TITLE: bilbrough.plant.readme.txt AUTHORS: PI: Jeffrey M. Welker co-PI/data questions: Carol J. Bilbrough Department of Renewable Resources University of Wyoming Laramie, WY 82071 USA phone: JMW: 307 766-2172 phone: CJB: 307 766-5472 facsimile: 307 766- web page: email JMW: jeff@uwyo.edu email CJB: carolb@uwyo.edu ABSTRACT FROM SUBMITTED MANUSCRIPT: Arctic tundra systems are characterized by growing season immobilization of nitrogen (N) and non-growing season release of N. In these N-limited systems, the capacity to acquire soil nutrients during periods of high N availability is important for plant growth and survival. We examined the ability of snow-covered arctic plants in dry heath and moist tussock tundra to take up inorganic N during snowmelt. In order to determine if plants could acquire N accumulated in the snowpack, we sprayed 99% enriched 15NH415NO3 (0.5 g N m-2) solution onto the snow. We applied the same quantity of N directly into the soil using a series of injections to determine if plants could utilize soil N resources during snowmelt. Plants were harvested immediately following snowmelt and analyzed for 15N content. We assessed 15N uptake at the plot level, for individual vascular plant species, mosses in the moist tussock tundra, and lichens in the dry heath. All plants acquired N from both N application treatments. Vascular plant species differed in their ability to capture N, however these differences were not explained by shrub growth form or tundra type. The sedge Eriophorum vaginatum acquired more N than moist tussock shrub species, while in the dry heath Arctostaphylos alpina acquired more N than other dry heath shrub species. Dry heath plants acquired more N from the snow application treatment, suggesting foliar uptake as a partial mechanism of N uptake. However, acquisition of 15N injected into the soil by vascular plant species in both tundra systms clearly demonstrates that below ground tissues play a role in N uptake in soils at temperatures near or below freezing. The most striking result was the capacity of mosses in the moist tussock tundra and lichens in the dry heath to acquire N, exceeding vascular plant uptake by an order of magnitude. These results demonstrate that plants are able to take advantage of limiting N resources during the non growing season which may be a time when N is more available. TIME PERIOD: June 1, 1998 through August 30, 1998 PHYSICAL LOCATION: Toolik Lake Field Station, dry heath tundra and moist tussock tundra snow fence sites (68o38'N, 149o38'W, elevation 760 m) DATA COLLECTION AND PROCESSING This research was conducted in two contrasting tundra types, dry heath and moist tussock tundra. Dry heath tundra is characterized by low plant cover (approximately 50%), and is dominated by numerous lichen species and the low-stature evergreen shrubs Dryas octopetala, Arctostaphylous alpina, Vaccinium vitus-idaea, and Loiseleuria procumbens, ranging in height from <5 to 10 cm. Winter snow accumulation is typically less than 30 cm, and the site becomes snow free in early to mid-May. The well-drained rocky mineral soils are overlain by an organic horizon 3 to 10 cm deep. Moist tussock tundra is a mixed shrub-sedge community dominated by the sedge Eriophorum vaginatum intermixed with mosses, lichens, and shrubs, including Betula nana, Ledum palustra, Vaccinium vitus-idaea and species of Salix. The soil substrate of Eriophorum tussocks may be 10-30 cm tall, and is composed of tightly woven dead Eriophorum roots. Intertussock soils are saturated, and are covered with an organic mat up to 20 cm thick. Win In each tundra type, we applied 98% enriched 15NH415NO3 onto the snowpack or into the soil in late winter prior to snowmelt. For each treatment and tundra type, we dug four snowpits to the soil surface, and cleared a circular area of 3 m2. Experimental microcosms were delineated using a circular plastic ring with a diameter of 30 cm. Each experimental ring was buried 5 cm into the frozen soil with a 20 cm lip remaining above ground. In one set of treatments (n=4), 200 ml of a 45 mMol solution of NH4NO3 was applied at a rate of 0.5 g N m-2 directly into the soil using 10 evenly spaced injections. For each injection, a syringe needle was inserted to a depth of 5 cm, and N solution injected as the needle was withdrawn. In the second set of treatments, 20 cm of snow was placed into the microcosm, and the same quantity of labeled N was applied by spraying the solution evenly onto the snowpack. The snow pits were then entirely filled in and left until snowmelt was nearly complete. The day that plants were first exposed through the snow, we collected soil samples to a depth of 15 cm and harvested all plants, both above- and belowground, from one quarter of each plot. Care was taken to get as much of the root system as possible. A wedge-shaped block of wood was placed into the area where sample was removed to prevent soil drying. The remaining subplots were harvested in the same manner 2, 4, and 6 weeks following the first harvest. Plants were separated into individual vascular plant species, mosses (moist tussock tundra), and lichens (dry heath), carefully rinsed, and then oven-dried at 70oC for 48 hours. Mosses and lichens were only on a per gram basis, rather than total plant weight. Vascular plant samples were then weighed and all samples were ground for analysis of %15N and N concentrations. Soil samples were weighed, dried at 105oC for 48 hours, reweighed for determination of soil moisture, and then ground for analysis of 15N and N content. Samples were analyzed for N content using a LECO CHN1000 analyzer (LECO Corporation, St. Josef, MO. USA), and for percent 15N using a VG Isochrom coupled to a Carlo Erba NA 1500 elemental analyzer (Micromass Inc., Manchester, UK). DATA FORMAT: -file structure: ASCII, tab delimited -data format and layout: The data base includes header with information on PI, location, and dates. The data consist of 12 columns and 264 rows of data and are both numeric and alphanumeric. - list of parameters 1. date, year and range of months 2. location, longitude and latitude 3. tundra type, moist tussock tundra or dry heath tundra 4. treatment, method of 15N application: sprayed onto the snow or injected into the soil. 5. harvest date, number of days after the plot was melted out of the snow. This number was specific to each plot and so the actual date is different for each plot. 6. replicate, the plot number the sample was collected from 7. species, the type of sample, either an individual vascular plant species, lichen, moss, or soil 8. sample weight, in grams. The weight of the shoot of the vascular plants. Weight for lichens, mosses, and soil samples is recorded as a 1, and calculations were on a unit weight basis. 9. N content, nitrogen concentration in the sample (mg/g) 10. N pool, total nitrogen content in a sample =N content*sample weight 11. 15N content, the percent enrichment with 15N of the N in the sample. Units are percent. 12. %15N excess, the increase in 15N enrichment of the sample due to uptake of the 15N tracer = 15N content -0.3663. 0.3663 is a standard enrichment for plant material. - data version: final version, September 28, 2000. DATA REMARKS The shoot biomass data are extremely variable and may not be reliable. REFERENCES: manuscripts in press/submitted that use this data: Bilbrough, C. J., J. M. Welker, and W. D. Bowman. Early spring nitrogen uptake by snow-covered plants: a comparison of arctic and alpine plant function under the snowpack. Arctic, Antarctic, and Alpine Research 32: in press. Bilbrough, C. J. and J. M. Welker. Arctic plant nitrogen acquisition during snowmelt: Evidence from a 15N labeling experiment. Submitted to Oikos A D