Paula Cartes

Uptake of Selenium and its Antioxidant Activity in Ryegrass When Applied as Selenate and Selenite Forms

Selenium (Se) is an essential micronutrient for animal and human nutrition, but whether it is essential to plants remains controversial. However, there are increasing experimental evidences that indicate a protective role of Se against the oxidative stress in higher plants through Se-dependent glutathione peroxidase (GSH-Px) activity. The effects of the Se chemical forms, selenite and selenate, the rate of their application on shoot Se concentration and their influence on the antioxidative system of ryegrass (Lolium perenne cv. Aries), through the measurement of GSH-Px activity and lipid peroxidation, were evaluated in an Andisol of Southern Chile. Moreover, a soil–plant relationship for Se was determined and a simple method to extract available Se from acid soils is proposed. In a 55-day experiment ryegrass seeds were sown in pots and soil was treated with sodium selenite or sodium selenate (0–10 mg Se kg−1). The results showed that the Se concentration in shoots increased with the application of both selenite and selenate. However, the highest shoot Se concentrations were obtained in selenate-treated plants. For both sources of Se, there was a significant positive correlation between the shoot Se concentration and the GSH-Px activity; and the Se-dependence of this enzymatic activity was related especially with the chemical form of applied Se rather than the Se concentration in plant tissues. Furthermore, the lipid peroxidation, as measured by Thiobarbituric Acid Reactive Substances (TBARS), decreased at low levels of shoot Se concentration, reaching the lowest level at approximately 20 mg Se kg−1 in plants and then increased steadily above this level. In addition, the acid extraction method used to evaluate available Se in soil showed a positive good correlation between soil Se and shoot Se concentrations irrespective of chemical form of Se applied.

Effects of lime and gypsum on pasture growth and composition on an acid Andisol in Chile, South America

The effects of amending an acid Andisol with lime and gypsum on soil pH, aluminum (Al) saturation, the plant-availability of sulfur (S) and phosphorus (P), and the growth, botanical, and chemical composition of a ryegrass/white clover pasture were measured in a field trial in southern Chile. The combined amendment of limestone, dolomite and gypsum raised soil pH slightly, decreased Al saturation from 20 to less than 1% and increased the concentration of plant available P, S, calcium (Ca), magnesium (Mg), and potassium (K) in the soil. The growth of a recently-sown rye grass–white clover pasture increased by 50% and the proportions of ryegrass, white clover and weed species changed from 12.6, 0.2, and 87% to 75, 7.7, and 17%, respectively. Plant chemical analysis suggested that, while N, P, and S concentrations in mixed pasture were less than critical values in spring, S was the most limiting nutrient in pastures from both the amended and control areas.

UREASE ACTIVITY AND NITROGEN MINERALIZATION KINETICS AS AFFECTED BY TEMPERATURE AND UREA INPUT RATE IN SOUTHERN CHILEAN ANDISOLS

Se realizaron estudios de incubacion para evaluar el efecto de la temperatura y niveles de suministro de urea sobre la actividad ureasa y la cinetica de mineralizacion de N en dos Andisoles del Sur de Chile. Nuestros resultados mostraron que la actividad ureasa fue mas alta en el suelo Piedras Negras (PNS) que en el suelo Freire (FS) a 24 y 48 h, y la enzima fue activada cuando la temperatura incremento desde 5 a 21 °C. La actividad ureasa siguio una cinetica simple de Michaelis-Menten. En PNS, la constante de Michaelis-Menten (Km) disminuyo, mientras que la velocidad maxima de reaccion de la enzima (Vmax) y la eficiencia catalitica aumentaron cuando la temperatura fue elevada hasta 21 °C a 24 y 48 h de incubacion del suelo. En FS, la actividad ureasa fue la mas alta a las 24 h, y esta disminuyo a las 48 h como consecuencia del agotamiento del sustrato. Por otra parte, los datos de cinetica de mineralizacion de N estrechamente se ajustaron a un modelo exponencial simple. A etapas tempranas de la incubacion, cantidades similares de N mineralizado (Nmin) fueron encontradas en ambos suelos. Sin embargo, Nmin fue 27 a 64 % mas alto en PNS que FS al final del experimento. Estos resultados tuvieron directa relacion con el contenido de materia organica del suelo, la temperatura y el nivel suministro de urea. En PNS, nosotros observamos que 47 a 80 % de Nmin permanecio como NH4+-N, mientras que en FS N03--N represento entre 80 y 96 %. Tales diferencias en la dinamica de transformacion de N estuvieron de acuerdo con la variacion del pH registrada durante el periodo experimental. Estos hechos tienen implicancias practicas para el manejo de los sistemas agricolas en una localidad en particular, debido a que la dinamica de la mineralizacion de N en Andisoles es principalmente controlada por el contenido de materia organica y las propiedades biologicas de suelos, asi como por la temperatura y el nivel de suministro de urea al sistema suelo-planta.

Silicon in vascular plants: uptake, transport and its influence on mineral stress under acidic conditions

AbstractMain conclusionSo far, considerable advances have been achieved in understanding the mechanisms of Si uptake and transport in vascular plants. This review presents a comprehensive update about this issue, but also provides the new insights into the role of Si against mineral stresses that occur in acid soils. Such information could be helpful to understand both the differential Si uptake ability as well as the benefits of this mineral element on plants grown under acidic conditions. Silicon (Si) has been widely recognized as a beneficial element for many plant species, especially under stress conditions. In the last few years, great efforts have been made to elucidate the mechanisms involved in uptake and transport of Si by vascular plants and recently, different Si transporters have been identified. Several researches indicate that Si can alleviate various mineral stresses in plants growing under acidic conditions, including aluminium (Al) and manganese (Mn) toxicities as well as phosphorus (P) deficiency all of which are highly detrimental to crop production. This review presents recent findings concerning the influence of uptake and transport of Si on mineral stress under acidic conditions because a knowledge of this interaction provides the basis for understanding the role of Si in mitigating mineral stress in acid soils. Currently, only four Si transporters have been identified and there is little information concerning the response of Si transporters under stress conditions. More investigations are therefore needed to establish whether there is a relationship between Si transporters and the benefits of Si to plants subjected to mineral stress. Evidence presented suggests that Si supply and its subsequent accumulation in plant tissues could be exploited as a strategy to improve crop productivity on acid soils.

Evaluation of biodegradable polymers as encapsulating agents for the development of a urea controlled-release fertilizer using biochar as support material.

Biochar constitutes a promising support material for the formulation of controlled-release fertilizers (CRFs). In this study we evaluated the effect of different polymeric materials as encapsulating agents to control nitrogen (N) leaching from biochar based CRFs. Nitrogen impregnation onto biochar was performed in a batch reactor using urea as N source. The resulting product was encapsulated by using sodium alginate (SA), cellulose acetate (CA) and ethyl cellulose (EC). Leaching potential was studied in planted and unplanted soil columns, monitoring nitrate, nitrite, ammonium and urea concentrations. After 90 days, plants were removed from the soil columns and plant yield was evaluated. It was observed that the ammonium concentration in leachates presented a maximum concentration for all treatments at day 22. The highest concentration of N in the leachates was the nitrate form. The crop yield was negatively affected by all developed CRFs using biochar compared with the traditional fertilization.

Selenium uptake and its antioxidant role in ryegrass cultivars as affected by selenite seed pelletization.

Abstract A greenhouse study was carried out to evaluate the effect of seed pelletization with increasing selenite doses (from 0 to 60 g Se ha -1 ) on the yield, Se uptake and the an-tioxidant responses of three ryegrass cultivars (Aries, Nui and Quartet) cultivated on an Andisol during two consecutive growth periods. In addition, a second assay was conducted to determine the residual effect of Se in the shoots during four consecutive plant cuts. Results showed that selenite-pelleted seeds at rates up to 60 g Se ha -1 did not influence the yield of shoots and roots of the three ryegrass cultivars. Selenium concentration in shoots and roots steadily increased as a consequence of increased Se supply, and it was accumulated mainly in the roots. Plants of the different cultivars accumulated similar amounts of Se in their shoots, but Quartet roots built up greater Se concentration than those of Aries or Nui at rates of application above 35 g Se ha -1 . Whereas Se doses above 10 g ha -1 increased the shoot Se concentration in the two yields of the three ryegrass cultivars to suitable levels according to the minimum dietary requirement of beef and dairy cattle, the residual effect of Se was maintained through four cuts at Se supply of 30 and 60 g ha

MOVEMENT OF N0(3)-N AND NH4-N IN AN ANDISOL AND ITS INFLUENCE ON RYEGRASS PRODUCTION IN A SHORT TERM STUDY

En suelos acidos, el uso de fertilizantes amoniacales acelera los procesos de acidificacion y disminuye la produccion y persistencia de las pasturas. El nitrogeno (N) es el principal factor limitante del crecimiento vegetal en la mayoria de los sistemas agricolas, pero tambien es uno de los principales problemas ambientales del mundo. En Chile, no han sido reportados estudios sistematicos en el primer periodo de crecimiento de la pastura ni las perdidas de N por lixiviacion asociadas. Los objetivos de este estudio fueron: (i) evaluar el efecto de la fuente de N a dosis crecientes de aplicacion sobre el rendimiento y calidad de ballica (Lolium perenne) y (ii) cuantificar en el corto plazo las perdidas potenciales de N por lixiviacion y los cambios de pH a traves del perfil del suelo bajo condiciones de campo. Se realizo un experimento de campo durante la temporada primavera-verano 2000-2001 en un Andisol del Sur de Chile bajo riego. Se aplico urea y nitrato de sodio en dosis de 0, 150 y 300 kg N ha-1. La pastura fue cortada tres veces y se determino la produccion de materia seca (DM) y la concentracion de N foliar. Ademas, se determino el pH del suelo y las concentraciones de N-NH4+ y N-N03 para los 0-10 cm, 10-20 cm y 20-40 cm de profundidad, y se estimaron las maximas perdidas potenciales de N por lixiviacion. La produccion de DM aumento en 128 % a medida que el suministro de N se incremento de 0 a 300 kg N ha-1. La fuente de N no mostro ningun efecto sobre el rendimiento. La urea y el nitrato de sodio generaron una concentracion de N foliar mas alta a medida que la dosis de N aumento, y no se observo un efecto acidificante de la urea sobre la produccion de DM y la calidad de la pastura. La aplicacion de nitrato de sodio y urea (300 kg N ha-1) genero la mayor concentracion de N-NH4+ y N-N03 en las capas mas profundas del suelo. Para los 20-40 cm de profundidad, las maximas perdidas potenciales de N a traves del perfil del suelo fueron alrededor de 90 kg N ha-1 y correspondieron al periodo de menor tasa de crecimiento de la pastura

Phosphorus and Nitrogen Fertilization Effect on Phosphorus Uptake and Phosphatase Activity in Ryegrass and Tall Fescue Grown in a Chilean Andisol

A series of short-term experiments were carried out to assess the effect of phosphorus (P) and nitrogen (ammonium [NH4+-N] or nitrate [NO3−-N]) fertilization on P uptake and phosphatase activity in ryegrass and tall fescue cultivated under greenhouse conditions. Ryegrass or tall fescue plants were grown in an acidic Andisol in the presence or absence of P and increasing doses of NO3−-N or NH4+-N fertilizers. At the end of the experiment, soil phosphatase activity (P-aseRhiz), pH, and Olsen-P were determined in the rhizosphere soil. Plant biomass, P uptake, and root surface phosphatase (P-aseRoot) were also assayed for both plant species. Furthermore, soil incubation experiments at increasing doses of P, NO3−-N, or NH4+-N were performed to evaluate the fertilizer effect on soil phosphatase activity (P-aseBulk) and microbial biomass carbon in the bulk soil. In the absence of plants, P-aseBulk was inhibited and microbial biomass carbon was raised at increasing P supply levels. In the greenhouse experiments, P uptake by tall fescue was about 67% higher than that of ryegrass at low soil P availability, which suggests that tall fescue was less sensitive to P deficiency than ryegrass. For both plant species, P-aseRhiz did not vary as a consequence of P addition. On the other hand, fertilization with the highest NH4+-N dose strongly decreased soil pH and shoot P content, as well as it increased P-aseRoot activity. This fact denotes that P-aseRoot behaved as a strategic response parameter to P stress with insufficient impact on plant P nutrition in both plant species.

Atrazine efficiency in an Andisol as affected by clays and nanoclays in ethylcellulose controlled release formulations.

Atrazine, a herbicide used for the control of broadleaf weeds of different crops, was incorporated in ethylcellulose controlled release formulations (CRFs) by using the solvent evaporation technique. Allophanic clays and nanoclays were incorporated as matrix modifying agents. The formulations were characterized by scanning electron microscopy (SEM) and infrared spectroscopy (FTIR), and their behavior was determined in aqueous phase. Dissipation studies and soil columns experiments with CRFs were also carried out, and compared with commercial formulations (CFs). In addition, a short-term bioassay was performed to evaluate the effect of CRFs and CFs on the emergence and growth of field mustard (Brassica campestris L.) under greenhouse conditions. The matrix modifiers (clays and nanoclays) showed little influence on the particle morphology and atrazine encapsulation efficiency. Furthermore, these matrix modifiers had a slight effect on the atrazine release into water, its dissipation and its behavior in soil compared with the formulation without them. All CRFs increased the atrazine herbicidal activity and reduced their loss by leaching in soil. Although some similarities were found in the efficiency to reduce the seedling emergence between CRFs and CFs, a greater death of seedlings was observed in the CRFs, especially when nanoclays were added into the formulation. These facts denote an advantage of CRFs over CFs due to prolonged bio-efficiency, and longer applications intervals will be produced, minimizing the harmful impact on the environment.

Arbuscular mycorrhiza effects on plant performance under osmotic stress

At present, drought and soil salinity are among the most severe environmental stresses that affect the growth of plants through marked reduction of water uptake which lowers water potential, leading to osmotic stress. In general, osmotic stress causes a series of morphological, physiological, biochemical, and molecular changes that affect plant performance. Several studies have found that diverse types of soil microorganisms improve plant growth, especially when plants are under stressful conditions. Most important are the arbuscular mycorrhizal fungi (AMF) which form arbuscular mycorrhizas (AM) with approximately 80% of plant species and are present in almost all terrestrial ecosystems. Beyond the well-known role of AM in improving plant nutrient uptake, the contributions of AM to plants coping with osmotic stress merit analysis. With this review, we describe the principal direct and indirect mechanisms by which AM modify plant responses to osmotic stress, highlighting the role of AM in photosynthetic activity, water use efficiency, osmoprotectant production, antioxidant activities, and gene expression. We also discuss the potential for using AMF to improve plant performance under osmotic stress conditions and the lines of research needed to optimize AM use in plant production.