Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.     

基于Translog生产函数的北京市西瓜最优种植规模研究

农业适度规模经营是未来农业的发展方向,本文以规模经济理论为基础,通过建立Translog生产函数模型和DEA包络分析法,最终得出以农户为经营主体的北京市西瓜最优种植规模为6670m2(10亩)。除此之外,研究还发现种植户年龄及文化程度对西瓜种植具有显著影响,但随着农村人口老龄化日趋严峻,培养新型职业农民可以衔接西瓜种植的"断层"。     

Long‐Term Field Drought Affects Leaf Protein Pattern and Chloroplast Ultrastructure of Winter Wheat in a Cultivar‐Specific Manner

Recurrent drought periods of varying duration often cause extensive crop damage and affect wheat production in Southern Europe. This study compares biochemical and ultrastructural responses of four wheat (Triticum aestivum L.) cultivars to long‐term field drought, and their contribution to final grain yield. Gel electrophoresis and immunoblotting analyses combined with transmission electron microscopy and grain yield evaluation were employed to assess drought susceptibility of the wheat cultivars. Two of them behaved as drought‐tolerant, the other two presented as drought sensitive. Enhanced degradation of Rubisco large subunit (RLS), Rubisco small subunit (RSS) and Rubisco activase (RA) accompanied by an increased protease activity and reduced levels of heat shock proteins (HSP70) and dehydrins (DHNs) were associated with drought sensitivity. Drought tolerance coincided with relatively stable or increased HSP70 and DHN contents, and unchanged/higher levels of RLS, RSS and RA. Sensitive cultivars were more vulnerable to ultrastructural damages, showing obvious degradation of chloroplast membrane systems and depletion of leaf starch reserves. These drought responses affected yield potential, as tolerant cultivars gave higher yield under intense drought. Thus, our results provide additional insights into the complexity of plant drought responses, identifying multiple interacting traits that may serve as indirect selection criteria for wheat drought tolerance.     

Biochemical indices (RNA/DNA ratio and protein content) in studying the nutritional status of Ruditapes decussatus (Linnaeus 1758) juveniles

In this work, we investigated the nutritional status of Ruditapes decussatus juveniles under different rearing conditions, using biochemical indices (RNA/DNA ratio and protein content) and the linear instantaneous growth rate (IGR). Two experiments were conducted to study the effect of starvation, addition of substrate (sand) as rearing support and diet composition on somatic growth and biochemical indices. Results show that biochemical indices of fed juveniles were significantly (P<0.05) higher. Highest RNA/DNA values and protein content were recorded in fed juveniles reared with substrate (P<0.05); conversely, lowest values were recorded in starved ones reared without substrate. In the second experiment, the highest RNA/DNA ratio was recorded in juveniles fed with control algal mixture composed of species commonly used in bivalve nurseries [Isochrysis galbana (clone T-Iso), Chaetoceros calcitrans and Tetraselmis suecica] and lowest in those fed with algal species isolated from Tunisian coasts. This confirms the usefulness of the RNA/DNA ratio and protein content in the clam's nutritional status evaluation. This assay is useful to provide information about the nutritional status and health of the clam in field conditions.     

浅谈城市中的高层建筑与节能

叙述了高层建筑节能与气候、地理条件的关系。建筑位置、朝向及接受太阳辐射热能的关系及高层围护结构墙体的保温、隔热存在的问题及今后的发展方向。     

Protein Phosphorylation and Protein Patterns in Developing Endosperms of Barley

The SDS-soluble protein-fractions of barley endosperms (2 and 3 weeks after anthesis) were compared using 1-D SDS-PAGE and 2-D IEF/SDS-PAGE. Similar procedures have been followed after in vivo phosphorylation of isolated endosperm with ³²PO₄.Protein patterns were similar when 1-D SDS-PAGE was used. On the other hand, 2-D IEF/SDS-PAGE revealed several major differences, the most important being the appearance of a major protein of Mr about 40,000 in the 3-weeks old endosperm. By contrast, the patterns of phosphorylated proteins, with both methods, were relatively simple. Only two phosphorylated bands showed up in the 3-weeks old endosperm: a highly labelled band of Mr about 65,000, and a band of about 75,000. In the case of 2-weeks old endosperm, where the phosphorylation was more active, these and several others were also labelled, but the Mr 75,000 band was labelled more intensely.     

马铃薯A病毒(PVA)运动相关蛋白质的研究进展

综述了马铃薯A病毒(PVA)运动相关蛋白的结构、功能方面的研究进展.     

洋葱苯丙氨酸解氨酶基因AcPAL2的克隆与表达分析

利用简并PCR技术和RACE技术克隆得到了一条洋葱的苯丙氨酸解氨酶(PAL)基因全长cDNA序列。该cDNA序列全长2349 bp,编码长685个氨基酸残基的多肽序列,命名为AcPAL2。Blast分析表明该序列与虎眼万年青Galtonia saundersiae、野蕉Musa balbisiana的相似性均较高。Real-time PCR表达及花青素含量分析表明,红皮洋葱该基因表达量最大,而黄皮和白皮洋葱表达量极低;在红皮洋葱中该基因在膨大初期大量表达,并迅速降低至一定程度后趋于相对平稳表达,且与花青素的积累过程相一致。     

Progress of ELMO family on malignant tumor invasion and metastasis

It is one of the main characters of malignant tumors that malignant tumor cells invade surrounding tissues and metastasize to distant tissues. Multiple factors are involved in this complicated dynamic process. Metastasis is the major factor influencing recurrence and prognosis. Therefore, it is important to explore the mechanism of invasion and metastasis for reducing recurrence rate and mortality of malignant tumors. Engulfment and cell mobility (ELMO) family is one kind of conserved protein in evolutional process. It includes 3 members, ELMO1, ELMO2 and ELMO3. The members of ELMO family play an important role in cell phagocytosis and cell migration, and they also have close correlation with malignant tumor cell invasion and metastasis. In this paper, we review the progress of the relationship between ELMO family and malignant tumor invasion and metastasis.