影响加拿大一枝黄花种子非随机脱落的因素

为揭示加拿大一枝黄花(Solidago canadensis)种群扩散机制, 明确种子的脱落及风传扩散在其种群蔓延中的作用, 在人工环境下测定了不同湍流强度、风速和湿度处理下种子脱落的差异, 并对脱落种子与未脱落种子进行形态学特征对比。结果表明: 加拿大一枝黄花的种子脱落受湍流、风速和湿度等因素的共同影响。水平气流下种子的脱落阈值为5.1 m·s^-1, 并随着风速增加, 种子的脱落率增加。与模拟水平气流相比, 模拟垂直气流下种子的脱落阈值显著偏小。相对于层流状态, 湍流的存在显著提高了种子的脱落率, 平均增幅超过300%; 但单纯提高湍流强度对种子脱落率的影响不显著。增加湿度则显著降低种子的脱落率。种子形态学特征对比结果表明, 脱落种子的冠毛数量和冠毛夹角显著高于未脱落种子。该研究结果为研究加拿大一枝黄花种子脱落规律和风传扩散机制提供了科学依据, 也为其他入侵性杂草种子的扩散机制及入侵过程提供了 借鉴。     

Factors influencing the nonrandom abscission of Solidago canadensis seeds

 为揭示加拿大一枝黄花(Solidago canadensis)种群扩散机制, 明确种子的脱落及风传扩散在其种群蔓延中的作用, 在人工环境下测定了不同湍流强度、风速和湿度处理下种子脱落的差异, 并对脱落种子与未脱落种子进行形态学特征对比。结果表明: 加拿大一枝黄花的种子脱落受湍流、风速和湿度等因素的共同影响。水平气流下种子的脱落阈值为5.1 m·s^–1, 并随着风速增加, 种子的脱落率增加。与模拟水平气流相比, 模拟垂直气流下种子的脱落阈值显著偏小。相对于层流状态, 湍流的存在显著提高了种子的脱落率, 平均增幅超过300%; 但单纯提高湍流强度对种子脱落率的影响不显著。增加湿度则显著降低种子的脱落率。种子形态学特征对比结果表明, 脱落种子的冠毛数量和冠毛夹角显著高于未脱落种子。该研究结果为研究加拿大一枝黄花种子脱落规律和风传扩散机制提供了科学依据, 也为其他入侵性杂草种子的扩散机制及入侵过程提供了借鉴。     

A comparison of two methods for measuring vessel length in woody plants

Vessel lengths are important to plant hydraulic studies, but are not often reported because of the time required to obtain measurements. This paper compares the fast dynamic method (air injection method) with the slower but traditional static method (rubber injection method). Our hypothesis was that the dynamic method should yield a larger mean vessel length than the static method. Vessel length was measured by both methods in current year stems of Acer, Populus, Vitis and Quercus representing short‐ to long‐vessel species. The hypothesis was verified. The reason for the consistently larger values of vessel length is because the dynamic method measures air flow rates in cut open vessels. The Hagen–Poiseuille law predicts that the air flow rate should depend on the product of number of cut open vessels times the fourth power of vessel diameter. An argument is advanced that the dynamic method is more appropriate because it measures the length of the vessels that contribute most to hydraulic flow. If all vessels had the same vessel length distribution regardless of diameter, then both methods should yield the same average length. This supports the hypothesis that large‐diameter vessels might be longer than short‐diameter vessels in most species.     

Velocity gradients and turbulence around macrophyte stands in streams

1. Submerged macrophytes strongly modify water flow in small lowland streams. The present study investigated turbulence and vertical velocity gradients using small hot-wire anemometers in the vicinity and within the canopies of four macrophyte species with the objective of evaluating: (a) how plant canopies influence velocity gradients and shear force on the surfaces of the plants and the stream bed; and (b) how the presence and morphology of plants influence the intensity of turbulence. 2. Water velocity was often relatively constant with water depth both outside and inside the plant canopies, but the velocity declined steeply immediately above the unvegetated stream bed. Steep vertical velocity profiles were also observed in the transition to the surface of the macrophyte canopy of three of the plant species forming a dense shielding structure of high biomass. Less steep vertical profiles were observed at the open canopy surface of the fourth plant species, growing from a basal meristem and having the biomass more homogeneously distributed with depth. The complex distribution of hydraulic roughness between the stream bed, the banks and the plants resulted in velocity profiles which often fitted better to a linear than to a logarithmic function of distance above the sediment and canopy surfaces. 3. Turbulence increased in proportion to the mean flow velocity, but the slope of the relationships differed in a predictable manner among positions outside and inside the canopies of the different species, suggesting that their morphology and movements influenced the intensity of turbulence. Turbulence was maintained in the attenuated flow inside the plant canopies, despite estimates of low Reynolds numbers, demonstrating that reliable evaluation of flow patterns requires direct measurements. The mean velocity inside plant canopies mostly exceeded 2 cm s^??1 and turbulence intensity remained above 0.2 cm s^??1, which should be sufficient to prevent carbon limitation of photosynthesis in CO₂-rich streams, while plant growth may benefit from the reduced physical disturbance and the retention of nutrient-rich sediment particles. 4. Flow patterns were highly reproducible within canopies of the individual species despite differences in stand size and location among streams. We propose that individual plant stands are suitable functional units for analysing the influence of submerged macrophytes on flow patterns, retention of particles and biological communities in lowland streams.     

Turbulence Under The Microscope

Our objective was to observe a new form of turbulence caused bybiological effects – biological micro-turbulence and explore itsprocess and controlling factors. The methods used were proteusmirabilis CGCs micro-cultured to render the occurrence of the specific movement on micro-organic suspension and its controllingfactors were determined by comparison with the control trials.The results showed that turbulence under the microscope was generally in a mass but partially regular. It was also confirmedthat the turbulence under the microscope exhibited hollow effect,temperature-dependent switching on of occurrence and self-controlof suspension quantity. It is clarified that this new form ofturbulence is a spontaneous and self-control process, which providesan experimental model with controllable conditions for studies ofturbulence and a new way for researches on the mechanism andphysiological functions of the flow of body liquid.     

Rare long-range cortical connections enhance human information processing

1. Download : Download high-res image (189KB)
2. Download : Download full-size image

     

Micro-pattern in an area of New Zealand alpine vegetation

An area of New Zealand alpine herbfield, 22×22 m, was sampled on a 3×3 m grid.Two community types could be distinguished, dominated respectively by the cushion epacrid Dracophyllum muscoides and the subshrub asterad Celmisia viscosa. Each type was subdivided into three communities. The distribution of these communities was correlated with the environmental factors measured, with a predictability of up to 81%. Some of the factors, such as soil organic matter, could have been influenced by the vegetation, but others were microtopographic ones, unlikely to have been so influenced. There was no evidence of cyclic succession. Possibly the distribution of the two major types reflects previous patch burns, but distributions of individual communities are related to the current environment.Association between the more common species revealed two very clear groups, which characterise, but are not exclusive to, the two community types.     

垂向湍流、温、光对浅水湖泊下沉藻类垂向分布的影响

垂向湍流、温、光等是影响藻类生长和垂向分布的关键因素。基于大型浅水湖泊（太湖）的背景物理场（辐射、水深、水温和消光等）,利用藻类生长-扩散模型的敏感性试验,探讨物理过程对浅水湖泊中下沉藻的垂向分布的影响机制。水温是次表层叶绿素峰值（Subsurface Chlorophyll Maxinmum：SCMax）或谷值（Subsurface Chlorophyll Minimum：SCMin）形成的限制性条件;当水温大于阈值时,随深度的增大,过强光能抑制藻类的生长转变为弱光限制藻类的生长是SCMax形成的关键;垂向湍流的裹挟作用是弱化SCMax强度的关键过程。该研究有利于厘清物理过程对藻类群落演替的作用机制,强化对水生态系统的修复效果。     

Successional patterns on tropical inselbergs: A case study on the Nouragues inselberg (French Guiana)

A number of plant communities have been described on tropical inselbergs, known as hot spots of plant and animal biodiversity. However, few studies tried to question what drives seral processes in these harsh environments, submitted to natural hazards (violent storms, intense runoff and lightning strikes) which may destroy the vegetation cover and its accumulated organic matter. We analysed quantitative data from the granitic Nouragues inselberg (French Guiana) in order to discern how successional processes featured their variety. We showed that the transition from herbaceous carpets (bromeliaceous mats and grassy meadows) to woody vegetation (shrub thickets) was not conditioned by slope, but was truly successional. We also showed that there was a cycle of change in shrub thickets, reinitiated by the destruction of scrub vegetation by fire (lightnings), wood-destroying fungi and termites.