1953-2011年小兴安岭森林火灾含碳气体排放的估算

根据1953-2011年小兴安岭森林调查数据和森林火灾统计资料,结合野外火烧迹地调查与室内控制试验数据,估算了小兴安岭1953-2011年森林火灾的碳排放量和含碳气体排放量.结果表明: 1953-2011年小兴安岭森林火灾的总碳排放量为1.12×10⁷ t,年均排放量为1.90×10⁵ t,约占全国年均森林火灾碳排放量的1.7%;其中,含碳气体CO₂、CO、CH₄和非甲烷烃(NMHC)的排放量分别为3.39×10⁷、1.94×10₅、1.09×10⁵和7.46×10⁴ t,相应年均排放量5.74×10⁵、3.29×10⁴、1.85×10³、1.27×10³ t分别占全国年均森林火灾含碳气体排放量的1.4%、1.2%、1.7%和1.1%.不同林型的燃烧效率和单位过火面积的碳排放量均为针叶林＞阔叶林＞针阔混交林.最后提出了合理的林火管理措施.     

Ionizing radiation-inducible miR-494 promotes glioma cell invasion through EGFR stabilization by targeting p190B RhoGAP

MicroRNAs (miRNAs) play an important role in various stages of tumor progression. miR-494, which we had previously identified as a miRNA induced by ionizing radiation (IR) in the glioma cell line U-251, was observed to enhance invasion of U-251 cells by activating MMP-2. The miR-494-induced invasive potential was accompanied by, and dependent on, epidermal growth factor receptor (EGFR) upregulation and the activation of its downstream signaling constituents, Akt and ERK. The upregulation of EGFR by miR-494 involved the suppression of lysosomal protein turnover. Among the putative target proteins tested, p190B RhoGAP (p190B) was downregulated by miR-494, and its reduced expression was responsible for the increase in EGFR expression. A reporter assay using a luciferase construct containing p190B 3′-untranslated region (3′UTR) confirmed that p190B is a direct target of miR-494. Downregulation of p190B by small interfering RNA (siRNA) transfection closely mimicked the outcomes of miR-494 transfection, and showed increased EGFR expression, MMP-2 secretion, and invasion. Ectopic expression of p190B suppressed the miR-494-induced EGFR upregulation and invasion promotion, thereby suggesting that p190B depletion is critical for the invasion-promoting action of miR-494. Collectively, our results suggest a novel function for miR-494 and its potential application as a target to control invasiveness in cancer therapy.     

胎儿肝脏中一种抑制HL—60细胞生长的因子初步研究

胎儿肝脏中存在着两类抑制HL-60细胞生长的抑制物,一类是精氨酸酶,它是一类非特异性的细胞毒剂,在我们的实验条件下,不仅对HL-60细胞,而且对正常人骨髓CFU-GM也具有相似的抑制细胞生长的毒性作用。此外,还存在着一类较小分子的抑制物,它对HL-60细胞生长的抑制作用明显高于对人骨髓CFU-GM的作用,因此,在一定程度上,这是一类对HL-60细胞生长具有选择性作用的抑制物。     

Suppression of soil-borne plant diseases with composts: A review

Numerous container-based studies in greenhouses or growth rooms have consistently demonstrated a suppressive effect of composts on soil-borne diseases such as damping-off and root rots (Pythium ultimum, Rhizoctonia solani, Phytophthora spp.), and wilts (Fusarium oxysporum and Verticillium dahliae). Composts have also been shown to suppress several diseases in the field, although the effects have been generally smaller and more variable than in container experiments. Several diseases of turf grass were suppressed by top-dressing with compost. These diseases are Fusarium patch (Microdochium nivale), red thread (Laetisaria fuciformis), damping-off (Pythium graminicola), brown patch (Rhizoctonia solani), dollar spot (Sclerotinia homoeocarpa) and snow mould (Typhula ishikariensis). The disease suppressive effect of compost generally increased with rate of application. Compost inclusion rates of at least 20% (v/v) were normally required to consistently obtain a disease suppressive effect, particularly in peat-based media, but significant disease suppression has been found at lower inclusion rates in soil. Reported levels of disease suppression were variable, even using apparently similar composted materials at the same rates. Sterilisation of composted materials generally resulted in a loss in disease suppressiveness, indicating that the mechanism was often or predominantly biological, although chemical and physical factors have also been implicated. The mechanisms and antagonistic micro-organisms involved in disease suppression are not fully understood. Physiological profiling and the use of DNA-based techniques such as denaturing gradient gel electrophoresis (DGGE) may lead to an improved understanding of the changes in microbial communities associated with disease control resulting from compost amendment of soil, sand or peat. The inoculation of composts with biological control agents may improve the efficacy and reliability of disease control obtained.     

Cross‐scale controls on carbon emissions from boreal forest megafires

Climate warming and drying is associated with increased wildfire disturbance and the emergence of megafires in North American boreal forests. Changes to the fire regime are expected to strongly increase combustion emissions of carbon (C) which could alter regional C balance and positively feedback to climate warming. In order to accurately estimate C emissions and thereby better predict future climate feedbacks, there is a need to understand the major sources of heterogeneity that impact C emissions at different scales. Here, we examined 211 field plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories (NWT), Canada after an unprecedentedly large area burned in 2014. We assessed both aboveground and soil organic layer (SOL) combustion, with the goal of determining the major drivers in total C emissions, as well as to develop a high spatial resolution model to scale emissions in a relatively understudied region of the boreal forest. On average, 3.35 kg C m^?2 was combusted and almost 90% of this was from SOL combustion. Our results indicate that black spruce stands located at landscape positions with intermediate drainage contribute the most to C emissions. Indices associated with fire weather and date of burn did not impact emissions, which we attribute to the extreme fire weather over a short period of time. Using these results, we estimated a total of 94.3 Tg C emitted from 2.85 Mha of burned area across the entire 2014 NWT fire complex, which offsets almost 50% of mean annual net ecosystem production in terrestrial ecosystems of Canada. Our study also highlights the need for fine‐scale estimates of burned area that represent small water bodies and regionally specific calibrations of combustion that account for spatial heterogeneity in order to accurately model emissions at the continental scale.     

Temperature thresholds of physically dormant seeds and plant functional response to fire: variation among species and relative impact of climate change

Variation in dormancy thresholds among species is rarely studied but may provide a basis to better understand the mechanisms controlling population persistence. Incorporating dormancy‐breaking temperature thresholds into existing trait frameworks could improve predictions regarding seed bank persistence, and subsequently species resilience in response to fire, climate change and anthropogenic management. A key ecological strategy for many species from fire‐prone ecosystems is the possession of a long‐lived seed bank, ensuring recovery after fire. Physical dormancy is dominant in these ecosystems and maintaining this dormancy is directly linked to seed bank persistence. We identified a suite of seed‐related factors relevant to maintaining populations in fire‐prone regions for 14 co‐occurring physically dormant species. We measured variation in initial levels of dormancy and then applied experimental heating treatments, based on current seasonal temperatures and those occurring during fires, to seeds of all study species. Additionally, higher seasonal temperature treatments were applied to assess response of seeds to temperatures projected under future climate scenarios. Levels of germination response and mortality were determined to assess how tightly germination response was bound to either fire or seasonal cues. Six species were found to have dormancy cues bound to temperatures that only occur during fires (80°C and above) and were grouped as having obligate pyrogenic dormancy release. The remaining species, classified as having facultative pyrogenic dormancy, had lower temperature dormancy thresholds and committed at least 30% of seeds to germinate after summer‐temperature treatments. Evidence from this study supports including dormancy‐breaking temperature thresholds as an attribute for identifying functional types. High temperature thresholds for breaking dormancy, found in our obligate pyrogenic group, appear to be a fire‐adapted trait, while we predict that species in the facultative group are most at risk to increased seed bank decay resulting from elevated soil temperatures under projected climate change.     

Synergistic effect of amino acids on production of lymphocyte proliferation-suppressing substances by rat intestinal epithelial cells

Conditioned culture medium of rat small intestinal epithelial cells suppressed proliferation of spleen lymphocytes stimulated with concanavalin A (approx. 10% of its control [³H]thymidine incorporation) whereas conditioned phosphate-buffered saline of the epithelial cells did not. On the other hand, conditioned saline of the epithelial cells exposed to a mixture of total 22 amino acids at their concentrations in the culture medium suppressed the proliferation (approx. 45% of its control [³H]thymidine incorporation). Neither conditioned saline of the epithelial cells exposed to other medium components nor lysates of freshly harvested epithelial cells suppressed the proliferation. Thus, amino acids synergistically stimulated intestinal epithelial cells to produce substances with the ability to suppress lymphocyte proliferation.     

Identification of symbiosis-regulated genes in Eucalyptus globulus-Pisolithus tinctorius ectomycorrhiza by differential hybridization of arrayed cDNAs

Ectomycorrhiza development alters gene expression in the fungal and plant symbionts. The identification of a large number of genes expressed exclusively or predominantly in the symbiosis will contribute greatly to the understanding of the development of the ectomycorrhizal symbiosis. We have constructed a cDNA library of 4-day-old Eucalyptus globulus-Pisolithus tinctorius ectomycorrhiza and sequenced 850 cDNAs cloned randomly or obtained through suppression subtractive hybridization (SSH). Based on the absence of a database match, 43% of the ectomycorrhiza ESTs are coding for novel genes. At the developmental stage analysed (fungal sheath formation), the majority of the identified sequences represented 'housekeeping' proteins, i.e. proteins involved in gene/protein expression, cell-wall proteins, metabolic enzymes, and components of signalling systems. We screened arrayed cDNAs to identify symbiosis-regulated genes by using differential hybridization. Comparisons of signals from free-living partners and symbiotic tissues revealed significant differences in expression levels (differential expression ratio >2.5) for 17% of the genes analysed. No ectomycorrhiza-specific gene was detected. The results successfully demonstrate the use of the cDNA array and SSH systems as general approaches for dissecting symbiosis development, and provide the first global picture of the cellular functions operating in ectomycorrhiza.     

Introduced annual grass increases regional fire activity across the arid western USA (1980–2009)

Non‐native, invasive grasses have been linked to altered grass‐fire cycles worldwide. Although a few studies have quantified resulting changes in fire activity at local scales, and many have speculated about larger scales, regional alterations to fire regimes remain poorly documented. We assessed the influence of large‐scale Bromus tectorum (hereafter cheatgrass) invasion on fire size, duration, spread rate, and interannual variability in comparison to other prominent land cover classes across the Great Basin, USA. We compared regional land cover maps to burned area measured using the Moderate Resolution Imaging Spectroradiometer (MODIS) for 2000–2009 and to fire extents recorded by the USGS registry of fires from 1980 to 2009. Cheatgrass dominates at least 6% of the central Great Basin (650 000 km²). MODIS records show that 13% of these cheatgrass‐dominated lands burned, resulting in a fire return interval of 78 years for any given location within cheatgrass. This proportion was more than double the amount burned across all other vegetation types (range: 0.5–6% burned). During the 1990s, this difference was even more extreme, with cheatgrass burning nearly four times more frequently than any native vegetation type (16% of cheatgrass burned compared to 1–5% of native vegetation). Cheatgrass was also disproportionately represented in the largest fires, comprising 24% of the land area of the 50 largest fires recorded by MODIS during the 2000s. Furthermore, multi‐date fires that burned across multiple vegetation types were significantly more likely to have started in cheatgrass. Finally, cheatgrass fires showed a strong interannual response to wet years, a trend only weakly observed in native vegetation types. These results demonstrate that cheatgrass invasion has substantially altered the regional fire regime. Although this result has been suspected by managers for decades, this study is the first to document recent cheatgrass‐driven fire regimes at a regional scale.     

综述: 病毒致瘤蛋白对肿瘤微环境的改造

致瘤病毒感染宿主后,相关的病毒蛋白通过“劫持”宿主细胞的生命机器,经历多阶段和涉及多因子的一系列复杂的转化和演变,最终导致细胞的癌变．在这一过程中,病毒因素始终与感染细胞微环境发生互作(包括细胞成分如免疫细胞、成纤维细胞等,以及非细胞成分如细胞因子等),从而促进感染细胞的免疫逃逸和肿瘤细胞的发生发展．本文以HPV、EBV、HBV为例,综述病毒蛋白影响肿瘤微环境的具体机制和最新研究进展,分析该领域面临的问题和前景．