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1

Electronic Resource

Nitrate deposition in northern hardwood forests and the nitrogen metabolism of Acer saccharum marsh (1996)

Rothstein, David E. ; Zak, Donald R. ; Pregitzer, Kurt S.

Springer

Oecologia 108 (1996), S. 338-344

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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

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Populus tremuloides photosynthesis and crown architecture in response to elevated CO2 and soil N availability (1997)

Kubiske, M. E. ; Pregitzer, Kurt S. ; Mikan, Carl J. ; [et al.]

Springer

Oecologia 110 (1997), S. 328-336

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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

Relationships among root branch order, carbon, and nitrogen in four temperate species (1997)

Pregitzer, Kurt S. ; Kubiske, Mark E. ; Yu, Chui Kwan ; [et al.]

Springer

Oecologia 111 (1997), S. 302-308

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ISSN: 1432-1939

Keywords: Key words Fine roots ; Architecture ; Nitrogen ; Turnover

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The objective of this study was to examine how root length, diameter, specific root length, and root carbon and nitrogen concentrations were related to root branching patterns. The branching root systems of two temperate tree species, Acer saccharum Marsh. and Fraxinus americana L., and two perennial herbs from horizontal rhizomes, Hydrophyllum canadense L. and Viola pubescens Ait., were quantified by dissecting entire root systems collected from the understory of an A. saccharum-Fagus grandifolia Ehrh. forest. The root systems of each species grew according to a simple branching process, with laterals emerging from the main roots some distance behind the tip. Root systems normally consisted of only 4–6 branches (orders). Root diameter, length, and number of branches declined with increasing order and there were significant differences among species. Specific root length increased with order in all species. Nitrogen concentration increased with order in the trees, but remained constant in the perennial herbs. More than 75% of the cumulative root length of tree seedling root systems was accounted for by short (2–10 mm) lateral roots almost always 〈0.3 mm in diameter. Simple assumptions suggest that many tree roots normally considered part of the dynamic fine-root pool (e.g., all roots 〈2.0 mm in diameter) are too large to exhibit rapid rates of production and mortality. The smallest tree roots may be the least expensive to construct but the most expensive to maintain based on an increase in N concentration with order.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050239

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4

Electronic Resource

Applications of minirhizotrons to understand root function in forests and other natural ecosystems (1996)

Hendrick, Ronald L. ; Pregitzer, Kurt S.

Springer

Plant and soil 185 (1996), S. 293-304

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ISSN: 1573-5036

Keywords: decomposition ; minirhizotron ; production ; soil biota ; turnover

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Minirhizotrons have proved useful to understand the dynamics and function of fine roots. However, they have been used comparatively infrequently in forests and other natural plant communities. Several factors have contributed to this situation, including anomalous root distributions along the minirhizotron surface and the difficulty of extracting data from minirhizotron images. Technical and methodological advances have ameliorated some of these difficulties, and minirhizotrons have considerable potential to address some questions of long standing interest. These questions include more fully understanding the role of roots in carbon and nutrient cycling, rates of root decomposition, responses to resource availability and the functional significance of interactions between plant roots and soil organisms. Maximizing the potential for minirhizotrons to help us better understand the functional importance of fine roots in natural plant communities depends upon using them to answer only those questions appropriate to both their inherent strengths and limitations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02257535

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5

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Soil Temperature, Matric Potential, and the Kinetics of Microbial Respiration and Nitrogen Mineralization (1999)

Zak, Donald R. ; Holmes, William E. ; MacDonald, Neil W. ; [et al.]

Springer

Soil Science Society of America journal 63 (1999), S. 575-584

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ISSN: 1435-0661

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: 2 and inorganic N. First-order kinetic models described the accumulation of CO2 and inorganic N and accounted for 96 to 99% of the variation in these processes. First-order rate constants (k) for net N mineralization significantly increased with temperature, but the k for microbial respiration did not increase in a consistent manner; it was 0.107 wk-1 at 5°C, 0.123 wk-1 at 10°C, and 0.101 wk-1 at 25° C. Matric potential did not significantly influence k for either process. Substrate pools for microbial respiration and net N mineralization declined between -0.01 and -0.30 Mpa, and the decline was greatest at the highest soil temperature; this response produced a significant temperature-matric potential interaction. We conclude that high rates of microbial activity at warm soil temperatures (e.g., 25°C) are limited by the diffusion of substrate to metabolically active cells. This limitation apparently lessens as physiological activity and substrate demand decline at relatively cooler soil temperature (e.g., 5°C).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/

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6

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Clonal variation in above- and below-ground growth responses of Populus tremuloides Michaux: Influence of soil warming and nutrient availability (1999)

King, John S. ; Pregitzer, Kurt S. ; Zak, Donald R.

Springer

Plant and soil 217 (1999), S. 119-130

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ISSN: 1573-5036

Keywords: biomass partitioning ; clonal variation ; N-availability ; Populus tremuloides ; root longevity ; soil warming

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Trembling aspen (Populus tremuloides Michx.) is the most widely distributed tree species in North America making it important to terrestrial carbon and nutrient cycles. Due to anthropogenic climate change high latitude temperatures are expected to increase, making it necessary to assess the feedback between above- and below-ground carbon pools to increased temperature at sites of both high and low N-availability. We grew four clones of aspen at two levels of soil temperature and two levels of soil N-availability for 98 days and quantified photosynthesis, growth, biomass allocation, and root length production and mortality. High soil temperature increased rates of photosynthesis (65%), resulting in greater whole-plant growth (37%) through increases in roots, stems, and foliage; however these increases generally occurred only in soil of high N-availability. Root:shoot biomass allocation varied between clones but was unaffected by the soil temperature or N-availability treatments. Root length production and mortality increased at elevated soil temperature, but this response was modified by soil N-availability. At high soil temperature, soil N-availability had little effect on root dynamics, while at low soil temperature, high soil N-availability increased both the production and mortality (turnover) of roots. We conclude that trembling aspen has the potential for substantially greater growth and root turnover under conditions of warmer soil at sites of both high and low N-availability, but that allometric patterns of growth are under strong genetic, rather than environmental control.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1004560311563

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Catastrophic disturbance in the presettlement forests of the Upper Peninsula of Michigan (1999)

Zhang, Quanfa ; Pregitzer, Kurt S ; Reed, David D

Canadian Science Publishing

In: Canadian Journal of Forest Research. 1999; 29(1): 106-114. Published 1999 Jan 01. doi: 10.1139/x98-184.

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Publication Date: 1999-01-01

Description: The General Land Office (GLO) survey notes (1840-1856) were used to examine the interaction among natural disturbance, vegetation type, and topography in the presettlement forests of the Luce District, an ecological unit of approximately 902 000 ha in the Upper Peninsula of Michigan, U.S.A. The surveyors recorded 104 fire and 126 windthrow incidences covering 3.1 and 2.8% of the total length of the surveyed lines, respectively. The rotation periods over the entire landscape were 480 years for fire and 541 years for windthrow, but these varied with vegetation type and topographic position. Fire occurred more frequently on southerly aspects and at elevations where pinelands were concentrated. The density of windthrow events increased with elevation and slope, with the highest occurrence on westerly aspects. Based on the estimated rotation periods, we calculated that 7.5, 24.4, and 68.1% of the presettlement forest were in the stand initiation, stem exclusion, and old forest (including both understory reinitiation and old growth) stages, respectively. Pinelands and mixed conifers were the major components in both the stand initiation (34.5 and 31.1%) and the stem exclusion stage (20.9 and 39.8%), while mixed conifers (39.3%) and northern hardwoods (34.7%) were the major old-forest cover types. The diverse mosaic of various successional stages generated by natural disturbance suggests a "shifting-mosaic" landscape in this region.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition