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  • Key words Carbon allocation   (1)
  • Nitrification  (1)
  • Nitrogen uptake  (1)
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  • 1
    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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  • 2
    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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  • 3
    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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