榨菜生长过程中硝酸盐分布规律初研

按照榨菜的正常播种时间和生长季节,连续3 a对榨菜移栽苗、返青苗、榨菜茎膨大初期、膨大期、成熟期及雨水节后期按GB/T 15401-94方法进行了硝酸盐含量的测定,从900多个检测数据中发现了硝酸盐蓄积量从移栽到成熟过程中的分布规律.     

人工湿地系统中梭鱼草和香蒲对镉积累的动态变化

为探讨人工湿地系统中挺水植物梭鱼草(Pontederia cordata)和香蒲(Typha orientalis)对镉(Cd)积累的动态变化,通过在室外表面流人工湿地采样和室内分析相结合的方法,对8-12月梭鱼草和香蒲地上部和地下部的生物量、镉含量及积累量的动态变化进行了分析。结果表明,梭鱼草根部和茎叶镉含量为0.25~0.70mg/kg和0.07~0.18mg/kg,香蒲根部和茎叶镉含量为0.16~0.39mg/kg和0.11~0.17mg/kg,根部镉含量均显著高于各自的茎叶部,两种植物各部位镉含量均在10月达到最大值,两者对镉的富集与转运能力均随着月份的变化而变化,都呈先增高、后降低的趋势;其中,梭鱼草对底泥镉的富集系数为0.76~3.13,香蒲为0.63~0.91,两者的富集系数最高值均出现在10月;两者的转运量系数分别为1.12~10.47、3.25~8.10,最大值分别出现在9月、10月。在10月之前,同一月份梭鱼草地上部的生物量和对湿地中镉积累量均极显著或显著高于香蒲。两种植物地上部分生物量和对湿地中镉积累量均极显著高于地下部分(P<0.01)。综合考虑两种植物的生物量及对镉的积累量,9月和10月分别为梭鱼草和香蒲地上部分最佳收获月份,能够最大化去除湿地系统中的镉。     

Effects of vertical distribution of soil inorganic nitrogen on root growth and subsequent nitrogen uptake by field vegetable crops

Information is needed about root growth and N uptake of crops under different soil conditions to increase nitrogen use efficiency in horticultural production. The purpose of this study was to investigate if differences in vertical distribution of soil nitrogen (N_inorg) affected root growth and N uptake of a variety of horticultural crops. Two field experiments were performed each over 2 years with shallow or deep placement of soil N_inorg obtained by management of cover crops. Vegetable crops of leek, potato, Chinese cabbage, beetroot, summer squash and white cabbage reached root depths of 0.5, 0.7, 1.3, 1.9, 1.9 and more than 2.4 m, respectively, at harvest, and showed rates of root depth penetration from 0.2 to 1.5 mm day^?1 °C^?1. Shallow placement of soil N_inorg resulted in greater N uptake in the shallow‐rooted leek and potato. Deep placement of soil N_inorg resulted in greater rates of root depth penetration in the deep‐rooted Chinese cabbage, summer squash and white cabbage, which increased their depth by 0.2–0.4 m. The root frequency was decreased in shallow soil layers (white cabbage) and increased in deep soil layers (Chinese cabbage, summer squash and white cabbage). The influence of vertical distribution of soil N_inorg on root distribution and capacity for depletion of soil N_inorg was much less than the effect of inherent differences between species. Thus, knowledge about differences in root growth between species should be used when designing crop rotations with high N use efficiency.     

灌溉量和氮肥增效剂对夏玉米产量及水肥利用的影响

为探究水分和氮肥增效剂对夏玉米生长及水肥利用的综合影响，通过设置40 mm（W1）和60 mm（W2）两个灌水水平下不施氮肥（N0）、施用氮肥（U）、氮肥+硝化抑制剂（U+DCD）、氮肥+脲酶抑制剂（U+NBPT）、氮肥+双效抑制剂（U+N+D）5种氮肥施用措施，开展夏玉米田间试验。结果表明：相较于施用氮肥处理，氮肥配施增效剂可以显著提高夏玉米产量、成熟期地上生物量、净收益、水分利用效率和氮肥偏生产力，增幅分别为5.92%~13.82%、5.85%~18.07%、11.12%~24.30%、12.35%~41.83%和5.93%~13.80%，其中氮肥配施双效抑制剂效果较优；氮肥配施脲酶抑制剂和双效抑制剂可以降低夏玉米农田土壤氨挥发累积量和成熟期土壤硝态氮残留量，前者效果最优。相比于W1，W2水平下氮肥配施双效抑制剂处理玉米产量、成熟期地上生物量、净收益、水分利用效率和氮肥偏生产力分别提高10.54%、15.51%、19.40%、20.31%和27.36%；氮肥配施脲酶抑制剂处理农田土壤氨挥发累积量和硝态氮残留量分别降低11.33%和48.46%。综合考虑夏玉米施肥灌水方案的经济效益、环境效益、水肥利用效率和玉米植株生长，构建模糊综合评价体系，得到最优处理为灌水量60 mm下氮肥配施双效抑制剂。     

杨树苗木叶硝酸还原酶活力的初步研究

硝酸还原酶是植物体内氮素代谢的关键酶。植物从外界环境中吸收的硝酸盐需要经过一系列酶促反应才能转化成氨基酸和蛋白质,以供生长需要。硝酸还原酶是这个代谢过程中的第一个酶,也是个限速酶,其活力的高低与植物同化NO_3~--N的能力和速度有直接关系。汤玉玮等的研究发现,硝酸还原酶活力与作物的耐肥性呈负相关,并在综述国内外有关研究文献中指出,该酶可以做为作物育种和营养诊断的生化指标。     

毛竹林凋落叶分解失重及养分累积归还模式

经过１０４周对２个试验点上包括３种立竹度和２种林分组成共５种处理条件下的毛竹林凋落叶的分解过程研究，结果表明：分解初期失重迅速，而后趋于缓慢。分解剩余率与分解时间之间存在着指数函数关系。林分立竹度和组成对竹林凋落叶分解速度有着显著影响，竹栎混交林及立竹度为３０１５株／ｈｍ＾２纯竹林处理下，凋落叶的分解速度分别高于纯竹林的其它２种立竹度处理。剩余物中的Ｎ、Ｐ的浓度随分解呈增加趋势，两者变化模式相似，     

磷素环境与马褂木种源的生长和干物质积累

自然土壤中有效磷含量很低,难以满足植物最佳生长的需要。据统计,在全世界13·19亿hm2的耕地中约有43%缺磷,而我国耕地则有2/3缺磷(何绪生等,1998)。我国南方地区高温多雨,富铝化作用明显,多数土壤呈酸性或强酸性,磷素固定强烈,土壤有效磷含量仅在1~2mg·kg-1(邱燕等,2003)。虽然施用磷肥的效果显著,但其利用率一般不超过10%,多为土壤固定并转变成植物较难吸收的Ca-P、Fe-P和Al-P等(熊毅,1997)。鉴于植物具有将土壤难溶态磷转化为有效态磷并加以吸收利用的能力,通过选育磷高效利用的植物品种来开发土壤中难溶态的磷素资源,可减小对施用磷…     

杜仲叶内杜仲胶的形成积累规律

通过对杜仲叶内杜仲胶形成与积累的动态进行全面系统的研究,探索杜仲叶含胶性状年变化和逐年变化的特点和规律以及不同着生部位叶片含胶率随叶龄变化的规律.结果表明:在一年的不同季节中,叶片含胶率差异很大,春季展叶时,叶片含胶率最低,6月下旬达到最大值,着生在枝条不同部位的叶片虽然展叶时间不同,但是叶片含胶率都是在展叶时最低,在叶龄50~65 d时,含胶率几乎都达到最大值,杜仲叶片含胶率与叶龄的相关性达到了极显著水平;杜仲叶片含胶率随着树龄的增大含胶率总体呈提高的趋势并逐步趋于稳定.     

A review of the effect of stresses between lifting and planting on nursery stock quality and performance

This paper presents the experimental evidence on the effects of desiccation, low and high temperatures, rough handling, root loss and storage between lifting and planting on plant quality and performance. The review concentrates on the impact of these stresses on outplanting performance; their effect on seedling properties, such as root growth potential and root electrolyte leakage, is also described. Stresses most often happen in combination but there is relatively little information on their interactions. Examples of desiccation plus rough handling, cold storage plus desiccation, frost damage plus freeze storage and the triple stress of desiccation, heating and rough handling are presented. The limited evidence on the cumulative effect of stresses suggests tentatively that damage from rough handling does not accumulate in the same way as damage from desiccation and prolonged storage. Factors affecting stress resistance are briefly reviewed.There are three impediments to producing a critical review of the literature: experimental treatments, particularly of desiccation and rough handling, can rarely be directly compared; the impact of stress treatments can be modified by a large number of factors, and the levels of stress have seldom been quantified in normal forestry practice. The first two problems also make it difficult to formulate general statements concerning critical thresholds for the stresses. However, instruments are now available for measuring and monitoring stresses between lifting and planting and it is, in theory, possible to model the effects of these stresses to take account of the many factors that modify their impact on seedling survival and growth. This offers the possibility of significant improvements in our ability to predict the effect of stresses between lifting and planting on seedling performance.