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1

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Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree (1998)

Livingston, N. J. ; Whitehead, D. ; Kelliher, F. M. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Plant, cell & environment 21 (1998), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The three dimensional distribution of intercepted radiation, intercellular CO2 concentration (Ci) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2-m-tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above- and below-canopy irradiance, leaf stable carbon isotopic composition (δ13C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) Ci would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (gs), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in gs. Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ13C and needle height above ground (r2 = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and Ci (r2 = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00314.x

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2

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Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree (1996)

WHITEHEAD, D. ; LIVINGSTON, N. J. ; KELLIHER, P.M. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 19 (1996), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Sudden but transient changes in the fraction or illuminated foliage area in a well-watered 7-year-old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (gt), stomatal conductance (gs) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in gt. However, when tree conductance was normalized with respect to the illuminated leaf area (gt'), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in gs and A up to 59 and 24%, respectively, for needles in the top third of (he crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00459.x

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3

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The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don (1997)

WALCROFT, A. S. ; WHITEHEAD, D. ; SILVESTER, W. B. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 20 (1997), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Responses of photosynthesis (A) to intercellular CO2 concentration (ci) in 2-year-old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4-fold increase in Vcmax, the maximum rate of carboxylation (10.7–43.3 μol m−2 s−1 and a 3-fold increase in Jmax, the maximum electron transport rate (20.5–60.2 μmol m −2 s−1). The temperature optimum for Jmax was lower than that for Vcmax, causing a decline in the ratio Jmax:Vcmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg−1, and there were linear relationships between N concentration and both Vcmax and Jmax. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg−1 near the base to 1.54 mol kg−1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-31.x

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4

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Photosynthetic acclimation to long-term exposure to elevated CO2 concentration in Pinus radiata D. Don. is related to age of needles (1998)

Turnbull, M. H. ; Tissue, D. T. ; Griffin, K. L. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 21 (1998), S. 0

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ISSN: 1365-3040

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The effects of CO2 enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressures. At this age trees were 3·5–4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO2 concentration [(pCO2)a] were lower in 1-year-old needles of trees grown at elevated CO2 concentrations than in those of trees grown at ambient (pCO2)a. At elevated CO2 concentrations Vcmax (maximum carboxylation rate) was reduced by 13% and Jmax (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO2)a of 4·68 ± 0·41 μmol m–2 s–1 and 6·15 ± 0·46 μmol m–2 s–1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO2)a were 6·2 ± 0·72 μmol m–2 s–1 at 36 Pa and 10·15 ± 0·64 μmol m–2 s–1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO2 treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO2)a in fully fexpanded needles of the current year cohort. These data show that enhancement of photosynthesis continues to occur in needles after 4 years’ exposure to elevated CO2 concentrations. Photosynthetic acclimation reduces the degree of this enhancement, but only in needles after 1 year of growth. Thus, responses to elevated CO2 concentration change during the lifetime of needles, and acclimation may not be apparent in current year needles. This transitory effect is most probably attributable to the effects of developmental stage and proximity to actively growing shoots on sink strength for carbohydrates. The implications of such age-dependent responses are that older trees, in which the contribution of older needles to the photosynthetic biomass is greater than in younger trees, may become progressively more acclimated to elevated CO2 concentration.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00374.x

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5

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Soldering with light! (1995)

Whitehead, D G ; J Foster, R

Bradford : Emerald

Assembly automation 15 (1995), S. 17-19

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ISSN: 0144-5154

Source: Emerald Fulltext Archive Database 1994-2005

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: With the ever-decreasing size of electronic components, examinesthe use of laser soldering, particularly of fine-pitch, high valuedevices. Discusses the advantages and disadvantages of using lasers and theapplications to which they are suited. Looks at the different types of lasersand how their different wavelength of operation affects the solderingprocess. Describes an experimental laser soldering station and its ability tosolder circuit boards. Concludes that modern electronic component packagingtechnology is demanding new techniques for the interconnection of devices,and that the application of lasers to the traditional technique of solderingwill enable this tested process to be applicable to the very fine pitchdevices now being introduced.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1108/01445159510146978

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6

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The application of semiconductor diode lasers to the soldering of electronic components (1995)

Beckett, P. M. ; Fleming, A. R. ; Foster, R. J. ; [et al.]

Springer

Optical and quantum electronics 27 (1995), S. 1303-1311

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ISSN: 1572-817X

Source: Springer Online Journal Archives 1860-2000

Topics: Electrical Engineering, Measurement and Control Technology , Physics

Notes: Abstract Work being carried out at the University of Hull into the application of high power laser diodes to the soldering process is described. The commercial availability of semiconductor diode lasers has brought an exciting new soldering tool to the manufacturers of electronics assemblies: trends in electronics assembly are to increasingly high-density interconnections and increasing device functionality. Packages are reducing in size and pin-out counts are increasing. Currently 0.010–0.016 inch lead pitch devices are being introduced by many manufacturers. Lasers can be used with advantage in the soldering of such fine and precise devices and high-power semiconductor laser diodes can be used to build compact, flexible and controllable soldering units. With computer control of the power and duration of the laser energy it is possible to ensure consistent and reliable soldering. To achieve this, however, the various parameters involved in the laser beam-solder assembly interaction need to be carefully defined. This paper reports on our identification of these parameters and the salient design features of an automated diode laser soldering system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00326483

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7

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The paleolimnology of North Pond: watershed-lake interactions (1996)

Huvane, J. K. ; Whitehead, D. R.

Springer

Journal of paleolimnology 16 (1996), S. 323-354

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ISSN: 1573-0417

Keywords: diatoms ; chrysophytes ; pollen ; charcoal ; hemlock decline ; Holocene ; Massachusetts

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract We examined the stratigraphic record of North Pond, a small, oligotrophic lake in western Massachusetts, U.S.A. to describe late and post-glacial watershed-lake interactions. In particular we investigated the effects of two similar vegetation changes in the watershed on lake biogeochemistry. There was a transient (about 100 years) decline in hemlock ca. 7500 yr B.P. that has not been recorded in other pollen stratigraphies in the northeast. The second event was the classical hemlock decline that occurred ca. 4800 yr B.P. and lasted about 2000 years. This decline occurred throughout the range of hemlock and is thought to have been caused by a pathogen. As the climate began to warm ca. 10 000 yr B.P., a spruce dominated boreal woodland was established in the watershed. Sediment chemistry data showed that as soils became more acidic, the lake also acidified as evidenced by diatom-inferred (DI) pH. Hemlock was established in the watershed by about 8000 yr B.P. This was accompanied by a slight decrease in DI pH. The transient hemlock decline ca. 7500 yr B.P. was associated with an increase in sedimentary charcoal particles, that suggested fire was responsible for its demise. The diatom stratigraphy indicated a brief, slight, increase in productivity and alkalinity and a brief decrease in lakewater dissolved organic carbon concentrations. Aquatic microfossil data indicated a decrease in the area of the littoral zone ca. 7500 yr B.P. Following the transient decline the lake became more acidic. There were only brief, subtle changes associated with the classical hemlock decline, including a slight decline in DI pH. Although the two disturbances involved a similar vegetation shift, the timing and mechanisms of the disturbances had a greater impact on lake biogeochemistry.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00207576

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