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The low-lying electronic states of Yb isolated in a solid Ar matrix grown at 4.2 K are characterized through absorption and emission spectroscopy. Yb atoms are found to occupy three distinct thermally stable trapping sites labeled "red," "blue," and "violet" according to the relative positions of the absorption features they produce. Classical simulations of the site structure and relative stability broadly reproduced the experimentally observed matrix-induced frequency shifts and thus identified the red, blue, and violet sites as due to respective single substitutional (SS), tetravacancy (TV), and hexavacancy (HV) occupation. Prolonged excitation of the ¹S → ¹P transition was found to transfer the Yb population from HV sites into TV and SS sites. The process showed reversibility in that annealing to 24 K predominantly transferred the TV population back into HV sites. Population kinetics were used to deduce the effective rate parameters for the site transformation processes. Experimental observations indicate that the blue and violet sites lie close in energy, whereas the red one is much less stable. Classical simulations identify the blue site as the most stable one. [ABSTRACT FROM AUTHOR]

Replanting with seedlings or regenerating with coppice in second rotation is a major forestry management regime in short rotation forestry (SRF), but little is known about its effects on understorey vegetation conservation, timber production and economic benefits. To evaluate the effects of second rotation seedlings and coppice regime on the composition, structure and biomass of understorey vegetation, timber production and economic benefits of Eucalyptus plantations, a long-term (14 years) comparative study was conducted using three rotation regimes: (1) the first rotation planted with seedlings (FRs), (2) second rotation replanted with seedlings (SRs) and (3) another second rotation regenerated with coppice (SRc). Both successive rotation regimes significantly decreased the species richness, diversity and evenness of the total understorey vegetation. SRs did not affect the abundance of understorey species but significantly decreased the coverage and biomass of understorey vegetation. SRc significantly increased the abundance of the understorey plant species and maintained the coverage and biomass of the understorey vegetation equivalent to FRs. SRs showed the highest stand volume and net present value, however the highest internal rate of return occurred in SRc due to the reduced establishment and management costs. This suggested regenerating with coppice should be a more suitable successive rotation regime for increasing economic benefits as well as biodiversity conservation in south China. [ABSTRACT FROM AUTHOR]

The distribution of root length density of maize in ridge culture under alternate partial root-zone furrow irrigation (APFI) and conventional furrow irrigation (CFI) was investigated, and two-dimensional models of root length density and root uptake were developed to investigate the water use efficiencies under different furrow irrigation modes. Results indicated that APFI increased root depth and horizontal extended distance of maize, as well as water use efficiency (WUE). Values of the mean absolute error (MAE), the root mean square error (RMSE), and the index of agreement (di) between measured and simulated values of root length density of maize under APFI ranged from 0.26 to 0.68, 0.03 to 1.51, and 0.64 to 0.85 cm m-3, respectively; and the coefficient of determination (R2) was greater than 0.80. Values of MAE, RMSE, and di between measured and simulated values of root length density of maize under CFI ranged from 0.01 to 0.26, 0.01 to 0.60, and 0.61 to 0.96 cm m-3, respectively; and R2 was higher than 0.86. Dynamics of root uptake at different sites were simulated using the model of root water uptake. Root growth of maize under furrow irrigation was modeled using the 2D model of root length density with reasonable accuracy. Compared with CFI, water consumption rate of the maize in APFI was lower in key water requirement period, root uptake rate was higher in the end period, and WUE in APFI was higher by 5% than that in CFI. [ABSTRACT FROM AUTHOR]

Eighty-eight isolates of Fusariunt oxysporum f. sp. niveum, collected from wilted watermelon plants and infested soil in Maryland and Delaware, were characterized by cross pathogenicity to muskmelon, race, and vegetative compatibility. Four isolates (4.5%) were moderately pathogenic to ≥2 of 18 muskmelon cultivars in a greenhouse test, and one representative isolate also was slightly pathogenic in field microplots. The four isolates all were designated as race 2, and were in vegetative compatibility group (VCG) 0082. Of the 74 isolates to which a VCG could be assigned, 41 were in VCG 0080, the VCG distributed most widely; 27 were in VCG 0082, and were distributed in half of the 20 watermelon fields surveyed; and 6 were in the newly described VCG 0083, and were restricted to three fields. Among the isolates in VCG 0080, 8 were designated as race 0, 21 as race 1, and 12 as race 2. Of the isolates in VCG 0082, 6 were designated as race 0, 11 as race 1, and 10 as race 2. All isolates in VCG 0083 were designated as race 2. Isolates from more than one race within the same VCG or isolates from more than one VCG were recovered from single plants and fields. No differences in aggressiveness on differential watermelon cultivars were observed among isolates from different VCGs of the same race. A diverse association between virulence and VCG throughout the Mid-Atlantic region suggests that the pathotypes of E oxysporum f. sp. niveum may be of local origin or at least long existent in the region. [ABSTRACT FROM AUTHOR]