Cytokinins: A key player in determining differences in patterns of canopy senescence in Stay-Green and Fast Dry-Down sunflower (Helianthus annuus L.) hybrids

Leaf senescence during grain filling can reduce crop yield. We studied, under field conditions and during grain-filling, the association between leaf cytokinin levels and the onset of leaf senescence in sunflower hybrids of contrasting canopy senescence patterns (Paraiso75, stay-green [SG] and Paraiso65, fast dry down [FDD]). At crop level, dynamics of live root length density (LRLD) and green leaf area index (GLAI) were followed, while at leaf level dynamics of total chlorophyll content, trans-Zeatin content, net photosynthesis and PSII quantum yield, were followed in leaf positions 17, 20, 22 and 24. Responses of these leaf variables to exogenous cytokinin applications to leaves at position 17 were also followed. SG exhibited greater (p < 0.05) LRLD and GLAI values at anthesis. In both hybrids, LRLD began to fall before GLAI. All variables decreased earlier (p < 0.05) in FDD. Initial leaf levels of trans-Zeatin were three times higher (p < 0.05) in SG. Exogenous cytokinin applications maintained leaf-level variables. These are the first results showing associations between LRLD dynamics with the dynamics of leaf cytokinin levels and changes in indicators of leaf functionality. Also, this is the first study in which estimates are made of cytokinin thresholds below which leaf senescence begins in two hybrids of contrasting canopy senescence patterns. These advances in the understanding, at both crop and leaf levels, of the controls and consequences of SG during grain filling, a trait known to improve crop water uptake under drought and increase biomass accumulation during grain filling, provide support for breeding efforts aimed at profiting from this trait to increase crop yields.     

财政分权、社会保障支出与城乡居民收入差距的实证分析

基于1998~2012年各省的面板数据，利用动态广义矩（GMM）和面板门槛模型实证分析财政分权、社会保障支出对城乡收入差距的影响，结果显示：由于中国城乡二元经济的特殊性，财政分权、人均社会保障支出与城乡居民收入差距均成正相关性。但社会保障支出对城乡收入差距的影响存在基于财政分权的双门槛效应，当财政分权水平较低时，社会保障支出的增加加剧了城乡收入差距；当财政分权高于一定水平时，社会保障支出有助于缩小城乡收入差距。     

Modeling and field-testing of Ovenbird (<Emphasis Type="Italic">Seiurus aurocapillus</Emphasis>) responses to boreal forest dissection by energy sector development at multiple spatial scales

Although the area disturbed by linear features in forested systems is small relative to many other human disturbances, linear features create significantly more amounts of edge per unit area. In the boreal plains of Alberta, Canada, energy sector exploration has resulted in extensive dissection of the landscape through 8 m wide seismic lines. A spatially explicit model was developed to test how bird abundance might change in response to increasing seismic line density if individuals use seismic lines as territory boundaries or actively avoid these edges. Assuming birds had fixed territory shape and size, increasing seismic line density from 0 to 8 km/km² resulted in a 38% decline and an 82% decline in bird abundance when individuals used lines as territory boundaries or avoided edges by 50 m, respectively. We tested the assumptions of our model using the Ovenbird (Seiurus aurocapillus). Based on radio-telemetry (n = 12), all Ovenbirds crossed seismic lines at some point during the breeding season. However, male Ovenbirds showed a distinct use of one side of the seismic line, suggesting lines acted as territory boundaries. In 12.25 ha plots (n = 24) spot-mapping detected no change in Ovenbird density as linear feature density increased from 0 to 8.6 km/km². In 4 km² landscapes (n = 62) sampled using a grid of nine point-counts, we also detected no changes in Ovenbird numbers across the same range of seismic line densities. Ovenbirds declined with seismic line density at the level of the individual point-count station (12 ha scale), but only when a threshold seismic line density of 8.5 km/km² was reached. Above the threshold, Ovenbirds declined 19% for each 1 km/km² increase in seismic line density. While relatively few places in Alberta’s boreal forest have local seismic line densities of 8.5 km/km², forest dissection could increasingly become an issue if current energy exploration practices continue.     

奶牛赘生乳头数遗传力的估计及其与产奶量的相关分析

奶牛赘生乳头数呈阈性状特点,本文采用阈性状分析法估测赘生乳头数的遗传力为0.33 0.04,因此,进行表型选择可获得较理想的选择效果。通过其对产奶量的相关分析表明,赘生乳头对产奶量虽无明显影响,但有遗传倾向。它不仅影响乳房的外形,也不利于机械化生产,无疑是一不合意性状,应在奶牛选种工作中予以重视。     

Genetic selection for increased mean and reduced variance of twinning rate in Belclare ewes

It is sometimes possible to breed for more uniform individuals by selecting animals with a greater tendency to be less variable, that is, those with a smaller environmental variance. This approach has been applied to reproduction traits in various animal species. We have evaluated fecundity in the Irish Belclare sheep breed by analyses of flocks with differing average litter size (number of lambs per ewe per year, NLB) and have estimated the genetic variance in environmental variance of lambing traits using double hierarchical generalized linear models (DHGLM). The data set comprised of 9470 litter size records from 4407 ewes collected in 56 flocks. The percentage of pedigreed lambing ewes with singles, twins and triplets was 30, 54 and 14%, respectively, in 2013 and has been relatively constant for the last 15 years. The variance of NLB increases with the mean in this data; the correlation of mean and standard deviation across sires is 0.50. The breeding goal is to increase the mean NLB without unduly increasing the incidence of triplets and higher litter sizes. The heritability estimates for lambing traits were NLB, 0.09; triplet occurrence (TRI) 0.07; and twin occurrence (TWN), 0.02. The highest and lowest twinning flocks differed by 23% (75% versus 52%) in the proportion of ewes lambing twins. Fitting bivariate sire models to NLB and the residual from the NLB model using a double hierarchical generalized linear model (DHGLM) model found a strong genetic correlation (0.88 ± 0.07) between the sire effect for the magnitude of the residual (V_E) and sire effects for NLB, confirming the general observation that increased average litter size is associated with increased variability in litter size. We propose a threshold model that may help breeders with low litter size increase the percentage of twin bearers without unduly increasing the percentage of ewes bearing triplets in Belclare sheep.     

基于图像阈值的年轮识别方法

本文主要讲述了年轮识别在林业信息化中的作用和阈值法的依据与闻值法的原理,以及用阈值法处理年轮图像和采用其他方法处理的结果的不同,从而得出用阈值法进行处理的优点.     

黄河源流域单元概念及其提取方法研究

针对黄河源高寒草地生态系统保护的流域属性与差异性，本研究提出了一种准确便捷的流域单元识别方法。以国产高分辨率遥感影像所提取水系矢量数据作为标准参照系，基于数字高程数据（Digital elevation model，DEM）汇流累积计算量阈值设置为30 000时所获取的水系信息与黄河源实际水系状况较为相近。通过合并集水区获取黄河源流域单元878个，其中干流单元1个，一级支流单元219个，二级支流单元420个，三级支流单元194个，四级支流单元21个，断流河流单元23个。受地形地貌影响黄河源流域单元中河流长度与流域面积差距较大。本研究完善了黄河源水系及流域单元特征信息，为黄河源生态治理工作提供参考。     

基于图像阈值的年轮识别方法

本文主要讲述了年轮识别在林业信息化中的作用和阈值法的依据与阈值法的原理，以及用阈值法处理年轮图像和采用其他方法处理的结果的不同，从而得出用阈值法进行处理的优点。     

水稻抽穗期叶色诊断指标与叶面积指数及结实期光强的关系

叶色是氮素营养诊断最常用的指标，获得准确的叶色诊断指标是水稻精确定量施氮的基础。叶色诊断指标实际上就是稻谷产量最高时的最适叶色。已有报告指出，叶色诊断指标受到群体大小和结实期光照条件的影响。研究的目的是，找出叶色诊断指标随群体大小和光照条件而变化的规律，为精确定量施氮提供理论和技术依据。2004—2005年早季和晚季，在广州以两系杂交稻粤杂122为试材，设置8种不同氮肥处理，进行2年4季田间试验，抽穗期测定叶色(SPAD)和叶面积指数(LAI)，成熟期测产。结果表明：(1)不同季节的最适叶色存在明显差异，4季变动于39~45之间。根据产量与叶色的定量关系，可以准确、快速地确定特定条件下的叶色诊断指标。(2)稻谷产量与抽穗期群体指数(SPAD与LAI的乘积)呈开口向下的抛物线关系。抽穗期SPAD、LAI和结实期日照时数，可以解释不同年度、季节和不同氮肥处理的稻谷产量变异的86%。最适群体指数随着结实期日照时数的增加而提高。(3)最适叶色随着日照时数的增加而提高，随着LAI的增加而降低，3者之间存在显著的定量关系。应用这一关系，可根据结实期光照条件，估计出异地异季的叶色诊断指标。     

不同性质农田土壤中铜的可提取性与生物有效性及毒性

以重金属总量为基础的土壤环境质量标准已不适用于当前土壤管理的需求，基于重金属生物有效性的生态风险评估和环境阈值研究对土壤重金属环境质量标准的修订具有重要的意义。本研究选取4种化学提取剂（HNO3、EDTA-Na2、NH4OAc和CaCl2）对我国3种不同性质的模拟Cu污染农田土壤（黑土、潮褐土和脱潜水稻土）进行有效态Cu提取，通过敏感性生态物种生菜和赤子爱胜蚓的Cu暴露实验，推导基于化学提取有效态的土壤Cu生态毒性阈值。研究结果表明，HNO3（41.38%）和EDTA-Na2（56.81%）对3种土壤中Cu的平均提取效率显著高于NH4OAc（0.12%）和CaCl2（8.70%）。CaCl2提取态Cu含量与生菜Cu富集量和毒性效应之间存在显著或极显著相关， HNO3提取态Cu含量则能很好地指示蚯蚓Cu富集量和30 d死亡率。不同生态受体毒性终点对土壤可提取态Cu的敏感性存在差异，选用物种最敏感指标推导了3种土壤中Cu的有效态毒性阈值EC 20和EC 50。基于不同化学提取态Cu含量的生菜毒性阈值EC 20范围分别是90.45~170.10 mg/kg（HNO3），102.78~195.31 mg/kg（EDTA-Na2），3.97~20.06 mg/kg（NH4OAc），和0.21~8.68 mg/kg（CaCl2）；EC 50范围分别是110.48~187.60 mg/kg（HNO3），118.63~230.49 mg/kg（EDTA-Na2），5.69~32.23 mg/kg（NH4OAc）和0.26~9.62 mg/kg（CaCl2）。基于不同化学提取态Cu含量的赤子爱胜蚓死亡率毒性阈值EC 20范围分别是138.26~193.16 mg/kg（HNO3）， 107.80~225.88 mg/kg（EDTA-Na2）， 8.92~11.58 mg/kg（NH4OAc），和0.36~10.57 mg/kg（CaCl2）；EC 50范围分别是183.07~221.23 mg/kg（HNO3），180.38~331.09 mg/kg（EDTA-Na2），13.06~18.30 mg/kg（NH4OAc）和0.54~13.21 mg/kg（CaCl2）。研究结果可为我国农田土壤重金属有效态化学提取方法的比选与优化提供科学依据，同时对基于生物有效性的土壤重金属环境质量基准与标准的研究和制定具有重要意义。