years when there was no burn). Care was taken to not resample areas that were previously clipped and the permanent species composition plots were never clipped. After clipping, biomass was dried at 60 °C for ca. 48 hours and then weighed. Previous year’s dead biomass (unburned years) was not included in estimates of annual productivity.
Note: Pretreament data in 2002. Starting in 2003, 0 or 10 g m-2 N added and 0, 2.5, 5, or 10 g of P g m-2 added in a fully factorial design. Experiment is located in watershed 2C, species community composition data and productivity data are collected annually. Additionally, mycorrhizal root colonization data and soil nutrient data has been collected sporadically. If anyone is interested in the mycorrhizal or nutrient data they should contact M. Avolio.
For additional metadata information see: http://lter.konza.ksu.edu/sites/default/files/DC.pdf
For additional methods information see: http://lter.konza.ksu.edu/sites/default/files/MM.pdf