What do we really know about alien plant invasion? A review of the invasion mechanism of one of the world’s worst weeds

This review provides an insight into alien plant invasion taking into account the invasion mechanism of parthenium weed ( Parthenium hysterophorus L.). A multi-lateral understanding of the invasion biology of this weed has pragmatic implications for weed ecology and management. Biological invasions are one of the major drivers of restructuring and malfunctioning of ecosystems. Invasive plant species not only change the dynamics of species composition and biodiversity but also hinder the system productivity and efficiency in invaded regions. Parthenium weed, a well-known noxious invasive species, has invaded diverse climatic and biogeographic regions in more than 40 countries across five continents. Efforts are under way to minimize the parthenium weed-induced environmental, agricultural, social, and economic impacts. However, insufficient information regarding its invasion mechanism and interference with ecosystem stability is available. It is hard to devise effective management strategies without understanding the invasion process. Here, we reviewed the mechanism of parthenium weed invasion. Our main conclusions are: (1) morphological advantages, unique reproductive biology, competitive ability, escape from natural enemies in non-native regions, and a C3/C4 photosynthesis are all likely to be involved\ua0in parthenium weed invasiveness. (2) Tolerance to abiotic stresses and ability to grow in wide range of edaphic conditions are thought to be additional invasion tools on a physiological front. (3) An allelopathic potential of parthenium weed against crop, weed and pasture species, with multiple modes of allelochemical expression, may also be responsible for its invasion success. Moreover, the release of novel allelochemicals in non-native environments might have a pivotal role in parthenium weed invasion. (4) Genetic diversity found among different populations and biotypes of parthenium weed, based on geographic, edaphic, climatic, and ecological ranges, might also be a strong contributor towards its invasion success. (5) Rising temperatures and atmospheric carbon dioxide (CO2) concentrations and changing rainfall patterns, all within the present day climate change prediction range are favorable for parthenium weed growth, its reproductive output, and therefore its future spread and infestation. (6) Parthenium weed invasion in South Asia depicts the relative and overlapping contribution of all the above-mentioned mechanisms. Such an understanding of the core phenomena regulating the invasion biology has pragmatic implications for its management. A better understanding of the interaction of physiological processes, ecological functions, and genetic makeup within a range of environments may help to devise appropriate management strategies for parthenium weed

Physiological responses of wheat (Triticum aestivum L.) germination to elevated ammonium concentrations: reserve mobilization, sugar utilization, and antioxidant metabolism

To elucidate the physiological mechanisms of wheat (Triticum aestivum L.) germination in response to elevated ammonium (NH ) concentrations (EAC), Yumai49 (NH -tolerant) and Lumai15 (NH -sensitive) cultivars were supplied with a 5.0\ua0mM NH -N (EAC) treatment or a 5.0\ua0mM NO -N (CON) treatment as the control. There was a reduction in the seed germination index, plant biomass, radicle length, and other deleterious effects following the EAC treatment in both cultivars, but Yumai49 was more tolerant to EAC than Lumai15. When compared to CON, α-amylase activity and ATP content in seeds were significantly lower after the 3rd and 5th\ua0day of the EAC treatment in Lumai15 and Yumai49, respectively. Moreover, the ratio of abscisic acid to gibberellins in seeds was higher under EAC treatment as compared to CON, with a smaller ratio increase in Yumai49 than in Lumai15, indicating that the differences in hormone ratio caused by the EAC treatment was associated with lower seed reserve mobilization. The soluble sugar content in radicles increased while it was reduced in coleoptiles for both cultivars under the EAC treatment. However, Yumai49 exhibited a slight increase in seedling soluble sugar content, while Lumai15 exhibited a significant reduction in sugar content, as compared to CON. Moreover, Yumai49 exhibited a lower ratio reduction in coleoptile to radicle soluble sugar content as compared with Lumai15, indicating that Yumai49 was undergoing greater reserve mobilization and transportation to the radicle to support growth. The activities of pyruvate kinase and phosphoenolpyruvate carboxylase were increased under the EAC treatment in the radicles, with a greater increase seen in Yumai49 than in Lumai15, indicating that Yumai49 had a greater capacity to assimilate NH . In addition, the EAC treatment enhanced the content of malonaldehyde and superoxide anions, and the activities of superoxide dismutase and peroxidase in the coleoptiles and radicles of both cultivars, with the magnitude of these increases greater in Yumai49 than in Lumai15. It is concluded that the NH -tolerant cultivar, as compared to the sensitive cultivar, has a greater capacity to undertake reserve mobilization and ATP production in its seeds, a greater sugar utilization in its radicles, and a stronger antioxidant protection mechanism

Isolation of natural herbicidal compound from Lantana camara

A flavone glucoside 'vitexin' (C21H20O10) was isolated from the leaves of Lantana camara through bioassay-guided isolation. Kupchan method of solvent-solvent partitioning of crude methanol extract from leaves of L. camara gave ethyl acetate, chloroform, hexane and aqueous fraction. Bio-assay with four fractions at 500 ppm, 1000 ppm and 10,000 ppm indicated chloroform fraction to be most potent phytotoxic against weeds (monocot: Phalaris minor, Avena fatua; Dicot: Chenopodium album, Rumex dentatus). Column chromatography of chloroform fraction with hexane: ethyl acetate (60:40) based on TLC profiling with vanillin visualisation stain and subsequent bioassays indicated sub-fraction (iii) of fraction 23 as most growth inhibitory. The chemical structure of the isolated compound was identified by gas chromatography-mass spectrometry (Shimadzu GC-MS-QP2010 ultra). The natural herbicidal activity of the isolated compound against various weeds in laboratory and field conditions is suggested

Whose Mass is it Anyway? Particle Cosmology and the Objects of Theory

Physicists in different branches of the discipline were puzzled by the problem of mass during the 1950s and 1960s: why do objects have mass? Around the same time, yet working independently, specialists in gravitational studies and in particle theory proposed that mass might arise due to objects’ interactions with a new (and as yet undetected) field. Although the questions they posed and even the answers they provided shared several similarities - and even though both proposals quickly became ‘hot topics’ in their respective subfields - virtually no one discussed one proposal in the light of the other for nearly 20 years. Only after massive, unprecedented changes in pedagogical infrastructure rocked the discipline in the early 1970s did a new generation of physicists begin to see possible links between the Brans-Dicke field and the Higgs field. For the new researchers, trained in different ways than most of their predecessors, the two objects of theory were not only similar - some began to proclaim that they were exactly the same. Charting the histories of these two objects of theory illuminates the complicated institutional and pedagogical factors that helped to produce a new subfield, particle cosmology, which today ranks at the very forefront of modern physics