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  • 1
    Electronic Resource
    Electronic Resource
    Soil nitrogen transformations under Populus tremuloides, Betula papyrifera and Acer saccharum following 3 years exposure to elevated CO2 and O3 (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: Increases in atmospheric CO2 and tropospheric O3 may affect forest N cycling by altering plant litter production and the availability of substrates for microbial metabolism. Three years following the establishment of our free-air CO2–O3 enrichment experiment, plant growth has been stimulated by elevated CO2 resulting in greater substrate input to soil; elevated O3 has counteracted this effect. We hypothesized that rates of soil N cycling would be enhanced by greater plant productivity under elevated CO2, and that CO2 effects would be dampened by O3. We found that elevated CO2 did not alter gross N transformation rates. Elevated O3 significantly reduced gross N mineralization and microbial biomass N, and effects were consistent among species. We also observed significant interactions between CO2 and O3: (i) gross N mineralization was greater under elevated CO2 (1.0 mg N kg−1 day−1) than in the presence of both CO2 and O3 (0.5 mg N kg−1 day−1) and (ii) gross NH4+ immobilization was also greater under elevated CO2 (0.8 mg N kg−1 day−1) than under CO2 plus O3 (0.4 mg N kg−1 day−1). We used a laboratory 15N tracer method to quantify transfer of inorganic N to organic pools. Elevated CO2 led to greater recovery of NH4+-15N in microbial biomass and corresponding lower recovery in the extractable NO3− pool. Elevated CO2 resulted in a substantial increase in NO3−-15N recovery in soil organic matter. We observed no O3 main effect and no CO2 by O3 interaction effect on 15N recovery in any soil pool. All of the above responses were most pronounced beneath Betula papyrifera and Populus tremuloides, which have grown more rapidly than Acer saccharum. Although elevated CO2 has increased plant productivity, the resulting increase in plant litter production has yet to overcome the influence of the pre-existing pool of soil organic matter on soil microbial activity and rates of N cycling. Ozone reduces plant litter inputs and also appears to affect the composition of plant litter in a way that reduces microbial biomass and activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00705.x
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  • 2
    Electronic Resource
    Electronic Resource
    Chemistry and decomposition of litter from Populus tremuloides Michaux grown at elevated atmospheric CO2 and varying N availability (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: It has been hypothesized that greater production of total nonstructural carbohydrates (TNC) in foliage grown under elevated atmospheric carbon dioxide (CO2) will result in higher concentrations of defensive compounds in tree leaf litter, possibly leading to reduced rates of decomposition and nutrient cycling in forest ecosystems of the future. To evaluate the effects of elevated atmospheric CO2 on litter chemistry and decomposition, we performed a 111 day laboratory incubation with leaf litter of trembling aspen (Populus tremuloides Michaux) produced at 36 Pa and 56 Pa CO2 and two levels of soil nitrogen (N) availability. Decomposition was quantified as microbially respired CO2 and dissolved organic carbon (DOC) in soil solution, and concentrations of nonstructural carbohydrates, N, carbon (C), and condensed tannins were monitored throughout the incubation. Growth under elevated atmospheric CO2 did not significantly affect initial litter concentrations of TNC, N, or condensed tannins. Rates of decomposition, measured as both microbially respired CO2 and DOC did not differ between litter produced under ambient and elevated CO2. Total C lost from the samples was 38 mg g−1 litter as respired CO2 and 138 mg g−1 litter as DOC, suggesting short-term pulses of dissolved C in soil solution are important components of the terrestrial C cycle. We conclude that litter chemistry and decomposition in trembling aspen are minimally affected by growth under higher concentrations of CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2001.00388.x
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  • 3
    Electronic Resource
    Electronic Resource
    Simulated chronic NO3− deposition reduces soil respiration in northern hardwood forests (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3− deposition (3 g N m−2 yr−1) to four sugar maple-dominated northern hardwood forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3−-amended plots. In all subsequent measurement years, soil respiration rates from NO3−-amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3− additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3−-amended plots are consistent with this explanation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2004.00737.x
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  • 4
    Electronic Resource
    Electronic Resource
    Nitrate deposition in northern hardwood forests and the nitrogen metabolism of Acer saccharum marsh (1996)
    Springer
    Oecologia 108 (1996), S. 338-344 
    Details
    ISSN: 1432-1939
    Keywords: Nitrogen deposition ; Nitrogen uptake ; Nitrate reductase ; 15N ; Acer saccharum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It is generally assumed that plant assimilation constitutes the major sink for anthropogenic Nitrate NO 3 − deposited in temperate forests because plant growth is usually limited by nitrogen (N) availability. Nevertheless, plants are known to vary widely in their capacity for NO 3 − uptake and assimilation, and few studies have directly measured these parameters for overstory trees. Using a combination of field and greenhouse experiments, we studied the N nutrition of Acer saccharum Marsh. in four northern hardwood forests receiving experimental NO 3 − additions equivalent to 30 kg N ha−1 year−1. We measured leaf and fine-root nitrate reductase activity (NRA) of overstory trees using an in vivo assay and used 15N to determine the kinetic parameters of NO 3 − uptake by excised fine roots. In two greenhouse experiments, we measured leaf and root NRA in A. saccharum seedlings fertilized with 0–3.5 g NO 3 − −N m−2 and determined the kinetic parameters of NO 3 − and NH 4 + uptake in excised roots of seedlings. In both overstory trees and seedlings, rates of leaf and fine root NRA were substantially lower than previously reported rates for most woody plants and showed no response to NO 3 − fertilization (range = non-detectable to 33 nmol NO 2 − g−1 h−1). Maximal rates of NO 3 − uptake in overstory trees also were low, ranging from 0.2 to 1.0 μmol g−1 h−1. In seedlings, the mean V max for NO 3 − uptake in fine roots (1 μmol g−1 h−1) was approximately 30 times lower than the V max for NH 4 + uptake (33 μmol g−1 h−1). Our results suggest that A. saccharum satisfies its N demand through rapid NH 4 + uptake and may have a limited capacity to serve as a direct sink for atmospheric additions of NO 3 − .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334659
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of vesicular-arbuscular mycorrhizae during old field succession (1991)
    Springer
    Oecologia 86 (1991), S. 349-358 
    Details
    ISSN: 1432-1939
    Keywords: VA-mycorrhizae ; Old field succession ; Infectivity ; Spore populations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The species composition of vesicular-arbuscular mycorrhizal (VAM) fungal communities changed during secondary succession of abandoned fields based on a field to forest chronosequence. Twenty-five VAM fungal species were identified. Seven species were clearly early successional and five species were clearly late successional. The total number of VAM fungal species did not increase with successional time, but diversity as measured by the Shannon-Wiener index tended to increase, primarily because the community became more even as a single species, Glomus aggregatum, became less dominant in the older sites. Diversity of the VAM fungal community was positively correlated with soil C and N. The density of VAM fungi, as measured by infectivity and total spore count, first increased with time since abandonment and then decreased in the late successional forest sites. Within 12 abandoned fields, VAM fungal density increased with increasing soil pH, H2O soluble soil C, and root biomass, but was inversely related to extractable soil P and percent cover of non-host plant species. The lower abundance of VAM fungi in the forest sites compared with the field sites agrees with the findings of other workers and corresponds with a shift in the dominant vegetation from herbaceous VAM hosts to woody ectomycorrhizal hosts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317600
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen mineralization, nitrification and denitrification in upland and wetland ecosystems (1991)
    Springer
    Oecologia 88 (1991), S. 189-196 
    Details
    ISSN: 1432-1939
    Keywords: N mineralization ; Nitrification ; Microbial biomass ; Denitrification ; Spatial variability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrogen mineralization, nitrification, denitrification, and microbial biomass were evaluated in four representative ecosystems in east-central Minnesota. The study ecosystems included: old field, swamp forest, savanna, and upland pin oak forest. Due to a high regional water table and permeable soils, the upland and wetland ecosystems were separated by relatively short distances (2 to 5 m). Two randomly selected sites within each ecosystem were sampled for an entire growing season. Soil samples were collected at 5-week intervals to determine rates of N cycling processes and changes in microbial biomass. Mean daily N mineralization rates during five-week in situ soil incubations were significantly different among sampling dates and ecosystems. The highest annual rates were measured in the upland pin oak ecosystem (8.6 g N m−2 yr−1), and the lowest rates in the swamp forest (1.5 g N m−2 yr−1); nitrification followed an identical pattern. Denitrification was relatively high in the swamp forest during early spring (8040 μg N2O−N m−2 d−1) and late autumn (2525 μg N2O−N m−2 d−1); nitrification occurred at rates sufficient to sustain these losses. In the well-drained uplands, rates of denitrification were generally lower and equivalent to rates of atmospheric N inputs. Microbial C and N were consistently higher in the swamp forest than in the other ecosystems; both were positively correlated with average daily rates of N mineralization. In the subtle landscape of east-central Minnesota, rates of N cycling can differ by an order of magnitude across relatively short distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320810
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  • 7
    Electronic Resource
    Electronic Resource
    Populus tremuloides photosynthesis and crown architecture in response to elevated CO2 and soil N availability (1997)
    Springer
    Oecologia 110 (1997), S. 328-336 
    Details
    ISSN: 1432-1939
    Keywords: Key words Carbon allocation  ;  Elevated CO2  ;   Nitrogen  ;  Photosynthesis  ;  Populus tremuloides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We tested the hypothesis that elevated CO2 would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO2. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO2 and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g−1 day−1 net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO2 resulted in significantly higher maximum leaf photosynthesis (A max) at both soil N levels. A max was higher at high N than at low N soil in elevated, but not ambient CO2. Photosynthetic N use efficiency was higher at elevated than ambient CO2 in both soil types. Elevated CO2 resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO2 and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport capacity (V cmax/J max) than at ambient CO2 and/or low N availability. From the top to the bottom of the tree crowns, V cmax/J max increased in ambient CO2, but it decreased in elevated CO2 indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO2. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A leaf for each segment. This analysis indicated that increased A leaf at elevated CO2 did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation to roots in young trees may increase in elevated CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008813
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  • 8
    Electronic Resource
    Electronic Resource
    Altered performance of forest pests under atmospheres enriched by CO 2 and O 3 (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 420 (2002), S. 403-407 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Human activity causes increasing background concentrations of the greenhouse gases CO2 and O3. Increased levels of CO2 can be found in all terrestrial ecosystems. Damaging O3 concentrations currently occur over 29% of the world's temperate and ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01028
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  • 9
    Electronic Resource
    Electronic Resource
    corrigendum: Altered performance of forest pests under atmospheres enriched by CO 2 and O 3 (2003)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 421 (2003), S. 190-190 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Nature 420, 403–407 (2002). In this Letter, the conversion to SI units led to several errors. On page 404, left column, lines 16 and 17, the values should read 10–15 and 30–40 nanolitres per litre. On page 405, right column, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01329
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  • 10
    Electronic Resource
    Electronic Resource
    Carbon and nitrogen cycling during old-field succession: Constraints on plant and microbial biomass (1990)
    Springer
    Biogeochemistry 11 (1990), S. 111-129 
    Details
    ISSN: 1573-515X
    Keywords: Carbon cycling ; nitrogen cycling ; microbial biomass ; plant biomass ; secondary succession ; soil organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Soil C and N dynamics were studied in a sequence of old fields of increasing age to determine how these biogeochemical cycles change during secondary succession. In addition, three different late-successional forests were studied to represent possible "steady state" conditions. Surface soil samples collected from the fields and forests were analyzed for total C, H2O-soluble C, total N, potential net N mineralization, potential net nitrification, and microbial biomass. Above-and belowground plant biomass was estimated within each of the old field sites. Temporal changes in soil organic C, total N and total plant biomass were best described by a gamma function [y =at b e ctd +f] whereas a simple exponential model [y =a(l − e−bt ) + c] provided the best fit to changes in H2O-soluble C, C:N ratio, microbial C, and microbial N. Potential N mineralization and nitrification linearly increased with field age; however, rates were variable among the fields. Microbial biomass was highly correlated to soil C and N pools and well correlated to the standing crop of plant biomass. In turn, plant biomass was highly correlated to pools and rates of N cycling. Patterns of C and N cycling within the old field sites were different from those in a northern hardwood forest and a xeric oak forest; however, nutrient dynamics within an oak savanna were similar to those found in a 60-yr old field. Results suggest that patterns in C and N cycling within the old-field chronosequence were predictable and highly correlated to the accrual of plant and microbial biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00002062
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