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9 results for “east of tvan”
N fertilization and recovery experiment (2-4-6) plant species composition data for East of Tvan from 1997 to 2017, yearly
The realization that anthropogenic nitrogen (N) deposition is causing significant environmental change in many ecosystems has led to lower emissions of reactive N and deposition rates in many regions. However, the impacts of N deposition on terrestrial ecosystems can be long-lasting, with significant inertia in the return of the biota and biogeochemical processes to baseline levels. To better understand patterns of recovery and the factors that may contribute to slow or no responses following declines in N deposition, we followed plant species composition, microbial abundance, N cycling rates, soil pH, and pools of NO3- and extractable cations in an impacted alpine ecosystem following cessation of 12-year experiment increasing N deposition rates by 0, 20, 40, and 60 kg N/ha/yr. Simulated N deposition had resulted in a tripling in the cover of the nitrophilic species Carex rupestris, while the dominant sedge Kobresia myosuroides had decreased by more than half at the highest N input level. In addition nitrification rates were elevated, soil extractable magnesium (Mg2+) and pH decreased, and aluminum (Al3+) and manganese (Mn2+) were elevated at the highest N treatment inputs. Over the nine years following cessation of N additions to the impacted plots only the cover of the nitrophilic C. rupestris showed any recovery to prior levels. Abundances of both bacteria and fungi were lower with N addition in both treatment and recovery plots. Rates of nitrification and pools of NO3- remained elevated in the recovery plots, likely contributing to the lack of biotic response to the cessation of N inputs. In addition, nutrient base cations (Ca2+ and Mg2+) and soil pH remained depressed, and the toxic metal cations (Al3+ and Mn2+) remained elevated in recovery plots, also potentially influencing biotic recovery. These results emphasize the importance of considering long-term environmental impacts of N deposition associated with legacy effects, such as elevated N cycling and losse
Krummholz island soil C and N data for East of Tvan, 1994.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). This data forms part of a study which seeks to further examine how changes in carbon storage capacity are associated with changes in soil physical properties. Soils were collected in 1994. We sought to determine whether there were changes in natural abundance of C and N isotopes associated with previously reported changes in C and N content. Any such changes in natural abundance of C and N isotopes may indicate differences in inputs to the ecosystem or differences in ecosystem processes that may account for the differences in N and C content that have been observed. In addition to measuring ratios of natural isotopes of C and N, we also measured C and N contents to provide a comparison with previous studies. To convert % N and C values to kgs of N and C per m2, we used bulk density values, averaged across sampling dates that had been previously measured for these sites. Metadata for these data are available at: https://portal.lternet.edu/nis/mapbrowse?scope=knb-lter-nwt&identifier=131 When N and C soil contents were considered on a percentage basis, levels at windward sites were significantly lower than those of undisturbed tundra, but levels directly beneath krummholz were not significantly different from tundra soils. Bulk density was significantly lower under krummholz than other sites. Thus when N and C amounts were expressed on a volume (Kg/m2, to a depth of 15cm), they were significantly lower in both krummholz and windward sites than in undisturbed tundra. D13C values of soils under krummholz were significantly less negative under krummholz than from windward or undisturbed tundra sites. A less negative d13C value is indicative of less discrimination and may be attributable to either vegetation differences
Krummholz island soil inorganic and organic property data for East of Tvan, 1995 - 1996.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). This study shows that levels of KCl extractable ammonium and percent organic matter were also significantly higher in the A horizon of undisturbed tundra sites compared with soils underneath or immediately adjacent to (windward or leeward) the krummholz. The response of soil KCl extractable NO3- also showed this trend but was not statistically significant. Holtmeier and Broll (1992) suggested that the depletion of organics and nutrients following the passage of tree island may be associated with a reduced clay content. We analyzed a subsample of these soils for cation exchange capacity (CEC) and texture. We did not find significantly lower clay content in soils under or adjacent to krummholz compared with those from undisturbed tundra. In fact, percent clay was greater in krummholz and windward sites than in tundra sites. The percent clay of windward sites was significantly greater in windward soils than either krummholz or tundra soils. Clearly, depletion of organics following the passage of tree islands does not appear to be associated with a depleted clay content. We found that CEC was very highly significantly correlated with percent organic content (using percent organic data only from the subset of soils on which CEC was measured). Therefore, the CEC content of these soils would appear to be strongly associated with the organic content but not with the clay content. Percent soil moisture was significantly higher directly underneath the krummholz compared with the other sites. There was no effect of treatment on pH. We also investigated whether the organic matter lost in association with krummholz colonization (i.e. 1m from the tree) was replenished as tundra vegetation recolonized in the wake of the tree is
Krummholz island soil N and root ingrowth data for East of Tvan, 1996 - 1997.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). The presence of tree islands (krummholz) on the tundra acts as a 'snowfence' causing snow to drift within the krummholz and in a semi-circular area leeward of the krummholz. This drifting causes soil within and leeward of the krummholz to have a much deeper, more consistent and longer lasting snow-cover than the adjacent tundra soils. The snowdrifts form a permanent cover over the leeward and krummholz sites from November through June, helping to insulate the soils beneath from the extreme low temperatures and supplying significantly more meltwater in the spring. In contrast, high winds cause the adjacent tundra to be free from snow and exposed to extremely cold temperatures for much of the winter. Studies have shown that atmospheric nitrogen deposition accumulates on snowpacks throughout the winter months and that this is released as a 'pulse' of nitrogen ions at snowmelt (Williams et al. 1996). We hypothesized that accumulation of snowpacks in krummholz and leeward sites may alter nitrogen dynamics in these areas relative to tundra, by either (a) affecting microbial activity via its insulating effect or (b) accumulating large amounts of atmospherically deposited N and releasing it as a pulse at snowmelt. This study sought to examine the nitrogen inputs into tundra, krummholz, and leeward soils over an entire winter season (using buried ion exchange resin bags which collect ions percolating down at snowmelt and early spring rains) and over a short period in spring, immediately following snowmelt (using microlysimeters to collect soil water over a 24 hour period). Belowground NPP (determined from root ingrowth cores) and d13C values of tundra and krummholz vegetation are also presented in this file. NH4+ and NO3-
Krummholz island plant species density data for East of Tvan, 2000.
Species richness (density) on one meter sq. plots were measured on windward and leeward sides of krummholz trees previously studied by Seastedt and colleagues. Species richness of adjacent dry meadow tundra areas was also sampled. The results indicate that species richness is initially increased by the passage of tree islands. Richness was higher in leeward areas than on either windward or open tundra sites. The hypothesis that successional species must tolerate low nitrogen conditions found in the windward sites of tree islands was not supported by findings obtained here.
Pocket gopher mound litter decomposition data for Saddle and East of Tvan, 1993 - 1995.
This research was designed to examine the interaction of effects of gopher disturbance and aspect on litter decomposition on alpine tundra. Kobresia myosuroides foliage collected from Niwot Ridge was dried and placed into 10x20 cm litter bags. About 2 g of plant material were placed in the litter bags. One-hundred and sixty (160) litter bags were constructed of polyester mesh with a mesh size of 2mm^2. Forty (40) litter bags were placed inside of gopher mounds, at the interface between the mounded (gopher excavated) soil and the original soil surface (top of the O horizon), located on a slope with a southern aspect. An additional 40 litter bags were placed on the soil surface near these gopher mounds. The remaining 80 bags were similarly paired on gopher mounds and undisturbed soils on a slope with a northern aspect. All litter bags were placed in the field on 1 July 1993, and an initial harvest was done on the same date in order to assess the effect of handling and transport to the field. The second harvest was undertaken on 11 September 1993, at which time 31 bags were harvested. Retrieved litter bags were dried at 80 degrees Celsius for approximately 24 hr. The litter was removed from the litter bags and weighed. Litter weight loss was calculated to estimate decomposition rates. The remaining harvests are were in autumn 1993, spring 1994, and autumn 1994.
Krummholz island soil bulk density data for East of Tvan, 1994 and 1996.
Previous work has shown that bulk density is lower in the A horizon of soils directly under tree islands (Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa)) than in adjacent tundra soil. We compiled a dataset of bulk densities from soils that had been previously collected at several dates in 1994 and 1996. The results from this large dataset confirmed those of Pauker and Seastedt (1996): soils within tree islands had lower bulk densities than those of other sites.
Responses of dry meadow Kobresia myosuroides and Carex rupestris to Nitrogen fertilization for East of Tvan, 2013 - 2015
A common response of plant communities to increased nitrogen (N) deposition is a shift in species’ abundances. Multiple factors have been proposed to explain the changes in abundance, notably competition and soil acidification. We hypothesized that a plant species that decreased in abundance with elevated N would have lower ectomycorrhizal fungi, altered root-associated bacteria communities, and/or greater susceptibility to Al toxicity than a species that increased in abundance with increasing N deposition. We examined changes in plant–microbe associations and Al toxicity in two dominant species from an alpine dry meadow community subjected to long-term low-level N addition. Carex rupestris has increased in cover over time with N addition and Kobresia myosuroides has decreased. We conducted field sampling of soil microbes from treatment plots and tested whether field levels of Al have toxic effects on sedge species in a greenhouse study. Declines in ectomycorrhizal infection of Cenococcum geophilum occurred on Kobresia with increasing N treatment. In contrast, neither Al level nor changes in bacteria community composition corresponded with the change in cover of sedge species. Decreased ectomycorrhizal infection may have contributed to the decrease in abundance of Kobresia. This study contributes to an understanding of the types of plant–soil interactions that may influence how plant species respond to N deposition and rejects Al toxicity and changes in bacteria composition as factors that likely play a role in changes in sedge abundance. Citations: Potter, T. S., Owens, W. M., Bowman, W. D. (2019). Do plant–microbe interactions and aluminum tolerance influence alpine sedge species’ responses to nitrogen deposition?. Ecosphere, 10(7), e02775.
Aboveground net primary productivity data for saddle, south of saddle, and east of Tvan, 1982 - ongoing.
Total aboveground biomass samples were collected as part of several studies conducted on Niwot Ridge between 1982 and 2011 and were combined into a single data set that contains the name of the original investigator who collected the data, the URL of the data offered on the Niwot Ridge website, the vegetation type, location, plot ID, subsample ID, plot type, size (if known), year sample was collected, and live vascular aboveground biomass. Contributing investigators were Marilyn Walker, Bill Bowman, Tim Seastedt, Katie Suding, and Hope Humphries. NOTE: This LTER data portal display does not contain important maintenance/log information. Please be sure to view the EML file (a text file that contains XML tags) which is included in the zip archive (click on "Download zip archive") for legacy maintenance/log information pertaining to each dataset. The EML file name will have the following format: knb-lter-nwt.[3 digit dataset number].[version number].xml. Most web browsers can parse the EML so it's easier to read. Scroll down to the "maintenance" tag.
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