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Stan D Wullschleger

Publications and source records attributed to Stan D Wullschleger.

6 recordsLinked to original sources
PubMed2003

Laser-induced breakdown spectroscopy for the environmental determination of total carbon and nitrogen in soils.

Soils from various sites have been analysed with the laser-induced breakdown spectroscopy (LIBS) technique for total elemental determination of carbon and nitrogen. Results from LIBS have been correlated to a standard laboratory-based technique (sample combustion), and strong linear correlations were obtained for determination of carbon concentrations. The LIBES technique was used on soils before and after acid washing, and the technique appears to be useful for the determination of both organic and inorganic soil carbon. The LIBS technique has the potential to be packaged into a field-deployable instrument.

Journal Article↗
PubMed2003

Diurnal and seasonal changes in stem increment and water use by yellow poplar trees in response to environmental stress.

To evaluate indicators of whole-tree physiological responses to climate stress, we determined seasonal, daily and diurnal patterns of growth and water use in 10 yellow poplar (Liriodendron tulipifera L.) trees in a stand recently released from competition. Precise measurements of stem increment and sap flow made with automated electronic dendrometers and thermal dissipation probes, respectively, indicated close temporal linkages between water use and patterns of stem shrinkage and swelling during daily cycles of water depletion and recharge of extensible outer-stem tissues. These cycles also determined net daily basal area increment. Multivariate regression models based on a 123-day data series showed that daily diameter increments were related negatively to vapor pressure deficit (VPD), but positively to precipitation and temperature. The same model form with slight changes in coefficients yielded coefficients of determination of about 0.62 (0.57-0.66) across data subsets that included widely variable growth rates and VPDs. Model R2 was improved to 0.75 by using 3-day running mean daily growth data. Rapid recovery of stem diameter growth following short-term, diurnal reductions in VPD indicated that water stored in extensible stem tissues was part of a fast recharge system that limited hydration changes in the cambial zone during periods of water stress. There were substantial differences in the seasonal dynamics of growth among individual trees, and analyses indicated that faster-growing trees were more positively affected by precipitation, solar irradiance and temperature and more negatively affected by high VPD than slower-growing trees. There were no negative effects of ozone on daily growth rates in a year of low ozone concentrations.

Circadian Rhythm↗
PubMed2002

Leaf respiration at different canopy positions in sweetgum (Liquidambar styraciflua) grown in ambient and elevated concentrations of carbon dioxide in the field.

Trees exposed to elevated CO2 partial pressure ([CO2]) generally show increased rates of photosynthesis and growth, but effects on leaf respiration are more variable. The causes of this variable response are unresolved. We grew 12-year-old sweetgum trees (Liquidambar styraciflua L.) in a Free-Air CO2 Enrichment (FACE) facility in ambient [CO2] (37/44 Pa daytime/nighttime) and elevated [CO2] (57/65 Pa daytime/nighttime) in native soil at Oak Ridge National Environmental Research Park. Nighttime respiration (R(N)) was measured on leaves in the upper and lower canopy in the second (1999) and third (2000) growing seasons of CO2 fumigation. Leaf respiration in the light (R(L)) was estimated by the technique of Brooks and Farquhar (1985) in the upper canopy during the third growing season. There were no significant short-term effects of elevated [CO2] on R(N) or long-term effects on R(N) or R(L), when expressed on an area, mass or nitrogen (N) basis. Upper-canopy leaves had 54% higher R(N) (area basis) than lower-canopy leaves, but this relationship was unaffected by CO2 growth treatment. In August 2000, R(L) was about 40% of R(N) in the upper canopy. Elevated [CO(2)] significantly increased the number of leaf mitochondria (62%), leaf mass per unit area (LMA; 9%), and leaf starch (31%) compared with leaves in ambient [CO(2)]. Upper-canopy leaves had a significantly higher number of mitochondria (73%), N (53%), LMA (38%), sugar (117%) and starch (23%) than lower-canopy leaves. Growth in elevated [CO2] did not affect the relationships (i.e., intercept and slope) between R(N) and the measured leaf characteristics. Although no factor explained more than 45% of the variation in R(N), leaf N and LMA were the best predictors for R(N). Therefore, the response of RN to CO2 treatment and canopy position was largely dependent on the magnitude of the effect of elevated [CO2] or canopy position on these characteristics. Because elevated [CO2] had little or no effect on N or LMA, there was no effect on R(N). Canopy position had large effects on these leaf characteristics, however, such that upper-canopy leaves exhibited higher R(N) than lower-canopy leaves. We conclude that elevated [CO2] does not directly impact leaf respiration in sweetgum and that barring changes in leaf nitrogen or leaf chemical composition, long-term effects of elevated [CO2] on respiration in this species will be minimal.

Carbohydrates↗
PubMed2002

Genomics and the tree physiologist.

During the last decade, a strong case has been made for viewing trees as model systems in plant biology. More recently, forest biologists have argued for the sequencing of the genome of a forest tree. Now, the United States Department of Energy has announced plans for sequencing the genome of the Populus trichocarpa clone, "Nisqually-1." Thus, forest biology is poised to enter an exciting period of scientific discovery. Embracing new technology and new research paradigms, however, is never easy. It is, therefore, timely to ask how tree physiologists will take advantage of the Populus genome data. We contend that the most attractive opportunities will arise through genome-wide research designed to: (1). examine the differences between trees and herbaceous annuals; (2). explore questions relating to the temporal and spatial scales that characterize the life histories and growth of trees; and (3). investigate cause-and-effect relationships that are intractable to conventional research methodologies. To highlight the potential applications of genomics in tree physiology, we briefly discuss each of these approaches.

Genome, Plant↗