CO2 enrichment reduces reproductive dominance in competing stands of Ambrosia artemisiifolia (common ragweed)

Plants growing in dense stands may not equally acquire or utilize extra carbon gained in elevated CO₂. As a result, reproductive differences between dominant and subordinate plants may be altered under rising CO₂ conditions. We hypothesized that elevated CO₂ would enhance the reproductive allocation of shaded, subordinate Ambrosia artemisiifolia L. (Asteraceae) individuals more than that of light-saturated dominants. We grew stands of A. artemisiifolia at either 360 or 720 μL L⁻¹ CO₂ levels and measured the growth and reproductive responses of competing individuals. To test whether elevated CO₂ altered size and reproductive inequalities within stands, we compared stand-level coefficients of variation (CV) in height growth and final shoot, root, and reproductive organ biomasses. Elevated CO₂ enhanced biomass and reduced the CV for all aspects of plant growth, especially reproductive biomass. Allocation to reproduction was higher in the elevated CO₂ than in the ambient treatment, and this difference was more pronounced in small, rather than large plant positive relationships between the CV and total stand productivity declined under elevated CO₂, indicating that growth enhancements to smaller plants diminished the relative biomass advantages of larger plants in increasingly crowded conditions. We conclude that elevated CO₂ stimulates stand-level reproduction while CO₂-induced growth gains of subordinate A. artemisiifolia plants minimize differences in the reproductive output of small and large plants. Thus, more individuals are likely to produce greater amounts of seeds and pollen in future populations of this allergenic weed.     

Adjuvant therapy with γ‐tocopherol‐induce apoptosis in HT‐29 colon cancer via cyclin‐dependent cell cycle arrest mechanism

Resistance to chemotherapy with 5‐fluorouracil (5‐FU) in patients with colorectal cancer (CRC) is the major obstacle to reach the maximum efficiency of CRC treatment. Combination therapy has emerged as a novel anticancer strategy. The present study evaluates the cotreatment of γ‐tocopherol and 5‐FU in enhancing the efficacy of chemotherapy against HT‐29 colon cancer cells. Cytotoxic effect of this combination was examined using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay and a synergistic effect was evaluated by a combination index technique. Nuclear morphology was studied via 4′,6‐diamidino‐2‐phenylindole staining and flow cytometric assays were conducted to identify molecular mechanisms of apoptosis and cell cycle progression. We investigated the expression of Cyclin D1, Cyclin E, Bax, and Bcl‐2 by a quantitative real‐time polymerase chain reaction. The IC₅₀ values for 5‐FU and γ‐tocopherol were 21.8 ± 2.5 and 14.4 ± 2.6 μM, respectively, and also this combination therapeutic increased the percentage of apoptotic cells from 35% ± 2% to 40% ± 4% (P < .05). Furthermore, incubation HT‐29 colon cells with combined concentrations of two drugs caused significant accumulation of cells in the subGsubG1 phase. Our results presented the combination therapy with 5‐FU and γ‐tocopherol as a novel therapeutic approach, which can enhance the efficacy of chemotherapy.     

EFFECT OF THE PARENTAL NUTRIENT REGIME ON GROWTH OF THE PROGENY IN ABUTILON THEOPHRASTI (MALVACEAE)

Two genets of Abutilon theophrasti were clonally replicated and grown to maturity in a glasshouse at two levels of nutrient supply. The seeds produced were weighed and the resulting seedlings exposed to two nutrient levels during development. The progeny plants were harvested on three occasions, and leaf areas and dry weights of the different plant parts were determined. At the early stages of growth an increase in the maternal nutrient supply significantly increased seedling height, cotyledon area, and leaf areas, and seed weight had a significant effect on several traits. The maternal nutrient addition had no significant effect at a later stage of growth (35 d after sowing), but at 56 d after sowing it did affect offspring leaf areas and dry weights. Significant interaction terms indicate that the response to parental nutrient addition may depend both on genotype and on the nutrient status of the progeny. Different plant characters are differentially sensitive to maternal conditions and these may be expressed at different stages of development.     

The calyx fluid of Microplitis rufiventris parasitoid and growth of its host Spodoptera littoralis larvae

The morphology of the female reproductive system of pupal and adult stages of Microplitis rufiventris and the ultrastructure of the ovaries are described and illustrated. Two morphologically distinct types of particles of nuclear origin, i.e., polydnavirus (PDV) and a virus-like filamentous particle (VLFP) were detected in the ovarian calyx fluid of the female wasp. It is likely that these particles are injected into the host during oviposition. PDV initiated replication in the calyx of mid-aged pupae and in pharate adults and were present throughout adult life. VLFP were only seen in the calyx fluid of newly emerged adults, and therefore observed after the PDV. Feulgen and methyl-green pyronin staining revealed the presence of DNA in both types of particles. The effects of injection of Spodoptera littoralis larvae with a combination of parasitoid viruses and venom of M. rufiventris females (CxFV) were investigated and the results were compared with two control groups, i.e., larvae injected with Pringle's saline (PS) and naturally parasitized larvae. CxFV-larvae showed significant declines (P<0.05) in food consumption, weight of ejected faeces and weight gain when compared with PS-larvae. However, naturally parasitized larvae (parasitoid egg+CxFV+ovarian protein) displayed a high significance score (P<0.01) in comparison with those of PS-larvae. The approximate digestibility (AD) values of S. littoralis larvae were positively affected as early as day 2 post-treatment by either injection of CxFV or parasitization. However, a reduction in AD was observed in both PS- and CxFV-larvae on day 3-7 in comparison with naturally parasitized larvae. Other indices of food utilization were unchanged in CxFV-larvae when compared to saline treated or parasitized controls.     

Within and between species variation in response to environmental gradients in Polygonum pensylvanicum and Polygonum virginianum

Summary The responses of Polygonum pensylvanicum L., an early successional annual, and of Polygonum virginianum L., a late successional perennial, were examined along discontinuous gradients of soil moisture, light and nutrient availability. In the case of P. virginianum both individuals grown from seed and individuals grown from rhizomes were examined. The results show that variation in the response of individuals of a species of different age to environmental variation is as great as that found between the two congeneric species of different successional habitats. In general, individuals of the two species were more similar to one another in response to the resource gradients when both were started from seed, than were individuals of P. virginianum grown from seed and from rhizomes. Potential differences in stored reserves (starting capital) between rhizomes and seeds appeared to have little effect upon responses to resource availability. A number of plant characters were found to vary along the gradients in ways that were unique to the character, the gradient, and the age of the individual. These characters included aspects of leaf size, shape, and orientation, as well as whole plant architecture. Many if not all of these characters are likely to have significant effects upon the functioning of plants. The origin of this difference in response to the gradients of individuals of P. virginianum of differing age may be ontogenetic or may reflect differences in genetic composition created by recombination.     

Maternal regulation of fecundity: non-random ovule abortion inCassia fasciculata Michx.

Summary We examined the extent of ovule abortion and the within-fruit pattern of abortion inCassia fasciculata, an annual legume, and tested the hypothesis that abortion can result from competition for limited maternal resources among developing fruits and seeds. In a natural population at Mayview, IL, 53.4% of ovules in mature fruits matured as seeds; 43.4% showed some development but aborted, and 3.1% showed no development over virgin ovules. In a greenhouse experiment in which treatments were applied after most fruits were initiated, nutrient addition and partial root removel had no effect on abortion, but drought reduced the proportion of ovules maturing to 75% of the control mean. A fruit thinning experiment was conducted in which the number of fruits initiated on certain plants was limited. Control plants had more ovule abortion than fruit-thinned plants, suggesting that abortion resulted from competition for limited maternal resources. A position effect was observed in both field and greenhouse populations; ovules toward the fruit base (pedicellar end) had higher frequencies of abortion than those at the distal end. Thus, ovule abortion, like fruit abortion in this species, is non-random. Indivisuals regulate fecundity at both the whole fruit and individual seed levels.Scientific contribution no. 1357 from the New Hampshire Agricultural Experiment Station     

Competition and patterns of resource use among seedlings of five tropical trees grown at ambient and elevated CO2

Summary Seedlings of five tropical trees, Cecropia obtusifolia, Myriocarpa longipes, Piper auritum, Senna multijuga and Trichospermum mexicanum, were grown both as individuals, and in competition with each other at ambient (350) and two levels of elevated CO₂ (525 and 700 l l^-1) for a period of 111 days. Growth, allocation, canopy architecture, mid-day leaf water potential and soil moisture content were assessed three times over this period for individually grown plants, and at the end of the experiment for competitively grown plants. In addition, leaf photosynthesis and conductance were assessed for the individually grown plants midway through the experiment, and light profile curves were determined for the competitive arrays at three stages of development. Elevated CO₂ did not affect photosynthesis or overall growth of the individually-grown plants but did affect canopy architecture; mean canopy height increased with CO₂ in Piper and Trichospermum and decreased in Senna. Stomatal conductance decreased slightly as CO₂ increased from 350 to 525 l l^-1 but this had no significant effect upon whole plant water use of leaf water potential. Soil moisture content for the individuals increased marginally as CO₂ increased, but this did not occur in the competitive arrays. There was a marked effect of CO₂ upon species composition of the competitive arrays; Senna decreased in importance as CO₂ increased while Cecropia, Trichospermum and Piper increased in importance. Stepwise regression analysis using competitive performance as the independent variable, and the various morphological and physiological parameters measured on the individually grown plants as independent variables, suggested that canopy height was the single most important variable determining competitive ability. Also significant were photosynthetic rate (particularly at low light levels) and allocation to roots early in the experiment. Light profiles in the canopy revealed that less than 15% of incident light penetrated to the level of mean canopy height. Results suggest that competition for light was the major factor determining community composition, and that CO₂ affected competitive outcome through its affect upon canopy architecture.This study was supported by a grant from the US Department of Energy     

Correlations between genet architecture and some life history features in three species of Solidago

Summary Members of the genus Solidago are among the most widely studied model systems in plant population biology. A comparative study of Solidago canadensis, S. altissima, and S. gigantea in an experimental garden showed that the three species had different patterns of shoot growth and development, leaf morphology and physiology, and biomass allocation at harvest. These differences were also found in the field. Contrary to some current taxonomic usage, our results show that S. canadensis should ecologically be treated as a separate taxon distinct from S. altissima, and that the latter may be grouped together with S. gigantea. Many of the biological differences between S. canadensis and the other two taxa, such as differential investment into sexual reproduction versus clonal growth, may be explained by differences in genet architecture. These architectures concern high compared to lower within-genet shoot density resulting from differences in rhizome lengths among the taxa (shorter in S. canadensis than in S. altissima and S. gigantea).     

The response of plants to elevated CO2

Summary Communities, consisting of six co-occurring, disturbed site annuals, were subjected to CO₂ unenriched (300 ppm) and to CO₂ enriched (450 and 600 ppm) atmospheres at different levels of light and nutrient availability. In general, total community production increased with CO₂ enrichment to 450 ppm, but a further increase in CO₂ to 600 ppm had little or no effect. The response of community production to CO₂ level was not affected by nutrient availability but was affected by light level.Of the six species, four display C₃ metabolism. The proportion of total community production contributed by these species increased as a result of CO₂ enrichment, and was dependent upon both light and nutrient availability. The relative success of some species, particularly in terms of reproduction (total seed biomass), was significantly altered by CO₂ concentration depending on the level of nutrients. There were not only changes in reproductive success (seed biomass) and shoot biomass but also changes in the proportion of biomass allocated to seed.These experiments demonstrate that CO₂ enrichment does affect annual plant communities both in terms of productivity and species composition and that the affect of CO₂ on such system may depend upon other resources such as light and nutrients.     

PHENOTYPIC PLASTICITY IN POLYGONUM PERSICARIA. III. THE EVOLUTION OF ECOLOGICAL BREADTH FOR NUTRIENT ENVIRONMENT

Norms of reaction for a number of growth and reproductive characters were determined for 15 randomly sampled Polygonum persicaria genotypes, from two natural populations originating in sites with very different nutrient availabilities. Under severely limiting nutrient conditions, these genotypes shared not only plastic responses such as increased root-to-shoot ratio, but a surprising constancy in such functionally essential characters as leaf area ratio, leaf nitrogen concentration, and propagule nitrogen content. Because functional homeostasis depends on flexibility in underlying characters, similar homeostatic results can be achieved through different combinations of underlying plastic and fixed responses in genetically different entities. For example, plants in each population maintained a relatively constant propagule nitrogen content under extreme low-nitrogen conditions by varying either the size or the tissue nitrogen concentration of propagules. These genotypes also tolerated excessive nutrient levels toxic to many plants, evidently by storing excess nutrients in shoots. Although development was altered under such circumstances, reproductive fitness was maintained.