Plant invasiveness is not linked to the capacity of regeneration from small fragments: an experimental test with 39 stoloniferous species

Fragmentation and vegetative regeneration from small fragments may contribute to population expansion, dispersal and establishment of new populations of introduced plants. However, no study has systematically tested whether a high capacity of vegetative regeneration is associated with a high degree of invasiveness. For small single-node fragments, the presence of internodes may increase regeneration capacity because internodes may store carbohydrates and proteins that can be used for regeneration. We conducted an experiment with 39 stoloniferous plant species to examine the regeneration capacity of small, single-node fragments with or without attached stolon internodes. We asked (1) whether the presence of stolon internodes increases regeneration from single-node fragments, (2) whether regeneration capacity differs between native and introduced species in China, and (3) whether regeneration capacity is positively associated with plant invasiveness at a regional scale (within China) and at a global scale. Most species could regenerate from single-node fragments, and the presence of internodes increased regeneration rate and subsequent growth and/or asexual reproduction. Regeneration capacity varied greatly among species, but showed no relationship to invasiveness, either in China or globally. High regeneration capacity from small fragments may contribute to performance of clonal plants in general, but it does not appear to explain differences in invasiveness among stoloniferous clonal species

Root Foraging Increases Performance of the Clonal Plant Potentilla reptans in Heterogeneous Nutrient Environments

Background Plastic root-foraging responses have been widely recognized as an important strategy for plants to explore heterogeneously distributed resources. However, the benefits and costs of root foraging have received little attention. Methodology/Principal Findings In a greenhouse experiment, we grew pairs of connected ramets of 22 genotypes of the stoloniferous plant Potentilla reptans in paired pots, between which the contrast in nutrient availability was set as null, medium and high, but with the total nutrient amount kept the same. We calculated root-foraging intensity of each individual ramet pair as the difference in root mass between paired ramets divided by the total root mass. For each genotype, we then calculated root-foraging ability as the slope of the regression of root-foraging intensity against patch contrast. For all genotypes, root-foraging intensity increased with patch contrast and the total biomass and number of offspring ramets were lowest at high patch contrast. Among genotypes, root-foraging intensity was positively related to production of offspring ramets and biomass in the high patch-contrast treatment, which indicates an evolutionary benefit of root foraging in heterogeneous environments. However, we found no significant evidence that the ability of plastic foraging imposes costs under homogeneous conditions (i.e. when foraging is not needed). Conclusions/Significance Our results show that plants of P. reptans adjust their root-foraging intensity according to patch contrast. Moreover, the results show that the root foraging has an evolutionary advantage in heterogeneous environments, while costs of having the ability of plastic root foraging were absent or very small.

不同生活型植物对机械刺激的反应

机械刺激效应（Effects of mechanical stimulation）是风生态学直接效应的主要表现形式。研究机械刺激对植物的影响，有利于将风的直接与间接效应区别开来，从而精确研究植物对风的反应格局;研究不同生活型植物对机械刺激的反应是植物力学与植物生态学的重要内容，有助于揭示植物对生境的适应机制。 本研究涉及三个实验。第一个实验探讨不同生活型植物对机械刺激和水分互作的响应格局;第二个实验研究匍匐茎草本植物蛇莓对部分机械刺激的反应;最后一个实验揭示不同水分供应条件下，番茄和紫花苜蓿对不同机械刺激频度的响应。在第一个实验中，克隆半灌木羊柴（Hedysarum laeve），一年生草本植物虫实（Corispermum mongolicum），多年生大型禾草沙鞭（Psammochloa villosa）和多年生丛生禾草黑麦草（Lolium perenne）分别接受由两个水平机械刺激（无刺激和刺激60 s d-1）和两个水平水分供应（200 ml d-1和400 ml d-1）组成的处理。在第二个实验中，匍匐茎草本蛇莓（Duchesnea indica）接受4个不同水平的机械刺激：（1）整个克隆不受机械刺激;（2）整个克隆都受机械刺激;（3）除顶端外其余克隆部分受机械刺激;（4）仅克隆顶端受机械刺激，其余部分不受机械刺激。在最后一个实验中，番茄（Lycopersicon esculentum）和紫花苜蓿（Medicago sativa）接受由三个水平机械刺激频度（0，25赫兹和50赫兹）和三个水平水分供应（50ml，150ml和250ml）组成的处理。这些实验主要回答不同生活型植物的生长和（或）机械性状如何响应机械刺激。主要结果如下： （1）在对机械刺激和水分交互效应的实验中，交互效应随物种发生变化。机械刺激和水分的交互效应对羊柴、番茄和紫花苜蓿作用不显著，但对虫实、沙鞭和黑麦草作用显著。 （2）在对机械刺激的研究中，机械刺激对植物的效应有正负之分。如机械刺激降低羊柴和沙鞭的总生物量，表明其是一种胁迫因子。但对于虫实、番茄和紫花苜蓿来说，机械刺激却能不同程度地促进植物的生长。 （3）机械刺激对虫实的机械性状没有显著影响，但对羊柴的机械性状恰好相反。此外，水分对虫实机械性状有显著影响。 （4）不同植物对机械刺激频度的敏感性存在差异。对番茄来而言，50赫兹的机械刺激对其生长具有较强的促进作用;对紫花苜蓿来说，25赫兹的机械刺激对其生长具有较强的促进作用。 （5）蛇莓对局部机械刺激具有显著反应，特别是在顶端进行机械刺激的处理中，整个克隆片段的叶柄长度缩短，根冠比发生改变，将较多的生物量分配到根。 这些结果表明：（1）不同物种对机械刺激和水分互作的反应可能与机械震动方式及物种本身有关;（2）单位植物大小所承受的机械刺激的强度及物种的生长速率是不一样的;（3）不同反应间的相互作用及相互独立可部分解释物种间的效应差异;（4）接触性形态建成的效应不能从一个物种外推到另外一个物种。 以前的研究集中探讨直立茎植物对机械刺激的响应，而对匍匐茎植物的研究极为贫乏。我们对蛇莓部分机械刺激的研究仅仅是一个初步探索。蛇莓的可塑性行为可能是一种适应性策略，因为这类植物常常生长在机械刺激频繁的开阔生境中。上述三个实验仅仅从生长和机械角度探讨了植物的适应性，而要真正揭示植物对多风生境的适应需要对不同物种进行多水平、多层面的研究，以期掌握不同生活型植物对机械刺激响应的一般格局。例如，从激素、细胞、解剖结构等方面探索其内在机制。

Studies on lemongrass oil

The thesis deals with the different properties and characteristics of oil of lemon grass.. The oil of lemongrass (Cymbopogon flexuosus) is one of the most important essential oils. It will continue to be one of the "big ten" of our essential oils1. Lemongrass oil is obtained from certain species of grasses of the genus cymbopogon. The genus consists of about 80 species, 10 to 12 of which are known to occur in India. Lemongrass is a stoloniferous plant. The plant grows wild in many tropical andsemitropical parts of Asia, Africa and in parts of Central America and South America. For the extraction of the oil however only cultivated lemongrass is employed. The trade distinguishes two Principal types of lemongrass oil, viz. the East Indian Oil and West Indian Oil. There was much confusion, years ago, about the taxonomy of the plants which yield theEast Indian and West Indian types of lemongrass oil, however Stapf2 ended the long controversy of identifying the plant yielding the East Indian type oil as Cymbopogon flexuosus (D.C.) Stapf and the plant yielding the West Indian type oil as Cymbopogon citrates (D.C.) stapf. The 2 plants have_been named variously also Andropogon nardus var. Flexuosus Hack or A. citratus D.C. respectively

United we stand, divided we fall: a meta-analysis of experiments on clonal integration and its relationship to invasiveness

Fragmentation and vegetative regeneration from small fragments may contribute to population expansion, dispersal and establishment of new populations of introduced plants. However, no study has systematically tested whether a high capacity of vegetative regeneration is associated with a high degree of invasiveness. For small single-node fragments, the presence of internodes may increase regeneration capacity because internodes may store carbohydrates and proteins that can be used for regeneration. We conducted an experiment with 39 stoloniferous plant species to examine the regeneration capacity of small, single-node fragments with or without attached stolon internodes. We asked (1) whether the presence of stolon internodes increases regeneration from single-node fragments, (2) whether regeneration capacity differs between native and introduced species in China, and (3) whether regeneration capacity is positively associated with plant invasiveness at a regional scale (within China) and at a global scale. Most species could regenerate from single-node fragments, and the presence of internodes increased regeneration rate and subsequent growth and/or asexual reproduction. Regeneration capacity varied greatly among species, but showed no relationship to invasiveness, either in China or globally. High regeneration capacity from small fragments may contribute to performance of clonal plants in general, but it does not appear to explain differences in invasiveness among stoloniferous clonal species.

Sexual selection in a tropical fruit fly : role of a plant derived chemical in mate choice

The specific mechanisms by which selective pressures affect individuals are often difficult to resolve. In tephritid fruit flies, males respond strongly and positively to certain plant derived chemicals. Sexual selection by female choice has been hypothesized as the mechanism driving this behaviour in certain species, as females preferentially mate with males that have fed on these chemicals. This hypothesis is, to date, based on studies of only very few species and its generality is largely untested. We tested the hypothesis on different spatial scales (small cage and seminatural field-cage) using the monophagous fruit fly, Bactrocera cacuminata. This species is known to respond to methyl eugenol (ME), a chemical found in many plant species and one upon which previous studies have focused. Contrary to expectation, no obvious female choice was apparent in selecting ME-fed males over unfed males as measured by the number of matings achieved over time, copulation duration, or time of copulation initiation. However, the number of matings achieved by ME-fed males was significantly greater than unfed males 16 and 32 days after exposure to ME in small cages (but not in a field-cage). This delayed advantage suggests that ME may not influence the pheromone system of B. cacuminata but may have other consequences, acting on some other fitness consequence (e.g., enhancement of physiology or survival) of male exposure to these chemicals. We discuss the ecological and evolutionary implications of our findings to explore alternate hypotheses to explain the patterns of response of dacine fruit flies to specific plant-derived chemicals.

Influence of host plant structure and microclimate on the abundance and behaviour of Tephritid fly

Microclimate and host plant architecture significantly influence the abundance and behavior of insects. However, most research in this field has focused at the invertebrate assemblage level, with few studies at the single-species level. Using wild Solanum mauritianum plants, we evaluated the influence of plant structure (number of leaves and branches and height of plant) and microclimate (temperature, relative humidity, and light intensity) on the abundance and behavior of a single insect species, the monophagous tephritid fly Bactrocera cacuminata (Hering). Abundance and oviposition behavior were signficantly influenced by the host structure (density of foliage) and associated microclimate. Resting behavior of both sexes was influenced positively by foliage density, while temperature positively influenced the numbers of resting females. The number of ovipositing females was positively influenced by temperature and negatively by relative humidity. Feeding behavior was rare on the host plant, as was mating. The relatively low explanatory power of the measured variables suggests that, in addition to host plant architecture and associated microclimate, other cues (e.g., olfactory or visual) could affect visitation and use of the larval host plant by adult fruit flies. For 12 plants observed at dusk (the time of fly mating), mating pairs were observed on only one tree. Principal component analyses of the plant and microclimate factors associated with these plants revealed that the plant on which mating was observed had specific characteristics (intermediate light intensity, greater height, and greater quantity of fruit) that may have influenced its selection as a mating site.