南极半岛海洋气候区的土壤Ⅴ.气候变化响应

气候变化导致南极海洋气候区冰川消退、多年积雪融化,为新的土壤形成与分布提供了潜在的母质基础与发展空间;地表和土壤内部水分活动在时间和空间上的加强促进了以自由水为基础的土壤过程和冰缘地貌过程;由气候变化引发的低等植物生境、群落结构变化、初级生产力与生物量的提高、海洋脊椎动物迁徙和栖息地的变迁,影响了本区土壤有机质积累过程以及土壤有机质结构与性状。已有的证据表明,气候变化正对南极海洋气候区土壤发生、发育及演变产生重要影响。     

Analysis of Genebank Evaluation Data by using Geostatistical Methods

Genebanks often characterize accessions based on evaluation trials. This paper evaluates geostatistical methods as a tool to increase the utility of evaluation data. These methods were selected to overcome limitations resulting from a relative lack of replication and the scarcity of standards or check varieties. The data employed in the present study comprise nine characteristics of spring and winter barley, evaluated mostly as ratings. Ratings with quasi-metric scales were transformed by using the folded exponential transformation. To estimate the genetic component of the total effect, we compared two methods: Method 1 whereby a variogram is fitted by non-linear regression, and subsequently the implied spatial correlation is embedded into a mixed model analysis, which estimates the genetic effect by Best Linear Unbiased Prediction (BLUP); and Method 2 where each data value is re-estimated by kriging to correct for spatial effects and then the corrected data are submitted to a mixed model analysis. For practical application we propose Method 1 (though occasionally we met convergence problems): Fit the short range of the empirical variogram, visually choose the suitable covariance model. Use this and the initial values from non-linear regression fit with the mixed model, fixing the spatial parts at their starting values from non-linear regression, and estimate genetic effects by BLUP by using the fitted mixed model. To improve performance, we recommend that more standard or check varieties be used and, wherever possible, replace rating scales with metric scales or free-percentage scales (without categories).     

The Solar Acoustic Spectrum and Eigenmode Parameters

The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10(-5). For a 3-year data set, the fractional error is expected to be 3 x 10(-6). The GONG m-averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.     

山萸果几种物理机械特性的测定及其应用

从实用设计出发,对山萸果的千粒重、容重、尺寸、挤压破坏和摩擦等物理机械特性进行了测定。这些特性均随环境因素而变化。文中用曲线表示了它们的变化规律。从而为去核方案的决定、机械参数和运动参数的选择、零部件结构设计提供了较为合理、准确的数据。可望对其他类似物料的物理机械特性的描述有所帮助。以便寻求方便、实用的参数表达方法和启发对加工方案的新思维。     

A Hitchhiker's Guide to Mixed Models for Randomized Experiments

Designed experiments conducted by crop scientists often give rise to several random sources of variation. Pertinent examples are split‐plot designs, series of experiments and repeated measurements taken on the same field plot. Data arising from such experiments may be conveniently analysed by mixed models. While the mixed model framework is by now very well developed theoretically, and good software is readily available, the technology is still under‐utilized. The purpose of the present paper is, therefore, to encourage more widespread use of mixed models. We outline basic principles, which help in setting up mixed models appropriate in a given situation, the main task required from users of mixed model software. Several examples are considered to demonstrate key issues. The theoretical underpinnings are briefly sketched in so far as they are practically relevant for making informed use of mixed‐model computer packages. Finally, a brief review is given of some recent methodological developments, which are of interest to the plant sciences. A German version of this paper is available from the corresponding author upon request.     

Trends in genetic variance components during 30 years of hybrid maize breeding at the University of Hohenheim

The ratio of variance due to specific vs. general combining ability (GCA) (σ²_SCA:σ²_GCA) is of central importance for predicting hybrid performance from GCA effects. The objectives of our study were to (1) analyse the changes in estimates of σ²_GCA, σ²_SCA and their ratio during 30 years of hybrid maize breeding and (2) compare the observed trends in genetic variances with those expected under a simple genetic model. We analysed multilocation yield trials based on the North Carolina Design II conducted in the maize breeding programme of the University of Hohenheim from 1975 to 2004 for grain yield (GY) and dry matter content (DMC). GY showed a significant (P < 0.05) annual increase of 0.17 Mg/ha, but no linear trend was found for DMC. Since the beginning of hybrid breeding at the University of Hohenheim, the sum of estimates of σ²_GCA of the flint and dent heterotic groups were higher than the estimates of their σ²_SCA. This predominance did not change with ongoing inter‐population improvement. Consequently, superior hybrids can be identified and selected mainly based on their prediction from GCA effects.     

Quantitative trait loci mapping for biomass yield traits in a Lolium inbred line derived F2 population

Lolium perenne L. (perennial ryegrass) is the principle forage grass species in temperate agriculture. Improving biomass yield still remains one of the most important aims of current forage breeding programmes. A quantitative trait locus (QTL) study investigating biomass yield traits in perennial ryegrass was carried out in greenhouse and field environments. The study is based on an F₂ population consisting of 360 individuals derived from two inbred grandparents where the F₁ has a large biomass yield phenotype. For both experimental environments co-localized QTL for biomass yield traits including fresh and dry weight and dry matter were identified on linkage groups 2, 3 and 7. A major QTL for fresh and dry weight was identified on LG 3 which explained around 30% of the phenotypic variance in the field experiment. The findings of this study are discussed with regard for their potential in research and breeding.     

Genetic and economic evaluation of a basic breeding programme for Kenya Boran cattle

The objective of this study is to describe the present organisational structure of Boran cattle breeding and develop a model breeding programme using a deterministic approach under the current structure of the Boran Cattle Breeders Society. A breeding unit of 13,000 cows supplying bulls to a commercial population of 39,000 cows was assumed. Selection criteria used were growth and reproduction traits while breeding objective traits targeted were growth, carcass, reproduction, survival, milk yield and feed intake traits. Higher selection intensity was possible for breeding sires resulting in higher genetic gains compared to dams even though selection accuracies were generally low. Annual genetic gains were positive except for dressing percentage, cow survival rate, and age at first calving. However, a reduction of age at first calving by 9.5 days obtained a return of Ksh 49.76. The overall monetary genetic gain obtained was Ksh 84.89 with a profit per cow per year of Ksh 377.98. The basic breeding programme could be expanded to accommodate a larger population of Boran cattle. The implications of the results are also discussed.     

The Effect of Preceding Crop and Pre-Sprouting on Crop Growth, N Use and Tuber Yield of Maincrop Potatoes for Processing Under Conditions of N Stress

Factorial field trials were carried out on an experimental farm near Kassel, Germany, in two consecutive seasons (2003 and 2004) in order to examine the impact of leguminous and cereal preceding crops (i) on soil N availability under subsequent potatoes and (ii) the effect of preceding crop and pre‐sprouting of seed tubers on crop development, N uptake, N utilization efficiency and total and size‐graded tuber yields relevant for processing into either crisps or French fries. In addition, an approach to analyse complex field experiments using mixed models is discussed. Soil mineralized nitrate‐N at emergence of the potato crop was affected by the preceding crop and was highest when potatoes followed peas, while the short‐term alfalfa/grass/clover ley appeared too sensitive to environmental conditions in the preceding cropping season, and its efficiency in terms of N supply may be hard to predict. Pre‐sprouting advanced crop development and dry matter accumulation of the canopy, translocation of assimilates and N from canopy into tubers and allowed an increased N utilization efficiency. The positive effect of pre‐sprouting on total tuber yield was compensated up to the final harvest, but a higher percentage of marketable tuber yield for French fries (>50 mm) was found independently of the date of harvest. An increasing N supply (after peas and a following catch crop) may be efficient in terms of higher yields of the marketable size‐grades (40–65 mm) for crisps, but increase oversized tuber yields in seasons not affected by Phytophthora infestans. Average tuber fresh weight responded consistently and positively to seed‐tuber preparation (pre‐sprouting), cultivar (cv. Agria) and an increased N supply (after peas).