华东植物区系成分与日本植物间的联系

华东和日本两地为东亚地区重组成部分,同属于中国－日本森林植物亚区。两地植区物系成具有较高的相似性。两地共有连香树科（Ｃｒｃｉｄｉｐｈｙｌｌａｃｅａｅ）、三尖杉科（Ｃｅｐｈａｌｏｔａｃｅａｅ）、领春木科（Ｅｕｐｔｅｌｅａｃｅａｅ）、旌节花科ǎ樱簦幔悖瑁酰颍幔悖澹幔澹┑榷翘赜锌啤;腿毡玖降毓灿惺粼迹叮福岸嗍簟Ｈ缌迹ǎ茫颍穑簦铮恚澹颍椋幔⑺荆ǎ模椋螅幔睿簦瑁酰螅⑿」炊ǎ拢澹颍悖瑁     

Impact of density of Aphis craccivora (Aphididae) on growth and yield of susceptible and resistant cowpea cultivars

Impact of initial density of cowpea aphid Aphis craccivora Koch (Aphididae) at infestation on the growth and yield of aphid-susceptible cowpea cultivar ICV-1 and aphid-resistant cultivar ICV-12, was investigated. Plants at the seedling, flowering and podding stages of development were infested with five aphid densities consisting of 0, 2, 5, 10 and. 20 aphids per plant and maintained for 22 days. Extended leaf heights of plants and aphid counts were recorded at 7, 12, 17 and 22 days after infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per plant and number of seeds per pod) were recorded. Due to the occurrence of parthenogenesis and changes in population dynamics during infestations, aphid densities were converted into cumulative cowpea aphid-days, to facilitate data analyses and interpretation. ANOVA indicated that there was significant (P=s 0.05) difference in aphid-day accumulations between the two cultivars when infested at the seedling stage. Accumulations on cv. ICV-1 were greater than on cv. ICV-12. However, no such differences between the cultivars were detected when plants were infested at flowering and podding stages. Therefore, the seedling stage was used for comparisons of the impact of cowpea aphid-days on the growth and yield parameters of the two cultivars. At the 95% confidence intervals, ICV-12 plants were consistently taller than ICV-1 plants. Infested ICV-1 seedlings showed stunting and other growth deformities which were not observed on ICV-12 plants. Regression analyses revealed substantial reductions in the growth and yield parameters of ICV-1 relative to ICV-12. Overall, cowpea aphid-days provided a convenient and reliable method for studying the aphid population dynamics and the subsequent impact on plant growth and yield performance.     

Effects of salinity on uptake and distribution of Na+, Cl- and K+ in two wheat cultivars

Plants of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance were grown in sand with nutrient solutions. 35-d-old plants were subjected to 5 levels of salinity created by adding NaCl, CaCl₂ and Na₂SO₄. Growth reduction caused by salinity was accompanied by increased Na⁺ and Cl^- concentrations, Na⁺/K⁺ ratio, and decreased concentration of K⁺. The salt tolerant cv. Kharchia 65 showed better ionic regulation. Salinity up to 15.7 dS m^-1 induced increased uptake of Na⁺ and Cl^- but higher levels of salinity were not accompanied by further increase in uptake of these ions. Observed increases in Na⁺ and Cl^- concentrations at higher salinities seemed to be the consequence of reduction in growth. Uptake of K⁺ was decreased; more in salt sensitive cultivar. This was also accompanied by differences in its distribution.     

Leaf litterfall,leaf area index,and radiation transmittance in cypress wetlands and slash pine plantations in north-central Florida

The seasonal dynamics of leaf litterfall and leaf area index (LAI, all-sided basis), light penetration and the vertical distribution of surface area index, and the feasibility of estimating LAI from radiation transmittance were studied from April 1993 to March 1994 in the canopies of three cypress (Taxodium ascendens) wetlands and their surrounding slash pine (Pinus elliottii) uplands in Florida flatwoods. Annual leaf litterfall ranged from 324 to 359 g m^–2 in the wetlands, which was very close to the average for 11 sites throughout Florida of 340±26 g m^–2. The seasonal pattern of the normalized LAI obtained for the dominant tree species in the ecosystems could be used to construct the seasonal dynamics of LAI at the ecosystem scale. The vertical distribution of surface area index in the wetlands was significantly different from that in the surrounding pine uplands. The maximum LAI of cypress wetlands in this area was about 8 m² m^–2, which was higher than the maximum of slash pine plantations of 6 m² m^–2. Cypress leaves were strongly erectophile in space. Results showed that the LAI-2000 canopy analyzer could generally be used to estimate forest LAI, whether the forest canopy was closed or not, if an overall clumping index of 2.00 was applied. However, as LAI decreased, the relative error contained in the radiation-based LAI estimates increased. This indicated that foliage clumping at the stand scale was more important than that at the tree or branch scale.     

Changes in foliage distribution with relative irradiance and tree size: Differences between the saplings ofAcer platanoides andQuercus robur

Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings ofAcer platanoides andQuercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform inA. platanoides than inQ. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased inQ. platanoides and decreased inQ. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance inA. platanoides, but it was independent of irradiance inQ. robur. Higher foliage maximum at lower irradiance in more shade-tolerantA. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior ofA. platanoides in understory.     

Determinants of peak muscle power: effects of age and physical conditioning

The relationships between absolute peak muscle power (W _peak), muscle cross sectional area (CSA_tot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20–35 years; B, 9 S aged 35–50 years; C, 9 S aged more than 50 years; D, 13 children aged 8–13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The W _peak was measured during a maximal vertical high jump off both feet on a force platform. The CSA_tot was measured anthropometrically. The [ATP] and [PC] were determined by ³¹Phosphorus nuclear magnetic resonance spectroscopy. The W _peak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSA_tot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in W _peak were only partially accounted for by changes in CSA_tot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of W _peak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.     

Growth analysis of UV-B-irradiated cucumber seedlings as influenced by photosynthetic photon flux source and cultivar

A growth analysis was made of ultraviolet-B (UV-B)-sensitive (Poinsett) and insensitive (Ashley) cultivars of Cucuumis satives L. grown in growth chambers at 600 μmol m⁻² s⁻¹ of photosynthetic photon flux (PPF) provided by red- and far-red-deficient metal halide (MH) or blue- and UV-A-deficient high pressure sodium/deluxe f HPS/DX) lamps. Plants were irradiated 6 h daiiy with 0.2 f-UV-B) or 18.2 C+UV-B) kJ m⁻² day⁻¹ of biologically effective UV-B for 8 or 15 days from time of seeding. In general, plants given supplemental UV-B for 15 days showed lower leaf area ratio (LARs, and higher specific leaf mass (SLM) mean relative growth rate (MRGR) and net assimilation rate (NAR) than that of control plants, but they showed no difference in leaf mass ratio (LMR), Plants grown under HPS/DX lamps vs MH lamps showed higher SLM and NAR. lower LAR and LMR. hut no difference in MRGR. LMR was the only growth parameter affected by cultivar: at 15 days, it was slightly greater in Poinsett than in Ashley. There were no interactive effects of UV-B. PPF source or cultivar on any of the growth parameters determined, indicating that the choice of either HPS/DX or MH lamps should not affect growth response to UV-B radiation. This was true even though leaves of UV-B-irradiated plants grown under HPS/DX lamps have been shown to have greater chlorosis than those grown under MH lamps.     

Presynaptic modulation by eicosanoids in cortical synaptosomes

In continuing experiments to determine the ionic basis of inhibitory presynaptic modulation, rat cortical synaptosomes were employed and receptor-activated K⁺ efflux was determined with a K⁺ sensitive electrode. When synaptosomes were sub-optimally depolarized by veratridine, the addition of agents that activated purinergic, ₂, muscarinic and opioid receptors all promoted K⁺ efflux. With 2-chloroadenosine as a model inhibitory presynaptic modulator, the increased K⁺ efflux evoked by this agent was blocked by the cyclooxygenase inhibitor indomethacin suggesting that arachidonic acid or its metabolites was an intermediary in opening the channel. When arachidonic acid and PGE₂ were tested, both promoted K⁺ efflux that was inhibited by dendrotoxin and mast cell degranulating peptide, two agents that are known to inhibit a delayed rectifier K⁺ current. Our results suggest that via eicosanoid second messengers, inhibitory presynaptic modulators open a sub-class of K channels that hyperpolarize nerve terminals, therefore less Ca²⁺ would enter per nerve impulse and thus the evoked release of neurotransmitters would be decreased.Abbreviations DTX dendrotoxin - MCDP mast cell degranulating peptide - NHGA norhydroguairetic acid - PGE₂ prostaglandin E₂     

橐吾属的起源、演化与地理分布

橐吾属Ligularia Cass．是菊科千里光族款冬亚族的一个大属。在款冬亚族中本属与大吾风草属 Farfugium Lindl．亲缘关系最近,但进化程度较高。本属包括6组,11系129种。所有种类均分布在 亚洲,仅2种扩散至欧洲。在东亚地区有119种,占该属总种数的96％。高度集中在横断山区的有4组、 6系67种,其中61种为特有种,占该属总组数的66％,总系数的54．5％,总种数的52％。这个事实 表明了横断山区是该属的多度中心和多样化中心。通过性状分析,伞房组伞房系Sect．Corymbosae, Ser．Calthifoliae叶肾形,具掌状叶脉,头状花序大而少,排列呈伞房状,总苞半球形,被认为是该属的 原始类群。原始种齿叶橐吾L. dentata和鹿蹄橐吾L.hodgsonii的分布区从我国四川东部经过湖北、湖 南、安徽、福建等省至日本。这个分布格局与近缘属大吴风草属Farfugium一致。 根据共同起源原理,这两个属的祖先极有可能就发生在这一地区。因此我们推测东亚地区从中国四 川东部至日本这一地区是本属的发源地,然而根据地质历史和现代分布,作者认为中国中部(包括四川 东部)是本属的初始起源地。该属起源后,基本上沿亚洲南缘的山地扩散,少数种类向东北至亚洲东北部。本属起源时间至少不晚于中白垩纪。     

贺兰山主要森林水文作用的初步研究

贺兰山主要森林水文作用的初步研究徐万仁,张永庆（宁夏科委,银川７５０００１）（宁夏农学院,永宁７５０１０５）杜和平,李丽英（宁夏贺兰山自然保护区管理局,银川７５０００３）（宁夏惠农县林业局,７５３２００）ＰｒｅｌｉｍｉｎａｒｙＳｔｕｄｙｏｎＨｙｄｒｏ...