Tree type and forest management effects on the structure of stream wood following wildfires

Wildfires are an increasingly common disturbance influencing wood recruitment to streams, and thereby affecting their physical and biological condition. Mediterranean countries such as Portugal, where more than 25% of the land area has burned since 1990, are ideal areas to study impacts of wildfire effects on streams. We evaluated the physical structure of 2206 downed wood pieces (DWP) across 27 first- to third-order streams in central Portugal, all of which had experienced recent wildfires. The streams flowed through monospecific upland forests of Eucalyptus, Maritime pines, or Cork oaks and were fringed by a mixture of riparian tree species. DWP structure differed between tree types and between burned and unburned pieces. Post-fire timber-production forests (Maritime pines and Eucalyptus) contributed a higher quantity of thinner, longer and straighter DWP to streams than Cork oak stands. Pieces from Maritime pines had more rootwads and branches than DWP from the other tree types. Pieces from Cork oak and riparian species generally had a bent form, were shorter and had no rootwads. Burned DWP in streams were often from riparian trees. Relative to unburned DWP, the burned DWP occurred more frequently, were larger and straighter, had branches less often, and were more decayed. With more complex branches, rootwads, and a larger diameter, inputs from burned Maritime pine forests are more likely to change stream hydraulics and habitat complexity, relative to inputs from Eucalyptus forests with their simpler structure. This study shows that, less than a decade after wildfires, structure of downed wood in and near streams is strongly influenced by wildfire, but also still reflects intrinsic species characteristics and respective silviculture practices, even after the effects of fire have been accounted for. Under an anticipated shift in landscape cover with higher shrubland proportions and more mixing of Maritime pine and Eucalyptus forests, our results suggest that instream large wood will become scarcer and more structurally homogeneous.     

Inputs of nitrogen and organic matter govern the composition of fungal communities in soil disturbed by overwintering cattle

Overwintering cattle outdoors causes soil surface disturbance, substantial increases of soil N_tot, C_org, and P and a shift in pH to alkaline levels. Since fungi predominate in unfertilized soils with acidic pH and have filamentous hyphae, we hypothesized that changes caused by overwintering cattle outdoors (trampling, excreta returns, and changes in soil chemistry) will lead to suppressed species richness, lower biomass, and alter the structure of fungal communities. The research was conducted on an upland pasture used more than 10 years for cattle overwintering. Both culture-dependent and -independent methods were used for the determination of either fungal species composition (cultivation; DGGE) or biomass (numbers of CFU; concentration of fungal PLFA marker 18:2ω6,9). Soils under three different levels of cattle disturbance (S - severe, M - moderate, C - no disturbance/control) were investigated during three subsequent years. In addition, the DGGE analysis of soils was completed by comparison with analysis of fresh cattle excrements (Ex). The composition of fungal communities showed significantly higher richness and a substantial shift in species composition in cattle-disturbed soils (S, M) in comparison to the non-disturbed soil (C). The number of separated DGGE bands was significantly higher in S (30.67 ± 1.63; mean ± SD) and M (25.50 ± 1.64) soils than in the C soil (19.33 ± 1.75). Sequencing of typical bands revealed common fungal genera - Alternaria, Penicillium, Fusarium, Rhizopus, Isaria, and Metarhizium. Profiles of the S soil were enriched by bands of rumen-born anaerobic fungi (Neocallimastix, Cyllamyces) occurring mainly in profiles of excrements, where relatively low band richness (14.33 ± 1.15) was observed. The increasing level of cattle disturbance induced an increase in the biomass of complex fungal community over the three-year experimental period from 3.39 ± 2.11 (mean ± SD) nmol of fungal PLFA per gram of the C soil to 5.87 ± 3.16 in the M soil and 9.21 ± 4.69 in the S soil. Concentrations of soil N_tot and C_org were evaluated as the parameters significantly correlating with biomass as well as composition of the fungal community.     

Reversibility of progression of the transformed phenotype in Ad5-transformed rat embryo cells

The carcinogenic process is extremely complex and is affected by diverse environmental and host factors. The mechanism for the gradual development of the transformed phenotype (a process termed "progression") was studied in type 5 adenovirus (Ad5)-transformed rat embryo cells. Progression was not correlated with major changes in the pattern of integration of viral DNA sequences. Instead, it was associated with an increased methylation of integrated viral sequences other than those corresponding to the E1 transforming genes of Ad5. A single exposure of progressed cells to the demethylating agent 5-azacytidine (Aza) resulted in a stable reversion to the unprogressed state of the original parental clone. A further selection of cells after growth in agar allowed the isolation of Aza-treated clones that had regained the progressed phenotype. These observations indicate that progression is a reversible process and suggest that progression may be associated with changes in the state of methylation of one or more specific genes.     

Watching vibrational energy transfer in liquids with atomic spatial resolution

Ultrafast spectroscopy was used to study vibrational energy transfer between vibrational reporter groups on different parts of a molecule in a liquid. When OH stretching vibrations of different alcohols were excited by mid-infrared laser pulses, vibrational energy was observed to move through intervening CH2 or CH groups, taking steps up and down in energy, ending up at terminal CH3 groups. For each additional CH2 group in the path between OH and CH3, the time for vibrational energy transfer increased by about 0.4 picosecond.     

Resource partitioning and sympatric differentiation among closely related bacterioplankton

Identifying ecologically differentiated populations within complex microbial communities remains challenging, yet is critical for interpreting the evolution and ecology of microbes in the wild. Here we describe spatial and temporal resource partitioning among Vibrionaceae strains coexisting in coastal bacterioplankton. A quantitative model (AdaptML) establishes the evolutionary history of ecological differentiation, thus revealing populations specific for seasons and life-styles (combinations of free-living, particle, or zooplankton associations). These ecological population boundaries frequently occur at deep phylogenetic levels (consistent with named species); however, recent and perhaps ongoing adaptive radiation is evident in Vibrio splendidus, which comprises numerous ecologically distinct populations at different levels of phylogenetic differentiation. Thus, environmental specialization may be an important correlate or even trigger of speciation among sympatric microbes.     

基于GIS小麦种质资源对麦长管蚜的抗性分析

[目的]探索和发掘优质抗麦长管蚜的种质资源及方法,为高效节本型和环境友好型的抗麦长管蚜小麦育种研究利用提供理论依据.[方法]以GIS的空间分布分析法和小麦种质资源抗蚜性鉴定为基础,从377份小麦种质资源中随机选取22个种质资源的13个主要性状,运用灰色系统理论对其进行综合分析.[结果]GIS的空间分布分析结果表明,麦长...