Claudio marco Ghersa - Academia.edu (original) (raw)
Papers by Claudio marco Ghersa
Journal of Production Agriculture, 1997
Seed dormancy has been viewed as problematic in grain and forage production for several reasons: ... more Seed dormancy has been viewed as problematic in grain and forage production for several reasons: (i) It is related to the development of persistent weed seed banks and failure in predicting establishment of weed stands. Both characteristics diminish the efficacy of weed control procedures; (ii) When agronomists domesticate wild species as crops, they find that if the crop seed has dormancy, its germination is restricted to a very narrow range of microenvironmental conditions. Instead, management of seed dormancy could be seen as a solution for many agronomic problems. Very few studies are focused on this idea.
Annals of Applied Biology, 1988
ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories acc... more ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses.In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.
Annals of Botany, 2006
Background and Aims Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to ex... more Background and Aims Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to exhibit an ecological advantage over endophyte-uninfected grasses under abiotic stressful conditions. It is predicted that endophyte-infected plant populations will display higher rates of germination and proportion of germinated seeds under limiting water conditions. Methods The hydrotime regression model was used to describe the effect of Neotyphodium endophyte on seed germination of Lolium multiflorum at different water potentials. Additionally, seed mortality after water stress exposure was estimated in endophyte-infected and-uninfected seeds. Key Results Endophyte infection inhibited seed germination at all water potentials. The hydrotime model described satisfactorily the germination responses, and revealed that endophyte-free seeds exhibited higher rates of and final percentage germination, probably due to a lower base water potential compared with endophyte-infected seeds. However, Neotyphodium endophyte conferred a higher rate of survival in those seeds that remained ungerminated when exposed to highly water stress conditions. Conclusions Changes produced by Neotyphodium endophyte in L. multiflorum seeds might affect fitness in particular ecological scenarios. For example, the presence of the endophyte may curtail seed germination when water is limiting, reducing the risk of seedling death. Conversely, endophyte-free seeds would display an enhanced germination, ensuring a more rapid seedling establishment if later water conditions do not restrict plant growth.
Weed Research, Apr 1, 1985
Ecología austral, Aug 1, 2017
R������. Se estudió la infestación de raíces por Meloidogyne incognita (Kofoid and White) Chitwoo... more R������. Se estudió la infestación de raíces por Meloidogyne incognita (Kofoid and White) Chitwood, en mezclas de plantas de Glycine max (L.) Merr. y Tagetes minuta L. en distintas proporciones, por medio de un experimento diseñado para probar cómo huéspedes en diferentes proporciones modifican la reproducción de la primera generación y la densidad de la segunda generación del nematodo. En ambos huéspedes se evaluó la densidad de agallas radicales, sitios de alimentación, reacciones histológicas y número de larvas de la segunda generación de M. incognita. La densidad de agallas fue mayor en los tratamientos donde las plantas de G. max se encontraban en más de 50%. En raíces de T. minuta se encontraron sitios de alimentación no funcionales y las larvas en estos sitios no alcanzaron la etapa reproductiva. La reducción de la densidad de las larvas en el suelo fue proporcional a las cantidades de T. minuta en la mezcla. Estos datos indican que T. minuta infectado por nematodos actúa como una "planta trampa" debido a la captura de algunos individuos, muchos de los cuales nunca alcanzan la madurez sexual, y por la reducción de la densidad de segunda generación de M. incognita. [Palabras clave: histopatología, mecanismos de defensa, interacción parasito-huésped, sobrevivencia] A�������. Effect of different proportions of Tagetes minuta and Glycine max on Meloidogyne incognita. 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.
Copies of this report can be ordered from the (first) author. The costs are € 50 per copy (includ... more Copies of this report can be ordered from the (first) author. The costs are € 50 per copy (including handling and administration costs), for which an invoice will be included.
Environmental Entomology, Apr 1, 2014
Ciencia hoy, 2005
Biblioteca de la Universidad Complutense de Madrid, Base de datos de artículos de revistas, ...
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
Ecología austral, Dec 1, 2006
RESUMEN. La implantación de masas forestales con fines productivos se realiza con un conjunto red... more RESUMEN. La implantación de masas forestales con fines productivos se realiza con un conjunto reducido de especies de las que se conoce su manejo silvícola e industrial. Por tal motivo se las introduce en áreas distintas a las de su origen. Potencialmente, estas introducciones pueden desencadenar procesos de invasión de los sistemas naturales o seminaturales contiguos a las plantaciones. En la región andino patagónica, la actividad forestal con especies introducidas es aún incipiente, tanto por la superficie forestada como por la edad de las plantaciones más importantes. Se estima la superficie implantada en aproximadamente 70000 hectáreas, con una tendencia creciente en el ritmo de forestación en la última década. La especie más plantada es el Pinus ponderosa Doug (Laws) (pino ponderosa), seguida por Pseudotsuga menziesii (Mirb)Franco (pino oregón) y Pinus contorta Dougl. (pino murrayana). Actualmente ha comenzado a observarse reclutamiento de renovales creciendo fuera de los macizos forestales en los sistemas lindantes, naturales o no. El presente trabajo evalúa, a escala regional, la presencia y la tasa de reclutamiento de renovales de estas especies en dos sistemas naturales, estepa y bosque de Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri (ciprés de la cordillera), con el fin diagnosticar si existe un proceso de invasión incipiente. Se muestrearon áreas cercanas a las principales masas forestales implantadas, desde el centro de la provincia de Neuquén (39º48'S) hasta el Norte de Chubut (42º10'S). Para ello, se registró la presencia de regeneración natural, su densidad (nº indiv/ha), distancia a la plantación, edad, altura, y si producían conos o semillas. Los resultados indican que es posible que se esté ante la invasión incipiente de las comunidades adyacentes a las masas forestales por dos de las especies consideradas: el pino murrayana estaría mostrando expansión invasora sobre la estepa y el pino oregón sobre los cipresales. El pino murrayana presenta la menor edad de inicio de reclutamiento (12 años). El pino ponderosa no parece comportarse como invasora. Sobre la base de esta información se discuten las posibles causas que podrían facilitar o limitar el proceso de expansión de estas especies relacionadas con la presión de propágulos, depredación de semillas y ocurrencia de disturbios. Se proponen recomendaciones de monitoreo y control orientadas a evitar que los renuevos generen nueva descendencia. [Palabras clave: invasiones, pino ponderosa, pino oregón, pino murrayana, estepa, bosque de ciprés, Patagonia] ABSTRACT. Tree conifers invasion in steppe areas and Austrocedus chilensis forests in NW Patagonia: Commercial forestry is carried out with a reduced set of species, with known silvicultural and industrial managements. Thus, these species are frequently planted far away from their natural habitats and introduced in new environments, creating a risk for starting invasion processes in natural or seminatural systems adjacent to the plantations. In NW Patagonia, commercial forestry with exotic species is recent (< 50 years), and presently only 70000 hectares
Nature, 2001
Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the ... more Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the quantity and quality of resources, and thus the energy supply to consumer populations at higher levels in the food chain. Empirical evidence on resource limitation of food webs points to primary productivity as a major determinant of consumer abundance and trophic structure. Prey quality plays a critical role in community regulation. Plants infected by endophytic fungi are known to be chemically protected against herbivore consumption. However, the influence of this microbe-plant association on multi-trophic interactions remains largely unexplored. Here we present 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. Herbivore-parasite webs on endophyte-free grasses show enhanced insect abundance at alternate trophic levels, higher rates of parasitism, and increased dominance by a few trophic links. These results mirror predicted effects of increased productivity on food-web dynamics. Thus 'hidden' microbial symbionts can have community-wide impacts on the pattern and strength of resource-consumer interactions.
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
Israel journal of botany, May 13, 1985
ABSTRACT Johnsongrass (Sorghum halepense (L.) Pers.) seed yield and seasonal seed production patt... more ABSTRACT Johnsongrass (Sorghum halepense (L.) Pers.) seed yield and seasonal seed production pattern were studied in two maize crops, an oat crop stubble and an unsown field using periodic harvests from permanent quadrats. The rates of seed and panicle production were strongly dependent on season and system. Two main periods of seed and panicle production were observed: the first, in early summer, lasted ca. 10 days and produced approx. 60% of the total seed yield; the second, at the end of the summer—early autumn, lasted ca. 40 days. The number of seeds per panicle was larger in early summer than in late summer—early autumn in all the studied situations. Johnsongrass produced more panicles and seeds under the maize crops than in the other agricultural systems. The influence of climatic conditions and crop system on seed and panicle production patterns is discussed.
Annals of Applied Biology, Nov 16, 2015
Intensive farming imposes harsh conditions impeding the persistence of most arthropod species wit... more Intensive farming imposes harsh conditions impeding the persistence of most arthropod species within crop fields. Hence, arthropods surviving the unfavourable conditions prevailing within crop fields may disperse towards nearby uncropped margins, such as fencerows. Here, we evaluate the influence of landscape heterogeneity on the abundance of different guilds, particularly herbivores and their natural enemies. Said heterogeneity mostly derives from fencerow network density. Hence, we developed an approach based on fitting linear-mixed models to elucidate the effects of landscape heterogeneity and field position (fencerows and crop interiors) on arthropod diversity. Mixed models were fitted to arthropod data obtained by pitfall trap samplings in 36 crop fields. Arthropod communities were structurally and functionally more complex along fencerows than within nearby crop interiors. Arthropods abundance was modulated by landscape heterogeneity, increasing the abundance of natural enemies as the landscape heterogeneity increased. On the contrary, herbivores abundance decreased as landscape heterogeneity increased. Consequently, the ratio between herbivores and natural enemies also decreased as landscapes became more heterogeneous. Natural enemies with larger body sizes, mostly carabid beetles, were more sensitive to landscape homogenisation. Our study reveals that, despite the coarse-grained landscapes in the Rolling Pampa, fencerow density appears as a key factor for structuring complex arthropod guilds in intensively farmed agricultural mosaics. In landscapes with higher density of fencerows, arthropods tend to concentrate along them, thus increasing the community structural complexity as well as the predation pressure over herbivores. This structural complexity of upper trophic levels enhances the 'top-down' regulation of herbivore populations, consequently decreasing the probability of pest outbreaks within crop fields.
Environmental Research, Nov 1, 2021
Tropospheric ozone is among the global change factors that pose a threat to plants and microorgan... more 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.
PLOS ONE, Sep 26, 2013
Tropospheric ozone is one of the major drivers of global change. This stress factor alters plant ... more 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.
Agriculture, Ecosystems & Environment, Mar 1, 2016
Agricultural intensification simplified environments, reduced their diversity, and hindered their... more 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 agroecosystems and its implications for ecosystem functioning. 2015 Elsevier B.V. All rights reserved.
Journal of Production Agriculture, 1997
Seed dormancy has been viewed as problematic in grain and forage production for several reasons: ... more Seed dormancy has been viewed as problematic in grain and forage production for several reasons: (i) It is related to the development of persistent weed seed banks and failure in predicting establishment of weed stands. Both characteristics diminish the efficacy of weed control procedures; (ii) When agronomists domesticate wild species as crops, they find that if the crop seed has dormancy, its germination is restricted to a very narrow range of microenvironmental conditions. Instead, management of seed dormancy could be seen as a solution for many agronomic problems. Very few studies are focused on this idea.
Annals of Applied Biology, 1988
ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories acc... more ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses.In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.
Annals of Botany, 2006
Background and Aims Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to ex... more Background and Aims Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to exhibit an ecological advantage over endophyte-uninfected grasses under abiotic stressful conditions. It is predicted that endophyte-infected plant populations will display higher rates of germination and proportion of germinated seeds under limiting water conditions. Methods The hydrotime regression model was used to describe the effect of Neotyphodium endophyte on seed germination of Lolium multiflorum at different water potentials. Additionally, seed mortality after water stress exposure was estimated in endophyte-infected and-uninfected seeds. Key Results Endophyte infection inhibited seed germination at all water potentials. The hydrotime model described satisfactorily the germination responses, and revealed that endophyte-free seeds exhibited higher rates of and final percentage germination, probably due to a lower base water potential compared with endophyte-infected seeds. However, Neotyphodium endophyte conferred a higher rate of survival in those seeds that remained ungerminated when exposed to highly water stress conditions. Conclusions Changes produced by Neotyphodium endophyte in L. multiflorum seeds might affect fitness in particular ecological scenarios. For example, the presence of the endophyte may curtail seed germination when water is limiting, reducing the risk of seedling death. Conversely, endophyte-free seeds would display an enhanced germination, ensuring a more rapid seedling establishment if later water conditions do not restrict plant growth.
Weed Research, Apr 1, 1985
Ecología austral, Aug 1, 2017
R������. Se estudió la infestación de raíces por Meloidogyne incognita (Kofoid and White) Chitwoo... more R������. Se estudió la infestación de raíces por Meloidogyne incognita (Kofoid and White) Chitwood, en mezclas de plantas de Glycine max (L.) Merr. y Tagetes minuta L. en distintas proporciones, por medio de un experimento diseñado para probar cómo huéspedes en diferentes proporciones modifican la reproducción de la primera generación y la densidad de la segunda generación del nematodo. En ambos huéspedes se evaluó la densidad de agallas radicales, sitios de alimentación, reacciones histológicas y número de larvas de la segunda generación de M. incognita. La densidad de agallas fue mayor en los tratamientos donde las plantas de G. max se encontraban en más de 50%. En raíces de T. minuta se encontraron sitios de alimentación no funcionales y las larvas en estos sitios no alcanzaron la etapa reproductiva. La reducción de la densidad de las larvas en el suelo fue proporcional a las cantidades de T. minuta en la mezcla. Estos datos indican que T. minuta infectado por nematodos actúa como una "planta trampa" debido a la captura de algunos individuos, muchos de los cuales nunca alcanzan la madurez sexual, y por la reducción de la densidad de segunda generación de M. incognita. [Palabras clave: histopatología, mecanismos de defensa, interacción parasito-huésped, sobrevivencia] A�������. Effect of different proportions of Tagetes minuta and Glycine max on Meloidogyne incognita. 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.
Copies of this report can be ordered from the (first) author. The costs are € 50 per copy (includ... more Copies of this report can be ordered from the (first) author. The costs are € 50 per copy (including handling and administration costs), for which an invoice will be included.
Environmental Entomology, Apr 1, 2014
Ciencia hoy, 2005
Biblioteca de la Universidad Complutense de Madrid, Base de datos de artículos de revistas, ...
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
Ecología austral, Dec 1, 2006
RESUMEN. La implantación de masas forestales con fines productivos se realiza con un conjunto red... more RESUMEN. La implantación de masas forestales con fines productivos se realiza con un conjunto reducido de especies de las que se conoce su manejo silvícola e industrial. Por tal motivo se las introduce en áreas distintas a las de su origen. Potencialmente, estas introducciones pueden desencadenar procesos de invasión de los sistemas naturales o seminaturales contiguos a las plantaciones. En la región andino patagónica, la actividad forestal con especies introducidas es aún incipiente, tanto por la superficie forestada como por la edad de las plantaciones más importantes. Se estima la superficie implantada en aproximadamente 70000 hectáreas, con una tendencia creciente en el ritmo de forestación en la última década. La especie más plantada es el Pinus ponderosa Doug (Laws) (pino ponderosa), seguida por Pseudotsuga menziesii (Mirb)Franco (pino oregón) y Pinus contorta Dougl. (pino murrayana). Actualmente ha comenzado a observarse reclutamiento de renovales creciendo fuera de los macizos forestales en los sistemas lindantes, naturales o no. El presente trabajo evalúa, a escala regional, la presencia y la tasa de reclutamiento de renovales de estas especies en dos sistemas naturales, estepa y bosque de Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri (ciprés de la cordillera), con el fin diagnosticar si existe un proceso de invasión incipiente. Se muestrearon áreas cercanas a las principales masas forestales implantadas, desde el centro de la provincia de Neuquén (39º48'S) hasta el Norte de Chubut (42º10'S). Para ello, se registró la presencia de regeneración natural, su densidad (nº indiv/ha), distancia a la plantación, edad, altura, y si producían conos o semillas. Los resultados indican que es posible que se esté ante la invasión incipiente de las comunidades adyacentes a las masas forestales por dos de las especies consideradas: el pino murrayana estaría mostrando expansión invasora sobre la estepa y el pino oregón sobre los cipresales. El pino murrayana presenta la menor edad de inicio de reclutamiento (12 años). El pino ponderosa no parece comportarse como invasora. Sobre la base de esta información se discuten las posibles causas que podrían facilitar o limitar el proceso de expansión de estas especies relacionadas con la presión de propágulos, depredación de semillas y ocurrencia de disturbios. Se proponen recomendaciones de monitoreo y control orientadas a evitar que los renuevos generen nueva descendencia. [Palabras clave: invasiones, pino ponderosa, pino oregón, pino murrayana, estepa, bosque de ciprés, Patagonia] ABSTRACT. Tree conifers invasion in steppe areas and Austrocedus chilensis forests in NW Patagonia: Commercial forestry is carried out with a reduced set of species, with known silvicultural and industrial managements. Thus, these species are frequently planted far away from their natural habitats and introduced in new environments, creating a risk for starting invasion processes in natural or seminatural systems adjacent to the plantations. In NW Patagonia, commercial forestry with exotic species is recent (< 50 years), and presently only 70000 hectares
Nature, 2001
Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the ... more Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the quantity and quality of resources, and thus the energy supply to consumer populations at higher levels in the food chain. Empirical evidence on resource limitation of food webs points to primary productivity as a major determinant of consumer abundance and trophic structure. Prey quality plays a critical role in community regulation. Plants infected by endophytic fungi are known to be chemically protected against herbivore consumption. However, the influence of this microbe-plant association on multi-trophic interactions remains largely unexplored. Here we present 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. Herbivore-parasite webs on endophyte-free grasses show enhanced insect abundance at alternate trophic levels, higher rates of parasitism, and increased dominance by a few trophic links. These results mirror predicted effects of increased productivity on food-web dynamics. Thus 'hidden' microbial symbionts can have community-wide impacts on the pattern and strength of resource-consumer interactions.
John Wiley & Sons, Inc. eBooks, Aug 21, 2007
Israel journal of botany, May 13, 1985
ABSTRACT Johnsongrass (Sorghum halepense (L.) Pers.) seed yield and seasonal seed production patt... more ABSTRACT Johnsongrass (Sorghum halepense (L.) Pers.) seed yield and seasonal seed production pattern were studied in two maize crops, an oat crop stubble and an unsown field using periodic harvests from permanent quadrats. The rates of seed and panicle production were strongly dependent on season and system. Two main periods of seed and panicle production were observed: the first, in early summer, lasted ca. 10 days and produced approx. 60% of the total seed yield; the second, at the end of the summer—early autumn, lasted ca. 40 days. The number of seeds per panicle was larger in early summer than in late summer—early autumn in all the studied situations. Johnsongrass produced more panicles and seeds under the maize crops than in the other agricultural systems. The influence of climatic conditions and crop system on seed and panicle production patterns is discussed.
Annals of Applied Biology, Nov 16, 2015
Intensive farming imposes harsh conditions impeding the persistence of most arthropod species wit... more Intensive farming imposes harsh conditions impeding the persistence of most arthropod species within crop fields. Hence, arthropods surviving the unfavourable conditions prevailing within crop fields may disperse towards nearby uncropped margins, such as fencerows. Here, we evaluate the influence of landscape heterogeneity on the abundance of different guilds, particularly herbivores and their natural enemies. Said heterogeneity mostly derives from fencerow network density. Hence, we developed an approach based on fitting linear-mixed models to elucidate the effects of landscape heterogeneity and field position (fencerows and crop interiors) on arthropod diversity. Mixed models were fitted to arthropod data obtained by pitfall trap samplings in 36 crop fields. Arthropod communities were structurally and functionally more complex along fencerows than within nearby crop interiors. Arthropods abundance was modulated by landscape heterogeneity, increasing the abundance of natural enemies as the landscape heterogeneity increased. On the contrary, herbivores abundance decreased as landscape heterogeneity increased. Consequently, the ratio between herbivores and natural enemies also decreased as landscapes became more heterogeneous. Natural enemies with larger body sizes, mostly carabid beetles, were more sensitive to landscape homogenisation. Our study reveals that, despite the coarse-grained landscapes in the Rolling Pampa, fencerow density appears as a key factor for structuring complex arthropod guilds in intensively farmed agricultural mosaics. In landscapes with higher density of fencerows, arthropods tend to concentrate along them, thus increasing the community structural complexity as well as the predation pressure over herbivores. This structural complexity of upper trophic levels enhances the 'top-down' regulation of herbivore populations, consequently decreasing the probability of pest outbreaks within crop fields.
Environmental Research, Nov 1, 2021
Tropospheric ozone is among the global change factors that pose a threat to plants and microorgan... more 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.
PLOS ONE, Sep 26, 2013
Tropospheric ozone is one of the major drivers of global change. This stress factor alters plant ... more 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.
Agriculture, Ecosystems & Environment, Mar 1, 2016
Agricultural intensification simplified environments, reduced their diversity, and hindered their... more 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 agroecosystems and its implications for ecosystem functioning. 2015 Elsevier B.V. All rights reserved.