The ability of plants to rapidly replace photosynthetic tissues following defoliation represents a resistance strategy referred to as herbivory tolerance. Rapid reprioritization of carbon allocation to regrowing shoots at the expense of roots following defoliation is a widely documented tolerance mechanism. An experiment was conducted in a controlled environment to test the hypothesis that herbivory-sensitive perennial grasses display less flexibility in reprioritizing carbon allocation in response to defoliation than do grasses possessing greater herbivory tolerance. An equivalent proportion of shoot biomass (60% dry weight) was removed from two C perennial grasses recognized as herbivory-sensitive, Andropogon gerardii and Schizachyrium scoparium, and two C perennial grasses recognized as herbivory-tolerant, Aristida purpurea and Bouteloua rigidiseta. Both defoliated and undefoliated plants were exposed to CO for 30 min, five plants per species were harvested at 6, 72 and 168 h following labeling, and biomass was analyzed by isotope ratio mass spectrometry. The tallgrass, A. geraiddii, exhibited inflexible allocation priorities while the shortgrass, B. rigidiseta, exhibited flexible allocation priorities in response to defoliation which corresponded with their initial designations as herbivory-sensitive and herbivory-tolerant species, respectively. A. gerardii had the greatest percentage and concentration of C within roots and lowest percentage ofC within regrowth of the four species evaluated. In contrast, B. rigidiseta had a greater percentage of C within regrowth than did A. gerardii, the greatest percentage ofC within new leaves of defoliated plants, and the lowest concentration of C within roots follwing defoliation. Although both midgrasses, S. scoparium and A. purpurea, demonstrated flexible allocation priorities in response to defoliation, they were counter to those stated in the initial hypothesis. The concentration ofC within new leaves of S. scoparium increased in response to a single defoliation while the percentage and concentration of C within roots was reduced. A. purpurea was the only species in which the percentate ofC within new leaves decreased while the percentage of C within roots increased following defoliation. The most plausible alternative hypothesis to explain the inconsistency between the demonstrated responsiveness of allocation priorities to defoliation and the recognized herbivory resistance of S. scoparium and A. purpurea is that the relative ability of these species to avoid herbivory may make an equal or greater contribution to their overall herbivory resistance than does herbivory tolerance. Selective herbivory may contribute to S. scoparium's designation as a herbivorysensitive species even though it possesses flexible allocation priorities in response to defoliation. Alternatively, the recognized herbivory resistance of A. purpurea may be a consequence of infrequent and/or lenient herbivory associated with the expression of avoidance mechanisms, rather than the expression of t...

Effect of solvent on molecular conformation: Microwave spectra and structures of 2-aminoethanol van der Waals complexesAb initio relativistic all-electron calculation of the Ar-I 2 ground state potential A study of the ArCl 2 Van der Waals complex: Ab initio-based potential energy surfaces, the relative stability of conformers, and the "hidden" microwave spectrumThe structure and ground state dynamics of the atom-diatom dimer interaction between Ar and HI has been investigated by microwave and near infrared supersonic jet spectroscopy. Ab initio molecular orbital calculations were used to provide greater insight into the nature of the interaction. The ground state is shown to be in the isomeric form Ar-IH with R cm ϭ3.9975(1) Å, ϭ149.33(1)°for the normal isotopomer and R cm ϭ3.9483(1) Å, ϭ157.11(1)°for Ar-ID. The potential surface from an ab initio molecular orbital calculation was scaled and shifted to yield a nonlinear least-squares fit of the rovibrational state energies to the experimental data. The ground state potential energy surface obtained in this manner has a barrier between the Ar-IH and Ar-HI isomers of 88.5 cm Ϫ1 with respect to the global minimum. Such calculations are also used to predict the presence of localized states in the secondary minimum associated with isomers Ar-HI and Ar-DI. Attempts to experimentally identify transitions associated with the latter were unsuccessful. The ground state, Ar-IH isomeric structure, contrasts with the corresponding ground state of the other members of the homologous series Ar-HX ͑XϭF, Cl, and Br͒ in which the Ar is bound to the proton.

This article examines long-run relationships and short-run dynamic causal linkages among the five largest emerging African stock markets and the US market, with particular attention to the 1997–1998 global emerging market crisis. In general, interdependence between the African markets and the influence of the US on these markets was limited during 1996–2002. There is evidence that both long-run relationships and short-run causal linkages between these markets were substantially weakened after the crisis.

Supersonic jet investigations of the (HBr)(2) dimer have been carried out using a tunable diode laser spectrometer to provide accurate data for comparison with results from a four-dimensional (4-D) ab initio potential energy surface (PES). The near-infrared nu(1) (+/-), nu(2) (+/-), and (nu(1)+nu(4))(-) bands of (H (79)Br)(2), (H (79)Br-H (81)Br), and (H (81)Br)(2) isotopomers have been recorded in the range 2500-2600 cm(-1) using a CW slit jet expansion with an upgraded near-infrared diode laser spectrometer. The 4-D PES has been calculated for (HBr)(2) using second-order Møller-Plesset perturbation theory with an augmented and polarized 6-311G basis set. The potential is characterized by a global minimum occurring at the H bond structure with the distance between the center of masses (CM) of the monomer being R(CM)=4.10 A with angles theta(A)=10 degrees, theta(B)=100 degrees and a well depth of 692.2 cm(-1), theta(A) is the angle the HBr bond of monomer A makes with the vector from the CM of A to the CM of B, and theta(B) is the corresponding angle monomer B makes with the same CM-CM vector. The barrier for the H interchange occurs at the closed C(2h) structure for which R(CM)=4.07 A, theta(A)=45 degrees, theta(B)=135 degrees, and the barrier height is 73.9 cm(-1). The PES was fitted using a linear-least squares method and the rovibrational energy levels of the complex were calculated by a split pseudospectral method. The spectroscopic data provide accurate molecular parameters for the dimer that are then compared with the results predicted on the basis of the 4-D ab initio PES.

The hydrogen bond OC–HI has been characterized using high resolution microwave and infrared spectroscopies in supersonic seeded molecular jets. Ground state molecular parameters of the 16O12C–HI and 16O13C–HI isotopic species determined by the pulsed-nozzle Fourier transform microwave supersonic jet technique include: for 16O12C–HI, B0 (MHz)=900.9522(1), DJ (kHz)=2.519(1), CN (kHz)=0.94(18), χ(MHz)=−1346.238(13), χJ (kHz)=−8.27(31). The corresponding values for 16O13C–HI are 882.5997(2), 2.404(2), 0.87(19), −1349.481(17), and −7.76(28). This analysis is consistent only with a linear equilibrium dimer structure in which the proton is bound to the carbon atom of carbon monoxide. Other derived dimer parameters include: r(C–I)=4.271(2) Å, αav=24.8°, kσ(N m−1)=1.713. Infrared diode laser investigations provide a band origin frequency ν0 of 2148.549 040(29) cm−1 for the ν2 C≡O stretching fundamental vibration. This corresponds to a blue shift of 5.277 28(37) cm−1 relative to free monomer CO. Excited state molecular constants B2=898.2728(33) MHz. and DJ(2)=2.614(24) kHz are also determined. Line profiles are consistent with an excited state lifetime ≥0.54 ns.