新疆昌吉州草地生产力年际动态分析

通过对新疆昌吉州草地生产力2006~2010年5年监测结果显示:各草地类型植被不同程度退化。植物种类减少,草群结构单一,优势种出现频率很低,一年生和短命植物比例增加,中山带毒害草(醉马草)大量出现;草层高度不同程度下降。除山地草甸外,高寒草甸、草甸草原、典型草原和荒漠草层高度下降明显,下降幅度都超过了10%;植被覆盖度降低。除荒漠外高寒草甸、山地草甸、草甸草原、荒漠草原和低地草甸下降明显,下降幅度都超过了10%;草地生产力不同程度下降,在2009~2010年草地生产力有所上升。     

Genotype by environment interaction for lamb weaning weight in the Norwegian White Sheep breed

Abstract

Genotype by environment (G×E) interaction effects influence phenotypic expressions of a trait and may be of importance for sheep breeding. Interaction effects are more likely to be present when there are large environmental differences. Norwegian sheep usually graze mountain or forest pastures during summer. In this study, we estimate G×E interactions in Norwegian White Sheep as genetic correlation between area-specific traits (autumn lamb weight) in three ram circles located in two different counties; two in Buskerud in the south and one in Troms to the north of the country. Using data from the National Sheep Recording System, a bivariate animal model was fitted and genetic correlations for each trait were obtained. None of the correlations were significantly different from unity indicating the absence of G×E interaction effect for weaning weight. To gain further insight, studies should include a breeding-goal level aggregation of all traits thought to contribute to profitability.     

Changing predictors of spatial and temporal variability in stocking rates in a severely degraded communal rangeland

Changes in vegetation and soils under heavy continuous grazing have been widely documented, but the effects of these on secondary production are debated. Sterkspruit is one of South Africa's most degraded districts, and soil erosion in the district increased substantially over the twentieth century. Despite this, records dating to the late‐1800s show no decline in livestock numbers. This study explores how high stocking rates have been maintained despite an apparent deterioration in the natural resource base. Multiple regression analyses were used to determine the best predictors of stocking rates in 1974, the 1980s and 1997 to determine whether the relative importance of mean annual rainfall and winter temperature (indicative of primary production), the percentage of area on nutrient‐poor sandstone‐derived soils (representing a dry season nutritional bottleneck), the percentage of an area on steep slopes (which make areas less accessible to livestock) and human population density and availability of arable land (indicative of potential inputs) had changed over time. While mean annual rainfall was the best predictor of stocking rates in 1974, stocking rates in the 1980s and 1997 were best predicted by human population densities. This suggests that a qualitative shift in how livestock populations are maintained has taken place. Copyright © 2010 John Wiley & Sons, Ltd.     

Growth patterns and annual growth cycle of Acacia karroo hayne in relation to water stress

Abstract

The use and replenishment of carbohydrate reserves in Acacia karroo is closely related to the successive events of the annual growth cycle. Acacia karroo displayed the rapid and substantial decline in non‐structural carbohydrates typical of deciduous woody species. In addition, each time shoot, leaf or reproductive organs grew rapidly, reserves declined.

Replenishment begins soon thereafter when the recently emerged leaves are still very small. Water stress does not change the pattern of use and replenishment. However, increasing water stress does slow replenishment down. This probably delays the beginning of the next growth event as well as the growth of organs already initiated.     

基于均方差权值法对不同培育措施高寒草甸的现状评价

在天然草地健康评价中各项指标的权重大小对评价结果有着直接而重要的影响。为探讨青藏高原东缘高寒草地健康状况的合理评价模型,通过均方差权值法对甘南桑科草原不同培育措施高寒草地的植物群落盖度、优势层高度、干草产量和植物根层土壤有机质进行客观赋值综合评价。结果表明:1.各种培育措施对高寒草地植物群落结构和特征均有不同程度的影响;2.施肥处理草地健康状况最好,而放牧干扰草地的最差;3.均方差权值法对草地植物盖度和植物群落优势层高度、干草产量及植物根层土壤有机质含量客观赋值可以用于甘南桑科草原草地健康评价。     

Grassland soil organic carbon and the effects of irrigated cropping in Alberta,Canada

High heterogeneity in the spatial distribution of soil organic carbon (SOC) in grasslands causes uncertainty in estimating its content and storage. In this study, we investigated the spatial distribution of SOC content and storage in the prairies of southern Alberta, Canada, and how it is affected by land use such as irrigated cropping and other environmental conditions such as cattle grazing, slope landscape position and dominant plant species. The mean SOC content was determined to be 11.5 g kg^–1 (range: 8.9 to 22.4 g kg^–1) in the 0–10 cm layer and 6.8 g kg^–1 (range: 4.0 to 13.3 g kg^–1) in the 10–30 cm layer; mean SOC storage was 1.59 kg C m^–2 (range: 1.23 to 2.78 kg C m^–2) in the 0–10 cm layer and 2.07 kg C m^–2 (range: 1.21 to 3.62 kg C m^–2) in the 10–30 cm layer. The SOC content was significantly affected by slope position in both the 0–10 and 10–30 cm layers, in the following order: bottom >middle > top position. Moreover, SOC storage was higher in sites dominated by shrubs than graminoid/forb communities. Thus, SOC content and storage had distinctly clustered spatial patterns throughout the study area and were significant differences between the 0–10 and 10–30 cm soil layers. Prior land-use change from arid grassland to irrigated cropland increased SOC content and storage in bulk soils.