Microbial nitrogen and phosphorus co-limitation across permafrost region

The status of plant and microbial nutrient limitation have profound impacts on ecosystem carbon cycle in permafrost areas, which store large amounts of carbon and experience pronounced climatic warming. Despite the long-term standing paradigm assumes that cold ecosystems primarily have nitrogen deficiency, large-scale empirical tests of microbial nutrient limitation are lacking. Here we assessed the potential microbial nutrient limitation across the Tibetan alpine permafrost region, using the combination of enzymatic and elemental stoichiometry, genes abundance and fertilization method. In contrast with the traditional view, the four independent approaches congruently detected widespread microbial nitrogen and phosphorus co-limitation in both the surface soil and deep permafrost deposits, with stronger limitation in the topsoil. Further analysis revealed that soil resources stoichiometry and microbial community composition were the two best predictors of the magnitude of microbial nutrient limitation. High ratio of available soil carbon to nutrient and low fungal/bacterial ratio corresponded to strong microbial nutrient limitation. These findings suggest that warming-induced enhancement in soil nutrient availability could stimulate microbial activity, and probably amplify soil carbon losses from permafrost areas.     

江苏海岸带陆生盐土植物矿质元素含量的特点及生物循环

陆生盐土植物在生长过程中吸收积累了大量的Cl和Na;从海向陆随着土壤和植被的生态演替,植物中Cl和Na的浓度逐渐降低;N与Cl、Na有相似的水平分布规律;植物种类是影响元素吸收积累的主要因素。在盐地碱蓬中N、P、K、Ca、Mg、Na、Cl、Mn和Zn的含量均是生长前期较高,随着其生长老化逐渐降低,大穗结缕草、白茅与盐地碱蓬相比,Ca的含量前期低后期高,Na、Mn、Cu和Zn的季节变化不明显。参加盐地碱蓬系统生物循环的元素中,Cl和Na的比例最大,在大穗结缕草和白茅生态系统中比例较小;由于白茅被收割利用,一些元素从此生态系统中流失。     

The use of thidiazuron in tissue culture

Summary Thidiazuron (N-phenyl-N’-1,2,3-thiadiazol-5-ylurea) was first reported to have cytokinin activity in 1982. Since then, thidiazuron has been used successfully in vitro to induce adventitious shoot formation and to promote axillary shoot proliferation. Thidiazuron is especially effective with recalcitrant woody species. Shoot numbers produced on medium containing thidiazuron are equivalent to or greater than numbers initiated on medium with purine-type cytokinins. Low concentrations of thidiazuron (0.0022 to 0.088 mg/liter) are effective for micropropagation. Prolonged exposure to thidiazuron should be avoided, as this may cause hyperhydricity, abnormal shoot morphology, or problems in rooting. Presented in the Session-in-Depth Novel Plant Growth Regulators at the 1992 World Congress on Cell and Tissue Culture, Washington, D.C., June 20–25, 1992.     

Acoustic response properties of single units in the torus semicircularis of the goldfish,Carassius auratus

Single units of the goldfish torus semicircularis (TS) were recorded in response to pure tones. Response areas (RA) were obtained by recording the number of spikes evoked by tones in a range of frequencies and levels within the units' dynamic range. RAs gave estimates of best sensitivity (BS), characteristic frequency (CF), most excitatory frequency at each level (BF), and Q_10dB. Peri-stimulus-time histograms (PSTH), interspike interval histograms (ISIH), and period histograms were obtained at various frequencies and levels to describe the units' temporal response patterns.The distribution of CF is nonuniform with modes at 155, 455, and 855 Hz. The distribution of the coefficient of synchronization to standard tones is also nonuniform, revealing a dichotomy between units with little or no phase-locking and those that phase-lock strongly. PSTHs for units without significant phase-locking vary widely and include patterns resembling those of the mammalian auditory brainstem. Compared with saccular afferents, torus units tend to have lower spontaneous rates, greater sensitivity, and sharper tuning. Unlike saccular afferents, BF is independent of level for most torus units. Some torus units are similar to saccular afferents while others reveal significant transformations of information between the periphery and the midbrain.Abbreviations BF best frequency - BS best sensitivity - CF characteristic frequency - ISIH inter-spike interval histogram - PSTH peri-stimulus-time histogram - RA response area - TS torus semicircularis     

The Relationship Between Phytoplankton Diversity and Ecosystem Functioning Changes with Disturbance Regimes in Tropical Reservoirs

Ecosystems - The relationship between species diversity and ecosystem functioning is one of central topics in modern ecology, but variable and controversial patterns have been found depending on...     

Reduction in animal abundance and oxygen availability during and after the end-Triassic mass extinction

The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η² = 0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η² = 0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.     

Loss of DNA repair mechanisms in cardiac myocytes induce dilated cardiomyopathy

Cardiomyopathy is a progressive disease of the myocardium leading to impaired contractility. Genotoxic cancer therapies are known to be potent drivers of cardiomyopathy, whereas causes of spontaneous disease remain unclear. To test the hypothesis that endogenous genotoxic stress contributes to cardiomyopathy, we deleted the DNA repair gene Ercc1 specifically in striated muscle using a floxed allele of Ercc1 and mice expressing Cre under control of the muscle-specific creatinine kinase (Ckmm) promoter or depleted systemically (Ercc1^−/D mice). Ckmm-Cre^+/−;Ercc1^−/fl mice expired suddenly of heart disease by 7 months of age. As young adults, the hearts of Ckmm-Cre^+/−;Ercc1^−/fl mice were structurally and functionally normal, but by 6-months-of-age, there was significant ventricular dilation, wall thinning, interstitial fibrosis, and systolic dysfunction indicative of dilated cardiomyopathy. Cardiac tissue from the tissue-specific or systemic model showed increased apoptosis and cardiac myocytes from Ckmm-Cre^+/-;Ercc1^−/fl mice were hypersensitive to genotoxins, resulting in apoptosis. p53 levels and target gene expression, including several antioxidants, were increased in cardiac tissue from Ckmm-Cre^+/−;Ercc1^−/fl and Ercc1^−/D mice. Despite this, cardiac tissue from older mutant mice showed evidence of increased oxidative stress. Genetic or pharmacologic inhibition of p53 attenuated apoptosis and improved disease markers. Similarly, overexpression of mitochondrial-targeted catalase improved disease markers. Together, these data support the conclusion that DNA damage produced endogenously can drive cardiac disease and does so mechanistically via chronic activation of p53 and increased oxidative stress, driving cardiac myocyte apoptosis, dilated cardiomyopathy, and sudden death.