Shoot nitrate reductase activities of field‐layer species in different forest types. II

Analysis of in vivo shoot nitrate reductase activity (NRA) of the grass Deschampsia flexuosa (L.) Trin. has been proposed as a method of indicating the availability of nitrate in northern temperate forest soils. We report the seasonal variation in NRA and the influence of temperature on the NRA assay. Studies were performed in the field or on natural populations on topsoil monoliths in a greenhouse.

The induced in vivo NRA as measured at 28°C was higher in plants grown at lower than at higher temperatures within the range 4–20°C, although the induction was faster at higher temperatures. When the assay was performed at various temperatures, enzyme activity was much lower at lower temperatures. The accumulation of organic nitrogen in shoots showed that reduction actually increased with temperature. Transfer of monoliths from high to low temperature led to an increase of in vivo NRA within a day, whereas the decline caused by the reverse began after six days. Variations in temperature accounted for between 0 and 80% of the seasonal variation in NRA in the field, depending on the influence of the variability in nitrate supply.

Maximally induced NRA after application of nitrate was mostly higher in a clearfelling than in a closed forest. In the forest, there was a close correlation between current and maximally induced NRA. One interpretation of this result is that low availability of nitrogen may have been a cause of the lower maximally induced NRA there. This is supported by results from other studies.

We conclude that variations in temperature and availability of nitrogen, particularly nitrate, are largely responsible for seasonal variations in NRA. The influence of temperature can be adjusted for.     

Prediction of daily reference evapotranspiration by a multiple regression method based on weather forecast data

Prediction of daily reference evapotranspiration (ET ₀) is the basis of real-time irrigation scheduling. A multiple regression method for ET ₀ prediction based on its seasonal variation pattern and public weather forecast data was presented for application in East China. The forecasted maximum temperature (T _max), minimum temperature (T _min) and weather condition index (WCI) were adopted to calculate the correction coefficient by multilinear regression under five time-division regimes (10 days, monthly, seasonal, semi-annual and annual). The multiple regression method was tested for its feasibility for ET ₀ prediction using forecasted weather data as the input, and the monthly regime was selected as the most suitable. Average absolute error (AAE) and root mean square error (RMSE) were 0.395 and 0.522 mm d^?1, respectively. ET ₀ prediction errors increased linearly with the increase in temperature prediction error. A temperature error within 3 K is likely to result in acceptable ET ₀ predictions, with AAE and average absolute relative error (AARE) <0.142 mm d^?1 and 5.8%, respectively. However, one rank error in WCI results in a much larger error in ET ₀ prediction due to the high sensitivity of the correction coefficient to WCI and the large relative error in WCI caused by one rank deviation. Improving the accuracy of weather forecasts, especially for WCI prediction, is helpful in obtaining better estimations of ET ₀ based on public weather data.     

小麦幼胚愈伤组织辐照后代的遗传变异分析

以３个普通小麦品种为材料，用＾６０Ｃｏγ射线辐照小麦幼胚愈伤组织，在ＭＲ１、ＭＲ２代中才观察到广泛变异，其后代在育性、株高、抽穗期、千粒重、株型、蛋白质含量等方面者发生了明显变异，这些变异较单纯用组织培养得到的无性系的后代的变异频率更大，变异范围也更为广泛，并且从ＭＲ２中得到了几个有较高利用价值的变异株系。     

Random amplified polymorphic DNA markers reveal low genetic variation and a single dominant genotype in Eichhornia crassipes populations throughout China

Genetic variation within and between 34 populations of Eichhornia crassipes (water hyacinth) in China was surveyed using random amplified polymorphic DNA (RAPD) markers. A total of 1009 individuals were analysed, for which 12 RAPD primers amplified 69 reproducible bands, with 22 (32%) being polymorphic. The percentage of polymorphic loci (p) within a population ranged from 4.4% to 17.4%, and the mean Nei's gene diversity (H_e) was 0.046 ± 0.0145, indicating a low genetic diversity of E. crassipes in China. Each population contained at least four RAPD phenotypes (genotypes), and the same particular genotype was invariably dominant in all the populations sampled. The mean proportion of distinguishable genotypes was 0.29. Analysis of molecular variance revealed a large proportion of genetic variation (83.9%) residing within populations and a slightly larger proportion (88.1%) within localities, indicating a low genetic differentiation of E. crassipes populations, both locally and regionally. Human-mediated dispersal, vigorous clonal growth, and a generally low level of sexual reproduction were thought to be responsible for such a pattern of genetic structure.     

Genetic diversity of Pueraria lobata (kudzu) and closely related taxa as revealed by inter-simple sequence repeat analysis

Kudzu (Pueraria lobata) is a noxious weed infesting some areas of the USA. Knowledge of its genetic variation in both native and invasive areas can lead to effective biological control measures. Inter-simple sequence repeat (ISSR) variations were studied in P. lobata and its four closely related congeneric species (P. edulis, P. montana, P. phaseoloides and P. thomsoni). ISSR results allowed a clear separation of these five species. For P. lobata, 108 plants from China and USA were analysed. The samples from the US were genetically closer to Chinese P. lobata populations than to other congeneric populations. High genetic differentiation was found for P. lobata, P. montana and P. thomsoni in Chinese samples. High genetic diversity and low population differentiation was found in P. lobata samples of the US. This supports the hypothesis of multiple introductions into the USA from different sources in Japan or China, followed by subsequent gene exchange and recombination.     

近百年中国北部南温带北界界限的动态变化

<正> 1.前言在研究气候冷暖变化时,气候学家所采用的指标主要有年平均气温、最冷(暖)月平均气温、气温距平、寒冷指数等;在研究农业气候的热量变化时,所采用指标集中在≥0℃或≥10℃积温上。本文则从农业气候的角度出发,采用农业气候带分界的热量指标,来研究近百年我国北部南温带北界界限的动态变化。采用农业气候带分界指标不仅可以反映出气候的冷暖变化,而且有一定的农业意义。     

利用TM图象监测水土流失变化及对策分析

<正> 水土保持作为国土整治的重要内容,已经引起全社会越来越多的重视。然而,不少地方由于人类不合理生产活动的破坏,不仅抵消了水土保持治理效果,而且水土流失进一步加剧。开展水土流失调查和监测,及时掌握水土流失变化情况,对加强水土流失的预防、保护、监督及管理,有效地减少和控制水土流失的发生和发展,贯彻落实水土保持法,具有十分重要的意义。     

关于随机小修费用模型的最优维修策略

采用变分方法考察了具有随机小费用的可修模型的维修策略问题，推导出了依赖年龄的最倨费用界维修策略所满足的微分方程及其边界条件。从而得到了费用界策略形式下的最优。对于包含预防性更换的可修模型也同样得到了费用界－预更换策略形式下的最优解。     

Genetic variation in captive population of chinese alligator, Alligator sinensis, revealed by random amplified polymorphic DNA (RAPD)

Chinese alligator (Alligator sinensis) is an endemic species in China. The likely extinction of it in the wild has been recognised. To prevent this species becoming extinct, the Anhui Research Centre of Chinese Alligator Reproduction (ARCCAR) was established in Xuanzhou, Anhui Province in 1979, where has been established the largest captive population of Chinese alligator (XZSP) in the world. Another farm (CXSP) was established by villagers in Changxin, Zhejiang Province. The results of an investigation of the two captive subpopulation structures by genetic analysis are presented in this paper. We examined the genetic variation in the two captive subpopulations using RAPDs. Thirty-one random primers were selected among 199 random primers screened. A total of 193 reproducible RAPD fragments were scored among 43 individuals, of which 21 (10.88%) were polymorphic. The genetic distances between 43 individuals ranged from 0 to 0.0376 with average of 0.0104±0.0055 S.E. The genetic similarity in CXSP (0.9948±0.0029 S.E.) was higher than that in XZSP (0.9894±0.0055 S.E.). The founder effect is a possible explanation for very low genetic variation in CXSP. Analysis of the RAPD data showed that the mean phenotypic band frequencies of each polymorphic loci was 0.6656±0.3730 S.E. The lowest phenotypic band frequency (0.0233) was found in four of those polymorphic loci. There was no genetic difference between the two subpopulations (D_ij=0.0009). According to the dendrogram and the distribution of polymorphic fragments in two subpopulations, CXSP originated genetically from XZSP. This paper summarises a preliminary research on genetic structure in populations of Chinese alligator. Although there is higher genetic similary (0.9896±0.0055 S.E.) in captive population of A. sinensis, we did not determine whether or not loss of genetic variation had occurred in relation to a wild control population. The data of malformed offspring will be collected carefully, and wild samples be added to set up a control population in future study.     

Genetic characterization of 2 novel feline caliciviruses isolated from cats with idiopathic lower urinary tract disease

Feline caliciviruses (FCVs) are potential etiologic agents in feline idiopathic lower urinary tract disease (I-LUTD). By means of a modified virus isolation method, we examined urine obtained from 28 male and female cats with nonobstructive I-LUTD, 12 male cats with obstructive I-LUTD, and 18 clinically healthy male and female cats. All cats had been routinely vaccinated for FCV. Two FCVs were isolated; I (FCV-U1) from a female cat with nonobstructive I-LUTD, and another (FCV-U2) from a male cat with obstructive I-LUTD. To determine the genetic relationship of FCV-U1 and FCV-U2 to other FCVs. capsid protein gene RNA was reverse transcribed into cDNA, amplified, and sequenced. Multiple amino acid sequence alignments and phylogenetic trees were constructed for the entire capsid protein, hypervariable region E, and the more conserved (nonhypervariable) regions A, B, D, and F. When compared to 23 other FCV isolates with known biotypes, the overall amino acid sequence identity of the capsid protein of FCV-U1 and FCV-U2 ranged from 83 to 96%; identity of hypervariable regions C and E ranged from 58 to 85%. Phylogenetically, FCV-U1 clearly separated from other FCV strains in phenograms based on nonhypervariable regions. In contrast, FCV-U2 consistently segregated with the Urbana strain in all phenograms. Clustering of isolates by geographic origin was most apparent in phenograms based on nonhypervariable regions. No clustering of isolates by biotype was apparent in any phenograms. Our results indicate that FCV-UI and FCV-U2 are genetically distinct from other known vaccine and field strains of FCV.