Botanical ratchets

Ratcheting surfaces are a common motif in nature and appear in plant awns and grasses. They are known to proffer selective advantages for seed dispersion and burial. In two simple model experiments, we show that these anisotropically toothed surfaces naturally serve as motion rectifiers and generically move in a unidirectional manner, when subjected to temporally and spatially symmetric excitations of various origins. Using a combination of theory and experiment, we show that a linear relationship between awn length and ratchet efficiency holds under biologically relevant conditions. Grass awns can thus efficiently transform non-equilibrium environmental stresses from such sources as humidity variations into useful work and directed motion using their length as a fluctuation amplifier, yielding a selective advantage to these organelles in many plant species.     

植物杀虫剂研究概况

简要综述不同资源类型的植物杀虫剂,通过其有效成份生物碱类、萜类、黄酮类、精油类、光活化毒素类等物质影响昆虫生长发育及消化系统、呼吸系统、代谢系统、神经肌肉系统等从而达到杀虫的目的。同时对其发展前景提出了展望。     

Botanical aspects of oregano

The condiment name “oregano” should be understood to refer, not to any one species but to a particular spice flavor, furnished by plants of several genera in different parts of the world. About one-half of the amount used in the United States comes chiefly from Mexico as dried leaves and flowers of Lippia graveolens; the rest from several species of Origanum in several European countries.     

Botanical Soceity of Edinburgh

Background: Economic activities are substantial factors in alien plant establishment and invasions. Climate also plays an important role in the distribution of alien species.

Aims: We evaluate the relationship between alien species density and both climatic and socio-economic factors at the scale of provinces located in a latitudinal-bioclimatic gradient in Chile.

Methods: We used generalised linear models with backward selection to evaluate the relative importance of each parameter (human population, gross domestic product, length of traffic routes, crop cover, abandoned crop cover, artificial plantations, protected areas, annual rainfall and temperature) on species density. We compared the average species density among climate types.

Results: Alien density was higher for provinces located in the most populated areas with Mediterranean and temperate oceanic climates (south-central Chile) and decreased for less populated provinces in the north and the southernmost parts (desert and sub-Antarctic wetlands). Human population, length of traffic routes and annual rainfall significantly explained the variation in alien species density in Chile.

Conclusions: Although human population still increases, the results can be used especially in high priority conservation areas where traffic routes and human settlements can be objectively reduced or managed, to reduce the potential increase in the number of alien species.