利用APSIM模型分析不同播期和耕作方式对旱地小麦籽粒干物质积累的影响

黄土丘陵区旱地小麦籽粒干物质积累的准确模拟可为调控小麦生产提供重要的技术支持。本研究利用甘肃省定西市安定区1971—2017年的气象资料和甘肃省定西市安定区凤翔镇安家沟村2016—2017年的大田试验数据,基于APSIM模型对旱地小麦籽粒干物质积累与分配进行模拟,并在模型验证的基础上,定量分析了播期和耕作方式对小麦籽粒干物质积累的影响。结果表明: 3个播期(早播、正常播、晚播)和4种耕作方式(传统耕作、传统耕作+覆盖、免耕、免耕+覆盖)下,籽粒干物质模拟值与实测值间的均方根误差(RMSE)为57.5～143.1 kg·hm^-2,归一化均方根误差(NRMSE)为1.4%～9.9%,模型模拟精度较高。不同播期下,耕作方式对籽粒干物质积累的促进效果排序均表现为: 免耕+覆盖>传统耕作+覆盖>免耕>传统耕作,免耕+覆盖最有利于小麦籽粒干物质积累,而免耕与传统耕作差异不显著。不同耕作方式下,小麦干物质积累过程均表现为早播好于正常播和晚播,晚播对干物质积累的影响较大,积累过程最不理想。     

基于地理加权回归拓展模型的天然次生林碳储量空间分布

为精准获取区域尺度天然次生林的碳储量及其空间分布格局,以吉林省汪清林业局浪溪林场的天然次生林为研究对象,基于165块局级固定样地,以林分因子、地形因子和土壤因子为影响因子,将普通地理加权回归模型(GWR)作为基础,从空间维度、参数异质性特征和残差空间自相关性3个方面进行改进,构建7类拓展模型,即地理海拔加权回归模型(G...     

Joint distribution of first exit times of a two dimensional Wiener process with jumps with application to a pair of coupled neurons

Motivated by a neuronal modeling problem, a bivariate Wiener process with two independent components is considered. Each component evolves independently until one of them reaches a threshold value. If the first component crosses the threshold value, it is reset while the dynamics of the other component remains unchanged. But, if this happens to the second component, the first one has a jump of constant amplitude; the second component is then reset to its starting value and its evolution restarts. Both processes evolve once again until one of them reaches again its boundary. In this work, the coupling of the first exit times of the two connected processes is studied.     

A new fast algorithm for solving the minimum spanning tree problem based on DNA molecules computation

The minimum spanning tree (MST) problem is to find minimum edge connected subsets containing all the vertex of a given undirected graph. It is a vitally important NP-complete problem in graph theory and applied mathematics, having numerous real life applications. Moreover in previous studies, DNA molecular operations usually were used to solve NP-complete head-to-tail path search problems, rarely for NP-hard problems with multi-lateral path solutions result, such as the minimum spanning tree problem. In this paper, we present a new fast DNA algorithm for solving the MST problem using DNA molecular operations. For an undirected graph with n vertex and m edges, we reasonably design flexible length DNA strands representing the vertex and edges, take appropriate steps and get the solutions of the MST problem in proper length range and O(3m + n) time complexity. We extend the application of DNA molecular operations and simultaneity simplify the complexity of the computation. Results of computer simulative experiments show that the proposed method updates some of the best known values with very short time and that the proposed method provides a better performance with solution accuracy over existing algorithms.     

Comparing methods for metabolic network analysis and an application to metabolic engineering

Bioinformatics tools have facilitated the reconstruction and analysis of cellular metabolism of various organisms based on information encoded in their genomes. Characterization of cellular metabolism is useful to understand the phenotypic capabilities of these organisms. It has been done quantitatively through the analysis of pathway operations. There are several in silico approaches for analyzing metabolic networks, including structural and stoichiometric analysis, metabolic flux analysis, metabolic control analysis, and several kinetic modeling based analyses. They can serve as a virtual laboratory to give insights into basic principles of cellular functions. This article summarizes the progress and advances in software and algorithm development for metabolic network analysis, along with their applications relevant to cellular physiology, and metabolic engineering with an emphasis on microbial strain optimization. Moreover, it provides a detailed comparative analysis of existing approaches under different categories.     

Dehydration mediated microRNA response in the African clawed frog Xenopus laevis

Exposure to various environmental stresses induces metabolic rate depression in many animal species, an adaptation that conserves energy until the environment is again conducive to normal life. The African clawed frog, Xenopus laevis, is periodically subjected to arid summers in South Africa, and utilizes entry into the hypometabolic state of estivation as a mechanism of long term survival. During estivation, frogs must typically deal with substantial dehydration as their ponds dry out and X. laevis can endure > 30% loss of its body water. We hypothesize that microRNAs play a vital role in establishing a reversible hypometabolic state and responding to dehydration stress that is associated with amphibian estivation. The present study analyzes the effects of whole body dehydration on microRNA expression in three tissues of X. laevis. Compared to controls, levels of miR-1, miR-125b, and miR-16-1 decreased to 37 ± 6, 64 ± 8, and 80 ± 4% of control levels during dehydration in liver. By contrast, miR-210, miR-34a and miR-21 were significantly elevated by 3.05 ± 0.45, 2.11 ± 0.08, and 1.36 ± 0.05-fold, respectively, in the liver. In kidney tissue, miR-29b, miR-21, and miR-203 were elevated by 1.40 ± 0.09, 1.31 ± 0.05, and 2.17 ± 0.31-fold, respectively, in response to dehydration whereas miR-203 and miR-34a were elevated in ventral skin by 1.35 ± 0.05 and 1.74 ± 0.12-fold, respectively. Bioinformatic analysis of the differentially expressed microRNAs suggests that these are mainly involved in two processes: (1) expression of solute carrier proteins, and (2) regulation of mitogen-activated protein kinase signaling. This study is the first report that shows a tissue specific mode of microRNA expression during amphibian dehydration, providing evidence for microRNAs as crucial regulators of metabolic depression.     

Neurologically normal development of a patient with severe methionine adenosyltransferase I/III deficiency after continuing dietary methionine restriction

Background

There is not much information on established standard therapy for patients with severe methionine adenosyltransferase (MAT) I/III deficiency.

Case presentation

We report a boy with MAT I/III deficiency, in whom plasma methionine and total homocysteine, and urinary homocystine were elevated. Molecular genetic studies showed him to have novel compound heterozygous mutations of the MAT1A gene: c.191T>A (p.M64K) and c.589delC (p.P197LfsX26). A low methionine milk diet was started at 31 days of age, and during continuing dietary methionine restriction plasma methionine levels have been maintained at less than 750 μmol/L. He is now 5 years old, and has had entirely normal physical growth and psychomotor development.

Conclusions

Although some severely MAT I/III deficient patients have developed neurologic abnormalities, we report here the case of a boy who has remained neurologically and otherwise normal for 5 years during methionine restriction, suggesting that perhaps such management, started in early infancy, may help prevent neurological complications.     

基于logistic模型的中国自然保护区增长动态分析

中国自然保护区建设已由数量扩张型进入质量效益型的新阶段,运用自然保护区统计年鉴数据,基于logistic模型,借助R语言,对自然保护区发展上限进行了估算。同时,运用高等数据曲线曲率求导方法,对发展阶段进行划分,对持续时长和增长速度进行了测算。结果表明:①面积理论饱和值为15470.00万hm²;②将自然保护区发展历程分为缓慢起步期(1956—1989年)、快速发展期(1990—2008年)和稳定完善期(2009—至今);③目前则处于稳定完善期,面积已渐近饱和值,数量仍在小幅度增加。希望本研究结果能为自然保护区主管部门制定管理政策、规划以及整合组建以国家公园为主体的自然保护地体系提供参考。     

Reynoutria niche modelling and protected area prioritization for restoration and protection from invasion: A Southeastern Europe case study

An important step in managing invasive species is determining the factors responsible for their current and potential distribution, especially when species distribution is climatically determined like in Reynoutria taxa case. The main aim of this paper was to integrate all available distribution data of the Reynoutria taxa in SE Europe and to predict in which habitats and along which corridors its future spread can be expected. Distribution data of the Reynoutria taxa were obtained from extensive field studies in the period from 2006 to 2016, as well as from the literature and herbarium sources. A total of 4081 localities in Serbia and the Kosovo region, Montenegro, Slovenia, Croatia, Bosnia and Herzegovina, Bulgaria and Romania have been recorded, most frequently in riparian and human-made habitats. Ecologically suitable ranges for the Reynoutria taxa were predicted using the MaxEnt program and 19 bioclimatic variables which were derived from the WorldClim data set. Results of this study showed that the most frequent Reynoutria taxa in SE Europe are R. japonica var. japonica and hybrid R. × bohemica. The most suitable geographical areas for R. japonica and R. sachalinensis are mostly located in the north, while for R. × bohemica the central part of SE Europe is suitable. The precipitation of the warmest quarter had a high influence on the potential distribution modelling of these closely related species. Potential distribution modelling revealed R. × bohemica’s high temperature tolerance in different seasons with high durability of drought (up to 60 mm per year less precipitation than parental species). Moreover, this research predicts which areas are most likely to be invaded, and makes suggestions where to focus management efforts for survey and removal of these invaders, especially in protected areas. According to the future climate analysis R. japonica and R. × bohemica could expand their range in riparian habitats up to 30–40%. Consequently, invasion in Slovenia’s and Croatia’s rivers requires urgent preventative measures. This study provides empirical evidence that these plants could become widespread throughout SE Europe within 25 years under the current trend and emphasizes that regionally specific management plans should be implemented to prevent further spread of these taxa.