不同龄阶梭梭根区土壤水分时空变化特征

土壤水是荒漠植被发育最主要的制约因子。不仅影响植物的生长和发育,还限制着植被的种类、数量和分布。梭梭作为北方荒漠区重要的固沙植物,研究梭梭林地土壤水分动态对其植被生存或恢复以及群落稳定性维持具有重要意义。鉴于少有学者研究过不同龄阶梭梭根区的土壤含水率差异,于2014年2月至2014年11月,采用中子仪法和烘干法对0—400 cm沙层土壤含水率进行了原位观测,分析了不同龄阶梭梭根区土壤水分的时空变化规律。结果表明:(1)梭梭根区土壤水分时间变化可分为4个阶段:2月下旬—3月下旬是土壤水分快速补给期,4月上旬—5月下旬是土壤水分均衡期,6月上旬—10月下旬是土壤水分耗损期,11月上旬—次年2月中旬是土壤水分稳定期;(2)梭梭根区0—50 cm土层,受降雨、融雪水入渗补给和蒸发的影响较大,土壤水分变异系数较大且随深度增加迅速减小,50 cm以下土层变异系数较小且随深度变化微小;(3)不同龄阶梭梭根区剖面平均土壤含水率全年与春、夏、秋季均表现为:枯树成熟梭梭中龄梭梭裸地;(4)随距梭梭树干距离的增大(0—5 m范围内),土壤含水率整体呈减小趋势;降雨前后,梭梭根区浅层(0—10 cm)土壤含水率增量大于裸地土壤含水率增量。     

Disappearance of deep profundal zoobenthos in Lake Ikeda, southern Kyushu, Japan, with relation to recent environmental changes in the lake

A benthological survey in a deep caldera, Lake Ikeda, southern Kyushu, Japan, in 1998 revealed that no zoobenthos were found in the deep profundal, although two tubificid oligochaetes, Tubifex tubifex and Limnodrilus hoffmeisteri, and a chironomid, Procladius sp., were distributed in the upper profundal zone. This is the first record of oligochaete composition in the lake. Lake Ikeda had been typically oligotrophic until the 1940s, and zoobenthic assemblages were recorded throughout the profundal bottom in the 1920s and 1970s. Recent disappearance of the deep profundal zoobenthos could be caused by the stagnation of anoxic waters in the hypolimnion, in connection with eutrophication triggered by nutrient loading, as well as change in the thermal circulation system presumably caused by global warming.     

Developmental changes in the expression pattern of the JNK activator kinase MUK/DLK/ZPK and active JNK in the mouse cerebellum

JNK is one of the key molecules regulating cell differentiation and migration in a variety of cell types, including cerebral cortical neurons. MUK/DLK/ZPK belongs to the MAP kinase-kinase-kinase class of protein kinases for the JNK pathway and is expressed predominantly in neural tissue. We have determined the expression pattern of MUK/DLK/ZPK and active JNK in the cerebellum at different stages of postnatal development. Quantitative analysis by Western blotting has showed that high expression levels of MUK/DLK/ZPK and active JNK are maintained during the postnatal development of the cerebellum, and that these levels decrease in the adult cerebellum. Immunohistochemical staining has revealed, however, that their distribution in the developing cerebellum is considerably different. Although active JNK is highly concentrated in the premigratory zone of the external germinal layer (EGL), high expression of MUK/DLK/ZPK has been observed in the molecular layer and in the premigratory zone. Neither the active JNK nor MUK protein has been detected in the proliferative zone of the EGL. These observations suggest that during the postnatal development of the cerebellum, the MUK-JNK signaling pathway contributes to the regulation of granule cell differentiation and migration; further, the activity of MUK/DLK/ZPK is tightly regulated by posttranslational mechanisms and by its expression level.This work was supported by a Ishizu Shun memorial scholarship and grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan.     

Spatial changes in carbon and nitrogen stable isotopes of the plankton food web in a saline lake ecosystem

We investigated spatial changes in the isotope ratios of the plankton food web in Lake Chany, Siberia, Russia, especially at an estuarine transition zone of the lake. The δ¹³C values of particulate organic matter (POM) varied among the sampling sites, and increased with increasing pH of the lake water. This may reflect a shift by phytoplankton from using CO₂ to using bicarbonate for photosynthesis with increasing pH. The δ¹³C values of zooplankton community also changed at each site along with those of the POM. This was indicative of carbon isotope changes of plankton food webs between the stations along an environmental gradient.     

The response of hyporheic invertebrate communities to a large flood in the Hunter River, New South Wales

Previous studies on recovery in hyporheic communities have found that communities rapidly return to pre-disturbance levels. However, most of these studies have concentrated on small floods or ones with short return periods. I studied the impact of a large 1 in 6 year flood on the hyporheic community at 2 sites in the Hunter River, a large coastal river in New South Wales with a mean daily flow of 15 m³ s⁻¹. The flood peaked at 1270 m³ s⁻¹ and afterwards invertebrate densities at the 2 sites were 83 and 67% less than they were before. Recovery to pre-flood densities was slow but was aided by increases in the oligochaete and cyclopoid populations. At Site 1, there was a boom in oligochaete and cyclopoid numbers 61 d after the flood, but the communities resumed their pre-flood densities by Day 139. Recovery at Site 2 took 139 d. Most groundwater taxa (stygobites) living in the hyporheic zone did not recover from the disturbance when compared to non-stygobites. Apart from Microturbellaria and the harpacticoid Parastenocaris sp., numbers of all stygobite taxa continued to decline after the flood, becoming absent after 61 d. The poor recovery of stygobites is probably due to their adaptations for survival in the relatively stable groundwater environment. This study shows that hyporheic communities are sensitive to large bed-moving floods and supports the hypothesis that ecotonal species with a strong affinity to one ecosystem can be poor at recovering from disturbances that occur in an adjacent ecosystem.     

植物器官脱落的机制及其研究进展

对植物器官脱落的机制及研究进展情况进行了综述，其中包括脱落的几种研究方法，脱落时离区的解剖学和细胞学特征，离层细胞的生理生化特征。重点对激素在脱落过程中的调节作用进行了综述     

Temporally regulated expression of Cre recombinase in neural stem cells

The use of mouse gene targeting to study molecules important in neural development is oftentimes impaired by early embryonic lethality. In order to address later roles for such molecules, specifically in neural stem cells, we generated transgenic mice that express both the tetracycline-inducible molecule rtTA-M2 and GFP under the control of the neural precursor specific form of nestin. Developmental analysis of these mice demonstrates that GFP expression is exclusive to the neural tube. Adult expression of GFP is seen only in known areas of adult neurogenesis, namely, the subventricular zone and the dentate gyrus. When crossed with a second transgenic mouse (TetOp-Cre) that expresses the Cre recombinase under the control of the tetracycline responsive promotor, we demonstrate temporal induction of Cre in bigenic animals exposed to doxycycline. We further demonstrate the feasibility of this approach by using the ROSA-26 reporter mouse to mediate recombination in neural precursor cells.     

Fluoro Jade-B Detection of Dying Cells in the SVZ and RMS of Adult Rats After Bilateral Olfactory Bulbectomy

A novel fluorochrome, Fluoro-Jade B, was used to detect dying precursor cells in the subventricular zone (SVZ) and rostral migratory stream (RMS) of adult rats after bilateral olfactory bulbectomy and in control intact rats. The animals in experimental group were left to survive 3 days and from 3 till 16 months after surgical procedure. 1. In the control animals, Fluoro-Jade B positive cells were visible in the SVZ and within the whole extent of the RMS. The number of Fluoro-Jade B positive cells increased in the elbow in comparison to the rest parts of the RMS. 2. In the experimental animals surviving either 3 days or from 3 till 16 months after bilateral olfactory bulbectomy, Fluoro-Jade B positive cells displayed the similar pattern of distribution as in the control animals. However, some quantitative differences in the labeled cells number along the rostral migratory pathway appeared. 3. The average number of degenerating cells within the control SVZ and RMS was 26.24+/- 0.686. In bulbectomized animals, regardless of survival time, an insignificant increase of Fluoro-Jade B positive cells number occurred. We can conclude that dying of precursor cells is a physiological process running within the SVZ/RMS in both control and experimental animals. Moreover, this physiological process is not influenced by survival period after bilateral olfactory bulbectomy. Our results demonstrate Fluoro-Jade B as a useful marker of dying cells.     

Small mammal diversity and dynamics within Nigeria,with emphasis on reservoirs of the lassa virus

Nigeria has a rich small mammal community, with several species implicated as carriers of zoonotic microbes such as the Lassa virus (LASV). We sought to elucidate the diversity and distribution of these animals (including known LASV reservoirs) geographically, habitat-wise and seasonally. Our DNA-assisted survey detected at least 19 small mammal species amongst 790 specimens. Diversity indices were similar between ecological zones and also between endemic and non-endemic areas for Lassa fever. Mastomys natalensis, the most renowned LASV host, was present in eight out of nine localities sampled. We also described the spatial occurrence of other known LASV hosts such as M. erythroleucus and Hylomyscus pamfi, including carriers of LASV-like arenaviruses such as Mus (Nannomys) spp. The most numerous rodents (Mastomys natalensis, M. erythroleucus, and Praomys daltoni) were captured mainly inside human dwellings. Reproductive activity occurred throughout the year, but led to population peaks for M. natalensis in the dry season and for M. erythroleucus and P. daltoni in the rainy season. Extensive geographic distribution of LASV rodent reservoirs, with population peaks in different seasons, shows that the risk of rodent-to-human transmission of LASV is greater than currently realized.     

Reliability of surface EMG matrix in locating the innervation zone of upper trapezius muscle

The identification of the motor unit (MU) innervation zone (IZ) using surface electromyographic (sEMG) signals detected on the skin with a linear array or a matrix of electrodes has been recently proposed in the literature. However, an analysis of the reliability of this procedure and, therefore, of the suitability of the sEMG signals for this purpose has not been reported.The purpose of this work is to describe the intra and inter-rater reliability and the suitability of surface EMG in locating the innervation zone of the upper trapezius muscle.Two operators were trained on electrode matrix positioning and sEMG signal analysis. Ten healthy subjects, instructed to perform a series of isometric contractions of the upper trapezius muscle participated in the study. The two operators collected sEMG signals and then independently estimated the IZ location through visual analysis.Results showed an almost perfect agreement for intra-rater and inter-rater reliability. The constancy of IZ location could be affected by the factors reflecting the population of active MUs and their IZs, including: the contraction intensity, the acquisition period analyzed, the contraction repetition. In almost all cases the IZ location shift due to these factors did not exceed 4 mm. Results generalization to other muscles should be made with caution.