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  • 1
    Electronic Resource
    Electronic Resource
    Experimental inducement of nitrogen saturation at the watershed scale (1993)
    s.l. : American Chemical Society
    Environmental science & technology 27 (1993), S. 565-568 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es00040a017
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  • 2
    Electronic Resource
    Electronic Resource
    Interactive effects of nitrogen deposition, tropospheric ozone, elevated CO2 and land use history on the carbon dynamics of northern hardwood forests (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Temperate forests are affected by a wide variety of environmental factors that stem from human industrial and agricultural activities. In the north-eastern US, important change agents include tropospheric ozone, atmospheric nitrogen deposition, elevated CO2, and historical human land use. Although each of these has received attention for its effects on forest carbon dynamics, integrated analyses that examine their combined effects are rare. To examine the relative importance of all of these factors on current forest growth and carbon balances, we included them individually and in combination in a forest ecosystem model that was applied over the period of 1700–2000 under different scenarios of air pollution and land use history.Results suggest that historical increases in CO2 and N deposition have stimulated forest growth and carbon uptake, but to different degrees following agriculture and timber harvesting. These differences resulted from the effects of each land use scenario on soil C and N pools and on the resulting degree of growth limitations by carbon vs. nitrogen. Including tropospheric ozone in the simulations offset a substantial portion of the increases caused by CO2 and N deposition. This result is particularly relevant given that ozone pollution is widespread across much of the world and because broad-scale spatial patterns of ozone are coupled with patterns of nitrogen oxide emissions. This was demonstrated across the study region by a significant correlation between ozone exposure and rates of N deposition and suggests that the reduction of N-induced carbon sinks by ozone may be a common phenomenon in other regions.Collectively, the combined effects of all physical and chemical factors we addressed produced growth estimates that were surprisingly similar to estimates obtained in the absence of any form of disturbance. The implication of this result is that intact forests may show relatively little evidence of altered growth since preindustrial times despite substantial changes in their physical and chemical environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00482.x
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  • 3
    Electronic Resource
    Electronic Resource
    Nitrogen oxide gas emissions from temperate forest soils receiving long-term nitrogen inputs (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: From spring 2000 through fall 2001, we measured nitric oxide (NO) and nitrous oxide (N2O) fluxes in two temperate forest sites in Massachusetts, USA that have been treated since 1988 with different levels of nitrogen (N) to simulate elevated rates of atmospheric N deposition. Plots within a pine stand that were treated with either 50 or 150 kg N ha−1 yr−1 above background displayed consistently elevated NO fluxes (100–200 µg N m−2 h−1) compared to control plots, while only the higher N treatment plot within a mixed hardwood stand displayed similarly elevated NO fluxes. Annual NO emissions estimated from monthly sampling accounted for 3.0–3.7% of N inputs to the high-N plots and 8.3% of inputs to the Pine low-N plot. Nitrous oxide fluxes in the N-treated plots were generally 〈 10% of NO fluxes. Net nitrification rates (NRs) and NO production rates measured in the laboratory displayed patterns that were consistent with field NO fluxes. Total N oxide gas flux was positively correlated with contemporaneous measurements of NR and 〈inlineGraphic alt="inline image" href="urn:x-wiley:13541013:GCB0591:GCB_0591_m101" location="equation/GCB_0591_m101.gif"/〉 concentration. Acetylene inhibited both nitrification and NO production, indicating that autotrophic nitrification was responsible for the elevated NO production. Soil pH was negatively correlated with N deposition rate. Low levels (3–11 µg N kg−1) of nitrite (〈inlineGraphic alt="inline image" href="urn:x-wiley:13541013:GCB0591:GCB_0591_m102" location="equation/GCB_0591_m102.gif"/〉) were detected in mineral soils from both sites. Kinetic models describing NO production as a function of the protonated form of 〈inlineGraphic alt="inline image" href="urn:x-wiley:13541013:GCB0591:GCB_0591_m103" location="equation/GCB_0591_m103.gif"/〉 (nitrous acid [HNO2]) adequately described the mineral soil data. The results indicate that atmospheric deposition may generate losses of gaseous NO from forest soils by promoting nitrification, and that the response may vary significantly between forest types under similar climatic regimes. The lowering of pH resulting from nitrification and/or directly from deposition may also play a role by promoting reactions involving HNO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00591.x
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  • 4
    Electronic Resource
    Electronic Resource
    Sources of Variability in Net Primary Production Predictions at a Regional Scale: A Comparison Using PnET-II and TEM 4.0 in Northeastern US Forests (1999)
    Springer
    Ecosystems 2 (1999), S. 555-570 
    Details
    ISSN: 1435-0629
    Keywords: Key words: climate; ecosystem process modeling; modeling uncertainty; net primary production; northeastern US; PnET; soil water holding capacity; spatial resolution; TEM; vegetation representation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT Because model predictions at continental and global scales are necessarily based on broad characterizations of vegetation, soils, and climate, estimates of carbon stocks and fluxes made by global terrestrial biosphere models may not be accurate for every region. At the regional scale, we suggest that attention can be focused more clearly on understanding the relative strengths of predicted net primary productivity (NPP) limitation by energy, water, and nutrients. We evaluate the sources of variability among model predictions of NPP with a regional-scale comparison between estimates made by PnET-II (a forest ecosystem process model previously applied to the northeastern region) and TEM 4.0 (a terrestrial biosphere model typically applied to the globe) for the northeastern US. When the same climate, vegetation, and soil data sets were used to drive both models, regional average NPP predictions made by PnET-II and TEM were remarkably similar, and at the biome level, model predictions agreed fairly well with NPP estimates developed from field measurements. However, TEM 4.0 predictions were more sensitive to regional variations in temperature as a result of feedbacks between temperature and belowground N availability. In PnET-II, the direct link between transpiration and photosynthesis caused substantial water stress in hardwood and pine forest types with increases in solar radiation; predicted water stress was relieved substantially when soil water holding capacity (WHC) was increased. Increasing soil WHC had little effect on TEM 4.0 predictions because soil water storage was already sufficient to meet plant demand with baseline WHC values, and because predicted N availability under baseline conditions in this region was not limited by water. Because NPP predictions were closely keyed to forest cover type, the relative coverage of low- versus high-productivity forests at both fine and coarse resolutions was an important determinant of regional NPP predictions. Therefore, changes in grid cell size and differences in the methods used to aggregate from fine to coarse resolution were important to NPP predictions insofar as they changed the relative proportions of forest cover. We suggest that because the small patches of high-elevation spruce-fir forest in this region are substantially less productive than forests in the remainder of the region, more accurate NPP predictions will result if models applied to this region use land cover input data sets that retain as much fine-resolution forest type variability as possible. The differences among model responses to variations in climate and soil WHC data sets suggest that the models will respond quite differently to scenarios of future climate. A better understanding of the dynamic interactions between water stress, N availability, and forest productivity in this region will enable models to make more accurate predictions of future carbon stocks and fluxes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100219900102
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen Controls on Fine Root Substrate Quality in Temperate Forest Ecosystems (2000)
    Springer
    Ecosystems 3 (2000), S. 57-69 
    Details
    ISSN: 1435-0629
    Keywords: Key words: fine roots; substrate quality; nitrogen; carbon fractions; temperate forest ecosystems.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT Nitrogen controls on fine root substrate quality (that is, nitrogen and carbon-fraction concentrations) were assessed using nitrogen availability gradients in the Harvard Forest chronic nitrogen addition plots, University of Wisconsin Arboretum, Blackhawk Island, Wisconsin, and New England spruce-fir transect. The 27 study sites encompassed within these four areas collectively represented a wide range of nitrogen availability (both quantity and form), soil types, species composition, aboveground net primary production, and climatic regimes. Changes in fine root substrate quality among sites were most frequently and strongly correlated with nitrate availability. For the combined data set, fine root nitrogen concentration increased (adjusted R 2 = 0.46, P 〈 0.0001) with increasing site nitrate availability. Fine root “extractive” carbon-fraction concentrations decreased (adjusted R 2 = 0.32, P 〈 0.0002), “acid-soluble” compounds increased (adjusted R 2 = 0.35, P 〈 0.0001), and the “acid-insoluble” carbon fraction remained relatively high and stable (combined mean of 48.7 ± 3.1% for all sites) with increasing nitrate availability. Consequently, the ratio of acid-insoluble C–total N decreased (adjusted R 2 = 0.40, P 〈 0.0001) along gradients of increasing nitrate availability. The coefficients of determination for significant linear regressions between site nitrate availability and fine root nitrogen and carbon-fraction concentrations were generally higher for sites within each of the four study areas. Within individual study sites, tissue substrate quality varied between roots in different soil horizons and between roots of different size classes. However, the temporal variation of fine root substrate quality indices within specific horizons was relatively low. The results of this study indicate that fine root substrate quality increases with increasing nitrogen availability and thus supports the substrate quality component of a hypothesized conceptual model of nitrogen controls on fine root dynamics that maintains that fine root production, mortality, substrate quality, and decomposition increase with nitrogen availability in forest ecosystems in a manner that is analogous to foliage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100210000010
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  • 6
    Electronic Resource
    Electronic Resource
    Long-Term Nitrogen Additions and Nitrogen Saturation in Two Temperate Forests (2000)
    Springer
    Ecosystems 3 (2000), S. 238-253 
    Details
    ISSN: 1435-0629
    Keywords: Key words: ammonium nitrate; biomass production; foliar chemistry; net mineralization; net nitrification; nitrogen deposition; nitrogen saturation; soil solution chemistry.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT This article reports responses of two different forest ecosystems to 9 years (1988–96) of chronic nitrogen (N) additions at the Harvard Forest, Petersham, Massachusetts. Ammonium nitrate (NH4NO3) was applied to a pine plantation and a native deciduous broad-leaved (hardwood) forest in six equal monthly doses (May–September) at four rates: control (no fertilizer addition), low N (5 g N m-2 y-1), high N (15 g N m-2 y-1), and low N + sulfur (5 g N m-2 y-1 plus 7.4 g S m-2 y-1). Measurements were made of net N mineralization, net nitrification, N retention, wood production, foliar N content and litter production, soil C and N content, and concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in soil water. In the pine stand, nitrate losses were measured after the first year of additions (1989) in the high N plot and increased again in 1995 and 1996. The hardwood stand showed no significant increases in nitrate leaching until 1995 (high N only), with further increases in 1996. Overall N retention efficiency (percentage of added N retained) over the 9-year period was 97–100% in the control and low N plots of both stands, 96% in the hardwood high N plot, and 85% in the pine high N plot. Storage in aboveground biomass, fine roots, and soil extractable pools accounted for only 16–32% of the added N retained in the amended plots, suggesting that the one major unmeasured pool, soil organic matter, contains the remaining 68–84%. Short-term redistribution of 15N tracer at natural abundance levels showed similar division between plant and soil pools. Direct measurements of changes in total soil C and N pools were inconclusive due to high variation in both stands. Woody biomass production increased in the hardwood high N plot but was significantly reduced in the pine high N plot, relative to controls. A drought-induced increase in foliar litterfall in the pine stand in 1995 is one possible factor leading to a measured increase in N mineralization, nitrification, and nitrate loss in the pine high N plot in 1996.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100210000023
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  • 7
    Electronic Resource
    Electronic Resource
    The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire (2000)
    Springer
    Ecosystems 3 (2000), S. 433-450 
    Details
    ISSN: 1435-0629
    Keywords: Key words: disturbance; dissolved organic carbon; dissolved organic nitrogen; fire; logging; nitrate leaching; nitrogen saturation; nitrogen retention; old growth; succession.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US, a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate may occur much sooner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100210000039
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  • 8
    Electronic Resource
    Electronic Resource
    Remote sensing of canopy chemistry and nitrogen cycling in temperate forest ecosystems (1988)
    [s.l.] : Nature Publishing Group
    Nature 335 (1988), S. 154-156 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Remote sensing is used increasingly for the measurements required to develop landscape, regional and global assessments of the state of the biosphere. To date, most applications of remote sensing to terrestrial ecosystems have involved the estimation of foliar area and biomass, or absorbed ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/335154a0
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  • 9
    Electronic Resource
    Electronic Resource
    Immobilization of a 15N-labeled nitrate addition by decomposing forest litter (1996)
    Springer
    Oecologia 105 (1996), S. 141-150 
    Details
    ISSN: 1432-1939
    Keywords: Decomposition ; N immobilization ; N saturation ; Nitrate ; 15N
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Effects of chronic HNO3 and H2SO4 additions on decomposition of senesced birch leaf, beech leaf, spruce needle, and wood chip litters were examined. Litters were incubated for up to 4 years in fiberglass mesh (1 mm) bags on experimental plots in a mixed-species forest near the Bear Brooks Watershed Manipulation (BBWM) site in eastern Maine, United States. Plot treatments included HNO3 additions at 28 and 56 kg N·ha−1·year−1, H2SO4 additions at 128 kg S·ha−1·year−1, and a combined HNO3 and H2SO4 treatment at 28 kg N and 64 kg S ·ha−1·year−1. The 15N content of all NO3 added was artificially increased to 344% δ15N. Litter bags were collected each fall and analyzed for organic matter loss, nitrogen concentration, and 15N abundance throughout the 4-year experiment. Extractive (non-polar-soluble+water-soluble), cellulose (acid-soluble), and lignin (acid-insoluble) fractions were analyzed for the first 2 years. In wood chips, nitrogen additions increased mass loss and N concentration, but not the mass of N after 4 years. Neither N nor S additions had large effects on mass loss, N concentration, or N content of leaf litters. All litters immobilized and mineralized N simultaneously, but we were able to place a lower bound on gross N immobilization by mass balancing 15N additions. Birch and spruce litters showed net mineralization, while beech leaf and wood chip litters showed net immobilization. Net immobilizing litters were those with the highest initial cellulose concentration (wood chips=80% beech leaves=54%), and we attribute the higher capacity for immobilization to more readily available carbon. Lignin mass increased initially in all litter types except spruce needles. Also, extractives in net immobilizing litters either increased initially (wood chips) or decreased at a slower rate than bulk litter (beech leaves). We calculate the potential of decomposing litter to immobilize exogenous nitrate in this system to be 1–1.5 kg N·ha−1·year−1, which is about half of the usual NO3 deposition at this site, but only a small fraction of the experimental addition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328539
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  • 10
    Electronic Resource
    Electronic Resource
    Extrapolating leaf CO2 exchange to the canopy: a generalized model of forest photosynthesis compared with measurements by eddy correlation (1996)
    Springer
    Oecologia 106 (1996), S. 257-265 
    Details
    ISSN: 1432-1939
    Keywords: Whole forest canopy ; Photosynthesis ; Foliar nitrogen concentration ; Model ; Gross carbon exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Over the last 4 years, two data sets have emerged which allow increased accuracy and resolution in the definition and validation of a photosynthesis model for whole forest canopies. The first is a greatly expanded set of data on the nitrogen-photosynthesis relationship for temperate and tropical woody species. The second is a unique set of long-term (4 year) daily carbon balance measurements at the Harvard Forest, Petersham, Massachusetts, collected by the eddy-correlation technique. A model (PhET-Day) is presented which is derived directly from, and validated against, these data sets. The PnET-Day model uses foliar nitrogen concentration to calculate maximum instantaneous rates of gross and net photosynthesis which are then reduced for suboptimal temperature, photosynthetically active radiation (PAR), and vapor pressure deficit (VPD). Predicted daily gross photosynthesis is closely related to gross carbon exchange at the Harvard Forest as determined by eddy-correlation measurements. Predictions made by the full canopy model were significantly better than those produced by a multiple linear regression model. Sensitivity analyses for this model for a deciduous broad-leaved forest showed results to be much more sensitive to parameters related to maximum leaf-level photosynthetic rate (A max) than to those related to light, temperature, VPD or total foliar mass. Aggregation analyses suggest that using monthly mean climatic data to drive the canopy model will give results similar to those achieved by averaging daily eddy correlation measurements of gross carbon exchange (GCE).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328606
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