Mineral nitrogen from KCl extractions of soil from the Jena Experiment (Main Experiment up to 30cm depth, year 2002)

As an estimate of plant-available N, this data set contains measurements of inorganic nitrogen (NO3-N and NH4-N, the sum of which is termed mineral N or Nmin) determined by extraction with 1 M KCl solution of soil samples from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Soil sampling and analysis: Five soil cores (diameter 0.01 m) were taken at a depth of 0 to 0.15 m and 0.15 to 0.3 m of the mineral soil from each of the experimental plots in September 2002. Samples of the soil cores per plot were pooled during each sampling campaign. NO3-N and NH4-N concentrations were determined by extraction of soil samples with 1 M KCl solution and were measured in the soil extract with a Continuous Flow Analyzer (CFA, Skalar, Breda, Netherlands).

Mineral nitrogen from KCl extractions of soil from the Jena Experiment (Main Experiment up to 30cm depth, year 2004)

As an estimate of plant-available N, this data set contains measurements of inorganic nitrogen (NO3-N and NH4-N, the sum of which is termed mineral N or Nmin) determined by extraction with 1 M KCl solution of soil samples from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Soil sampling and analysis: Five soil cores (diameter 0.01 m) were taken at a depth of 0 to 0.15 m and 0.15 to 0.3 m of the mineral soil from each of the experimental plots in March and October 2004. Samples of the soil cores per plot were pooled during each sampling campaign. NO3-N and NH4-N concentrations were determined by extraction of soil samples with 1 M KCl solution and were measured in the soil extract with a Continuous Flow Analyzer (CFA, Skalar, Breda, Netherlands).

Dissolved phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2003)

This data set contains measurements of dissolved phosphorus (total dissolved nitrogen: TDP, dissolved inorganic phosphorus: PO4P and dissolved organic phosphorus: DOP) in samples of soil water collected in 2003 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 mm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled bi-weekly, in 2003 at the 07.03.2003; 24.03.2003; 07.04.2003; 22.04.2003; 07.05.2003; 20.05.2003; 03.06.2003; 28.07.2003; 12.09.2003; 22.09.2003; 07.10.2003; and 21.10.2003, and analyzed for dissolved inorganic P (PO4P) and total dissolved phosphorus (TDP). Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (CFA SAN++, Skalar [Breda, The Netherlands]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. Total dissolved P in soil solution was analyzed by irradiation with UV and oxidation with K2S2O8 followed by reaction with ammonium molybdate (Skalar catnr. 503-553w/r). As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.02 mg P l-1 (CFA, Skalar). Dissolved organic P (DOP) in soil solution was calculated as the difference between TDP and PO4P. In a low number of samples, TDP was equal to or smaller than PO4P; in these cases, DOP was assumed to be zero.

Dissolved phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of dissolved phosphorus (total dissolved nitrogen: TDP, dissolved inorganic phosphorus: PO4P and dissolved organic phosphorus: DOP) in samples of soil water collected in 2004 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled bi-weekly, in 2004 at the 15.01.2004; 30.01.2004; 12.02.2004; 27.02.2004; 09.03.2004; 25.03.2004; 21.04.2004; 07.05.2004; and 24.05.2004, and analyzed for dissolved inorganic P (PO4P) and total dissolved phosphorus (TDP). Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (for samples collected until spring 2004: CFA SAN++, Skalar [Breda, The Netherlands]; for samples collected later: CFA Autoanalyzer [Bran&Luebbe, Norderstedt, Germany]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. Total dissolved P in soil solution was analyzed by irradiation with UV and oxidation with K2S2O8 followed by reaction with ammonium molybdate (Skalar catnr. 503-553w/r). As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.02 mg P l-1 (CFA, Skalar) and 0.04 mg P l-1 (Autoanalyzer, Bran&Luebbe). Dissolved organic P (DOP) in soil solution was calculated as the difference between TDP and PO4P. In a low number of samples, TDP was equal to or smaller than PO4P; in these cases, DOP was assumed to be zero.

Dissolved nitrogen in soil solution of the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of dissolved nitrogen (total dissolved nitrogen: TDN, dissolved organic nitrogen: DON, dissolved ammonium: NH4+, and dissolved nitrate: NO3-) in samples of soil water collected from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. In April 2002 glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in depths of 10, 20, 30 and 60 cm to collect soil solution. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for nitrate (NO3-) and ammonium (NH4+) concentrations with a continuous flow analyzer (CFA, Skalar, Breda, The Netherlands). Nitrate was analyzed photometrically after reduction to NO2- and reaction with sulfanilamide and naphthylethylenediamine-dihydrochloride to an azo-dye. Our NO3- concentrations contained an unknown contribution of NO2- that is expected to be small. Simultaneously to the NO3- analysis, NH4+ was determined photometrically as 5-aminosalicylate after a modified Berthelot reaction. The detection limits of NO3- and NH4+ were 0.02 and 0.03 mg N L-1, respectively. Total dissolved N in soil solution was analyzed by oxidation with K2S2O8 followed by reduction to NO2- as described above for NO3-. Dissolved organic N (DON) concentrations in soil solution were calculated as the difference between TDN and the sum of mineral N (NO3- + NH4+). In 5% of the samples, TDN was equal to or smaller than mineral N. In these cases, DON was assumed to be zero.

Seasonally aggregated values of dissolved inorganic phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of inorganic phosphorus in samples of soil solution collected in 2004 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below) that have been aggregated to seasonal values. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for dissolved inorganic P (PO4P). Here volume-weighted mean values are provided as aggregated seasonal values (spring = March to May, summer = June to August, fall = September to November, winter = December to February) for 2004 in spring, fall, and winter. To calculate these values, the sampled volume of soil solution is used as weight for P concentrations of the respective sampling date. Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (for samples collected until spring 2004: CFA SAN++, Skalar [Breda, The Netherlands]; for samples collected later: CFA Autoanalyzer [Bran&Luebbe, Norderstedt, Germany]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.02 mg P l-1 (CFA, Skalar) and 0.04 mg P l-1 (Autoanalyzer, Bran&Luebbe).

Mineral nitrogen from KCl extractions of soil from the Jena Experiment (Main Experiment up to 15cm depth, year 2005)

As an estimate of plant-available N, this data set contains measurements of inorganic nitrogen (NO3-N and NH4-N, the sum of which is termed mineral N or Nmin) determined by extraction with 1 M KCl solution of soil samples from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Soil sampling and analysis: Five soil cores (diameter 0.01 m) were taken at a depth of 0 to 0.15 m of the mineral soil from each of the experimental plots in April and September 2005. Samples of the soil cores per plot were pooled during each sampling campaign. NO3-N and NH4-N concentrations were determined by extraction of soil samples with 1 M KCl solution and were measured in the soil extract with a Continuous Flow Analyzer (CFA, Skalar, Breda, Netherlands).

Phosphorus fractions in soil of the Jena Experiment (Main Experiment, year 2007)

This data set contains measurements of phosphorus fractions (Hedley fractions) in soil collected 2007 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Soil sampling and analysis: Five independent soil samples per plot were taken in a depth of 0-15 cm using a soil corer with an inner diameter of 1 cm. The five samples per plot were combined to one composite sample per plot. A four-step sequential P fractionation (Hedley fractions) was applied. Sequentially, 20 ml NaHCO3 (adjusted to pH 8.5), 30 ml NaOH, and 35 ml HCl were used as extraction solutions for 0.5 g soil. The last step comprised the combustion (550 °C) of the remaining soil to destroy all organic material followed by shaking with 20 ml H2SO4. Organic P concentrations of the respective fractions were calculated as the difference between total dissolved P and inorganic P. Duplicate phosphate concentrations of P fractions in soil were measured photometrically (molybdenum blue-reactive P) with a Continuous Flow Analyzer (Bran&Luebbe, Germany).

Dissolved inorganic carbon isotopes in pore waters of ODP Leg 204 sediments

Isotopic characterization of carbon in the dissolved inorganic carbon (DIC) pool is fundamental for a wide array of scientific studies directly related to gas hydrate research. In order to generate integrated and internally consistent data of d13C of DIC in pore waters from Hydrate Ridge, we used the modern continuous flow technology of a GasBench II automated sampler interfaced to a gas source stable isotope mass spectrometer for the rapid determination (~80 samples/day) of d13C DIC in small-volume water samples. The overall precision of this technique is conservatively estimated to be better than ±0.15 per mil (1 sigma), which is similar to the precision of methods in current use. Here we present the data generated from Ocean Drilling Program Leg 204 pore water samples.

Stable carbon isotopes, Methane Index, and distributions of different GDGTs

Gas hydrates represent one of the largest pools of readily exchangeable carbon on Earth's surface. Releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history. Many of these inferred events, however, were based on carbonate carbon isotopes which are susceptible to diagenetic alterations. Here we propose a molecular fossil proxy, i.e., the "Methane Index (MI)", to detect and document the destabilization and dissociation of marine gas hydrates. MI consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers (GDGTs), the core membrane lipids of archaea. The rational behind MI is that in hydrate-impacted environments, the pool of archaeal tetraether lipids is dominated by GDGT-1, -2 and -3 due to the large contribution of signals from the methanotrophic archaeal community. Our study in the Gulf of Mexico cold-seep sediments demonstrates a correlation between MI and the compound-specific carbon isotope of GDGTs, which is strong evidence supporting the MI-methane consumption relationship. Preliminary applications of MI in a number of hydrate-impacted and/or methane-rich environments show diagnostic MI values, corroborating the idea that MI may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change.

Pedology, geochronology, palynology and macrofossils of soil profiles in the Altdarss area, german Baltic Sea coast

A new site with Lateglacial palaeosols covered by 0.8 - 2.4 m thick aeolian sands is presented. The buried soils were subjected to multidisciplinary analyses (pedology, micromorphology, geochronology, dendrology, palynology, macrofossils). The buried soil cover comprises a catena from relatively dry ('Nano'-Podzol, Arenosol) via moist (Histic Gleysol, Gleysol) to wet conditions (Histosol). Dry soils are similar to the so-called Usselo soil, as described from sites in NW Europe and central Poland. The buried soil surface covers ca. 3.4 km**2. Pollen analyses date this surface into the late Aller0d. Due to a possible contamination by younger carbon, radiocarbon dates are too young. OSL dates indicate that the covering by aeolian sands most probably occurred during the Younger Dryas. Botanical analyses enables the reconstruction of a vegetation pattern typical for the late Allerod. Large wooden remains of pine and birch were recorded.

Carbon/Nitrogen ratio of plant tissues and biomass of belowground consumers after 11 years of experimental treatment, Toolik lake

Theory and observation indicate that changes in the rate of primary production can alter the balance between the bottom-up influences of plants and resources and the top-down regulation of herbivores and predators on ecosystem structure and function. The Exploitation Ecosystem Hypothesis (EEH) posited that as aboveground net primary productivity (ANPP) increases, the additional biomass should support higher trophic levels. We developed an extension of EEH to include the impacts of increases in ANPP on belowground consumers in a similar manner as aboveground, but indirectly through changes in the allocation of photosynthate to roots. We tested our predictions for plants aboveground and for phytophagous nematodes and their predators belowground in two common arctic tundra plant communities subjected to 11 years of increased soil nutrient availability and/or exclusion of mammalian herbivores. The less productive dry heath (DH) community met the predictions of EEH aboveground, with the greatest ANPP and plant biomass in the fertilized plots protected from herbivory. A palatable grass increased in fertilized plots while dwarf evergreen shrubs and lichens declined. Belowground, phytophagous nematodes also responded as predicted, achieving greater biomass in the higher ANPP plots, whereas predator biomass tended to be lower in those same plots (although not significantly). In the higher productivity moist acidic tussock (MAT) community, aboveground responses were quite different. Herbivores stimulated ANPP and biomass in both ambient and enriched soil nutrient plots; maximum ANPP occurred in fertilized plots exposed to herbivory. Fertilized plots became dominated by dwarf birch (a deciduous shrub) and cloudberry (a perennial forb); under ambient conditions these two species coexist with sedges, evergreen dwarf shrubs, and Sphagnum mosses. Phytophagous nematodes did not respond significantly to changes in ANPP, although predator biomass was greatest in control plots. The contrasting results of these two arctic tundra plant communities suggest that the predictions of EEH may hold for very low ANPP communities, but that other factors, including competition and shifts in vegetation composition toward less palatable species, may confound predicted responses to changes in productivity in higher ANPP communities such as the MAT studied here.

X-ray fluorescence scanning of discrete samples on the Schwalbenberg II loess-paleosol sequence, raw data, magnetic susceptibility, organic carbon and U-ratio as grainsize index

The Schwalbenberg II loess-paleosol sequence (LPS) denotes a key site for Marine Isotope Stage (MIS 3) in Western Europe owing to eight succeeding cambisols, which primarily constitute the Ahrgau Subformation. Therefore, this LPS qualifies as a test candidate for the potential of temporal high-resolution geochemical data obtained X-ray fluorescence (XRF) scanning of discrete samplesproviding a fast and non-destructive tool for determining the element composition. The geochemical data is first contextualized to existing proxy data such as magnetic susceptibility (MS) and organic carbon (Corg) and then aggregated to element log ratios characteristic for weathering intensity [LOG (Ca/Sr), LOG (Rb/Sr), LOG (Ba/Sr), LOG (Rb/K)] and dust provenance [LOG (Ti/Zr), LOG (Ti/Al), LOG (Si/Al)]. Generally, an interpretation of rock magnetic particles is challenged in western Europe, where not only magnetic enhancement but also depletion plays a role. Our data indicates leaching and top-soil erosion induced MS depletion at the Schwalbenberg II LPS. Besides weathering, LOG (Ca/Sr) is susceptible for secondary calcification. Thus, also LOG (Rb/Sr) and LOG (Ba/Sr) are shown to be influenced by calcification dynamics. Consequently, LOG (Rb/K) seems to be the most suitable weathering index identifying the Sinzig Soils S1 and S2 as the most pronounced paleosols for this site. Sinzig Soil S3 is enclosed by gelic gleysols and in contrast to S1 and S2 only initially weathered pointing to colder climate conditions. Also the Remagen Soils are characterized by subtle to moderate positive excursions in the weathering indices. Comparing the Schwalbenberg II LPS with the nearby Eifel Lake Sediment Archive (ELSA) and other more distant German, Austrian and Czech LPS while discussing time and climate as limiting factors for pedogenesis, we suggest that the lithologically determined paleosols are in-situ soil formations. The provenance indices document a Zr-enrichment at the transition from the Ahrgau to the Hesbaye Subformation. This is explained by a conceptual model incorporating multiple sediment recycling and sorting effects in eolian and fluvial domains.

Sea surface fugacity of carbon dioxide measurements in the Pacific ocean

As part of the JGOFS field program, extensive CO2 partial-pressure measurements were made in the atmosphere and in the surface waters of the equatorial Pacific from 1992 to 1999. For the first time, we are able to determine how processes occurring in the western portion of the equatorial Pacific impact the sea-air fluxes of CO2 in the central and eastern regions. These 8 years of data are compared with the decade of the 1980s. Over this period, surface-water pCO2 data indicate significant seasonal and interannual variations. The largest decreases in fluxes were associated with the 1991-94 and 1997-98 El Niño events. The lower sea-air CO2 fluxes during these two El Niño periods were the result of the combined effects of interconnected large-scale and locally forced physical processes: (1) development of a low-salinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific, (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific, and (3) the weakening of the winds in the eastern half of the basin. These processes serve to reduce pCO2 values in the central and eastern equatorial Pacific towards near-equilibrium values at the height of the warm phase of ENSO. In the western equatorial Pacific there is a small but significant increase in seawater pCO2 during strong El Niño events (i.e., 1982-83 and 1997-98) and little or no change during weak El Niño events (1991-94). The net effect of these interannual variations is a lower-than-normal CO2 flux to the atmosphere from the equatorial Pacific during El Niño. The annual average fluxes indicate that during strong El Niños the release to the atmosphere is 0.2-0.4 Pg C/yr compared to 0.8-1.0 Pg C/yr during non-El Niño years.

(Table 3) Soil temperatures at 10 cm depth after different treatments of wet sedge meadows on Ellesmere Island

Wet sedge tundra communities in the High Arctic are valuable sources of forage for several resident and migratory herbivores; however, the effects of grazing on these systems have been rarely studied. We simulated grazing in two wet sedge meadows at a site on Ellesmere Island that has not been affected by grazing. Over two summers, we clipped plots at four different frequencies and removed litter to assess effects on aboveground net primary production, availability of soil nitrogen, shoot concentrations of carbon and nitrogen, and soil temperature and moisture regimes. Available soil nitrate and ammonium were highest in plots with intermediate clipping frequencies. Shoot nitrogen concentrations were also greater at intermediate clipping frequencies in two of the four species studied. Aboveground net primary production decreased after clipping, regardless of frequency. Litter removal resulted in slightly increased soil moisture, but had no effect on aboveground net primary production. Soil temperature was not affected by any of our treatments. These results suggest that nitrogen cycling is stimulated by intermediate frequencies of simulated grazing, but clipping decreased aboveground net primary production in ungrazed high arctic wet sedge tundra.