Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn,Norway          下载免费PDF全文

Martin A. Svenning  Øyvind K. Hanssen  J. Malcolm Elliott 《Ecology of Freshwater Fish》2015,24(4):591-599

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.  相似文献   

海水中规模化培养西藏拟溞的技术优化研究     

由志欣  赵文  魏杰  王珊  刘钢 《大连海洋大学学报》2015,(1)

为了给北方海水鱼虾蟹类育苗增添一种新的生物活饵料,利用循环水培养装置研究了西藏拟溞Daphniopsis tibetana Sars在稀释海水(盐度为18~20)中规模化培养的技术工艺参数,即起始放养密度、充纯氧和日采收率。结果表明:起始放养密度对西藏拟溞种群增长和日产量影响显著(P0.05),不同起始放养密度(200、550、900、1250 ind./L)培养试验中,放养密度为1250ind./L时,培养第33天时种群密度达最高,为(9500±550.73)ind./L,平均日产量为(125.00±8.35)g/(m3·d);充纯氧与充空气相比较,充纯氧能显著提高种群密度和日产量(P0.05),当放养密度为1250 ind./L、充纯氧时,西藏拟溞种群密度最高达(11 600±560.45)ind./L,平均日产量为(156.82±8.49)g/(m3·d);日采收率对西藏拟溞的种群增长和日产量也有显著影响(P0.05),日采收率为20%时最佳,放养密度为1250ind./L、日采收率为20%时,西藏拟溞种群密度最高为(12 900±995.04)ind./L,平均日产量为(176.52±15.08)g/(m3·d)。  相似文献   

薄型高密度纤维板生产设备的要求分析     

何剑锋 《林业机械与木工设备》2011,39(8)

对薄型中高密度纤维板生产设备的要求作了简要分析。

Abstract：

A brief analysis is made of the requirements for thin medium high density fiberboard product manufacturing equipment.  相似文献   

种植密度对滴灌马铃薯生长、产量的影响   总被引：1，自引：0，他引：1  

王岩  刘畅  李云开  顾涛  苏艳平 《排灌机械工程学报》2020,38(1):90-94

为了了解耕培土滴灌条件下种植密度对马铃薯生长、产量以及水分利用效率的影响.试验共设密度分别为7.28×10⁴ 株/hm²(RS25),6.67×10⁴ 株/hm²(RS35),5.55×10⁴ 株/hm²(CK)3个处理.结果表明:随着种植密度的增加,株高、茎粗、干物质积累量以及商品薯率均有降低的趋势;产量、水分利用效率随种植密度的增加表现出先增大后减少,其中RS35处理产量和水分利用效率均表现最高,分别达到47 325 kg/hm²和12.05 kg/m³;在马铃薯品质方面,种植密度对马铃薯粗蛋白含量的影响不具有统计学意义;淀粉和维生素C随着密度的大幅增加而降低,其中RS25处理的淀粉较CK降低了5.57%,RS25处理的维生素C较CK降低了7.96%,同时RS35与CK处理不具有统计学意义.综上所述,种植密度为6.67×10⁴ 株/hm²的RS35处理马铃薯高产优质,且水分利用效率最高,为黑龙江地区滴灌马铃薯较为适宜的种植密度.  相似文献   

史密斯桉造林密度与施肥模式研究     

朱晓梅  康文玲  施庭有  段福文 《桉树科技》2015,(1):26-29

针对史密斯桉造林密度与施肥模式进行了研究，对试验地设置3种造林密度作主区，4种施肥模式作副区。对17个月生史密斯桉的试验调查进行分析，结果表明：造林密度对树高生长量的影响差异不显著，而对胸径影响差异显著，适宜密度为2000株·hm^-2。施肥对史密斯桉幼树树高、胸径生长的影响极显著，不同的施肥模式对史密斯桉幼林生长的效果是：桉树专用肥>复混肥+微肥>复混肥+磷肥+微肥>复混肥+磷肥。  相似文献   

氮肥与密度互作对单粒精播花生根系形态、植株性状及产量的影响   总被引：1，自引：0，他引：1  

Jun-Hua LIU  Zheng-Feng WU  Pu SHEN  Tian-Yi YU  Yong-Mei ZHENG  Xue-Wu SUN  Lin LI  Dian-Xu CHEN  Cai-Bin WANG  Shu-Bo WAN 《作物学报》2020,46(10):1605-1616

为明确花生单粒精播适宜的氮肥水平和种植密度,本研究于2018年和2019年以‘花育22’为供试花生品种,设置3个氮肥水平(0 kg hm~(–2), N0; 60 kg hm~(–2), N1; 120 kg hm~(–2), N2), 3个种植密度(7.93万株hm~(–2), D1; 15.86万株hm~(–2),D2; 23.79万株hm~(–2), D3),采用二因素裂区试验设计,研究氮肥、密度及其互作对单粒精播花生根系形态、植株性状及产量的影响。氮肥对花生根长、根表面积、根体积、根干重的影响不显著,而密度的影响显著。单株根长、根表面积、根体积及根系干重随密度的增加而降低, D1显著高于D2和D3, D2、D3处理间差异不显著;单位面积根长、根表面积、根体积及根系干重随密度的增加而增加, D1显著低于D2和D3, D2、D3处理间差异不显著。氮肥和密度互作对2019年收获期单位面积根长、根表面积的影响显著,与D1相比, N1处理下D3的增幅显著高于N0和N2处理。氮肥及氮肥与密度互作对植株性状的影响存在年度和时期间的差异,主茎叶片数、侧枝数和主茎第一节间粗随密度增加有降低趋势。氮肥对荚果产量的影响不显著,荚果产量随密度的增加呈增加的趋势。产量与根体积、根干重、主茎叶片数、主茎高及侧枝长呈显著正相关。综上所述,在本试验条件下,花生单粒精播适宜的氮肥(N)水平为60 kg hm~(-2),种植密度为18.8万株hm~(-2)。  相似文献   

网络嵌入性、商业模式创新与企业竞争优势关系研究     

孟迪云  王耀中  徐莎 《湖南农业大学学报(自然科学版)》2016,(5):108-114

基于商业模式创新中介效应，依据全国314家企业问卷调查的样本数据，运用多元线性回归方法，考量网络嵌入性、商业模式创新和企业竞争优势之间关系，结果发现：关系嵌入性、结构嵌入性与竞争优势均有显著的正向关系；商业模式创新在关系嵌入性、结构嵌入性与企业竞争优势的关系中起着中介作用。鉴此，企业应注重构建不同形式的网络嵌入，推动商业模式的调整与变革，以提高企业竞争优势。  相似文献   

密度与环境因子对蒙古黄芪育苗影响研究   总被引：2，自引：1，他引：1  

王晓飞  魏国江  关向军  刘淑霞  肖宇  吴耀坤  徐海军 《中国农学通报》2020,36(15):43-47

为了明确育苗时密度与环境因子对蒙古黄芪生长特征影响,本试验以蒙古黄芪为研究对象,通过单因素田间随机区组试验,测定蒙古黄芪株高、茎粗、根粗和根长4个指标。结果表明,密度对蒙古黄芪影响最大,其次是湿度,最后是光照和电导率。密度与蒙古黄芪株高、茎粗、根粗呈现负相关性,与根长呈正相关性(P<0.05),密度为400株/m ²时,株高、茎粗及根粗最大,密度为1000株/m ²时根长最大。  相似文献   

Short time effects of biological and inter-row subsoiling on yield of potatoes grown on a loamy sand,and on soil penetration resistance,root growth and nitrogen uptake     

《European Journal of Agronomy》2016

Soil compaction, especially subsoil compaction, in agricultural fields has increased due to widespread use of heavy machines and intensification of vehicular traffic. Subsoil compaction changes the relative distribution of roots between soil layers and may restrict root development to the upper part of the soil profile, limiting water and mineral availability. This study investigated the direct effects of inter-row subsoiling, biological subsoiling and a combination of these two methods on soil penetration resistance, root length density, nitrogen uptake and yield. In field experiments with potatoes in 2013 and 2014, inter-row subsoiling (subsoiler) and biological subsoiling (preceding crops) were studied as two potential methods to reduce soil penetration resistance. Inter-row subsoiling was carried out post planting and the preceding crops were established one year, or in one case two years, prior to planting. Soil resistance was determined with a penetrometer three weeks after the potatoes were planted and root length density was measured after soil core sampling 2 months after emergence. Nitrogen uptake was determined in haulm (at haulm killing) and tubers (at harvest). Inter-row subsoiling had the greatest effect on soil penetration resistance, whereas biological subsoiling showed no effects. Root length density (RDL) in the combined treatment was higher than in the separate inter-row and biological subsoiling treatments and the control, whereas for the separate inter-row and biological subsoiling treatments, RLD was higher than in the control. Nitrogen uptake increased with inter-row subsoiling and was significantly higher than in the biological subsoiling and control treatments. However, in these experiments with a good supply of nutrients and water, no yield differences between any treatments were observed.  相似文献   

宁夏绿洲禾豆牧草混播组合及其比例效应   总被引：1，自引：0，他引：1  

祁亚淑  朱林  许兴 《草业科学》2015,(9):1463-1472

在宁夏中部半干旱带有补灌的条件下,以紫花苜蓿(Medicago sativa)、沙打旺(Astragalus adsurgens)、羊草(Leymus chinensis)和老芒麦(Elymus sibiricus)为试验材料,豆科与禾本科牧草分别按照3∶7、5∶5、7∶3共3种不同比例进行混播,研究了不同混播组合及比例对其经济投入产出比、干草及主要营养成分产量、相对总产量及竞争力等方面的影响。两年的试验结果表明,3种豆禾牧草混播比例的产量均显著大于单播禾本科牧草的产量(P0.05)。苜蓿与禾本科牧草混播组合2013年及2014年的产量均显著高于沙打旺与禾本科牧草的混播组合(P0.05),其中,紫花苜蓿∶羊草为7∶3的混播组合的产量为最高(P0.05),粗蛋白和粗脂肪的总产量最高且投入产出比最低。紫花苜蓿+禾草组合中豆科牧草竞争力均大于相同比例下沙打旺+禾本科牧草组合中豆科牧草竞争力。沙打旺+禾本科牧草混播组合中,相对总产量(RYT)大于1的组合多于紫花苜蓿+禾本科牧草混播组合,其中,沙打旺∶羊草为7∶3的混播组合的两年平均RYT最高。以上结果说明,在宁夏中部半干旱带建植栽培草地时,紫花苜蓿∶羊草为7∶3的混播组合有较好的产量效应和最低的投入产出比;而沙打旺∶羊草为7∶3的混播组合中不同物种生长较为均衡。  相似文献