植被类型变化对土壤微生物碳利用效率的影响研究进展

植被类型变化强烈影响着土壤碳循环。土壤微生物碳利用效率（CUE）是微生物将从环境中获取的碳分配给自身生长的比例，是土壤碳循环的综合指标。研究植被类型变化对CUE的影响有助于从微生物视角理解该过程中的土壤碳动态，可以为评估植被类型变化对土壤质量及生态系统碳循环的影响提供基础，具有重要的理论及实际价值。通过系统查阅相关文献，综述了植被类型变化导致的CUE变化情况，以及该过程中影响CUE的因子与机制。目前，相关研究主要涉及以林地、草地和农业用地为起点或终点的植被变化类型。天然林（原生林、次生林）变化为人工林、林地变化为草地后CUE普遍下降，随终点植被的发展CUE可能恢复至起点水平。植被成熟度越高，发生转变时CUE变化越剧烈。植被类型变化以农业用地为起点或终点时，CUE变化方向的不确定性及幅度的变异性均增加。植被类型变化导致的CUE变化主要受到植被、土壤、微生物因子及其交互作用的驱动，指示CUE的指标、采样季节和土层也会一定程度上影响CUE的变化。今后相关研究应采用直接的CUE测定方法，拓宽研究气候区及植被变化类型，关注植被变化过程中CUE变化的土层差异及动态监测，深入对植被类型变化导致的生态环境因子变化与CUE的关系及作用机制的研究。     

模拟穿透雨减少对锐齿栎(Quercus aliena var. acuteserrata)树干液流密度的影响

降水格局变化是全球气候变化的重要特征之一,未来气候变化下,较为频繁和严峻的干旱将威胁地球中纬度部分地区的森林,但森林植被如何响应季节性干旱胁迫及其机制尚不清楚。北亚热带-暖温带过渡区分布着以锐齿栎(Quercus aliena var.acuteserrata)为优势树种的落叶阔叶林,研究其水分蒸腾代谢过程对干旱的响应是评估气候变化对过渡区天然落叶阔叶林生态系统水碳影响的关键科学问题。在典型的锐齿栎天然林中通过开展模拟穿透雨减少大型野外实验,采用Granier热扩散式探针技术监测锐齿栎树干液流密度的动态变化,研究了不同径级锐齿栎树干液流密度对模拟干旱的响应规律。结果表明:(1)穿透雨减少对树干液流密度的影响呈现季节变异。在7月份,林内穿透雨减少显著降低了锐齿栎的树干液流密度,但生长季后期的10月份林内穿透雨减少反而使锐齿栎树干液流密度显著升高。(2)不同径级的锐齿栎树干液流密度在生长季内对干旱有不同的响应,特别是小径级的树干液流密度与其他径级有较多的不同。小径级的锐齿栎树干液流密度在5、7月份表现为减雨样地显著小于对照样地,在9、10月份则表现为减雨样地显著大于对照样地。中径级的锐齿栎树干液流密度在5、10月份表现为减雨样地显著大于对照样地,在7月份则表现为减雨样地极显著小于对照样地。大径级的锐齿栎树干液流密度在6、7月份表现为减雨样地显著小于对照样地,在10月份则表现为减雨样地显著大于对照样地。     

Channel-forming properties and structural homology of major outer membrane proteins from Pseudomonas fluorescens MFO and OE 28.3

Abstract The major outer membrane proteins (OprF) from Pseudomonas fluorescens MFO and OE 28.3 were purified by a new method involving native electrophoresis in octyl-polyoxyethylene media. Both proteins, characterized by the same size, heat-modifiability and N-terminal sequence were re-incorporated in virtually solvent-free planar lipid bilayers. They displayed very similar channel-forming properties: the major conductance level was between 250 pS and 270 pS in l M NaCl. From experiments of zero-current potential, both porins were determined weakly cation selective. Amplification by PCR and sequencing of the oprF gene of strain MFO allowed to point out 94% identity between the amino acid sequences of these two OprFs isolated from ecological niches as different as milk (strain MFO) and soil (strain OE 28.3).     

The effects of Bombyx mori silk strain and extraction time on the molecular and biological characteristics of sericin

Sericin was extracted from three strains of Thai Bombyx mori silk cocoons (white shell Chul1/1, greenish shell Chul3/2, and yellow shell Chul4/2) by a high-pressure and high-temperature technique. The characteristics of sericin extracted from different fractions (15, 45, and 60 min extraction process) were compared. No differences in amino acid composition were observed among the three fractions. For all silk strains, sericin extracted from a 15-min process presented the highest molecular weight. The biological potential of the different sericin samples as a bioadditive for 3T3 fibroblast cells was assessed. When comparing sericin extracted from three silk strains, sericin fractions extracted from Chul4/2 improved cell proliferation, while sericin from Chul 1/1 activated Type I collagen production to the highest extent. This study allows the natural variability of sericin obtained from different sources and extraction conditions to be addressed and provides clues for the selection of sericin sources.     

Role of actin-binding proteins in the regulation of cellular mechanics

The viscoelastic parameters of the cell can report on the cell state, cellular processes and diseases. Cell mechanics strongly rely on the properties of the cytoskeleton, an important system of subcellular filaments, especially on the high-level structures that actin forms together with actin-binding proteins (ABPs). In normal cells, components of the cytoskeleton are highly integrated, and their functions are well orchestrated. In contrast, impaired expression and functioning of ABPs lead to the increasing ability of cancer cells to resist chemotherapy and metastasize. ABP-mediated changes in the cytoskeleton architecture can lead to changes in the mechanical properties of the actin network, both locally and at the level of the whole cell. Until now, in cancer-related studies, mechanical data have been used less frequently, compared to biochemical tests or cell migration assays. Here, we will review current methods for analyzing the mechanical properties of cells and provide the available data on the contribution of ABPs in determining cell mechanical properties important for the investigation of cellular functions, particularly in cancers.     

Invertebrate seedbanks: rehydration of soil from an unregulated river floodplain in the south-eastern U.S.

1. We investigated the responsiveness of aquatic invertebrates to rehydration of floodplain soil in a south‐eastern U.S. river floodplain. Non‐inundated soil divots containing invertebrate seedbanks were collected from three floodplain elevations with different inundation histories (inundated for 2, 38, and 78% of a year), and subjected to rehydration (experimental inundation) in aquaria for 10 weeks. 2. Before rehydration, samples were collected to assess the initial density and composition of invertebrates in non‐inundated soil at each elevation. After rehydration, benthic samples were collected biweekly and emergence of aquatic insects was collected weekly from aquaria. 3. The surviving invertebrates were classified as aquatic, semi‐aquatic and terrestrial. Some aquatic invertebrates survived the non‐inundated period in an active state (e.g. Chironomidae and Ceratopogonidae), while others appeared to be dormant (e.g. Heptageniidae, microcrustaceans and Chironomidae). The response for several invertebrates (e.g. Chironominae, Oligochaeta, Collembola and terrestrial invertebrates) depended on the length of rehydration and inundation history. 4. The capacity of aquatic invertebrates to survive and recover was greatest at the most frequently inundated site. Despite variation in floodplain environments, both active and dormant invertebrates persisting in non‐inundated floodplain soil contributed to the floodplain assemblage during flooding. Thus, maintaining the connection between river and floodplain appears to be important in sustaining the invertebrate seedbank and its capacity to recover during inundation. River channelisation and regulation that severs this connection may result in a loss of diversity and abundance.     

The synthesis and characterisation of Rh(III) complexes with pyridyl triazole ligands

A series of Rh(III) mixed ligand polypyridine type complexes have been prepared. Complexes of the form [Rh(L)₂(L^′)]ⁿ⁺, where n=2/3, L=2,2^′-bipyridine (bpy)/1,10-phenanthroline (phen) and L^′=3-(pyridin-2-yl)-1,2,4-triazole (Hpytr), 1-methyl-3-(pyridin-2-yl)-1,2,4-triazole (1M3pytr), 4-methyl-3-(pyridin-2-yl)-1,2,4-triazole (4Mpytr), 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt), 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (NH₂bpt) and 3-(pyridin-2-yl)-5-phenyl-1,2,4-triazole (HPhpytr), have been prepared and their synthesis and characterisation are reported. Crystals of [Rh(bpy)₂(Phpytr)](PF₆)₂ and [Rh(phen)₂(NHbpt)](PF₆)₂ were obtained and their structures determined. Analysis of X-ray crystallographic data showed that coordination of the metal centre in [Rh(phen)₂(NHbpt)](PF₆)₂ occurs via the amine moiety and a nitrogen of the pyridine ring. NMR studies illustrated that coordination to the NH₂bpt ligand was also possible via a nitrogen of the triazole ring and the pyridine ring forming the complex [Rh(phen)₂(NH₂bpt)](PF₆)₃. The absorption and emission properties of the complexes studied were found to be π-π^* in nature and preliminary evidence suggests that all complexes with the exception of [Rh(phen)₂(NHbpt)](PF₆)₂ and [Rh(bpy)₂(NHbpt)](PF₆)₂ are dual emitting at 77 K.     

Unusual rheological properties of a new associative polysaccharide in salt media

New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530 gmol⁻¹) with various amounts from 3% to 15% were prepared. Rheological properties in aqueous solutions of such systems have been investigated as a function of polymer concentration, added salt and temperature in semi-dilute regime. Strong hydrophobic intermolecular associations were clearly demonstrated in pure water whatever the PCL chain length and extend of modification. Increasing polymer concentration, grafting rate and/or PCL chains length can lead to a structured liquid behaviour. Rheological properties of the most organized system have been found independent to the temperature (until 60 °C). In salt media, a strong dependence of hydrophobic interactions to the length of PCL chains was observed. For M_PCL = 1250 g.mol⁻¹ the screening of charges promotes the establishment of intermolecular interactions and leads to a strong physical gel for the highest grafting rates. For M_PCL = 530 g mol⁻¹, ionic strength leads to a decrease of rheological properties when increasing grafting rate. This result may indicate an increase of hydrophobic clusters even in the entangled regime. This unusual behaviour opens the ways for the preparation of suitable hydrogels for drug release.