Sprouting ability of two‐year‐old Betula pendula stumps exposed to different light intensities during five years

Altogether 1 080 two‐year‐old silver birch (Betula pendula Roth) were planted in groups of 36 plants at aspacing of 20 x 20 Cm in spring 1983 on a nursery field at lat. 60° 15 N and long. 16°00 E. In spring 1984 all plants were cut with 10 cm high stumps and light screens were arranged on the stump groups. Relative ¡rradiance (RI) 5, 10, 25, 50, 75 and 100% of full sunlight were used. After five growing seasons, all stumps exposed to 5 or 10% light intensity were dead, and 64–94% of stumps exposed to 25–100% RI were alive. 1.3–1.4 sprouts per living stump were living five years after cutting. The mean height of sprouts was highest on stumps exposed to 100% light. Also dry weights of leaves and sprouts, number of leaves per sprout, and leaf area were highest on stumps exposed to full sunlight. Stumps producting only one sprout five years after cutting have higher height and dry weight values than stumps with more sprouts. The biomass production per hectare and year for silver birch sprouts at a spacing of 0.2 m and with 90% survival was calculated as 5.4 tonnes. The biomass of leaves was 8.1 tonnes/ha/year five years after cutting.     

Dependence of dormancy release on temperature in different origins of Pinus sylvestris and Betula pendula seedlings

The chilling requirement of rest completion and the high temperature requirement of growth initiation were determined in three origins of silver birch (Betula pendula Roth.) seedlings and five origins of Scots pine (Pinus sylvestris L.) seedlings. In both the pine and birch the chilling requirement was highest in maritime Scottish origins and lowest in the most continental Finnish and Russian origins. The requirement for southern mountainous Spanish and Bulgarian pine origins was in between. In terms of the high temperature requirement, there were no clear differences between origins. These results suggest that owing to their high chilling requirement, which prevents the beginning of growth and the loss of frost hardiness during the frost‐exposed season, origins from a maritime climate could be the most tolerant under climatic warming.     

不同鲢密度对千岛湖沿岸池塘浮游植物群落结构的影响

为了进一步检验中营养条件下滤食性鲢（Hypophthalmichthys molitrix）的控藻效应,于2017年5-9月,在浙江省淳安县千岛湖邵家鱼种场选择8口大小、形状等各种条件基本一致的池塘,设置无鱼（CK）0 g/m3、低密度（LD）10 g/m3、中密度（MD）20 g/m3和高密度（HD）30 g/m3共计4个鲢处理组,放养的鲢体重为（61.03±3.70）g、体长为（14.21±0.27）cm,经每月3次浮游植物样品采集和观察,探究不同密度的鲢放养对浮游植物群落结构的影响。结果表明,浮游植物优势种组成在不同处理组池塘间无显著差异。双因素方差分析表明,鲢密度和月份对浮游植物密度和生物量均有显著作用,月份而非鲢密度对其多样性产生显著影响,2个因素对浮游植物生物量有而对其密度和多样性指数无交互作用。3个有鲢处理组池塘藻类总密度和蓝藻密度均有较大幅度下降,它们的蓝藻密度、中高密度组池塘藻类总密度显著低于无鱼组;中、高密度组池塘蓝藻生物量、中密度组池塘藻类总密度均显著低于无鱼组和低密度组。实验结果表明,鲢对浮游植物的抑制作用具有密度效应,随鲢放养密度和水体藻类现存量的变化而变化,鲢中等密度放养能显著遏制浮游植物现存量,密度依赖的鲢滤食量对浮游植物的抑制作用明显大于营养短路和藻类小型化对浮游植物的促进效应。     

银铺户——宋代钱荒产生的重要原因

宋代,随着白银在国家经济活动中地位的上升,社会上产生了银铺户这一食利阶层。他们利用国家要求地方上缴白银的政令,抬高白银与铜钱的兑换价格,大量地从民间吃进囤积铜钱,每年少则储蓄几万贯,多则几十万贯铜钱,这样大量的铜钱被他们所掌握,退出了流通领域,加之政府每年新铸铜钱的数量有限,从而诱发了宋代的钱荒。     

Comparison between microscopic and automated differential leukocyte counts in the silver fox (Vulpes vulpes) and the blue fox (Alopex lagopus)

Differential leukocyte (WBC) counts in blood from clinically healthy silver foxes (n=32) and blue foxes (n=37) obtained from an automated hematology analyzer (Technicon H*1 Hematology System) with canine software were compared with microscopic differential WBC counts (M-diff). There was good agreement between the automated differential cell count (A-diff) and the M-diff for neutrophil and lymphocyte percentages. The correlation was lower for monocyte percentages and variable for eosinophil percentages. There was no significant difference between the A-diff and M-diff in either fox species. The A-diff counts were very precise, and may be a good alternative to the traditional M-diff for screening populations of clinically healthy foxes or for studies on stress and animal welfare. Intercept values, however, indicated a constant bias that must be taken into account before interpreting results based on different methods of analysis     

Localization of potato leafroll virus in leaves of secondarily-infected potato plants

Potato leafroll virus (PLRV) antigen was localized by immunogold labelling in semi-thin leaf sections of secondarily-infected potato plants cv. Bintje. Viral antigen was present in all cell types of the phloem tissue. but occurred most abundantly in the companion cells. Detectable amounts of PLRV antigen were found only in the sieve elements in veins with a large number of infected companion cells. Occasionally, parenchyma cells were also found to be infected. PLRV was not exclusively limited to the phloem tissue in the infected potato plants, but was also found in mesophyll cells neighbouring minor phloem vessles. Spread of virus from cell to cell in the mesophyll was not observed. The distribution of PLRV in the potato leaf tissue has implication on its availability, for acquisition by aphids.     

臭氧氧化对鲢肌球蛋白流变特性的影响

为探究鲢鱼糜加工中臭氧的氧化作用对鱼糜凝胶品质的改善效果，以臭氧氧化的鲢肌球蛋白为原料，采用流变仪并结合Ostwald-de Waele方程、Burgers方程拟合，研究臭氧氧化鲢肌球蛋白的流变特性，并分析其凝胶化过程中凝胶特性的变化。结果显示，肌球蛋白溶液储能模量G''始终大于损耗模量G''，臭氧氧化45 s时，肌球蛋白溶液G''和G''最大，对频率依赖性最弱；臭氧氧化使肌球蛋白溶液黏性系数k值下降；不同臭氧氧化时长的肌球蛋白凝胶化趋势相似，但臭氧氧化作用使肌球蛋白G''达到峰值所需时间减小、峰值增加；在蠕变-恢复扫描测试中，臭氧氧化作用使肌球蛋白弛豫时间减少，弹性响应变快，臭氧氧化45 s时形变量ε最小。结果表明，肌球蛋白溶液属于弱凝胶及假塑性流体，一定程度的臭氧作用可使肌球蛋白在热诱导凝胶化中加速形成凝胶且凝胶特性得到一定程度提升。     

稳定性同位素营养级估算的差异性与影响因素——以鲢鳙为例

为了优化稳定性同位素估算消费者营养级的计算过程,降低算法和样品质量对其的影响,应用贝叶斯算法对中国水域已发表文献中的鲢（Hypophthalmichthys molitrix）、鳙（Hypophthalmichthys nobilis）营养级进行了估算和分析。结果显示：贝叶斯算法下鲢、鳙营养级与总磷（TP）、总氮（TN）2种环境因素无显著相关性。部分研究存在采样个数过少、采样频率过低,忽略了基准季节性和种内的变异性等问题,从而无法准确代表目标生物的营养特征,可能导致了营养级估计中出现异常值。贝叶斯算法与传统算法之间无显著性差异,表明其依然无法冲淡采样设计所带来的影响。曲线拟合的结果表明,维持采样数在6个以上有助于提高贝叶斯算法的计算结果的准确性。因此,在试验设计中,建议采样样品数多于6,并考虑季节与空间的差异,避免单次、少量的采集。     

CAFTA背景下广西农产品贸易竞争力研究

广西农产品贸易竞争力增强的根源在于提升农产品贸易主体的核心竞争能力,产业政策的调整、政府的支持等因素是外因,居于客观地位,竞争主体核心能力的提升是内因,居于主导地位。在中国—东盟自贸区建立的背景下,提升广西农产品贸易竞争力变得十分迫切,新经济形势要求作为主要竞争者的农产品经营主体从软、硬环境的建设入手创造核心竞争优势,取得地区贸易的优势地位。