Threats to at-risk salmonids of the Canadian Rocky Mountain region

Trout and charr, members of the salmonid family, have high conservation value but are also susceptible to anthropogenic threats in part due to the specificity of their habitat requirements. Understanding historical and future threats facing these species is necessary to promote their recovery. Of freshwater trout and charr in the Canadian Rocky Mountain region, westslope cutthroat trout (Oncorhynchus clarkii lewisi), bull trout (Salvelinus confluentus; a charr species) and Athabasca rainbow trout (Oncorhynchus mykiss) are of conservation concern. And indeed, range contractions and declining populations are evident throughout much of their ranges. Range contraction was most evident in the southern Alberta designatable unit (DU) of westslope cutthroat trout. Diminished populations were also evident in the downstream watersheds of the Alberta bull trout range, and throughout the Athabasca rainbow trout range. We assessed historical and future threats to evaluate the relative importance of individual threats to each DU and compare their impact among species. Individual threats fall into the broad categories of angling, non-native species and genes, habitat loss and alteration, and climate change. Severity of each threat varies by DU and reflects the interaction between species’ biology and the location of the DU. Severity of threats facing each DU has changed over time, reflecting extirpation of native populations, changes in management and industry best practices, expansion of non-native species and progressing climate change. The overall threat impact for each DU indicates a high probability of substantial and continuing declines and calls for immediate action.     

Compatibility of root growth and tuber production of potato cultivars with dynamic and static water‐saving irrigation managements

The important root characteristics of root length density (RLD) and root mass density (RMD) generally differ among irrigation managements and potato cultivars. The objective of this study was to investigate the RLD and RMD variations and their functional relationships with gross potato tuber yield for two commercial potato cultivars, Agria and Sante, under different irrigation strategies. Full irrigation and water‐saving irrigation strategies, deficit and partial root drying irrigations, were applied statically (S) and dynamically (D) based on daily crop evapotranspiration. Results showed that SPRD had significantly greater RLD (3.64 cm/cm³) and RMD (132.7 μg/cm³) than other irrigation treatments. Between the potato cultivars, Agria had significantly larger values of RLD (3.50 cm/cm³) and RMD (138.7 μg/cm³) than Sante. The functional relationship between the root growth characteristics and tuber yield showed that under water‐saving irrigations, Agria increased root mass at the expense of gross tuber yield but Sante increased root mass to maintain larger gross tuber yields. However, Agria produced more roots and gross tuber yield than Sante, and it is concluded that Agria is a more drought‐tolerant potato cultivar, which is recommended for tuber production in regions where water might be scarce. It was shown that larger root production in potatoes was associated with improved tolerance to water stress.     

干旱胁迫下不同品种杨树矿质离子含量变化

【目的】了解杨树在干旱胁迫下矿质离子分布及其动态变化。【方法】以吴屯杨、新疆杨和荷兰杨为实验材料,在中度和重度干旱条件下测定了根、茎、叶和质外体的K^+、Ca^2+、Na^+和Mg^2+等4种离子含量的变化。【结果】干旱胁迫使K^+、Ca^2+和Na^+离子含量上升,Mg^2+含量下降,其中K^+和Ca^2+含量自胁迫开始明显升高,Na^+含量则在中度胁迫之后明显增加。离子在各器官分布情况为:K^+主要分布于杨树的叶片,Ca^2+、Na^+和Mg^2+主要分布于杨树根部,且离子分布存在品种间差异,荷兰杨和新疆杨中K^+分布为:叶>根>茎,而吴屯杨体内K^+分布则为:叶>茎>根;3种杨树中Ca^2+分布均为:根>叶>茎;吴屯杨和荷兰杨中Na^+分布为:根>茎>叶,新疆杨则为:根>叶>茎;在Mg^2+的分布上吴屯杨和新疆杨较为类似即:根>叶>茎,而荷兰杨为叶>根>茎。【结论】干旱胁迫下杨树首选吸收的离子是K^+和Ca^2+,K^+主要分布在杨树的叶片中,其次是根部,Ca^2+主要分布在杨树的根部。重度干旱胁迫下,杨树开始吸收Na^+,储存在杨树的根部。不同品种杨树之间离子的分布和吸收都存在品种差异。质外体作为离子的运输通道,在各干旱条件下运输4种矿质离子至杨树的其他部位,Mg^2+存在滞留在质外体中的情况。本研究可为植物在干旱胁迫下矿质离子吸收和分布的研究提供理论依据。     

异速对辊式玉米秸秆粉碎还田装置设计与试验

针对玉米秸秆量大、韧性强,导致还田后秸秆粉碎不均匀影响后续整地和播种等问题,该研究提出了一种异速对辊及动态双支撑形式的玉米秸秆粉碎还田方式,并研制了相应的玉米秸秆还田装置,主要由捡拾粉碎单元、对辊滑切支撑单元、支撑板和机壳等组成。在异速动态双支撑条件下,通过对作业过程中玉米秸秆动力学分析和秸秆漏捡面积分析,对捡拾粉碎刀和对辊滑切支撑刀进行设计,建立了影响秸秆粉碎合格率的数学模型。以捡拾粉碎刀转速、L型甩刀折弯角、L型甩刀刃口长度和滑切支撑刀滑切角为因素,秸秆粉碎合格率为试验指标进行Box-Behnken试验。田间试验结果表明:当滑切支撑刀滑切角45°、捡拾粉碎刀转速1 700 r/min、L型甩刀刃口长度45 mm和L型甩刀折弯角40°时,玉米秸秆粉碎合格率为92.58%,与预测值误差5%,满足国家标准要求。该研究提出的秸秆粉碎还田方式和研制的秸秆粉碎装置为玉米秸秆粉碎还田机设计和优化提供新的方案和技术支撑。     

《四川农业科技》期刊读者群现状浅析

对《四川农业科技》2 0 0 0年～ 2 0 0 2年读者群现状分析结果表明 ,影响读者群的因素有期刊自身原因和地域性原因等 ,扩大和稳定读者群关键在合理定位、栏目设计有特色、多渠道宣传等。     

数量化理论Ⅲ在土地质量综合评价中的应用

木文对土地质量综合评价的方法进行了探讨,首次提出将数量化理论Ⅲ应用于土地质量分级。与目前使用的系统聚类、动态聚类方法相比,数量化理论Ⅲ更适合于变量类型为定性变量的土地资源调查资料的分类。它弥补了系统聚类方法和动态聚类方法在土地资源评价中应用的局限性,数量化理论Ⅲ是一种可用于土地质量分级的理想方法。     

Relating Kirtland's warbler population to changing landscape composition and structure

The population of male Kirtland's warbler (Dendroica kirtlandii) in the breeding season has averaged 206 from 1971 to 1987. The Kirtland's warbler occupies dense jack pine (Pinus banksiana) barrens from 5 to 23 years old and from 1.4 to 5.0 m high, formerly of wildfire origin. In 1984, 73% of the males censused were found in habitat naturally regenerated from wildfire or prescribed burning. The rest were in plantations (11%) or in harvested, unburned jack pine stands stocked by natural regeneration (16%). Twenty-two percent (630 of 2,886) of the Kirtland's warbler males counted in the annual censuses from 1971 through 1984 were found in 26 stands that were unburned and naturally regenerated following harvest. From 1982 to 1987, suitable regenerating areas were barely sufficient to replace currently occupied maturing stands, so population growth was impeded. Ecosystems of suitable size and regeneration characteristics (wildfire and plantation) doubled in area by 1989. In response, the population of Kirtland's warblers increased from 167 to 398 males between 1987 and 1992, but they withdrew almost entirely from the unburned, unplanted barrens by 1989 when the area of more suitable regeneration types increased. Minimum (368 males) and maximum (542 males) population estimates for 1996 were calculated based on 1984 average density (1.9 males per 40 ha) and peak population in burns (2.8 males per 40 ha).     

Importance of the River Teviot to Atlantic salmon, Salmo salar, rod catches in the River Tweed, Scotland

Abstract  The body mass distributions and variations in abundance of the spring and autumn catches of Atlantic salmon, Salmo salar L., were compared between fisheries above and below the confluence of the rivers Tweed and Teviot, Scotland. Significant differences between the distributions were found over three periods, one in spring and two in autumn, when salmon catches were high. Correlations were found between abundance trends for periods when distributions were similar or dissimilar. Abundance of salmon returning to the River Teviot was proportional to the main river. However, its population structure differed when abundances were high, suggesting different survival strategies. It appears that changes in the numbers returning to the river were resultant of changes in the marine rather than freshwater environment.     

Markers, old and new, for examining Phytophthora infestans diversity

Late blight, caused by Phytophthora infestans , is an ongoing threat to potato and tomato crop production worldwide and considerable fundamental and applied research is conducted with the long-term aim of improved disease control. Understanding the mechanisms, processes and rates of P. infestans evolution is an important factor in predicting the effectiveness and durability of new management practices. A range of phenotypic and genotypic tests has been applied to achieve this goal, but each has limitations and new methods are sought. Recent progress in P. infestans genomics is providing the raw data for such methods and new high-throughput codominant biomolecular markers are currently being developed that have tremendous potential in the study of P. infestans population biology, epidemiology, ecology, genetics and evolution. This paper reviews some key applications, recommends some changes in approach and reports on the status and potential of new and existing methods for probing P. infestans genetic diversity.     

潜江小城镇景观规划

潜江小城镇的水资源丰富但开发落后，绿系统不完善，街景缺乏工艺性。在对现状调查分析的基础上，提出了对过境公路、水体、街景进行动感空间、情感空间规划的建议，对乡土化设计、恢复性设计进行了探讨。