Electron balance during steady‐state production of CH4 and CO2 in anoxic rice soil

In methanogenic rice‐field soil, organic matter (SOM) is anaerobically fermented to acetate, CO₂ and H₂ which then serve as substrates for methanogenesis. The whole process is a disproportionation reaction in which part of the SOM is oxidized to CO₂ and part is reduced to CH₄. We were interested in the electron balance during this process. The rates V_CO2 and V_CH4 at which CO₂ and CH₄ are produced by anaerobic degradation of SOM, and the fraction R_H2 of the CH₄ produced by reduction of CO₂ with H₂ (as opposed to acetotrophic methanogenesis), depend on (i) the presence or absence of inorganic oxidants and (ii) the electron balance ΔZ. Under pseudo steady‐state conditions, where inorganic oxidants are exhausted and the rate of SOM degradation is small compared with the size of the pool, V_CO2, V_CH4 and R_H2 are constrained by ΔZ. Conversely, ΔZ may be determined from V_CO2, V_CH4 and R_H2, all of which may be independently measured. We measured V_CO2 (0.149–0.308 μmol g^?1 day^?1), V_CH4 (0.169–0.466 μmol g^?1 day^?1) and R_H2 (0.19–0.35) in eight soils and obtained values of ΔZ ranging from ?0.918 to 0.035 μmol g^?1 day^?1. The majority (six) were negative, indicating a decrease in the oxidation state of the SOM carbon on degradation. This could be caused by humic acids acting as an electron acceptor and allowing more of the SOM to be oxidized to CO₂ rather than reduced to CH₄. Direct measurement of SOM carbon oxidation state Z produced values around zero (?0.1 ± 0.1), but is too insensitive to reveal changes of the magnitude of ΔZ.     

刈牧后休闲期对草地牧草生产的影响

通过不同间隔时期对多年生黑麦草、白三叶混播草地牧草产量的监测与分析,得出随着休闲期的增加,青绿物质和死亡物质均呈现上升趋势,在较低和较高草地牧草现存量下都会降低牧草生长率。     

贵州足球场草坪建植及化管理模型研究

在一定的生境和管理条件下,以修剪高度、修剪次数和施N、P、K量为因素,利用二次正交回归设计,用模糊综合评分法评定草坪质量,最佳3因子水平为:修剪高度5～7.4cm,修剪次数4～6次/月,施N量为2.5～3.7g/(m2·年),施P、K量各为L25～1.85g/(m2·年),建立了草坪质量与养护3因子间的显著相关回归模型.     

Strong association of de novo copy number mutations with autism

We tested the hypothesis that de novo copy number variation (CNV) is associated with autism spectrum disorders (ASDs). We performed comparative genomic hybridization (CGH) on the genomic DNA of patients and unaffected subjects to detect copy number variants not present in their respective parents. Candidate genomic regions were validated by higher-resolution CGH, paternity testing, cytogenetics, fluorescence in situ hybridization, and microsatellite genotyping. Confirmed de novo CNVs were significantly associated with autism (P = 0.0005). Such CNVs were identified in 12 out of 118 (10%) of patients with sporadic autism, in 2 out of 77 (3%) of patients with an affected first-degree relative, and in 2 out of 196 (1%) of controls. Most de novo CNVs were smaller than microscopic resolution. Affected genomic regions were highly heterogeneous and included mutations of single genes. These findings establish de novo germline mutation as a more significant risk factor for ASD than previously recognized.     

Relative Contributions of Uranium, Thorium, and Potassium to Heat Production in the Earth

Data from a wide variety of igneous rock types show that the ratio of potassium to uranium is approximately 1 X 10(4). This suggests that the value of K/U approximately 1 X 10(4) is characteristic of terrestrial materials and is distinct from the value of 8 X 10(4) found in chondrites. In a model earth with K/U approximately 10(4), uranium and thorium are the dominant sources of radioactive heat at the present time. This will permit the average terrestrial concentrations of uranium and thorium to be 2 to 4.7 times higher than that observed in chondrites. The resulting models of the terrestrial heat production will be considerably different from those for chondritic heat production because of the longer half-life of U(238) and Th(238) compared with K(40).     

Large-scale copy number polymorphism in the human genome

The extent to which large duplications and deletions contribute to human genetic variation and diversity is unknown. Here, we show that large-scale copy number polymorphisms (CNPs) (about 100 kilobases and greater) contribute substantially to genomic variation between normal humans. Representational oligonucleotide microarray analysis of 20 individuals revealed a total of 221 copy number differences representing 76 unique CNPs. On average, individuals differed by 11 CNPs, and the average length of a CNP interval was 465 kilobases. We observed copy number variation of 70 different genes within CNP intervals, including genes involved in neurological function, regulation of cell growth, regulation of metabolism, and several genes known to be associated with disease.     

Parent volatiles in comet 9P/Tempel 1: before and after impact

We quantified eight parent volatiles (H2O, C2H6, HCN, CO, CH3OH, H2CO, C2H2, and CH4) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk.