Acoustic evaluation of the vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in Lake Biwa

SUMMARY: The vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in the pelagic waters of Lake Biwa was evaluated from June to September in 1995–97 from eight acoustic surveys using a quantitative echosounder. In each survey, echoes from a depth range of 3 m to the sea bottom were collected at a station every 2.7 s for 24 h together with measurements of vertical profiles of water temperature and chlorophyll-a. The ayu's echoes were identified using an underwater video camera. The ayu were observed near the maximum chlorophyll-a depth and above the thermocline. Their density was highest at depths of 4–11 m with 2–4 individuals/m ³ and was almost zero below 20 m. Echo signs were recorded as having a frequent duration of more than 1 h at night, whereas were of a shorter duration in the day. The fish stay in the epilimnion during the day without any clear vertical migration, but are distributed more uniformly at night. The advantages of remaining in the epilimnion are discussed in terms of food availability and predator avoidance.     

奶牛难产激发应激性急性肾上腺皮质功能不全——心衰、水电解质严重失调辩析

应激性急性肾上腺皮质功能不全症的病理机制十分复杂,目前人医的各类文献中大都以“垂体—肾上腺轴”功能不全、功能衰竭、或发生广泛性出血坏死性病演作解释。本病在奶牛分娩难产过程中并不少见,病牛的症状表现以心衰和失钠性低血症为主征。但在兽医临床上由于认识不足,曾有不少中外学者将奶牛产后卧地不起的各类疾病,含糊地统称为“母牛睡倒爬不起来综合征”;更由于救治不当,病牛常以淘汰或死亡告终。本文通过对一具体典型病例辨析,着重讨论了本病的基本病理反应和确立诊断依据,强调对本病救护施治时应遵循的基本原则,供同道们在分析和解决这一实际问题时参考。     

滴水量对新大豆27号根系生长及产量的影响

为揭示滴水量对超高产大豆根系生长的影响规律,设置975 m3·hm-2(W1)、1 575 m3·hm-2(W2)、2175 m3·hm-2(W3)、2 775 m3·hm-2(W4)4种滴水处理,对各处理0~100 cm土层含水量、新大豆27号根系干重、侧根长和产量进行测定分析。结果表明:随着滴水量的增加,0~40 cm土层的含水量增加;0~20 cm土层根干重密度和侧根长密度增幅最大,20~40 cm土层增幅其次;增加生育中后期0~80 cm土层总根干重和总侧根长,鼓粒初期W2、W3、W4处理的根干重分别较W1增加14.2%、30.4%、41.1%,侧根长分别较W1增加17.4%、25.7%、40.3%;提高0~40 cm土层根系活力,增加根系伤流量,提高水分利用效率,W3、W4鼓粒初期0~80 cm土层根干重分别为88.6、95.8 g·m-2,侧根长为432.4~482.9 m·m-2,产量分别为6 082.6 kg·hm-2、6 404.7 kg·hm-2,水分利用效率为1.30左右。新疆伊宁地区大豆的适宜滴水量为2 175~2 775 m3·hm-2。     

浅析灌溉对作物根系及产量的影响

结合文献资料,从作物根系的水平分布、垂直分布、硝态氮运移及产量等几个方面,概述了不同灌溉量和灌溉方式对作物的影响,分析了滴灌、渗灌等微灌技术的应用。最后,针对经济林木生产的实际现状,进行了展望：探索一种成本低、简单易操作、便于推广应用的灌溉措施更具有理论和实践意义。     

立辊式玉米收获割台夹持输送装置设计与试验

针对现有立辊式玉米收获机割台夹持输送装置存在的夹持稳定性差、断茎率高等问题,该研究基于立辊式玉米割台摘穗特点,设计了一种夹持输送间隙随植株茎秆粗细自适应调节的夹持输送装置。该装置由分禾机构和夹持输送机构组成,分禾机构保证玉米植株的单株有序喂入,并辅助往复式切割器完成植株根部的切割;夹持输送机构实现切断植株在立辊式割台上的有效夹持和输送。通过对拨禾喂入过程植株的运动分析以及夹持切割和夹持输送过程植株的姿态变化规律分析,确定夹持输送装置有效拨禾段链条长度为500 mm,夹持输送机构轨道长度为1 100 mm,割台最大夹持输送量为3株,夹持轨道间的垂直距离为40 mm,两夹持链条间的夹持间隙可调节范围为16～40 mm。采用响应曲面法分析了收获机前进速度、主动链轮转速、割台倾角和植株喂入角对夹持输送装置作业性能的影响。试验结果表明,当收获机前进速度为2.8 m/s、主动链轮转速1 210 r/min、割台倾角18°、植株喂入角为60°时,果穗总损失率为0.83%,断茎率为0.12%;相比现有普通夹持输送装置,果穗总损失率和断茎率分别由2.80%和0.98%降低到0.83%和0.12%,分别降低了30%和12%。研究结果可为立辊式玉米收获割台的优化改进提供理论依据和参考。     

辽东山区胡桃楸次生林垂直结构特征研究

以辽东山区胡桃楸次生林为研究对象,采用树冠光竞争高法将胡桃楸次生林划分为上、中、下3个林层,并在此基础上分析了各林层的树种组成、径级结构、空间结构特征等。结果表明：上、中、下3个林层平均树高分别为14.86～17.02、11.18～12.77 m和7.33～8.01 m,方差分析结果表明,不同林层树高间差异极显著,分层效果较好。上林层为林分蓄积量主要贡献层,占林分总蓄积量61.86%～78.7%;其次为中林层,下林层最少。各林层径级分布曲线不同,下林层径级分布呈反“J”曲线,中林层呈左偏单峰曲线,上林层为多峰曲线。林分整体处于中度混交向强度混交的过渡状态,3块标准地上、中林层的混交度平均值分别为0.512、0.574,为中度混交,下林层平均混交度为0.671,接近强度混交,各林层平均混交度表现为随垂直高度的降低而增大。标准地1和标准地3为聚集分布,标准地2属于随机分布。随林层垂直高度的降低,林分聚集度和竞争指数均有所增加。从林分的垂直结构判断胡桃楸次生林的林分结构相对稳定,其未来的演替方向可能为以落叶松和胡桃楸为优势种的针阔混交林或者以胡桃楸、蒙古栎和花曲柳为优势种的阔叶混交林,下林层的更新能力较差,应采取人工措施促进其天然更新。     

南海中部海域夏季叶绿素a浓度垂向分布特征

根据2014年7月～8月南海中部海域(12N～18N,110E～117E) 调查获得的水柱方向上连续的叶绿素a浓度(Chl-a)数据,分析了南海中部海域夏季Chl-a垂向分布特征。结果表明:1)南海中部海域Chl-a垂向分布呈现先增加后减小的趋势,在30～70 m水层出现Chl-a高浓度区;2)次表层Chl-a最大值(subsurface chlorophyll a concentration maximum,SCM)强度变化为0.94～4.69 mgm-3, 平均为1.90 mgm-3, 是遥感表层Chl-a平均值的18.10倍,SCM深度变化为4～75.36 m,SCM厚度变化为19.01～80.36 m;3)从断面分布来看,局部海域Chl-a垂向分布受到上升流的显著影响,断面A上沿岸上升 流区表现出明显的SCM强度大、深度浅和厚度大的特征, 而断面B上中沙群岛岛礁上升流区同样表现出SCM强度大、深度浅的特征,但是厚度相对较小。     

Risk Assessment and Biosafety Studies of Transgenic Bt Rice （Oryza sativa L.）

Transgenic crops having alien genes from different sources are getting popularity. A Rice （Oryza sativa L.） containing gene from Bacillus thuringiensis, a soil bacterium, was assessed to study the potential risks of transgenic plants on environment. The crop was found resistant to target insect pests. Rice variety Basmati-370 transformed with two insecticidal genes, crylAc and cry2A, was grown under field conditions for several years. Data were collected at different stages of the plant growth. Fate of Cry protein in soil, effect of Bt protein on non-target insects, risks of vertical and horizontal gene flow were evaluated. No potential hazard was found at all levels. Bt protein was unstable and degraded significantly in soil within 30 days after harvesting the crop. No harmful effects were found on non-target insects （insects other than order lepidoptera）. Maximum gene flow of 0.02% was observed at close spacing and no evidence of horizontal gene transfer to Rhizobium spp. was found. In conclusion, the transgenic rice plants transformed with Bt genes have no harmful effects on the environment.     

北京东南郊再生水灌区土壤PAHs污染特征

采用Eijkelkamp土壤采样器对北京东南郊再生水灌区进行了3个钻孔剖面采样,同时采集了灌溉用水及地下水样品,并采用气相色谱-质谱联用仪对16种多环芳烃(PAHs)进行定量分析。结果表明,表层土壤中有14种PAHs检出,浓度在0.4～53.1μg·kg-1之间,∑PAHs平均含量为206.7μg·kg-1,达到了土壤污染临界值;表层以下PAHs的检出种类和含量显著减少,以中、低环的萘、菲、芴、荧蒽、芘为主,∑PAHs仅占表层的3.8%～12.0%,从剖面PAHs含量变化可以判断,低环PAHs较易迁移,迁移性强弱顺序为萘、芴>菲>芘、荧蒽;污灌区表土中PAHs组成与大气降尘接近,但与再生灌区有明显差异,这种差异主要由于灌溉用水不同所造成;再生水灌区表土以下土壤剖面检出的PAHs与再生水中的PAHs一致,说明再生水灌溉是导致土壤剖面PAHs污染的主要原因,同时地下水中检出的PAHs种类也与土壤剖面基本一致,但含量较高,可能是早期污水灌溉所造成。