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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
    Foliar and fine root nitrate reductase activity in seedlings of four forest tree species in relation to nitrogen availability (1993)
    Springer
    Trees 7 (1993), S. 233-236 
    Details
    ISSN: 1432-2285
    Keywords: Nitrate reductase ; Nitrogen deposition ; Forests ; Nitrate ; Seedlings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Seedlings of red maple, white pine, pitch pine and red pine were fertilized with nutrient solutions containing 4 levels of nitrate or ammonium additions. These levels corresponded to approximately 0.5, 1, 2 and 4 times normal availability of nitrogen in northeastern forests. Nitrate reductase (NR) activity was assayed in roots and leaves. Red maples treated with nitrate showed much higher leaf activities and higher ratios of leaf NR activity to root NR activity than any other species. Ammonium additions to red maple and white pine appeared to inhibit NR activity in leaves. With high nitrate additions, NR activity was induced in roots and leaves of pine species, but activity in roots remained much higher than in leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202079
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  • 5
    Electronic Resource
    Electronic Resource
    A 15N tracer technique for assessing fine root production and mortality (1997)
    Springer
    Oecologia 112 (1997), S. 300-304 
    Details
    ISSN: 1432-1939
    Keywords: Key words Fine roots ; Production ; Mortality ; 15N ; Methodology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We tested a 15N tracer technique to assess fine root production and mortality based on temporal measurements of the 15N mass in fine root structural tissues and the 15N concentration of the plant-available soil N pool. The results of a pilot study indicated that this technique is based on sound methods and reasonable assumptions. The 15N tracer technique avoids most of the major limitations which hinder existing methods and may provide valuable insight into the rates and controls of fine root production and mortality in terrestrial ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050312
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Fine root turnover in forest ecosystems in relation to quantity and form of nitrogen availability: a comparison of two methods (1985)
    Springer
    Oecologia 66 (1985), S. 317-321 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two methods of estimating fine root production and turnover are compared for 13 forest ecosystems exhibiting a wide range in form (NH4 + vs. NO3 -) and quantity of available nitrogen. The two methods are by comparison of seasonal maxima and minima in biomess and by nitrogen budgeting. Both methods give similar results for stands with low rates of nitrification. The budgeting method predicts higher fine root turnover and productivity than the max-min method for systems with significant rates of nitrification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378292
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  • 8
    Electronic Resource
    Electronic Resource
    A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems (1992)
    Springer
    Oecologia 92 (1992), S. 463-474 
    Details
    ISSN: 1432-1939
    Keywords: Conductance ; Foliar nitrogen ; Water balance ; LAI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary PnET is a simple, lumped-parameter, monthlytime-step model of carbon and water balances of forests built on two principal relationships: 1) maximum photosynthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. Monthyly leaf area display and carbon and water balances are predicted by combining these with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with effects of soil water stress and vapor pressure deficit (VPD). PnET has been validated against field data from 10 well-studied temperate and boreal forest ecosystems, supporting our central hypothesis that aggregation of climatic data to the monthly scale and biological data such as foliar characteristics to the ecosystem level does not cause a significant loss of information relative to long-term, mean ecosystem responses. Sensitivity analyses reveal a diversity of responses among systems to identical alterations in climatic drivers. This suggests that great care should be used in developing generalizations as to how forests will respond to a changing climate. Also critical is the degree to which the temperature responses of photosynthesis and respiration might acclimate to changes in mean temperatures at decadal time scales. An extreme climate change simulation (+3° C maximum temperature, −25% precipitation with no change in minimum temperature or radiation, direct effects of increased atmospheric CO2 ignored) suggests that major increases in water stress, and reductions in biomass production (net carbon gain) and water yield would follow such a change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317837
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  • 9
    Electronic Resource
    Electronic Resource
    The influence of substrate quality and stream size on wood decomposition dynamics (1983)
    Springer
    Oecologia 58 (1983), S. 281-285 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Woody materials decayed more rapidly in a first order stream than in larger streams in eastern Quebec, Canada. The rate of annual mass loss (k) was highest (k=1.20) for alder wood chips in a first order stream and lowest (k=0.04) for black spruce wood chips in a ninth order stream. Decay rates for woody materials in a first order stream were inversely related to their initial lignin to nitrogen ratios. In larger streams, decay rates of woody materials were inversely related to their initial lignin concentrations. A number of quantifiable relationships were found to exist between the initial lignin and nitrogen contents of woody materials and the nitrogen dynamics of decaying wood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385224
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  • 10
    Electronic Resource
    Electronic Resource
    The fate of 15N-labelled nitrate additions to a northern hardwood forest in eastern Maine, USA (1995)
    Springer
    Oecologia 103 (1995), S. 292-301 
    Details
    ISSN: 1432-1939
    Keywords: Nitrogen deposition ; Nitrate assimilation ; N saturation ; Fagus grandifolia ; Picea rubens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We followed the movements of 15N-labelled nitrate additions into biomass and soil pools of experimental plots (15×15 m each) in a mid-successional beech-maple-birch-spruce forest in order to identify sinks for nitrate inputs to a forest ecosystem. Replicate plots (n=3) were spray-irrigated with either 28 or 56 kg N ha−1 year−1 using 15N-labelled nitric acid solutions (δ15N = 344‰ ) during four successive growing seasons (April–October). The 15N contents of foliage, bolewood, forests floor and mineral soil (0–5 cm) increased during the course of treatments. Mass balance calculations showed that one-fourth to one-third of the nitrate applied to forest plots was assimilated into and retained by above ground plant tissues and surface soil horizons at both rates of nitrate application. Plant and microbial assimilation were of approximately equal importance in retaining nitrate additions to this forest. Nitrate use among tree species varied, however, with red spruce showing lower rates of nitrate assimilation into foliage and bolewood than American beech and other deciduous species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328617
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