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Aphids exploit different patches that offer a favourable habitat during their life cycle. Continuous colonization of new patches is critical for the survival of these insect pests. We developed a mesocosm experimental system to study the effects of stress regimes on the colonization of plants by aphids. In the first experiment, we treated Eruca sativa Mill (arugula) plants with either low ozone (O3) (ambient air with no O3 added), elevated O3 (ambient air with O3 addition) or low O3 + Myzus persicae aphid feeding, with subsequent observation of natural aphid infestation over time. The second experiment consisted of aphid sources and differently treated aphid sinks. The aphid sources were also exposed to either low or high O3 levels. The colonization of the sinks was then monitored over time and distance from source. The infestation rate was increased if the patches had been recently exposed to aphid herbivory. On the contrary, aphids did not colonize patches that experienced a recent O3 episode. The patches of E. sativa plants without prior biotic or abiotic stress were colonized by aphids at the beginning of the experiment, but infestation was poor and most of the plants remained aphid‐free throughout the experiment. Aphids from control patches had a better chance of successfully disseminate on hosts with previous herbivory, and aphid spread from O3‐stressed plants was generally poor. Hence, the colonization risk for a generalist aphid plague will depend on the space–time arrangement between crop patches with different stress levels. Ozone contamination could have a negative effect on the spread infestation of aphids in annual crops, because of habitat fragmentation. Here, we present important information to understand how physiological traits of individuals can be scaled up to predict changes within populations in a scenario of climate change. [ABSTRACT FROM AUTHOR]

Abstract: In order to determine the independent and joint effects of: (1) crop management; (2) soil condition; and (3) site location on soil biota assemblage, we examined the effects of several crop management and soil condition descriptors on the abundance and diversity of soil microarthropods in crop fields. Data were analyzed using linear regression, canonical correspondence analysis and variance partitioning. Our results indicated that: (1) soil mites was the most affected group by crop management; (2) most of the variance on microarthropod abundance remained unexplained as none of the descriptors were able to explain more than 10% of total species matrix variance; (3) tillage intensity resulted in higher variance explained of the species matrix than pesticide use or crop rotation; (4) soil carbon was the most influential factor among soil condition descriptors; and (5) a significant component of species variation was accounted for by the spatially structured fraction of the explanatory descriptors and other underlying spatial processes. Following the methods proposed in this work, further studies based on the obtained results may increase their power to detect agriculturally induced effects on soil biota by including more soil fauna groups and more controlled environmental factors or by improving the description of the local scale spatial heterogeneity. [Copyright &y& Elsevier]

The invasive potential of a species can be assessed by propagule pressure, which measures the chances for propagules of a species to find a suitable habitat for establishment and reproduction. Seeds, fruits, and vegetative structures that contribute to the propagule pressure are morphologically, physiologically and genetically different from one another, thus each kind should have a specific way of contributing to a successful invasion. In this paper we review plant traits that contribute to the propagule pressure. Seed production provides an estimate of the potential multiplication rate of the weed. However, it is gap-sensing mechanisms of seeds based on dormancy termination and germination requirements, which significantly contribute to the naturalization and invasion processes assuring a successful seedling establishment in environments of high competition. Dispersal of propagules reduces competition, mating with a sibling, and subsequent inbreeding depression, and increases colonization opportunities and range of expansion. Some of those benefits can be achieved in a population by existence of dormancy mechanisms and thus, the existence of a seed bank. Finally, vegetative propagation may ensure expansion of local populations when seedling establishment is low. Broadening the scope of traits that are considered in the breeding programs aimed at commercial production of plant propagules, to include those related to propagule pressure, is essential for adequate evaluation of invasive potential. [ABSTRACT FROM AUTHOR]

Continuous biomass removal by grazing usually changes the resource allocation pattern of plants. These changes often increase resistance to tissue removal and produce individuals with different morphometric traits, such as root to shoot or blade to sheath ratios. Shifts in morphometric traits, in turn, may alter nutrient cycling through changes in the average quality of litter that decomposes in soil. Previous work has shown that Paspalum dilatatum, a native grass from the Pampas grasslands, which inhabits a vast area and supports a wide range of grazing conditions, increases its blade to sheath ratio under continuous grazing with respect to ungrazed conditions. Here, we explored the consequences of these changes apparently associated with grazing regime on litter quality and nutrient dynamics during litter breakdown in soil. We separately analysed litter quality of blades and sheaths of P. dilatatum and determined under controlled conditions their decomposition and nutrient release kinetics over a maximum period of 1 year. We also studied the mineral nitrogen contents in soil amended with each litter type. Blade quality was significantly higher than sheath quality, nitrogen concentrations of blades and sheaths were approximately 1% and 0.6%, respectively, and lignin to nitrogen ratios were approximately 5 and 11 for blades and sheaths, respectively. Phosphorus concentration, however, was similar in both litter types. Blades decomposed 10% faster than sheaths, released 20% more nitrogen and released 15% more phosphorus than sheaths during the last half of the incubation period. During the first 3 months, the soil nitrogen content of litter-amended incubations indicated immobilization with respect to non-amended control; however, later blade incubations mineralized nitrogen, whereas sheath incubations continued immobilizing it. Results revealed that grazing potentially accelerates nutrient cycling during decomposition by increasing the blade to sheath ratio of P. dilatatum individuals, and suggest that this may be an important mechanism underlying grazing impact on nutrient cycling. [ABSTRACT FROM AUTHOR]

Application of a series of sublethal rates of diclofop-methyl (DM) herbicide to cloned individuals of Lolium multiflorum Lam increased their level of resistance to this herbicide.Under controlled environmental and field conditions, individuals of L. multiflorum genotypes herbicide-acclimated with 35 and 70 g a.i. ha-1 diclofop-methyl rates showed up to 80% survival and produced more aboveground biomass when exposed to four times higher rates compared to herbicide non-acclimated plants. The acquired increase in individual herbicide tolerance was not transmitted to their offspring, denoting the nature of acclimation response.The lack of transmission of resistant traits to the progeny highlights that exposure to sublethal rates of herbicide in susceptible individuals allowed for the expression of pre-existing cytoplasmatic information or simultaneously induced and selected extra-nuclear contents associated with resistance. The potential mechanisms through which induced tolerance may occur in L. multiflorum plants treated with sublethal concentrations of diclofop-methyl are discussed.Any recommendation or attempt to control weeds by reducing herbicide rates to increase economic returns and reduce the risk of environmental contamination should (a) acknowledge the potential acclimation responses in target plants and (b) be made and based on long-term studies. [Copyright &y& Elsevier]

Lolium multiflorum (Italian ryegrass), an annual weed invading wheat and barley cropping systems, has evolved resistance to diclofop-methyl (DM) herbicide. Earlier studies on the mode of action of DM in susceptible L. multiflorum and L. rigidum populations have shown that herbicide promotes oxidative stress leading to senescence, a process reversible through the action of auxins. The disruption of cell membrane potential ( E m) appears to be correlated with DM phytotoxicity in susceptible populations, suggesting that the continuous H+ extrusion from plasmalemma to extracellular space is inhibited. L. multiflorum usually establishes a symbiotic relationship with fungal endophytes of the Neotyphodium genus. This fungus confers to host plants higher survival at sublethal dosages of DM, probably due to the production of auxinic compounds. Our goal was to characterize DM-resistant and DM-susceptible L. multiflorum populations infected (E+) and non-infected (E−) with endophytes, by studying the capacity of H+ bumping of plasmalemma of intact roots under DM selection. We correlated the effects of DM on H+ disruption with plant survival. DM inhibited acidification markedly more in susceptible than in resistant populations. Continued extrusion of H+ by DM-resistant cell membranes was positively related to plant survival and growth. There was no detectable difference in the capacity of bumping H+ between DM-susceptible E+ and E− seedlings, even though survival was higher in E+ plants. The basis for the differential response in H+ extrusion between resistant and susceptible populations of L. multiflorum is discussed. [ABSTRACT FROM AUTHOR]

Sustainable agriculture requires an adequate analysis framework. Fuzzy logic-based and field scale indicators were developed to evaluate the effects of pesticides and tillage on agroecosystems. All the assumptions and rules for making inferences reflect the current knowledge and the expert perception and judgment about the potential environmental impact of pesticides and tillage. The proposed indicators require four input variables: (1) number and type of applied pesticides, (2) rate of applied pesticides, (3) number and type of tillage tools, and (4) land capability class of each field. In regards to pesticide impact, the indicators consider the toxicity effects on: (1) mammals and (2) insects, while the tillage impact is evaluated taking into account the effects of different tillage operations on: (1) the retention of crop stubble on the soil surface, and (2) the stability of soil aggregates. Two overall outputs were obtained: (1) pesticide index and (2) tillage index. The developed indicators were used to compare the potential environmental effect of current practices carried out in Inland Pampa (Argentina). Concerning pesticide use, cropping winter wheat did less harm to the agroecosystem than cropping maize and sunflower. The overall values of tillage index were similar within crops. However, large differences in pesticide and tillage effects were found among tillage systems. Soybean showed the highest variability in both indexes. The type of analysis carried out in this study using farm-level variables may help find more sustainable ways to manage agricultural inputs. [Copyright &y& Elsevier]

Information on the geographical distribution of plant invasion has been recorded in detail in some areas of the world; however, in large regions such as South America there are a few, if any, records of the spread of alien plants and invasive species and even less information about their effects on ecosystems at different levels of organization. This study examines the extent to which woody species introduced during the last centuries are invading the Rolling Pampa (which is typical of the entire region of the Argentina pampas) and discusses whether this invasion is related to the species’ genetics or to environmental factors. All woody species were surveyed along landscape corridors (highways and intersecting secondary dirt roads and streams), as well as in farmed fields under three different tillage systems: zero tillage in the entire field for all crops in the rotation (where tillage was replaced by a presowing herbicide application), zero tillage for selected crops, and conventional tillage. Landscape corridors along the roads had been invaded by 40 woody species (mostly trees). On the farmed land, fields under the zero tillage farming system were invaded by seven woody species (three tree species and four shrubs). With zero tillage for select crops only, woody species richness was reduced to three (one tree and two shrub species). In the conventional tillage, there were only three invading species, all shrubs. In both the roadside and riparian corridors, the species with the highest constancy values were Gleditsia triacanthos L., Morus alba L., and Melia azedarach L. In both types of zero tillage farmed fields, M. alba was absent, but G. triacanthos and M. azedarach remained the species with the highest constancy values. Both genetic and ecological factors were important determinants for the invasion of the pampas by woody species. The woody invasion process has reached a point at which the pampean grasslands on the better-drained soils will no longer be restored to a grassland biome without human intervention. [Copyright &y& Elsevier]

AbstractWeed invasion in cropland can be estimated by measuring specific constancy (Number of fields of occurence/Number of fields surveyed). Since the beginning of this century, many floristic surveys have been carried out in fields with similar soil types in the Pampas of Argentina. Thus, weed species with high constancy in maize or wheat crops over more than 60 years could be identified. Convergence among species of any trait having a selective advantage in the cropping environment would be expected. However, no evidence of such convergence was found in seed bank persistence or in dormancy and germination characteristics of summer or winter annuals selected as model species: Amaranthus retroflexus, Datura ferox, Echinochloa crus-galli, Tagetes minuta, Avena fatua, Galinsoga parviflora. On the other hand, changes in dormancy and germination traits were recorded in seeds of E. crus-galli and A. fatua in different agricultural systems, suggesting an adaptive value for invasion of human disturbed habitats. We used a simulation approach to investigate the importance of ecophysiologic seed phenotypes for the invasion of plants into specific human disturbed habitats. Results of the simulations showed that rainfall pattern and soil type interactions changed relative fitness of the tested phenotypes. [ABSTRACT FROM AUTHOR]

Compares the impact on crop yields of reducing the weed capacity to disperse with increasing the relative crop capacity to compete for resources. Examination of some assumptions and models currently used to describe dispersal; Changes in distribution of weed propagules; The effect of weed competition on crop yields; Modeling development of weed infestations; Conclusions.

Tropospheric ozone is an abiotic stress of increasing importance in the context of global climate change. This greenhouse gas is a potent phytotoxic molecule with demonstrated negative effects on crop yield and natural ecosystems. Recently, oxidative stress has been proposed as a mechanism that could regulate the interaction between cool‐season grasses and Epichloë endophytes. We hypothesized that exposure of Lolium multiflorum plants, hosting endophytes to an ozone‐polluted environment at different ontogenetic phases, would impact the trans‐generational dynamics of the vertically transmitted fungal symbiont. Here, we found that the ozone‐induced stress on the mother plants did not affect the endophyte vertical transmission but it impaired the persistence of the fungus in the seed exposed to artificial ageing. Endophyte longevity in seed was reduced by exposure of the mother plant to ozone. Although ozone exposure did not influence either the endophyte mycelial concentration or their compound defences (loline alkaloids), a positive correlation was observed between host fitness and the concentration of endophyte‐derived defence compounds. This suggests that fungal defences in grass seeds were not all produced in situ but remobilized from the vegetative tissues. Our study reveals ozone trans‐generational effects on the persistence of a beneficial symbiont in a host grass. Mother plant exposure to ozone did not affect the growth and the transmission of fungal endophytes into host seeds. Seed alkaloid concentration correlated with endophyte mycelial concentration and host fitness. However, ozone‐induced stress on mother plants did impair the longevity of the endophytes in the seeds. [ABSTRACT FROM AUTHOR]

Agricultural intensification simplified environments, reduced their diversity, and hindered their ecosystem processes. Permanently vegetated areas (uncultivated margins) embedded in the cultivated matrix play a critical role in maintaining diversity and soil properties, and so mitigate the negative impact of intensification. We performed two studies aimed at evaluating the role of uncultivated margins on soil heterotrophic bacteria. In the first study, we sampled soybean fields and herbaceous and woody margins in three locations along a 100-kilometer transect. In a second study, in one location we sampled uncultivated margins and perpendicular 50-meter transects from each margin towards the centre of its adjacent soybean field. As control, we sampled similar transects in soybean fields that had cropped fields as margins. In both studies, we characterized the catabolic profiles and diversity of the heterotrophic bacterial community and soil properties. Soil microbial communities of uncultivated margins differed in composition and were more diverse than the cropped matrix. In turn, these differences positively correlated with soil pH. Woody margins also influenced the soil microbial composition, diversity and soil pH of neighbouring cultivated fields. In contrast, herbaceous margins did not influence their cultivated neighbours. These results broaden our understanding of soil heterotrophic bacterial community in agro-ecosystems and its implications for ecosystem functioning. [ABSTRACT FROM AUTHOR]

Highlights: [•] In intensified landscapes, crop diversity is the main source of heterogeneity. [•] We developed a multi-scale heterogeneity approach based on linear-mixed models. [•] At local scale, field position was a major determinant of arthropod diversity. [•] Fence density at landscape scale, contributed to retain diverse communities. [•] Diverse mechanisms linked to heterogeneity benefit the arthropod diversity. [Copyright &y& Elsevier]

Highlights: [•] Woody margins had the largest soil carbon stocks while herbaceous margins had the smallest ones. [•] Woody margins increased soil carbon stocks of neighbouring crops. [•] Differences in litter quality and decomposition among margins accounted for variation in soil carbon stocks. [Copyright &y& Elsevier]

Tropospheric ozone is among the global change factors that pose a threat to plants and microorganisms. Symbiotic microorganisms can assist plants to cope with stress, but their role in the tolerance of plants to ozone is poorly understood. Here, we subjected endophyte-symbiotic and non-symbiotic plants of Lolium multiflorum , an annual species widely distributed in temperate grasslands, to high and low (i.e., charcoal-filtered air) ozone levels at vegetative and reproductive phases. Exposure to high ozone reduced leaf photochemical efficiency and greenness in both symbiotic and non-symbiotic plants. However, ozone-induced oxidative damage at biochemical level (i.e., lipid peroxidation) was mostly detected in symbiotic plants. Ozone exposure at the vegetative phase did not affect the reproductive investment in seeds, indicating full recovery from stress. Ozone exposure at the reproductive phase reduced biomass and seed production only in symbiotic plants indicating a symbiont-associated cost. At low ozone, endophyte-symbiotic plants showed a steeper slope in the relationship between seed number and seed weight (i.e., a number-weight trade-off) compared to non-symbiotic plants. However, when plants were treated at the reproductive phase, ozone increased the imbalance between seed number and seed weight in both endophyte-symbiotic and non-symbiotic plants. Plants with endophytes at the reproductive stage produced fewer seeds, which were not compensated by increased seed weight. Thus, fungal mycelium growing within ovaries or ozone-induced antioxidant systems may result in costs that finally depress the fitness of plants. Despite ozone pollution could destabilize plant-endophyte mutualisms and render them dysfunctional, other endophyte-mediated benefits (e.g., resistance to herbivory, tolerance to drought) could over-compensate these losses and explain the high incidence of the symbiosis in nature. • Symbiotic and non-symbiotic plants were exposed to low and high ozone (O 3). • Plant fitness was more sensitive to O 3 at reproductive than vegetative stages. • Symbiotic plants exposed to O 3 at flowering displayed reduced investment in reproduction. • O 3 caused a seed number−seed weight trade-off of non-symbiotic plants without compromising fitness. • Low frequency of symbiotic plants may be found in populations under O 3 pollution. [ABSTRACT FROM AUTHOR]

Abstract: Agro-ecosystem biodiversity is threatened by increasing spatial homogenisation of intensively managed farmland. Yet current understanding of patterns of arable plant diversity at various scales remains limited. We evaluated the extent to which species richness of arable plants in the Rolling Pampas of Argentina is determined by field position (fencerow, edge and centre) and crop type, at both field (local) and landscape scales. Plant richness was assessed in maize, soybean and wheat–soybean fields across four landscape types differing in spatial complexity, as defined by percentage area devoted to cropland. Species richness was hierarchically nested within landscape types, field positions and crop types. Landscape richness (γ-diversity, the cumulative number of species in a set of fields) was additively partitioned into two components, one for local richness (α-diversity, the mean number of species per field) and one denoting differences in species composition among fields (β-diversity, where β = γ − α). Field position was the main determinant of landscape-scale plant richness. Overall, γ-diversity declined from fencerows, through field edges to field centres, but was unaffected by crop type. Spatial variation in species composition (β-diversity), rather than species packing within fields (α-diversity), accounted for most of the variation in arable γ-diversity. Higher β-diversity in field edges than in field centres suggested that propagule dispersal from fencerow vegetation may create a ‘mass effect’ onto certain crop types. Shifts in γ-diversity of major perennial life-forms (chamaeophytes and phanerophytes) between field positions and crop types reflected the contrasting disturbance regimes affecting plant communities of fencerows and cultivated fields. Our results indicate that preserving coherent and extensive fencerow networks is essential to conserve farmland biodiversity. Moreover, maintaining landscape heterogeneity to support elevated β-diversities of arable plants requires cropping systems that promote crop diversity in both space and time. [Copyright &y& Elsevier]

Abstract: Agro-ecosystems still retain part of the original biodiversity, although agricultural intensification threatens to eliminate refuge patches from farmland mosaics. Landscape complexity resulting from networks of uncultivated corridors associated with fencerows may play a key role in sustaining biodiversity across scales, and may further influence diversity in adjacent, cultivated fields. We evaluated the relationship between farmland complexity and plant diversity of fencerows and crop fields at local and landscape scales in the Rolling Pampas of Argentina. We surveyed 222 fencerows and fields cultivated with winter or summer crops, and characterised farmland complexity by the perimeter/area ratio of cropland in 2-km diameter circles surrounding each field. Plant diversity was additively partitioned into alpha, beta, and gamma components. Fencerows had noticeably higher richness than cropped fields at local and landscape scales. Gamma and beta diversities of fencerows and fields were positively related to farmland complexity, supporting the role of spatial heterogeneity in maintaining plant diversity in agro-ecosystems. Landscape complexity did not influence alpha diversity of fencerows but significantly increased diversity within fields, a likely result of enhanced mass effects from uncultivated habitats in more varied farmland. More complex landscapes contained greater gamma diversity of exotic perennials in fencerows, and of exotic and native annuals within fields. Importantly, alpha and gamma diversities of native perennials from the pristine Pampa grassland increased with landscape complexity within cropped fields. In the face of ongoing landscape homogenisation under agricultural intensification, maintaining fencerow networks may become critical for conserving habitat heterogeneity and farmland biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Plant emission of volatile organic compounds (VOCs) has a significant impact on arthropods and plants and alters important functions in the agroecosystems. Three field source–sink microcosm experiments evaluated variation in wheat plants volatile emissions and its impact on neighbouring wheat plants’ performance caused by genotype, aphid herbivory and soil nutrient availability due to different cropping histories. An electronic nose detected qualitative differences in volatile emissions. Two of the experiments established the source–sink relationships forcing the volatiles through pipes. In these experiments wheat genotype was introduced as a variable of the source plants. In the third experiment, the emissions of volatiles dispersed naturally affecting the neighbourhood only by proximity and wheat genotype was a controlled factor. Plant genotype, aphid attack and soil chemical changes caused by different cropping histories affected wheat volatile emissions despite independent variations in plant biomass or resource allocation. This is the first report of changes in distant plant biomass according to neighbouring plant genotype and agricultural history. Wheat VOCs emissions were associated with changes in soil organic C, Ca, Mg, total nitrogen and cation exchange capacity caused by the different cropping histories of the soils tested. Variability in total biomass and resource allocation increased due to changes in VOCs emissions promoted by longer cropping history or aphid feeding in two genotypes. When volatiles were naturally dispersed into the neighbourhood, tiller weight in the sink individuals depended on plant genotype and cropping history of its neighbours (i.e. VOCs source). These findings highlight that ecological and environmental consequences of agricultural practices are more complex than normally thought. [Copyright &y& Elsevier]

Abstract: Multi-location trials are commonly used to estimate the effects of different explanatory factors on crop yield. Conversely, the analysis of production databases could also be useful for exploring and understanding such effects. These data require flexible and robust methods for dealing with multivariate, non-linear and unbalanced data structures, high-order interactions and missing values. In this paper, we explore the issue of crop yield explanation using a 5-year period (1999–2005) of sugarcane (Saccharum officinarum L.) yield data from Northern Argentina. Using a data mining technique such as classification and regression trees (CART) we show that farm membership (FARM) was among the main splitting factors for total cane per hectare (TCH) cluster variability. Crop class (AGE) was at the second level in the hierarchy and values of AGE higher than 2,5 splitted low and medium from the high TCH clusters. Sugarcane cultivar (VAR) was the most important explanatory factor regarding total sugar per hectare (TSH), and crop class (AGE) was second in importance. In this case, farm membership did not appear among the main splitting factors. The growth period duration, field area and precipitation did not show remarkable importance values for explaining final TCH and TSH values. By-year CART models also showed low values of importance of weather related variables across the years analyzed suggesting that other environmental conditions than precipitation is controlling yearly variation in sugar and cane yield (e.g. radiation, water-use efficiency or temperature regime). The CART analysis developed here is the first systematic analysis for explanatory factors of biomass and sugar content in Argentina''s cane most productive region. However, we believe this methodology could be applicable for a wider geographic area and other sugarcane production regions as well as other cropping systems. Although regression trees provide less formal statistical inference, its results could be added as an additional analytical tool to traditional experimental analyses that use mixed models. Also, they could be useful for elaborating hypotheses and suggest mechanistic studies to test them. [Copyright &y& Elsevier]

Neotyphodium frequently occurs as an endophyte in grasses. Evidence shows enhanced fitness of endophyte infected grasses relative to non-infected ones. Some studies of seed germination show endophyte enhancement of plant fitness in various environments, but inconsistent results indicate that further studies are needed. So far, experiments have failed to separate the confounded effects of population origin and seed management. For this reason, we evaluated the effects of endophyte infection on seed dormancy and germination in Lolium multiflorum using an experimental design controlling these factors. Depending on the year of seed production, endophyte infection modified seed response to light quality, affecting predominantly seed dormancy levels. Nevertheless, the endophyte did not affect base temperature or thermal time of germination. We concluded that endophytes were not a strong influence on germination behaviour. We speculate from our results that the presence of the endophyte changes germination by an indirect effect, in extending growth of the maternal plant during seed development and ripening. The direct effect of hyphae in the seed on seed behaviour was disregarded, because the difference between infected and non-infected seed varied within the year of seed production. Future experiments should focus on effects of the endophyte on the canopy of parent plants during seed production and ripening, and, hence, on subsequent dormancy and germination of the seeds. [ABSTRACT FROM AUTHOR]

Lolium multiflorumis a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodiumsp.) from early successional stages. We assessed the effect ofNeotyphodiuminfection on the biology ofL. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non-competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands. [ABSTRACT FROM AUTHOR]

Symbiotic infection with fungal endophytes has been shown to decrease herbivory in several temperate grasses. We tested the hypothesis that foliar endophytes of grasses may also affect below-ground processes upon their host death, by altering the litter quality for detritivores or the microenvironment for decomposition. Microcosm–litterbag experiments were used to assess decay rates for litter produced by endophyte ( Neotyphodium sp.) infected vs uninfected Lolium multiflorum plants, and to examine endophyte-mediated effects of prior site occupants on current litter decomposition. We found that litter from endophyte-infected L. multiflorum decomposed more slowly than litter from endophyte-free conspecifics and from a naturally uninfected grass, Bromus unioloides. Furthermore, the endophyte–grass association modified the decomposition environment, so that B. unioloides litter decomposed faster when placed underneath a thick layer of endophyte-free L. multiflorum litter. Litter decay rates increased with the amount of root debris remaining in situ from the previous season, but were not affected by the infection status of prior site occupants. The lower decomposability of litter from infected L. multiflorum plants persisted across a range of microenvironments, as determined by different amounts of above-ground litter and soil moisture conditions. Endophyte infection tended to reduce the N content of decaying litter; however, litter N and C/N ratio mainly accounted for interspecific differences in decomposition. Our results imply that fungal endophytes not only can affect herbivory food chains, but also soil organisms and the ecosystem processes they regulate. This study suggests a novel role for symbiotic foliar endophytes in linking above-ground and below-ground sub-systems. [ABSTRACT FROM AUTHOR]

Ground‐level ozone is a global air pollutant with high toxicity and represents a threat to plants and microorganisms. Although beneficial microorganisms can improve host performance, their role in connecting environmentally induced maternal plant phenotypes to progeny (transgenerational effects [TGE]) is unknown. We evaluated fungal endophyte‐mediated consequences of maternal plant exposure to ozone on performance of the progeny under contrasting scenarios of the same factor (high and low) at two stages: seedling and young plant. With no variation in biomass, maternal ozone‐induced oxidative damage in the progeny that was lower in endophyte‐symbiotic plants. This correlated with an endophyte‐mediated higher concentration of proline, a defence compound associated with stress control. Interestingly, ozone‐induced TGE was not associated with reductions in plant survival. On the contrary, there was an overall positive effect on seedling survival in the presence of endophytes. The positive effect of maternal ozone increasing young plant survival was irrespective of symbiosis and only expressed under high ozone condition. Our study shows that hereditary microorganisms can modulate the capacity of plants to transgenerationally adjust progeny phenotype to atmospheric change. Ozone induced positive transgenerational effects (TGE) by increasing plant survival. It depended on fungal endophytes symbiosis, progeny size, and current ozone condition. Endophytes were determinant for seedlings, while current ozone allowed TGE to express in young plants. Our results give insights on the role of seed‐borne fungi into environmentally induced transgenerational responses of plants. [ABSTRACT FROM AUTHOR]

Presents the effects of fungal endophytes on insect food webs that reflect limited energy transfer to consumers as a result of low plant quality, rather than low productivity. Characteristics of herbivore-parasite webs on endophyte-free grasses; How these results reflect predicted effects of increased productivity on food-web dynamics; Conclusion that hidden microbial symbionts can have community-wide impacts on the pattern and strength of resource-consumer interactions.

Plants are expected to face novel challenges as consequence of human-driven global change. Outbreaks of pests and higher incidence of contaminants are increasing. Plants can improve tolerance to stress factors through associations with symbiotic microorganisms. Certain grasses establish persistent and asymptomatic symbioses with Epichloë fungal endophytes, which are known to confer protection against Herbivores and improve plant tolerance to abiotic stress factors. Nonetheless, accumulating evidence suggests the symbiosis outcome is context-dependent. We evaluated the capacity of the endophyte fungus E. occultans in protecting the annual grass Lolium multiflorum against a spontaneous larva attack of the generalist herbivore Agrotis ipsilon under episodic exposure of plants to ozone. Symbiotic and non-symbiotic plants were individually grown outdoors and exposed to ozone at different stages resulting in four treatments: control (plant never exposed to ozone), plant exposed to ozone at vegetative stage, plant exposed to ozone at reproductive stage, and plant exposed to ozone at both stages. After the last exposure, there was an outbreak of A. ipsilon larvae. We evaluated herbivore damage, seed production per plant, and endophyte transmission to the seeds. Frequency of attacked plants was irrespective of both the endophyte and ozone exposure. However, the damage level per plant was only reduced by the endophyte. Seed production was slightly lower in endophyte-symbiotic plants and not affected by ozone. Interestingly, herbivore damaged and undamaged endophyte-symbiotic plants contributed equally to seed production. However, in plants exposed to ozone once at vegetative or reproductive stage, endophyte-free undamaged plants had higher seed production than endophyte-free damaged plants. Ozone treatments did not affect the transmission efficiency of endophytes to the seeds. Mean endophyte transmission efficiency per plant was 95%. Medium doses of ozone seem to have undetectable effects on grass-endophyte symbiosis, not affecting the defensive mutualism nor the persistence of the symbiont across generations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Root infestation by Meloidogyne incognita (Kofoid and White) Chitwood, in mixtures of Glycine max (L.) Merr. and Tagetes minuta L. was studied through an experiment designed to test how host different proportions influenced nematode reproduction and second generation density. Root-knot density, feeding sites, histological reactions and number of second generation M. incognita in both host species were evaluated. Gall density was higher in treatments where G. max plants were in more than 50%. In roots of T. minuta feeding sites they were found nonfunctional and larvae on these sites did not reach reproductive stage. Density reduction of soil larvae was proportional to the amounts of T. minuta in the mixture. These data indicate that T. minuta infected by nematodes acts as a "trap-plant", capturing some individuals, many of which will never reach sexual maturity, and reducing second generation density. [ABSTRACT FROM AUTHOR]

The decline of bees is a major concern due to their vital role in pollinating many crops and wild plants. Some regions in South America, and especially the Pampas, are amongst those parts of the world where stressors of bee populations have been little studied. The Pampas has been intensively transformed for agriculture, being presently one of the most productive areas of agricultural commodities in the world. Here, we aim to provide first insights on the taxonomic and functional composition of bee assemblages in the Rolling Pampa, the most intensively managed part of the Pampas. Soybean (herbicide-tolerant genetically modified varieties) is the predominant crop in this region. Bees were sampled with coloured pan traps. Sampling points were located on field margins in either the cropped or the semi-natural grassland area of a farmland site devoted to annual cropping. A total of 2384 individuals were caught, representing 33 taxa [mainly (morpho)species]. The subgenusLasioglossum(Dialictus) largely dominated captures (78% of the total abundance) and was relatively abundant in the entire study area, suggesting that some species are likely to reach their ecological requirements in cropped areas. No-till fields and field margins may provide large areas for these below-ground nesting species, while their polylectic food preferences allow them to collect pollen on a wide range of plant species, among them possibly soybean. On the contrary, the richness and the abundance of other taxa were higher in the semi-natural area than in the cropped area. Among them, above-ground nesting or oil-collecting species, which have more specialised nesting and floral requirements, were highly associated with the semi-natural area. Our findings highlight the large dominance ofL. (Dialictus) species in this highly intensively managed landscape, and the urgent need of preserving semi-natural habitats to maintain species-rich and functionally diverse bee communities in the Pampas. [ABSTRACT FROM AUTHOR]

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., 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., 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., 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. [ABSTRACT FROM AUTHOR]

Most of our knowledge about the consequences of tropospheric ozone pollution on aphid-plant interaction assumes the absence of a direct effect of ozone on aphids. However, the biological effects of ozone encompass changes in reactive oxygen species signalling, oxidative stress accumulation, and the immune response of both plants and animals. The main objective of this work was to evaluate the direct effect of ozone on Metopolophium dirhodum ( Walker) aphids ( Hemiptera: Aphididae), linking mechanisms that operate at individual scale (oxidative stress parameters and aphid-bacteria symbiosis persistence) with their consequences at population scale (mortality, dispersion, and population growth). Two experiments were conducted in open-top chambers with three contrasting ozone exposure regimes (6 h at 0.5 ± 0.3, 50 ± 5, or 150 ± 10 p.p.b.) and artificial diets to evaluate the direct effect of ozone on aphids. Exposure of aphids to ozone increased insect mortality compared to the control treatment. However, the populations established from the surviving insects of each treatment increased similarly. Consistently, aphid symbiosis with Buchnera aphidicola Munson et al. ( Proteobacteria) and Hamiltonella defensa Moran et al. ( Enterobacteriaceae) persisted in all treatments. Ozone also affected aphid behaviour. The proportion of insects dispersing from diet cages was lower in the ozone treatments than in the control treatment. In addition, lipid peroxidation was higher at 150 p.p.b. than at 50 p.p.b. treatment, although not different from that in the control. The reduction in aphid dispersion coupled with increased mortality suggests that direct exposure to ozone could lower aphid efficiency as virus vectors. These results could be partially associated with mechanisms operating at individual scale (accumulation of oxidative damage). Overall, these experiments encourage reconsidering the impact of the direct effects of ozone on aphids when assessing the consequences of this component of global change on plant-aphid interactions. [ABSTRACT FROM AUTHOR]

In sugarcane cropping systems, green-cane harvesting has progressively replaced the traditional burning of standing crop prior to harvest, increasing the role of decomposition as a mechanism to replenish soil nutrients. We examined the impact of cultivar choice and irrigation water quality on decomposition of sugarcane residue. In two independent litterbag experiments, we isolated the effects of changes in plant residue quality and irrigated water quality. Cultivar residue exhibited significant variation of carbon and nitrogen concentrations and carbon to nitrogen ratio. Decomposition rate varied among cultivars, and those with greater carbon-to-nitrogen ratios decomposed faster than cultivars with lower ratios. Soil irrigated with river water showed a lower mineral and organic nitrogen concentration and decomposition rate than those irrigated with industry effluent wastewater. These results provide empirical evidence that both cultivar choice and water used for irrigation have a limited but significant impact on plant residue decomposition. [ABSTRACT FROM AUTHOR]

Certain species of the Pooideae subfamily develop stress tolerance and herbivory resistance through symbiosis with vertically transmitted, asexual fungi. This symbiosis is specific, and genetic factors modulate the compatibility between partners. Although gene flow is clearly a fitness trait in allogamous grasses, because it injects hybrid vigor and raw material for evolution, it could reduce compatibility and thus mutualism effectiveness. To explore the importance of host genetic background in modulating the performance of symbiosis, Lolium multiflorum plants, infected and noninfected with Neotyphodium occultans, were crossed with genetically distant plants of isolines (susceptible and resistant to diclofop-methyl herbicide) bred from two cultivars and exposed to stress. The endophyte improved seedling survival in genotypes susceptible to herbicide, while it had a negative effect on one of the genetically resistant crosses. Mutualism provided resistance to herbivory independently of the host genotype, but this effect vanished under stress. While no endophyte effect was observed on host reproductive success, it was increased by interpopulation plant crosses. Neither gene flow nor herbicide had an important impact on endophyte transmission. Host fitness improvements attributable to gene flow do not appear to result in direct conflict with mutualism while this seems to be an important mechanism for the ecological and contemporary evolution of the symbiotum. [ABSTRACT FROM AUTHOR]

Neotyphodium endophytic fungi, the asexual state of Epichloë species, protect cool-season grasses against stresses. The outcomes of Neotyphodium-grass symbioses are agronomically relevant as they may affect the productivity of pastures. It has been suggested that the mutualism is characteristic of agronomic grasses and that differential rates of gene flow between both partners' populations are expected to disrupt the specificity of the association and, thus, the mutualism in wild grasses. We propose that compatibility is necessary but not sufficient to explain the outcomes of Neotyphodium-grass symbiosis, and advance a model that links genetic compatibility, mutualism effectiveness, and endophyte transmission efficiency. For endophytes that reproduce clonally and depend on allogamous hosts for reproduction and dissemination, we propose that this symbiosis works as an integrated entity where gene flow promotes its fitness and evolution. Compatibility between the host plant and the fungal endophyte would be high in genetically close parents; however, mutualism effectiveness and transmission efficiency would be low in fitness depressed host plants. Increasing the genetic distance of mating parents would increase mutualism effectiveness and transmission efficiency. This tendency would be broken when the genetic distance between parents is high (out-breeding depression). Our model allows for testable hypotheses that would contribute to understand the coevolutionary origin and future of the endophyte-grass mutualism. [ABSTRACT FROM AUTHOR]

1. Many grass species are associated with maternally transmitted fungal endophytes. Increasing evidence shows that endophytes enhance host plant success under varied conditions, yet studies have rarely considered alternative mechanisms whereby these mutualistic symbionts may affect regeneration from seed. 2. We performed a microcosm experiment to evaluate whether infection with Neotyphodium occultans affects recruitment in the annual grass Lolium multiflorum either directly, by infecting the seeds, or indirectly, by altering the suitability of recruitment microsites through the litter shed by host plants. Endophyte effects on establishment were tested for different litter depths and watering regimes under natural herbivory by leaf-cutting ants. 3. Seed infection increased seedling emergence through the litter as well as final recruitment, irrespective of microsite conditions. However, litter produced by infected plants delayed emergence and decreased density of both infected and non-infected grass populations. 4. Individual plant biomass did not change with seed infection but was increased under deep litter from endophyte-infected plants. Although seed infection did not protect establishing plants from leaf-cutting ants, herbivory was reduced in the presence of deep litter shed by infected plants. 5. We conclude that fungal endophytes may affect host plant recruitment across subsequent generations not only by infecting the seeds but also through the host’s dead remains. While the former effect entailed an advantage to infected plants, litter-mediated effects did not discriminate by infection status, and generally promoted the establishment of fewer and larger plants. Thus hidden foliar symbionts may play an underappreciated role in maintaining host species dominance through the litter produced by prior patch occupants. [ABSTRACT FROM AUTHOR]

Cool-season grasses establish symbioses with vertically transmitted Neotyphodium endophytes widespread in nature. The frequency of endophyte-infected plants in closed populations (i.e., without migrations) depends on both the differential fitness between infected and non-infected plants, and the endophyte-transmission efficiency. Most studies have been focused on the first mechanism ignoring the second. Infection frequency and endophyte transmission from vegetative tissues to seeds were surveyed in two grasses growing in vegetation units that differ in flood and grazing regimes, and soil salinity. Transmission efficiency and infection frequency for tall fescue did not vary significantly and were 0.98 and 1.00, respectively. For Italian ryegrass, transmission efficiency and infection frequency were 0.88 and 0.57 in humid prairies, and 0.96 and 0.96 in the other vegetation units. Only in humid mesophytic meadows, the observed pattern was irrespective of the presence or absence of grazers. Our results suggest that selection forces for endophyte infection are different for both species. Imperfect transmission was only compensated in tall fescue through an increased fitness of infected plants. Interpreting variations of infection frequency only in terms of differential fitness can be misleading, considering that endophyte transmission can be imperfect and variable in nature. Therefore, this study highlights the importance of measuring transmission efficiency. [ABSTRACT FROM AUTHOR]

Neotyphodium endophyte fungi are vertically transmitted symbionts of cool-season grasses. The seed phase of the grass’ life cycle appears to be critical for the persistence of the fungus. Endophyte viability decreases faster than seed viability, but little is known of the effects of this endophyte on seed viability. The endophyte could affect seed viability through changes in water content. Here, we assessed the effects of the endophyte on seed viability, the differential survival of endophyte and seed, and the effects of infection on seed water content. Viability of endophyte-infected and noninfected seeds and endophyte were evaluated over a period of 729 d under 12 controlled environmental conditions. Seed viability was reduced by the infection at high temperature and high relative humidity, but not under other conditions. Moreover, endophyte viability decreased faster than seed viability only under high humidity or high temperature. Seed water content was not affected by endophyte presence. The proportion of viable infected seeds was mainly affected by the loss in endophyte viability and secondly by the differential survival of infected and noninfected seeds. Knowledge on the relative importance of these processes is critical to understand the factors affecting the efficiency of endophyte vertical transmission and the frequency of endophyte-infected plants. [ABSTRACT FROM AUTHOR]

The authors comment on the study about the relationship between the pattern of Neotyphodium spp. endophyte infection frequency and the gradient of grazing pressure by pikas and hoary marmots in Canada. They propose that the effect of herbivores on infection frequency might be through phenotypic traits and interaction with other environmental factors. They also show the relation of relative fitness to herbivory deterrence.

Abstract: Arthropod assemblies are frequently determined by bottom-up interactions that include emission of organic volatile compounds. Therefore, changes in soil characteristics associated with land use history can influence the volatile emissions of plants affecting the structure of arthropod assemblies in croplands. This study aims (1) to study the relationships between soil degradation levels due to land-use history, and the change in particular soil chemical characteristics; (2) to analyze plant–soil interactions quantifying the effect of soil degradation on the production of biomass and grain yield of coriander and wheat crops, and on the production and chemical composition of volatile secondary metabolites in coriander grain; (3) to find the relationship between the analyzed plant–soil interactions and the emission of volatile signals affecting arthropod assemblies; and (4) to determine the relationship between particular chemical soil characteristics and the structure of arthropod assemblies. For these purpose, two experiments were carried out in which volatile compounds were conducted from source plots with soils with different levels of degradation, sown with wheat or coriander, to sink plots with similar soil, sown with wheat. Crops were evaluated on source plots, and the arthropods communities were assessed on sink-plots. Coriander produced high biomass, grain yield and essential oil in the favorable environments and wheat produced higher biomass and grain yield in soil with low degradation than with high degradation. Particular chemical soil elements, for example, Na, Fe, Mn, N and CEC and essential oil components, for example, γ-trepanned, p-cymene, asinine and β-pinene could be involved in the arthropods assemblies. Based on these results, arthropods communities in agricultural systems are, at least, partially controlled by chemical signals, which depend on plant–soil interactions. [Copyright &y& Elsevier]

Abstract: Intensive land use in the Rolling Pampa of Argentina have resulted in a mosaic of fields with different cultural histories creating different soil environments, which interact with crops and cropping activities producing a wide range of habitats for insects. Species and functions in canopy structure, food quality and essential oils of the crop–weed associations may vary depending on the field''s cropping history and management (i.e. crops, soil degradation, weeding and fertilization). Species composition and functional structure of insect communities may respond to these changes. We studied insect communities in wheat and coriander crops that differed in their canopy structures, essential oil production, and the cropping histories of the fields on which they grew. For this purpose we planted wheat (Triticum aestivum L.), and two coriander (Coriandrum sativum L.) landraces in plots with two levels of weeding and fertilization. The crops were grown in two consecutive years at two locations differing in cropping history and related to this in level of soil degradation. Insects were sampled in all plots at crop full flowering, and were classified and related to agronomic variables and to essential oils using multivariate techniques. Among all the environmental factors tested in this study, year and soil degradation were the main factors explaining insect community structure; and also weed community structure in unweeded plots. The proportion of essential oil components varied with cropping history, suggesting an association among soil properties indicative of soil degradation, plant chemical signals and insect distribution. Although insect community composition varied widely, functional structure was very similar among crop–weed communities. Soil degradation appeared to have affected directly crop–weed communities and insects’ assemblages, since no consistent relationship was found between plant composition and insect community structure. It can be hypothesized that soil degradation might have affected the amount of volatiles produced especially by coriander, generating a “soil degradation scent” that determined the structure in the insect community, and/or the soil itself emitted different signals, in relation to changes in its physical, chemical and biological characteristics. [Copyright &y& Elsevier]

One of the potential mechanisms for the impact of herbivores on nutrient cycling is the effect of selective grazing on litter quality through changes in species composition. However, the scarce evidence collected on this mechanism is controversial and seemingly influenced by site-specific variables. In this paper, we explored the consequences of grazing-induced changes in species composition on litter quality and nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall gradient, we selected species promoted and diminished by grazing from three natural rangelands of Argentina, analyzed their litter quality, and determined their decomposition and nutrient release kinetics under common greenhouse conditions. Litter quality and decomposition rates were strongly associated with plant response to grazing. However, the magnitude and direction of these differences depended on the ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had higher nitrogen and phosphorus contents, faster decomposition rates, and higher release of nitrogen to the soil than species diminished by grazing (C3 and C4 grasses). In the intermediate and dry sites, species promoted by grazing had lower nitrogen and phosphorus contents, and slower decomposition rates than those diminished by grazing (C3 grasses in both cases). Decomposition of the entire group of species was not correlated with mean annual rainfall, but when litter of the species diminished by grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was immobilized more often than mineralized, even after one year of incubation. Immobilization was negatively correlated with precipitation. All these results indicate that grazing may significantly alter nutrient cycling by affecting litter quality through changes in species composition. These effects seem to be larger when species replacements induced by grazing either involve functional groups, as it was the case in our wettest site, or change root to shoot ratios. Therefore, the functional groups involved in the replacement of species as well as shifts between belowground and aboveground allocation should play a key role in grazing-induced changes on nitrogen cycling. [ABSTRACT FROM AUTHOR]

Intensive land use in the Rolling Pampa of Argentina generates heterogeneous environmental and ecological conditions associated with agronomic practices. The yields of crops with different resource allocation to the production of primary or secondary metabolites could vary with the environment. Crops that mainly produce primary metabolites would have high yields under favorable environments, and crops that produce high quantities of secondary metabolites would have high essential oil yield under unfavorable environments. To test whether this hypothesis is applicable under the Rolling Pampa conditions, field experiments were conducted with the following objectives: (1) to compare biomass and grain yield in three winter crops: wheat (Triticum aestivum L.), coriander (Coriandrum sativum L.) landrace with high essential oil content (HEO) and coriander landrace with low essential oil content (LEO), grown at different levels of N fertilization and weed control; and (2) to determine relative changes in grain yield, essential oil production and harvest index with environment in the coriander landraces. The crops were grown at two locations differing in physical and chemical soil degradation due to the intensity of land use. Wheat allocated resources mainly to the production of primary metabolites, producing higher biomass and grain yield in the favorable environments. The HEO coriander landrace, which allocates resources to the production of both primary and secondary metabolites, produced similar biomass and grain yield in both locations, but resource partitioning to the production of essential oils was high under unfavorable environmental conditions. The LEO coriander landrace which allocates resources mainly to the production of primary metabolites and, in a minor proportion, to secondary metabolites, produced high biomass and grain yield in intermediate environments and high essential oil yield under unfavorable environments. The environmental conditions of the Rolling Pampa that curtailed the allocation of resources to the production of grain yield promoted the production of essential oils. Based on these results, under poor soil environments, one option is to produce crops with essential oils as marketable yields, instead of adding inputs to improve soil condition and produce traditional crops, where yield is very sensitive to environmental variations. [Copyright &y& Elsevier]

• Parental environment affects functional characteristics of seeds. • Seed-transmitted fungal endophytes mediate transgenerational effects in plants. • Negative effects of transgenerational ozone were detected in endophyte-symbiotic seeds but not in non-symbiotic seeds. • Parental ozone impacted seed progeny when it occurs close to reproductive phase of the plant. • Under accelerated ageing conditions, endophyte-symbiotic seeds showed deteriorated physiological state and reduced longevity. The transition from mother plant seed production to seedlings recruitment is critical for annual plant species but also for vertically transmitted microbial symbionts. Evidence indicates that microbial symbionts play important roles in plant response to environmental changes. However, their role in plant facing gaseous tropospheric pollutants such as the highly reactive and phytotoxic ozone, have been scarcely studied. Here, we experimentally tested the consequences of maternal plant exposure to ozone on the longevity of Lolium mutiflorum seeds mediated by a vertically-transmitted fungal endophyte (Epichloë occultans). Seeds were produced by mother plants exposed to contrasting levels of ozone (low and high concentrations) in two phases of the life cycle (vegetative and reproductive). We first characterized the consequences of plant exposure to ozone on the state of the antioxidant glutathione in the seeds. Then, we examined viability dynamics of the seeds through an accelerated ageing trial and followed the physiological variables seed water content (SWC) and electrical conductivity (EC). Irrespectively of maternal ozone, seeds produced by endophyte-symbiotic plants presented higher contents of the oxidised form of glutathione. In the same direction, the fungal endophyte presence was associated with a dramatic reduction in seed longevity. The SWC was higher in endophyte-symbiotic seeds that in endophyte-free seeds. As time under accelerated ageing condition advanced, EC increased more in endophyte-symbiotic seeds than in endophyte-free seeds. Mother plant exposure to ozone tended to have a negative synergistic effect with the endophyte symbiosis. Ozone transgenerational effect was not detected on endophyte-free seeds. Our work contributes to understand the transgenerational effects of vertically transmitted fungal endophytes in plants in response to a currently important factor of stress. [ABSTRACT FROM AUTHOR]

Tropospheric ozone is one of the major drivers of global change. This stress factor alters plant growth and development. Ozone could act as a selection pressure on species communities composition, but also on population genetic background, thus affecting life history traits. Our objective was to evaluate the consequences of prolonged ozone exposure of a weed community on phenotypic traits of Spergula arvensis linked to persistence. Specifically, we predicted that the selection pressure exerted by high ozone concentrations as well as the concomitant changes in the weed community would drive population adaptive changes which will be reflected on seed germination, dormancy and longevity. In order to test seed viability and dormancy level, we conducted germination experiments for which we used seeds produced by S. arvensis plants grown within a weed community exposed to three ozone treatments during four years (0, 90 and 120 ppb). We also performed a soil seed bank experiment to test seed longevity with seeds coming from both the four-year ozone exposure experiment and from a short-term treatment conducted at ambient and added ozone concentrations. We found that prolonged ozone exposure produced changes in seed germination, dormancy and longevity, resulting in three S. arvensis populations. Seeds from the 90 ppb ozone selection treatment had the highest level of germination when stored at 75% RH and 25 °C and then scarified. These seeds showed the lowest dormancy level when being subjected to 5 ºC/5% RH and 25 ºC/75% followed by 5% RH storage conditions. Furthermore, ozone exposure increased seed persistence in the soil through a maternal effect. Given that tropospheric ozone is an important pollutant in rural areas, changes in seed traits due to ozone exposure could increase weed persistence in fields, thus affecting weed-crop interactions, which could ultimately reduce crop production. [ABSTRACT FROM AUTHOR]