北京地区典型绿化树种水分利用效率及其影响因素

[目的]在北京地区绿化率需求提升和水资源短缺背景下,城市绿化与城市生产、生活用水矛盾日益尖锐.因此,探寻城市绿化树种对干旱生境的响应机制,筛选低耗水、高水分利用的园林绿化树种,成为北京高质量城市森林景观建设的重要需求.[方法]该研究以北京地区落叶树种银杏、栾树、国槐和常绿树种侧柏、油松和白皮松盆栽幼树为研究对象,基于碳...     

Inter‐relationship between photosynthetic efficiency, Δ13C,antioxidant activity and sugarcane yield under drought stress in field conditions

Drought is one of the major climatic factors that reduce crop yields in cultivated areas around the world, and studies on physiological responses may help in the selection of drought tolerant genotypes. Thus, this work aimed to correlate gas exchange, photosynthetic efficiency, carbon isotope discrimination (Δ¹³C) and antioxidant activity in sugarcane varieties submitted to water stress under field conditions. Six sugarcane varieties were submitted to drought stress in three development stages: tillering, intense growth and ripening. In all varieties, the photosynthetic apparatus was severely affected by drought, with a reduction in photosynthetic rate and chlorophyll content. During the tillering stage, reductions in gas exchange and increase in Δ¹³C and bundle sheath leakiness (φ) were observed. In the intense growth stage, water stress caused increases in leaf temperature, intrinsic water use efficiency, antioxidant enzyme activity and lipid peroxidation, and reductions in stomatal conductance and transpiration in the RB72454, RB855113 and RB855536 varieties. However, the RB92579 variety maintained a better physiological homeostasis at all development stages and presented higher stalks yielding when submitted to drought. This work suggests that screen sugarcane genotype to drought stress should be performed during the intense growth stage, when plants are more sensitive to drought conditions.     

政策措施落实显效,生猪生产趋稳向好——2019年生猪市场回顾与未来走势展望

2019年是真正的金猪年。由于非洲猪瘟疫情影响,生猪产能持续下降,导致生猪价格年内一度创下出栏均价40元/kg以上的罕见高位,并维持较长时间,行业盈利达到历史最好最高水平。目前,年关将至,已进入猪肉的传统消费旺季,加之“灌香肠、制腊肉”相继启动,元旦、春节来临,或将再度推动全国猪价阶段性上行。而随着一系列稳定生猪生产的扶持政策落实显效,目前全国生猪生产呈现整体趋稳向好态势。预计,2020年猪价仍将在高位区间波动运行,后市或将逐渐震荡回调。     

Dispersal strategies of juvenile pike (Esox lucius L.): Influences and consequences for body size,somatic growth and trophic position

Individual variability in dispersal strategies, where some individuals disperse and others remain resident, is a common phenomenon across many species. Despite its important ecological consequences, the mechanisms and individual consequences of dispersal remain poorly understood. Here, riverine Northern pike (Esox lucius) juveniles (age 0+ (young-of-the-year) and 1+ years) were used to investigate the influence of body size and trophic position (at capture) on the dispersal from off-channel natal habitats and the subsequent consequences for body sizes, specific growth rate and trophic position (at recapture). Individuals that dispersed into the river (“dispersers”) were not significantly different in body size than those remaining on nursery grounds (“stayers”). For trophic position, 0+ dispersers were of significantly lower trophic position than stayers, but with this not apparent in the 1+ fish. Following dispersal into the river, the dispersers grew significantly faster than stayers and, on recapture, were significantly larger, but with no significant differences in their final trophic positions. Early dispersal into the river was, therefore, not associated with early dietary shifts to piscivory and the attainment of larger body sizes of individuals whilst in their natal habitats, contrary to prediction. These results suggest that despite an increasing risk of mortality for individuals dispersing early from natal areas, there are long-term benefits via elevated growth rates and, potentially, higher fitness. Such early dispersal behaviour could be driven by early competitive displacement.     

地质样品中Mo同位素测试前处理化学方法研究

通过对地质样品中Mo同位素测试前处理的方法的比较,对传统的阴、阳离子树脂交换法进行了改进研究。经改进后的方法实用范围较宽,Mo的回收率达到97.49%±0.27%,Mo同位素质谱分析过程中可能的同重干扰元素Zr、Fe、Mn等的去除效果理想,其它金属元素的去除效果也较理想,且在阴离子交换柱洗脱Mo的过程中总计约需的提取液(盐酸和硝酸)体积只有75 ml,只占文献报道用量的45%,从而减少了试剂对样品,特别是对低含量地质样品可能带来的潜在污染。     

荒漠植物白刺新固定碳在植物-土壤系统中的分配

定量生长季内荒漠植物新固定碳在植物-土壤的分配规律,对理解全球碳循环有着重要意义。采用野外原位¹³C-CO₂脉冲标记法,测定植物各器官及土壤¹³C丰度值,比较不同标记时间段白刺新固定碳分配在不同器官、土壤和呼吸损失中的分配规律,并量化了白刺光合碳向地上、地下碳库的转移。结果表明:不同标记时间段内¹³C-新固定碳在白刺叶、茎、根、土壤中的分配差异明显。在标记后1 h内,叶片和茎中¹³C丰度值迅速上升到最高值,¹³C丰度值分别达到520.1‰和592.5‰,比对照分别增加14和20倍,此后¹³C丰度值随时间推移逐渐下降,直至趋于稳定;而标记后18 h在根系和土壤中发现被标记的¹³C,¹³C丰度值分别达到9.5‰和-23.8‰,白刺新固定碳经地上部呼吸和土壤呼吸损失量分别在标记1和18 h后达到最大。标记32 d后,白刺新固定碳在地上部和地下部¹³C分配比例分别占35.59%和32.49%,呼吸损失(地上呼吸+土壤呼吸)占31.92%。荒漠植物白刺生长季年固碳量为2895.6 kg C·hm^-2·yr^-1,表明白刺在荒漠生态系统碳循环中起着重要的碳汇作用。     

稳定同位素在农产品溯源中研究进展

稳定同位素质谱技术准确度很高,根据元素稳定同位素在产品中比例的不同,可以实现农产品溯源、辨别农产品真伪、判断污染物来源、成矿年代追溯等目的。本文分别从植物产品和动物产品两方面,介绍了轻同位素及矿物元素(以锶为例)在农产品溯源中的研究进展,重点围绕碳、氮、氢、氧和锶稳定同位素在产地溯源中的应用进行了总结。稳定同位素溯源将会不断完善和发展,并广泛应用于地质、生态、法医、考古等更多的领域。     

Degree of feeding niche overlap uniformises the distribution of interspecific territories in a Malawian cichlid community

Cichlid fishes in the rocky littoral zones of Lake Malawi are among the most diverse endemic fish communities of the world. They segregate food resources, but considerable niche overlaps have been reported by numerous studies in this field. If their niches largely overlap, the heterospecific individuals are expected to behave like conspecific individuals. Instead of studying their niche segregation, we investigated the spatial distribution patterns of adult males of nine abundant cichlid species by point process analysis, with due attention to niche partitioning, as measured by stable isotope analysis. Because their feeding habitats are restricted by intra‐ and interspecific interferences over the mating and feeding territories respectively, we hypothesised that the interspecific feeding territories of species with nearly similar niche tended to be distributed uniformly. Although the typical territorial animals are expected to be distributed uniformly, the distribution pattern of intraspecific mating territory was judged to be uniform only for two out of nine species. This result suggests that each species has its specific preference for territorial locations or their locations are restricted by interspecific interactions. The latter explanation was partially supported by the agreed locations of gravity centres between intraspecific mating and interspecific feeding territories. Species pairs with similar isotope ratios tended to show a uniform distribution of interspecific feeding territories. Thus, individual species pairs keep a certain distance from each other by using nearly similar food resources. This result suggests that some cichlid species coexist not only through niche segregation but also through territorial interactions, like conspecific individuals.     

Trophic overlap between non‐native brown bullhead (Ameiurus nebulosus) and native shortfin eel (Anguilla australis) in shallow lakes

We quantified trophic overlap between the invasive, non‐native catfish brown bullhead (Ameiurus nebulosus) and the New Zealand native shortfin eel (Anguilla australis) in four peat and riverine lakes using stable isotope (δ¹³C and δ¹⁵N) and gut content analyses. Across all lakes and fish sizes over the austral spring–summer period, shortfin eel guts were dominated numerically by fish prey (57% occurrence cf 42% in brown bullhead), while Diptera larvae were most commonly encountered in guts of brown bullhead (45% cf 14% in eels). Significant differences in % composition of animal contents in guts were detected between fish species and sampling occasions (n = 4) but not between lakes. In contrast, stable isotope signatures of brown bullhead and shortfin eel did differ significantly between lakes but not between sampling occasions, indicating enduring sources of nutrition despite apparently differing ingestion patterns over time. The R mixing model MixSIAR indicated that shortfins likely assimilated higher proportions of fish prey carbon compared to brown bullheads, which appeared to show greater assimilation of invertebrates, consistent with the results of gut content analyses. Isotopic niche regions, calculated in nicheROVER using probabilistic ellipses, indicated that shortfin eels occupied at least c.60% of brown bullhead trophic niche, which occupied less than 30% of eel trophic niche in all but one lake. These estimates suggest that brown bullhead has higher potential to influence shortfin eel nutrition than vice versa, or that a broad trophic niche occupied by eels provides resilience to the effects of overlapping consumption patterns with invasive omnivores.