Shoot nitrate reductase activities of field‐layer species in different forest types. II

Analysis of in vivo shoot nitrate reductase activity (NRA) of the grass Deschampsia flexuosa (L.) Trin. has been proposed as a method of indicating the availability of nitrate in northern temperate forest soils. We report the seasonal variation in NRA and the influence of temperature on the NRA assay. Studies were performed in the field or on natural populations on topsoil monoliths in a greenhouse.

The induced in vivo NRA as measured at 28°C was higher in plants grown at lower than at higher temperatures within the range 4–20°C, although the induction was faster at higher temperatures. When the assay was performed at various temperatures, enzyme activity was much lower at lower temperatures. The accumulation of organic nitrogen in shoots showed that reduction actually increased with temperature. Transfer of monoliths from high to low temperature led to an increase of in vivo NRA within a day, whereas the decline caused by the reverse began after six days. Variations in temperature accounted for between 0 and 80% of the seasonal variation in NRA in the field, depending on the influence of the variability in nitrate supply.

Maximally induced NRA after application of nitrate was mostly higher in a clearfelling than in a closed forest. In the forest, there was a close correlation between current and maximally induced NRA. One interpretation of this result is that low availability of nitrogen may have been a cause of the lower maximally induced NRA there. This is supported by results from other studies.

We conclude that variations in temperature and availability of nitrogen, particularly nitrate, are largely responsible for seasonal variations in NRA. The influence of temperature can be adjusted for.     

Seasonal Variations in Physicochemical and Textural Properties of North Atlantic Cod (Gadus morh.ua) Mince

Abstract

Seasonal variations in physicochemical and textural properties of minced cod muscle from Icelandic coastal areas were evaluated. Measurements were performed on mince from the white muscle. Compared to the winter and summer values, hardness and cohesiveness, as measured by Instron, showed a drop in March to May and another drop was observed for cohesiveness during the autumn months. Expressible moisture changed slightly from March to August whereas results from the winter months indicate greater fluctuations. A minimum was observed for protein solubility in March and July. The surface hydrophobicity of proteins, increased gradually from November to May followed by a sudden drop, then a gradual increase again.     

Prediction of daily reference evapotranspiration by a multiple regression method based on weather forecast data

Prediction of daily reference evapotranspiration (ET ₀) is the basis of real-time irrigation scheduling. A multiple regression method for ET ₀ prediction based on its seasonal variation pattern and public weather forecast data was presented for application in East China. The forecasted maximum temperature (T _max), minimum temperature (T _min) and weather condition index (WCI) were adopted to calculate the correction coefficient by multilinear regression under five time-division regimes (10 days, monthly, seasonal, semi-annual and annual). The multiple regression method was tested for its feasibility for ET ₀ prediction using forecasted weather data as the input, and the monthly regime was selected as the most suitable. Average absolute error (AAE) and root mean square error (RMSE) were 0.395 and 0.522 mm d^?1, respectively. ET ₀ prediction errors increased linearly with the increase in temperature prediction error. A temperature error within 3 K is likely to result in acceptable ET ₀ predictions, with AAE and average absolute relative error (AARE) <0.142 mm d^?1 and 5.8%, respectively. However, one rank error in WCI results in a much larger error in ET ₀ prediction due to the high sensitivity of the correction coefficient to WCI and the large relative error in WCI caused by one rank deviation. Improving the accuracy of weather forecasts, especially for WCI prediction, is helpful in obtaining better estimations of ET ₀ based on public weather data.     

福建马铃薯S病毒的分子鉴定及发生情况

为明确福建省马铃薯S病毒(PVS)的发生与分布情况,对福建省马铃薯主要种植区的PVS进行了鉴定和普查.在利用电镜技术和传统生物学方法鉴定的基础上,克隆了PVS外壳蛋白(cp)基因,依据PVS外壳蛋白氨基酸序列建立了PVS不同分离物的系统进化树.研究表明,利用PVS 外壳蛋白氨基酸序列分析可准确鉴定PVS,同时可分析不同分离物间的分子差异.利用病毒特异性引物和DIG标记的PVS cp基因为探针,分别利用RT-PCR技术和核酸斑点杂交技术(NASH)对PVS进行了检测,并对检测技术进行了改进.调查结果表明,PVS在福建省广泛分布,发病率最高可达80%以上,当地农家自留种可能是田间PVS的主要来源.     

台湾75毛豆病毒病防治技术研究

研究表明,台湾75毛豆病毒病主要由蚜虫传毒而致,其发生与蚜虫的成虫迁飞时间与发生量关系极为密切.若成虫高峰正遇毛豆1、2叶展平期,毛豆上落蚜量大,发生就重.所以早播的重于迟播的,露地栽培重于套播的.防治上应以栽培避蚜为主,药剂防治为辅,才可取得理想效果.     

南美斑潜蝇及其寄生蜂消长规律

对云南省南美斑潜蝇及其主要寄生蜂潜蝇姬小蜂和潜蝇茧蜂的种群消长规律进行了研究。南美斑潜蝇在昆明关上菜区于 4、7、10月出现 3个高峰。潜蝇姬小蜂在春季蚕豆上种群数量较高 ,是控制南美斑潜蝇的主要蜂种。潜蝇茧蜂在秋季大棚内种群数量较高 ,是控制大棚南美斑潜蝇的主要蜂种。这两种寄生蜂对作物寄主有明显的选择性 ,潜蝇姬小蜂在春季的蚕豆、豌豆和芹菜上种群数量较高 ,潜蝇茧蜂在秋季的莴笋上种群数量较高     

苹果斯氏刺瘿螨发生与危害调查

斯氏刺瘿螨是四川省苹果上新发现的一种危害苹果叶片的害螨，以雌成螨在苹果芽的芽腋两侧越冬，翌年苹果芽萌动时开始出蛰。全年以５月中旬至６月中旬发生数量最多。气候温暖、低湿、少雨发生重，相反则轻。在调查的８个品种中，叶片多茸毛的品种受害重。天敌主要为捕食螨     

华北棉田二代棉铃虫发生程度中期预测

在华北棉区用扫网法和目测查虫法调查麦田一代棉铃虫幼虫发生量，用比较法和生命表分析法预测二代棉铃虫在棉田的发生程度和虫口密度。经1991—1994年应用检验，预测结果均与实际发生情况吻合。     

宁夏苜蓿病虫害发生现状及防治对策

通过2001—2002年的田间调查和室内鉴定,明确了宁夏苜蓿病虫害的发生种类、分布和危害程度。目前,在宁夏苜蓿生产中大面积发生并引起灾害性损失的害虫为蚜虫、蓟马、草地螟、象甲和潘叶蝇,病害为苜蓿褐斑病、霜霉病、白粉病和花叶病,并提出相应的防治对策。     

不同育秧方式对稻瘟病发生为害的影响

不同育秧方式对比试验的结果显示,秧田期在接种菌源条件下,旱育秧叶瘟较水育秧发生早、为害重;大田期在不防治条件下,旱育秧叶瘟、穗瘟发生为害显著轻于水育秧。说明在防止菌源进入的前提下,旱育秧是控制稻瘟病的一项好措施。