Decomposition of emergent macrophyte roots and rhizomes in a northern prairie marsh

Dry mass, nitrogen and phosphorus content in belowground litter of four emergent macrophytes (Typha glauca Godr., Phragmites australis (Cav.) Trin., Scolochloa festucacea (Willd.) Link and Scirpus lacustris L.) were followed for 1.2 years in a series of experimental marshes, Delta Marsh, Manitoba. Litter bags containing roots and rhizome materials of each species were buried in unflooded soil, or soil flooded at three water depths (1–30, 31–60, > 60 cm). There were few differences in dry mass loss in unflooded or flooded soils, and depth of flooding also had little effect on decomposition rates. In the flooded sites, Scolochloa and Phragmites roots lost more mass (48.9–63.8% and 59.2–85.5%, respectively) after 112 days than Typha and Scirpus (36.3–43.6 and 37.0–47.2%, respectively). These differences continued through to the end of the study, except in the shallow sites where Scirpus roots lost more mass and had comparable mass remaining as Scolochloa and Phragmites. In the unflooded sites, there was little difference between species. All litters lost nitrogen (22.9–90.0%) and phosphorus (46.3–92.7%) during the first 112 days, then levels tended to remain constant. Decay rates for our belowground root and rhizome litters were comparable to published literature values for aboveground shoot litter of the same species, except for Phragmites roots and rhizomes which decomposed at a faster rate (−k = 0.0014−0.0032) than shoots (−k = 0.0003−0.0007, [van der Valk, A.G., Rhymer, J.M., Murkin, H.R., 1991. Flooding and the decomposition of litter of four emergent plant species in a prairie wetland. Wetlands 11, 1–16]).

vertical growth of thalassia testudinum seasonal and interannual variability

The vertical growth of shoots of the seagrass Thalassia testudinum Banks ex Konig in four meadows, along a range of exposure to waves, in the Mexican Caribbean was examined to elucidate its magnitude and its relationship to sediment dynamics. Average internodal length varied between 0.17 and 12.75 mm, and was greatest in the meadow which experienced the greatest burial by sand waves moved by Hurricane Gilbert (September 1988). Internodal length showed annual cycles, confirmed by the flower scars always preceding or coinciding with the annual minimum internodal length. These annual cycles on the shoot allowed estimation of annual leaf production, which varied, on average, between 14.2 and 19.3 leaves per shoot year-1. High vertical shoot growth was associated with long internodes and high leaf production rate, which increased with increasing vertical shoot growth to a maximum of approximately 25 leaves per shoot year-1, with vertical growth of about 30 mm year-1 or more. Average internodal length showed substantial interannual differences from perturbations derived from the passage of Hurricane Gilbert. The growth response of the plants surviving moderate burial and erosion after the hurricane involved enhanced vertical growth and increased leaf production, and reduced vertical growth, respectively, after 1988. The variability in shoot vertical growth of T testudinum can be separated into seasonal changes in plant growth, and long-term variability associated with episodic perturbations involving sediment redistribution by hurricanes.

Seed germination and seedling morphology of the seagrass, Halophila engelmannii (Hydrocharitaceae)

Seeds of Halophila engelmannii Aschers., that were collected in Redfish Bay, Texas, at weekly intervals from mid-May to mid-June 1986, began to germinate 3–4 weeks after collection. Most of the collections subsequently showed an increase in the rate of germination under increased light intensity and all had a stoppage of germination after transfer to darkness, indicating a light requirement to break endogenous seed dormancy. During the 5 weeks after seeds germinated, seedlings in soil culture produced a rosette of six leaves before the appearance of a rhizome bud in the axil of the third leaf. The first node of the rhizome produced a root and an upright shoot with a pseudowhorl of three to five leaves.

黄土丘陵区生态修复地不同抗侵蚀植物的消长变化过程

依据黄土丘陵区生态修复过程中植被演替阶段与植物生长型,将抗侵蚀植物分为一年生草本植物,多年生根茎禾草植物,多年生根蘖性草本和半灌木植物、灌木植物和乔木植物5类。一年生草本植物、多年生根茎禾草植物适应土壤侵蚀环境的能力比较强,同时具有一定程度的防止土壤侵蚀的作用;灌木和乔木植物适应土壤侵蚀环境的能力比较弱,而防止土壤侵蚀的作用很强;多年生草本和半灌木植物适应土壤侵蚀环境的能力适中,而防止土壤侵蚀作用的能力优于一年生草本和多年生根茎禾草群落,但不及乔灌木群落。并提出了在天然草本植被恢复的基础上进行人工造林的相关建议。

氮磷营养对小麦水分关系的影响

比较研究了氮磷营养对春小麦水分关系影响的差异。结果表明 ,土壤干旱情况下 ,氮磷营养虽然皆增强了春小麦的渗透调节能力 ,但由于氮磷营养对作物地上地下部生长的不同进促作用而对作物的水分状况产生了完全相反的影响。氮营养增强了作物对干旱的敏感性 ,使其水势和相对含水量大幅度下降 ,蒸腾失水减少 ,自由水含量增加而束缚水含量减少 ,并使膜稳定性降低 ;而磷营养则明显改善了植株的水分状况 ,增大了气孔导度 ,降低了其对干旱的敏感性 ,增加了束缚水含量 ,并使膜稳定性增强

原子吸收光谱法测定膜荚黄芪不同器官矿质元素含量

应用混合酸HNO3-HClO4(4∶1)在常压微沸条件下对膜荚黄芪根系及茎叶样品进行消解,采用原子吸收光谱法测定了膜荚黄芪不同器官即根及茎叶中五种人体必需矿质元素K,Fe,Zn,Mn和Cu含量,并对结果进行了统计分析与比较。该方法标准曲线相关系数为0.997 3~0.999 9,加标回收率为92.88%~109.25%,相对标准偏差(RSD,n=5)为0.393 5%~3.175 2%。方法简单,结果可靠。结果显示,膜荚黄芪根及茎叶中5种矿质元素含量顺序均为K>Fe>Zn>Mn>Cu。膜荚黄芪不同器官矿质元素含量不同,根中富含Fe,Zn,Cu元素,根内Fe含量是茎叶的1.54倍。茎叶中也含有丰富的矿质元素,特别是K和Mn元素。茎叶中K含量是根的1.63倍,这与黄芪的药效相符合。试验结果将为研究矿质元素在黄芪植株中的分布以及矿质元素含量与黄芪药效相关性提供理论依据。

土壤水分与氮肥对玉米根系生长的影响

利用田间小区试验研究了不同土壤水分条件下N肥对根系生长(根长、根重和根冠比)的影响。结果表明,玉米拔节期和开花期无论水分条件如何,施N肥可增加其总根长、表层根长和根重并使根冠比下降;灌浆期施N肥可增加总根长和表层根长,但正常水分条件下N肥使根重和根冠比下降,而干旱条件下N肥对根重和根冠比则无影响。不同处理根冠比大小与N吸收和分配有很大关系。

水肥空间组合对冬小麦生物学性状及生物量的影响

目的】研究水肥空间组合对冬小麦形态指标及生物量的影响,对指导旱地施肥具有一定理论和实践意义。【方法】以肥熟土垫旱耕人为土为供试土壤,在全生育期遮雨和人工控制土壤水分条件下,采用分层隔水土柱试验法研究与田间土层分布相同土柱不同土层水分、氮、磷组合对冬小麦叶面积、株高、分蘖数、生物量、根冠比和收获指数等指标的影响。【结果】与整体湿润水分处理相比,上干下湿水分处理(0～30cm土层干旱胁迫,30～90cm土层湿润)下,抽穗期小麦旗叶面积、株高分别降低7.03%和3.77%;小麦地上部和根系生物量及收获指数也不同程度降低,但根冠比增加。从肥料处理看,单施磷和氮磷配施处理,小麦叶面积、株高、有效分蘖数和总生物量均极显著高于单施氮和CK,这与供试土壤各土层严重缺磷,而氮素供应相对丰富有关。从不同土层施肥看,在两种水分处理下,单施氮时,以均匀施入0～90cm土层小麦叶面积、株高、有效分蘖数、地上部生物量和根系生物量最高,施入0～30cm土层最低;单施磷和氮磷配施时,0～90cm与0～30cm土层施肥间总叶面积、旗叶面积、株高、有效分蘖数以及总生物量差异不显著,但均显著高于30～60cm和60～90cm土层相应施肥处理。【...

采用了剪枝优化的子类型关系判定算法

静态类型化XML处理语言为处理XML数据提供了新的途径,但现有的此类语言大多数效率较低.研究此类语言的一个重要问题——子类型关系的判定,并使用剪枝优化策略对XDuce的子类型关系判定算法进行优化.实验数据显示,优化后算法的执行效率平均提高20%.该策略具有普遍性,对所有使用类似算法的静态类型化XML处理语言都有效.

Formation and early development of tetraspores of Polysiphonia urceolata (Rhodomelaceae, Rhodophyta)

Polysiphonia urceolata is one type of potential commercial red seaweeds used for breeding and cultivation, because of its significant biochemical and biomedical application. However, the information of breeding and seedling incubation for cultivation is limited, especially the early development. In this study, tetrasporohyte and gametophyte of P. urceolata were taken as the study materials in Huiquan Bay, Qingdao, China. The cleaned and sterilized tetrasporophytes and gametophytes were pre-cultured in sterilized seawater, then nurtured at 18A degrees C, 25 mu mol photons m(-2) s(-1) in 12:12 h (light:dark) photoperiod. Continuous observation under microscope showed that the early development consists of bipolar division stage and seedling stage. In the division stage, tetraspores germinate into bipolar sporelings that further differentiate into a colorless rhizoidal portion and a lightly pigmented upright shoot. The lightly pigmented rhizoidal cell develops to a rhizoid and the larger pigmented cell transforms to an erect axis. In the seedling stage, several quasi-protuberances appear on the erect axis and form juvenile seedlings. The results demonstrate the culture of P. urceolata from tetraspores under laboratory conditions.

Screening of salt tolerant watercress variants on natural seawater contained medium

The responses of stem segments of watercress (Nasturtium officinale R. Br.) to 6-BA,NAA and 2,4-D were studied. MS medium supplemented with 2.0 mg/L 6-BA, 0.2 mg/L 2,4-D was used for callus initiation and maintenance. MS medium supplemented with 4.0 mg/L 6-BA was suitable for plant regeneration and MS medium without plant hormone supplement was used for rooting and plant propagation. For screening of salt tolerant calli, stem segments of watercress were plated onto callus initiation medium containing 1/3 natural seawater. Seventeen out of the 325 plated explants produced calli. The growth curves demonstrated that the growth rate of salt-tolerant calli on saline medium almost matched that of the control calli on normal medium. Some of the salt-tolerant calli were transferred to the normal regeneration medium or saline regeneration medium to induce plant regeneration. In the first case, buds and shoots were regenerated in the same way as those of control calli on normal regeneration medium. More than 1 000 regenerated shoots were obtained of which 83 regenerated shoots were cut and transferred to saline MS base medium. At first, all shoot growth was inhibited, but 40 days after the transfer, rapid-growing axillary shoots were observed on 16 of the original shoots but none on the control shoots on saline MS base medium. Moreover, green spots appeared on most calli 10 days after they were transferred to saline medium, however buds appeared only on 5 calli from the 30 transferred calli and at the end only 2 rapid-growing shoots were obtained from two calli. In total, 18 variant lines were obtained through. propagation of the salt-tolerant shoots on saline MS base medium. RAPD analysis was performed in 10 of the 18 salt-tolerant variant lines and DNA variation was detected in all the tested variant lines.

Competition between Stipa grandis and Cleistogenes squarrosa

Competitive strategy for resources between Cleistogenes squarrosa (Trin.) Keng which is a dominant species of grasslands degraded by moderate-heavy grazing, and Stipa grandis P. Smirnov, which is a dominant species of ungrazed communities, was studied using a replacement series method in a greenhouse. The knowledge would be helpful in managing grasslands and restoring the degraded C. squarrosa grassland. Although there was neither inter- nor intra-specific competition between the two species when no nutrients were added, intra-specific competition of C. squarrosa was observed and increased with increased nutrient availability and more sulfur (S) was allocated to the aboveground partition of the plant. Relative competitive ability of C. squarrosa was greater than that of S. grandis when nutrients were supplied regardless of S. There was no significant difference between shoot and root competition based on dry matter yields. However, root competition was significantly greater than that of shoot based on S uptake under all treatments. A significant interaction was not observed between shoot and root competition. Therefore, nutrients addition benefits the restoration of degraded grassland of C. squarrosa, which may not exclude S. grandis. Also productivity and forage quality of the community will be increased. (C) 2007 Elsevier Ltd. All rights reserved.

Effect of N fertilizer on the productivity and nutritive values of perennial grass mixtures in the alpine region of Qinghai-Tibetan Plateau, China

A study was conducted on grass mixtures that included smooth bromegrass (SB) + drooping wild ryegrass (DW), smooth bromegrass + Siberian wild ryegrass (SW) + crested wheatgrass (CW) and smooth bromegrass + Siberian wild ryegrass + drooping wild ryegrass + crested wheatgrass in the alpine region of Qinghai-Tibetan Plateau. The study was conducted from 1998 to 2000 to investigate the effects of N application rates and growing year on herbage dry matter (DM) yield and nutritive values. Herbage DM production increased linearly with N application rates. The effect of N application on DM yields was greater (P < 0.05) in the 2nd and 3rd production years than in the establishment year. Dry matter yields of SB + SW + CW and SB + SW + DW + CW can reach as high as 15 000 kg ha(-1) at 345 kg ha(-1) N rate in the 3rd growing year. With increased N application rates, crude protein (CP) contents and 48 h in sacco DM degradability of grasses increased (P < 0.05). No effect (P > 0.05) of N application was detected on organic matter (OM) and acid detergent fibre (ADF) concentration. It can be concluded that for increased biomass production in the alpine region of the Qinghai-Tibetan Plateau, a minimum of 345 kg N ha(-1) should be applied to grass stands in three split application of 115 kg N ha(-1), in early June, early July and late July

数控自动编程专家系统

本文简要地介绍了数控自动编程专家系统.其中包括:专家系统知识表示的形式;分层次的黑板结构;前向推理求解策略和相应的解释功能;系统针对不同类型的曲线组合,采用不同的独立的知识源(KS)进行处理.由于在知识的处理上采用编码技术,在前向推理求解策略中使用启发信息和“剪技”技术,提高了系统的时空效率.系统中的规划程序能自动规划切削路径.输出供数控车床使用的 NC 代码,并可在显示屏上进行图形显示和切削仿真.目前原型系统已经在 IBM-PC 和 Sun3/60计算机上利用FORTRAN 语言实现.

地震反射界面形态与介质各向异性属性联立成像：地震反射波旅行时与偏振信息综合反演

It has been a difficult problem faced by seismologists for long time that how exactly to reconstruct the earth's geometric structure and distribution of physical attributes according to seismic wave's kinematical and dynamic characteristics, obtained in seismological observation. The jointing imaging of seismic reflector and anisotropy attributes in the earth interior is becoming the research hot spot. The limitation of shoot and observation system makes that the obtained seismic data are too scarce to exactly reconstruct the geological objects. It is popular that utilizing only seismic reflection traveltimes or polarizations information make inversion of the earth's velocity distribution by fixing seismic reflector configuration (vice versa), these will lead to the serious non-uniqueness reconstruction due to short of effective data, the non-uniqueness problem of reconstructing anisotropy attributes will be more serious than in isotropy media. Obviously it is not enough to restrict the media structure only by information of seismic reflection traveltimes or polarizations, which even sometimes will lead to distorted images and misinterpretation of subsurface structure. So we try to rebuild seismic reflection structure (geometry) and media anisotropic structure (physics) in the earth interior by jointing data of seismic wave kinematics and dynamics characteristics, we carry out the new experiment step by step, and the research mainly comprises of two parts: one is the reconstruction of P-wave vertical velocity and anisotropic structure(Thomsen parameter s and 8) in the transversely isotropic media with vertical symmetrical axis(VTI) by fixing geometrical structure, and the other is the simultaneous inversion of the reflector surface conformation and seismic anisotropic structure by jointing seismic reflection traveltimes and polarizations data. Simulated annealing method is used to the first research part, linear inversion based on BG theory and Simulated annealing are applied to the second one. All the research methods are checked by model experiments, then applied to the real data of the wide-angle seismic profile from Tunxi, Anhui Province, to Wenzhou, Zhejiang Province. The results are as following The inversion results based on jointing seismic PP-wave or PSV-wavereflection traveltimes and polarizations data are more close to real model than themodels based simply on one of the two data respectively. It is shown that the methodwe present here can effectively reconstruct the anisotropy attributes in the earth'sinterior when seismic reflector structure is fixed.The layer thickness, P-wave vertical velocity and Thomsen anisotropicparameters {s and 8) could be resolved simultaneously by jointing inversion ofseismic reflection traveltimes and polarizations with the linear inversion methodbased on BG theory.The image of the reflector structure, P-wave vertical velocity and theanisotropy parameters in the crust could be obtained from the wide-angle seismicprofile from Tunxi (in Anhui Province), to Wenzhou (in Zhejiang Province). Theresults reveal the difference of the reflector geometrical structure and physicalattributes in the crust between Yangtze block and Cathaysia block, and attempt tounderstand the characteristics of the crustal stress field in the areas.