Germination (%) of <i>Spergula</i><i>arvensis</i> seeds for each ozone selection treatment, pre-treatment and incubation temperature.

<p>White, grey and black bars represent germination of seeds (n = 3, ± SE) for 0, 90 and 120 ppb ozone selection treatment, respectively, after 22 days of exposure to pre-treatments: storage at 10 °C and dry condition (control) (A), storage at 5 °C and 75% RH followed by scarification (B), and storage at 25 °C and 75% followed by scarification (C); and then incubated at 10, 15 and 15/25 °C. Above each plot, <i>P-values</i> indicate the effects of Incubation Temperature (Temp.), Ozone selection treatment (Ozone) and the interaction (Temp. xOzone) within each Pre-treatment.</p

Overview of the history of ozone exposure and the experimental designs.

<p>Starting from a four-year exposure of a weed community under three ozone selection treatments (0, 90 and 120 ppb) [8]; the subsequent sowing of the soil seed bank samples, coming from each ozone selection treatment replication, in nine plots; the <i>Germination </i><i>experiments</i> (Seed germination and Seed dormancy experiments) carried out with <i>S. arvensis</i> seeds harvested from the plots; and the <i>Soil </i><i>seed </i><i>bank </i><i>experiment</i> developed with seeds harvested from plants exposed to ambient and added ozone (control and added ozone treatment respectively; maternal ozone treatments).</p

Germination (%) of <i>Spergula</i><i>arvensis</i> seeds for each ozone selection treatment

<p><b>, storage condition and incubation temperature</b>. White, grey and black bars represent germination of seeds (n = 3, ± SE) for 0, 90 and 120 ppb ozone selection treatment, respectively, after being exposed for 22 days to storage conditions combining two temperatures (panels A, B and C: 5 °C, and panels D, E and F: 25 °C) and three relative humidity regimes (panels A and D: 5% RH; panels B and E: 75% RH; panels C and F: 11 days at 75% and 11 days at 5% RH) and incubation temperatures (10, 15 and 15/25 °C). Above each plot, <i>P-values</i> indicate the effects of Incubation Temperature (Temp.), Ozone selection treatment (Ozone) and the interaction (Temp. xOzone) within each storage condition.</p

Neotyphodium endophyte infection frequency in annual grass populations: relative importance of mutualism and transmission efficiency

Persistence and ubiquity of vertically transmitted Neotyphodium endophytes in grass populations is puzzling because infected plants do not consistently exhibit increased fitness. Using an annual grass population model, we show that the problems for matching endophyte infection and mutualism are likely to arise from difficulties in detecting small mutualistic effects, variability in endophyte transmission efficiency and an apparent prevalence of non-equilibrium in the dynamics of infection. Although endophytes would ultimately persist only if the infection confers some fitness increase to the host plants, such an increase can be very small, as long as the transmission efficiency is sufficiently high. In addition, imperfect transmission limits effectively the equilibrium infection level if the infected plants exhibit small or large reproductive advantage. Under frequent natural conditions, the equilibrium infection level is very sensitive to small changes in transmission efficiency and host reproductive advantage, while convergence to such an equilibrium is slow. As a consequence, seed immigration and environmental fluctuation are likely to keep local infection levels away from equilibrium. Transient dynamics analysis suggests that, when driven by environmental fluctuation, infection frequency increases would often be larger than decreases. By contrast, when due to immigration, overrepresentation of infected individuals tends to vanish faster than equivalent overrepresentation of non-infected individuals

Data from: Mutualism effectiveness of a fungal endophyte in an annual grass is impaired by ozone

1. Ozone is an increasing tropospheric contaminant of climate change. Exposure to ozone may affect the symbiotic relationship between plants and beneficial microorganisms. In particular, the herbivore resistance mechanism conferred by fungal endophytes (defensive mutualism) may be affected, as any of the ozone-triggered effects (such as elicitation of defence mechanisms against biotrophic fungi or oxidative stress in the apoplastic space) may target the symbiont. 2. Symbiotic and non-symbiotic Lolium multiflorum plants were exposed to ozone for two consecutive days (2 h per day), after which half were infested with 10 aphids (Rhopalosiphum padi). We measured variables related to performance of plants, the endophyte symbiont (alkaloids) and the herbivores. 3. Aphid populations were smaller on symbiotic plants than in non-symbiotic plants in low-ozone conditions. However, this difference disappeared in exposed plants to high-ozone conditions. Under low-ozone conditions, structure of aphid populations on endophyte-symbiotic plants was characterized by a low number of nymphs and a high number of adults. This pattern was not observed with high-ozone exposure. Level of fungal alkaloids (lolines) was not affected by either ozone or herbivory. 4. Results indicate that ozone impairs the grass-endophyte symbiosis without affecting production of alkaloids generally linked with aphids’ response to endophyte presence. Since neither plant biomass nor alkaloid level were affected by ozone, other ozone-mediated mechanisms at molecular or biochemical level may underlie plant-herbivore interaction mediated by fungal endophytes. Thus, the mechanism behind this effect must be determined in future experiments

Legacy of historic ozone exposure on plant community and food web structure.

Information on whole community responses is needed to predict direction and magnitude of changes in plant and animal abundance under global changes. This study quantifies the effect of past ozone exposure on a weed community structure and arthropod colonization. We used the soil seed bank resulting from a long-term ozone exposure to reestablish the plant community under a new low-pollution environment. Two separate experiments using the same original soil seed bank were conducted. Plant and arthropod richness and species abundance was assessed during two years. We predicted that exposure to episodic high concentrations of ozone during a series of growing cycles would result in plant assemblies with lower diversity (lower species richness and higher dominance), due to an increase in dominance of the stress tolerant species and the elimination of the ozone-sensitive species. As a consequence, arthropod-plant interactions would also be changed. Species richness of the recruited plant communities from different exposure histories was similar (≈ 15). However, the relative abundance of the dominant species varied according to history of exposure, with two annual species dominating ozone enriched plots (90 ppb: Spergula arvensis, and 120 ppb: Calandrinia ciliata). Being consistent both years, the proportion of carnivore species was significantly higher in plots with history of higher ozone concentration (≈3.4 and ≈7.7 fold higher in 90 ppb and 120 ppb plots, respectively). Our study provides evidence that, past history of pollution might be as relevant as management practices in structuring agroecosystems, since we show that an increase in tropospheric ozone may influence biotic communities even years after the exposure

FE-Ueno A. et al., Database

This file contains the data that was used in the analyses

Competitive and allelopathic interference between soybean crop and annual wormwood (Artemisia annua L.) under field conditions

Annual wormwood interference on soybean crop growth and yield may result from competition and allelopathy, which are modulated by crop management. Allelochemicals released by annual wormwood (e.g. artemisinin) may affect the crop directly or indirectly through the effect on the nitrogen fixing symbiont, Bradyrhizobium japonicum. The objectives were (i) to quantify the crop response (i.e. biomass production, nodulation and yield) to weed interference and (ii) to determinate the relative change of competition and allelopathy interferences, when a sublethal dose of herbicide is applied. Two split plot field experiments with three replications were used. The experiment involved a factorial combination of five weed-crop density (soybean/annual wormwood, plantsm-2) levels: D1, pure soybean, 40/0plantsm-2; D2, 40/2plantsm-2; D3, 40/4plantsm-2 and D4, 40/8plantsm-2, and D5, pure annual wormwood, 0/8plantsm-2, two activated carbon (allelopathy) levels: C-, with activated carbon (reduced allelopathy) and C+, non activated carbon applied (with allelopathy) and two herbicide levels: H-, untreated and H+, treated with a sub-lethal dose of glyphosate. Activated carbon to adsorb allelochemicals (with and without activated carbon) and glyphosate application (with and no herbicide) were assigned to sub-plots. Increasing weed density did not affect crop biomass at flowering, but changed nodule number and soybean yield with a different pattern depending on carbon and herbicide treatment. Relative crop yield decreased with increasing relative weed biomass. This decrease was particularly drastic when allelopathy was reduced by activated carbon and without herbicide application. The maximum yield losses of 33% in 2006 and 17% in 2007 were observed with the highest weed density (8plantsm-2). In contrast, without carbon (high allelopathy level), soybean yield remained stable within the explored range of annual wormwood biomass, despite the fact that weed biomass at high densities (D4) was high enough to generate competition. The lack of response to increasing weed density could be related to the indirect effect of allelochemicals interacting with soil microorganisms (i.e. B. japonicum) that positively affected the nodulation (e.g. larger nodules in 2006 and increased nodules biomass due to higher number of roots in 2007 at high densities). With herbicide application, soybean yield of both carbon treatments remained stable when biomass of annual wormwood increased. This research provided strong evidence in support of the existence of positive effect of allelopathic and competitive interactions between annual wormwood and soybean crop under field conditions that may be overridden under herbicide application. © 2011 Elsevier B.V.This work was supported by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT)PICT 01617, by University of Buenos Aires (UBA) (G039), by MAEC-AECID and YPF Foundation grants.Peer Reviewe

Concentration of defense hormones and lolines of L. multiflorum plants and S. frugiperda performance measurements

MeJA: methyl jasmonate; SA: salicylic acid; JA: jasmonic acid; nanl: N-acetylnorlolines; nfl: N-formyllolines; DW: dry weight

Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.

<p>Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.</p