Species richness of herbivores on exotic host plants increases with time since introduction of the host

Aim Species richness of insect herbivores feeding on exotic plants increases with abundance as well as range size of the host in the area of introduction. The formation of these herbivore assemblages requires a certain amount of time, and the richness of insect faunas should also increase with the length of time an exotic plant has been present in the introduced range. Location Central Europe. Methods We analysed the variation in species richness of leaf‐chewing Lepidoptera larvae and sap‐sucking Auchenorrhyncha (Hemiptera) associated with 103 exotic woody plant species in Germany in relation to time since introduction, range size, growth form (trees versus shrubs), biogeographical origin (distance from Central Europe) and taxonomic isolation of the host plant (presence or absence of a native congener in the introduced area). Results Using simple correlation analyses we found for Lepidoptera and Auchenorrhyncha that species richness increased with time since introduction of the host plant. For the Lepidoptera the increase of species richness with time since introduction remained significant even after removing the effects of all other independent variables. Main conclusions Our results provide some evidence that assemblages of insects on exotic plants do not reach saturation within a time scale of few hundred years. This contrasts with previous findings for crop plants.     

Implications of transgenic, insecticidal plants for insect and plant biodiversity

Genetically modified plants are widely grown predominantly in North America and to a lesser extent in Australia, Argentina and China but their regions of production are expected to spread soon beyond these limited areas also reaching Europe where great controversy over the application of gene technology in agriculture persists. Currently, several cultivars of eight major crop plants are commercially available including canola, corn, cotton, potato, soybean, sugar beet, tobacco and tomato, but many more plants with new and combined multiple traits are close to registration. While currently agronomic traits (herbicide resistance, insect resistance) dominate, traits conferring “quality” traits (altered oil compositions, protein and starch contents) will begin to dominate within the next years. However, economically the most promising future lies in the development and marketing of crop plants expressing pharmaceutical or “nutraceuticals” (functional foods), and plants that express a number of different genes. From this it is clear that future agricultural and, ultimately, also natural ecosystems will be challenged by the large-scale introduction of entirely novel genes and gene products in new combinations at high frequencies all of which will have unknown impacts on their associated complex of non-target organisms, i.e. all organisms that are not targeted by the insecticidal protein. In times of severe global decline of biodiversity, pro-active precaution is necessary and careful consideration of the likely expected effects of transgenic plants on biodiversity of plants and insects is mandatory.In this paper possible implications of non-target effects for insect and plant biodiversity are discussed and a case example of such non-target effects is presented. In a multiple year research project, tritrophic and bitrophic effects of transgenic corn, expressing the gene from Bacillus thuringiensis (Bt-corn) that codes for the high expression of an insecticidal toxin (Cry1Ab), on the natural enemy species, Chrysoperla carnea (the green lacewing), was investigated. In these laboratory trials, we found prey-mediated effects of transgenic Bt-corn causing significantly higher mortality of C. carnea larvae. In further laboratory trials, we confirmed that the route of exposure (fed directly or via a herbivorous prey) and the origin of the Bt (from transgenic plants or incorporated into artificial diet) strongly influenced the degree of mortality. In choice feeding trials where C. carnea could choose between Spodoptera littoralis fed transgenic Bt-corn and S. littoralis fed non-transgenic corn, larger instars showed a significant preference for S. littoralis fed non-transgenic corn while this was not the case when the choice was between Bt- and isogenic corn fed aphids. Field implications of these findings could be multifold but will be difficult to assess because they interfere in very intricate ways with complex ecosystem processes that we still know only very little about. The future challenge in pest management will be to explore how transgenic plants can be incorporated as safe and effective components of IPM systems and what gene technology can contribute to the needs of a modern sustainable agriculture that avoids or reduces adverse impacts on biodiversity? For mainly economically motivated resistance management purposes, constitutive high expression of Bt-toxins in transgenic plants is promoted seeking to kill almost 100% of all susceptible (and if possible heterozygote resistant) target pest insects. However, for pest management this is usually not necessary. Control at or below an established economic injury level is sufficient for most pests and cropping systems. It is proposed that partially or moderately resistant plants expressing quantitative rather than single gene traits and affecting the target pest sub-lethally may provide a more meaningful contribution of agricultural biotechnology to modern sustainable agriculture. Some examples of such plants produced through conventional breeding are presented. Non-target effects may be less severe allowing for better incorporation of these plants into IPM or biological control programs using multiple control strategies, thereby, also reducing selection pressure for pest resistance development.     

南昌市不同植物类群叶片氮磷浓度及其化学计量比

对南昌大学前湖校区89种主要植物叶片的N、P浓度及其化学计量比进行了研究,结果表明:乔灌、常绿、针叶、种子、裸子和单子叶植物类群的N浓度分别低于相对应的草本、落叶、阔叶、蕨类、被子和双子叶植物类群,而C3和C4植物差异不显著;乔灌、常绿和裸子植物类群的P浓度含量分别低于相对应的草本、落叶和被子植物类群,而针叶和阔叶、蕨类和种子、单子叶和双子叶、C3和C4植物类群间差异不显著;乔木、阔叶、被子和双子叶植物类群叶片N/P分别高于相对应的灌草、针叶、裸子和单子叶植物类群,而常绿和落叶、蕨类和种子、C3和C4植物类群之间差异不显著.可见,不同类型植物对N和P的吸收利用存在差异,且对不同养分供应采取不同的适应对策.结合研究区土壤养分现状,建议优先选择常绿、针叶、裸子和单子叶植物类群作为城市园林植物.     

Ecological variations and role of heat shock protein in Artemisia judaica L. in response to temperature regimes of Tabuk,Saudi Arabia

Artemisia judaica L. (Compositae) are shrubby herbs growing wildly in Tabuk region and distributed in the desert regions. This region is characterized by extremely variable environmental conditions where the temperature varies from extreme low to extreme high. These temperature regimes have a profound effect on morphology, growth physiology and biochemistry of the plants. The plant samples were collected from Tabuk–Jordan road (760 m above sea level) in the month of January, April, July and October 2013 to evaluate the effect of temperature dynamics on A. judaica L. in four different seasons. Physiological, biochemical alterations and heat shock proteins (HSPs) were studied during these seasons in order to evaluate the environmental adaptation and stress tolerance in response to temperature variations. Plant growth parameters showed a significant increase in height, fresh and dry matter accumulation, total chlorophyll, nitrogen, phosphorus, potassium, artemisinin and leaf relative water contents investigated in the month of April and October. Growth of plant was suppressed and an active role of carbonic anhydrase (CA), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) was observed to cope with the extreme low temperature in January and extreme high temperature in July 2013. However, the plants collected in October and April did not show a statistical difference. Inductions in the expression of HSP90 were recorded in all the plants collected during April and October 2013 with no statistically significant difference. Therefore, based on the results it is recommended that during April and October the environmental conditions are best suitable for growth, development and medicinal use of Artemisia.     

Photosynthesis and root growth in Spartina alterniflora in relation to root zone aeration

Spartina alterniflora Lois. is a dominant species growing in intermediate and saline marshes of the US Gulf coast and Atlantic coastal marshes. S. alterniflora plants were subjected to a range of soil redox potential (Eh) conditions representing a well aerated to reduced conditions in a rhizotron system under controlled environmental conditions. The low soil Eh resulted in inhibition of root elongation shortly after treatment initiation. Root elongation was reduced as soil Eh approached values below ca. +350 mV. Substantial decrease in root elongation was noted when soil Eh fell below +200 mV. Generally, net photosynthetic rate (PN) decreased as soil Eh was reduced, with substantial reductions in PN found when Eh approached negative values. Average PN was reduced to 87, 64, and 44% of control under +340, +245, and -180 mV treatments, respectively. The reductions in root elongation and PN in response to low soil Eh indicated the adverse effects of low soil Eh on plant functioning and the need for periods of soil aeration that allow plants to resume normal functioning. Thus periods of drainage allowing soil aeration during the growing season appear to be critical to S. alterniflora by providing favorable conditions for root growth and gas exchange with important implications for plant carbon fixation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Distribution of plant functional types along gradients of disturbance intensity and resource supply in an agricultural landscape

Abstract. In this study, plant functional types are understood as groups of plants with similar biological traits displaying significant optima or maxima on a gradient plane of resource supply and disturbance intensity. The biological traits refer to expansion, vegetative regeneration, generative reproduction, dispersal and seed bank longevity. 129 vegetation samples were taken in an agricultural landscape in southwestern Germany, covering a wide range of terrestrial vegetation types – but with the exception of forests and wetlands. For each site, also soil data were recorded. Mean daily soil moisture was estimated with a simple model. Soil moisture, balanced nitrogen supply and available phosphorus were combined into a factor ‘resource supply’. In addition, disturbance intensity was estimated for each site. This factor was based on (1) frequency of disturbance, (2) disturbance depth below or above the soil surface, and (3) proportion of the area affected by a discrete disturbance event. 30 plant groups with similar biological characteristics resulted from a cluster analysis, based on a compilation of 19 biological traits for a regional species pool. Logistic regression on a gradient plane of disturbance intensity and resource supply yielded response curves for 28 groups. The dependent variable was defined as the probability of encountering all members of a group in a sample. 17 groups display a significant response curve on the gradient plane. Plants with a potential for long- range dispersal are concentrated on sites with low or high disturbance intensities (e.g. fallow land, fields, lawns). On sites with medium disturbance intensity (e.g. meadows) and low to medium resource supply, small-range dispersal predominates. There are no distinct trends concerning seed bank longevity. The potential for vertical and lateral expansion increases with decreasing disturbance intensity. Only at medium disturbance intensities does vertical expansion correlate positively with resource supply. Rapid detachment of daughter individuals occurs more often on productive sites than on less productive sites. Diversity of groups with similar biological traits is highest on sites with medium disturbance intensities.     

Performance of a clonal species in patchy environments: effects of environmental context on yield at local and whole-plant scales

Yield of the clonal plant Glechoma hederacea was compared at different spatial scales, in heterogeneous and homogeneous environments providing the same amount of nutrients. For the heterogeneous treatments, environments were created with different patch sizes and different degrees of contrast in nutrient concentration between patches of different quality. Total clone yield differed by almost 2.5-fold across treatments, being highest in environments with large patches and high contrast, lowest in environments with small patches and high contrast, and intermediate under homogeneous conditions. Compared with plants in homogeneous conditions, there were significant increases or decreases in yield at all scales of measurement in many of the heterogeneous treatments. These effects on yield reflected a combination of local responses to growing conditions and modification of these responses due to physiological integration with other parts of the plant growing in contrasting conditions, supporting the proposal of de Kroon et al. (2005 New Phytol 166:73–82). The results show that plant yield at all scales is strongly dependent on environmental context, and that maximum yield can only be realized under a limited range of heterogeneous conditions.     

Signaling role of action potential in higher plants

The signaling role of action potential (AP) in higher plants is considered. The principles underlying realization of this role and the significance of AP-induced short-term effector response are discussed. The notion is put forward that the effect of propagating AP on plant cells is similar to nonspecific component of the cell functional response to external stimuli.