Browsing by Subject "Carbon dioxide -- Physiological effect"
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Item Effects of elevated COb2s on sweetgum ecophysiology(Texas Tech University, 2002-12) Sholtis, Johnna DThe photosynthetic responses of sweetgum {Liquidambar styraciflua L.) trees growing in a forest stand to exposure to an elevated-C02 atmosphere were examined over three growing seasons at the Oak Ridge National Laboratory's Free-Air CO2 Enrichment (FACE) facility in eastern Tennessee, USA. Net photosynthetic rates at the growth CO2 concentration (Agrowth) of mature upper-canopy leaves were found to be 44% higher in trees grown in elevated CO2 (-553 µmol mo-1) compared with ambient CO2 (-364 µmol mol''). There were no significant CO2 treatment effects on the CO2- and light-saturated rate of photosynthesis (Amax), maximum rubisco carboxylation rate (Vcmax) or the rate of ribulose bisphosphate (RuBP) regeneration via electron transport (Jmax), indicating that exposure to 1.5 times ambient CO2 did not limit the photosynthetic capacity of sweetgum leaves. In addition, a more-complete canopy profile was developed by examining the photosynthetic response of young leaves and leaves sampled from lower in the tree crown. The Agrowth of leaves exposed to elevated CO2 was enhanced by 76% in young and mature leaves growing in the upper canopy, and 48% in mature leaves collected in the upper and middle canopies. Within each leaf-age and canopy-position class, growth in elevated CO2 enhanced Agrowth by 123% in young leaves and 31% in mature leaves, and by 45% and 52% in mature upper- and middle-canopy leaves, respectively. There were no CO2 effects on Amax, Vcmax or Jmax of leaves in either of the age or canopy-position classes. A profile of the vertical distribution of nitrogen through the sweetgum canopy was developed to provide for the estimate of CO2 effects on canopy- and stand-level carbon assimilation in sweetgum. Mean nitrogen concentration (mass-based; NM) was 9% lower in the leaves of trees grown in ambient versus elevated CO2 concentrations, with no CO2 effects noted on foliar nitrogen when analyzed per unit leaf area {NA), and per unit leaf volume {Nv). These results provide evidence that leaves sampled throughout the sweetgum canopy exhibit enhanced photosynthesis in a C02-enriched atmosphere, and that the indeterminate growth exhibited by this tree species provides sufficient sink strength so that photosynthetic capacity is not downregulated.Item Studies on the mechanism of carbon monoxide-induced coronary vasodilation(Texas Tech University, 1993-05) Wright, Jackie ADissolved carbon monoxide (CO) produces increased coronary flow, i.e., vasodilation, in isolated rat hearts. It has been suggested that CO may be part of the nitric oxide family of endogenous autacoids and neurotransmitters with physiologic effects. In order to more fully understand the actions of endogenous CO, we investigated the vasodilatory effects of 5% CO dissolved in Krebs-Henseleit buffer on ventricular function in isolated rat hearts and further investigated the mechanism of this vasodilation in porcine coronary artery rings. Dissolved CO (5%-CO 90%-O2 5%CO2) produced 6±2% vasodilation without a significant change in any ventricular function parameters in isolated isovolumic rat hearts. The control group of hearts (95% O2 5%-CO2) vasoconstricted 3±1%. Over the experimental time period only perfusion pressure rose significantly, and the developed pressure and the ±dP/dt (the first derivative of the developed pressure) declined in the control group. The comparison of the ventricular compliance curves revealed no significant differences between either the CO group or the control group compared to a group of hearts perfused with red blood cell-containing perfusate. The best indicators of cardiac work were heart rate and -dP/dt for the control group and heart rate and developed pressure for the CO group. In porcine coronary artery rings, 5% CO (5%-CO 90%-O2 5% CO2) dissolved in Krebs-Henseleit buffer produced a significant transient vasodilation in rings precontracted with 20mM potassium chloride (KCl), but not with 74.7mM KCl. A significant transient vasodilation was also seen at 3 x 10^-6M Prostaglandin F2a(PGF2a), but not at 3 x 10^-5M. In rings equilibrated in calcium-free Krebs-Henseleit buffer precontracted with 3 x 10^-6 M PGF2a, calcium transfer through receptor-operated channels was affected significantly only at 4.0 mM calcium chloride, but not at 0, 0.5, 1.5, 2.5, and 4.0 mM calcium. CO did not significantly affect calcium transfer through voltage-operated calcium channels in rings precontracted with 20 mM KCl. Our results demonstrate that CO does cause transient coronary vasodilation at low but not high doses of KCl and PGF2a but his vasodilation does not involve inhibition of calcium transfer through receptor- or voltage-operated calcium channels. the transient nature of this effect may be related to postulated physiologic effects.