Comparison of individual and combined effects of salinity and deficit irrigation on physiological, nutritional and ornamental aspects of tolerance in Callistemon laevis plants

The effect of water deficit, salinity and both applied simultaneously on several physiological and morphological parameters in the ornamental plant Callistemon laevis was studied to identify the tolerance mechanisms developed by this species to these sources of stress and to evaluate their adaptability to such conditions. C. laevis plants were grown in pots outdoors and subjected to four irrigation treatments lasting ten months: control (0.8dSm-1, 100% water holding capacity), water deficit (0.8dSm-1, 50% of the amount of water supplied in control), saline (4.0dSm-1, same amount of water supplied as control) and saline water deficit (4.0dSm-1, 50% of the water supplied in the control). Water and saline stress, when applied individually, led to a reduction of 12% and 39% of total biomass, respectively, while overall plant quality (leaf color and flowering) was unaffected. However, saline water deficit affected leaf color and flowering and induced an excessive decrease of growth (68%) due to leaf tissue dehydration and a high leaf Cl and Na concentration. Biomass partitioning depended not only on the amount of water applied, but also on the electrical conductivity of the water. Water stress induced active osmotic adjustment and decreased leaf tissue elasticity. Although both Na and Cl concentrations in the plant tissues increased with salinity, Cl entry through the roots was more restricted. In plants submitted to salinity individually, Na tended to remain in the roots and stems, and little reached the leaves. However, plants simultaneously submitted to water and saline stress were not able to retain this ion in the woody parts. The decrease in stomatal conductance and photosynthesis was more marked in the plants submitted to both stresses, the effect of which decreased photosynthesis, and this together with membrane damage delayed plant recovery. The results show that the combination of deficit irrigation and salinity in C. laevis is not recommended since it magnifies the adverse effects of either when applied individually. © 2015 Elsevier GmbH.This work was supported by the Spanish Ministry of Economy and Competitiveness (project CICYT AGL 2011-30022-C02-01-02) and Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia (15356/PI/10).Peer Reviewe

Changes in growth rate, root morphology and water use efficiency of potted Callistemon citrinus plants in response to different levels of water deficit

Callistemon is widely used as a flowering shrub in gardening and landscaping in the Mediterranean area. However, prolonged or severe water stress may alter its physiological and morphological behaviour. Callistemon citrinus plants were grown in nursery conditions and subjected to three irrigation treatments: a control (watered to container capacity) and two water deficit treatments of 50 and 25% of the amount of water supplied in the control treatment (moderate and severe deficit irrigation, respectively). After 53 weeks, the moderate deficit irrigation plants showed a lower relative growth rate but increased root/shoot ratio, improved the root system and increased water use efficiency, while flowering and leaf colour were unaffected. However, severe deficit irrigation reduced flowering and affected leaf colour. Both deficit irrigation treatments reduced stomatal conductance, suggesting an efficient and adaptive stomatal control in this species. These reductions were marked after longer periods in plants submitted to severe deficit irrigation, which decreased photosynthesis and could delay plant recovery and cause permanent damage. Differences between stem and leaf water potential values have seen to be a good indicator of instantaneous shoot transpiration. Water consumption was influenced by the active periods of growth and inflorescence formation. It is concluded that moderate deficit irrigation can be used successfully in C. citrinus plant production to reduce water consumption while maintaining good overall quality. © 2013 Elsevier B.V.This work was supported by the Spanish Ministry of Science and Innovation (AGL 2008-05258-C02-1-2, AGL 2011-30022-C02-01) and Fundación Séneca (15356/PI/10).Peer Reviewe

Long-term effect of salinity on plant quality, water relations, photosynthetic parameters and ion distribution in Callistemon citrinus

The effect of saline stress on physiological and morphological parameters in Callistemon citrinus plants was studied to evaluate their adaptability to irrigation with saline water. C. citrinus plants, grown under greenhouse conditions, were subjected to two irrigation treatments lasting 56 weeks: control (0.8 dS·m-1) and saline (4 dS·m-1). The use of saline water in C. citrinus plants decreased aerial growth, increased the root/shoot ratio and improved the root system (increased root diameter and root density), but flowering and leaf colour were not affected. Salinity caused a decrease in stomatal conductance and evapotranspiration, which may prevent toxic levels being reached in the shoot. Net photosynthesis was reduced in plants subjected to salinity, although this response was evident much later than the decrease in stomatal conductance. Stem water potential was a good indicator of salt stress in C. citrinus. The relative salt tolerance of Callistemon was related to storage of higher levels of Na+ and Cl- in the roots compared with the leaves, especially in the case of Na+, which could have helped to maintain the quality of plants. The results show that saline water (around 4 dS·m-1) could be used for growing C. citrinus commercially. However, the cumulative effect of irrigating with saline water for 11 months was a decrease in photosynthesis and intrinsic water use efficiency, meaning that the interaction of the salinity level and the time of exposure to the salt stress should be considered important in this species. © 2014 German Botanical Society and Royal Botanical Society of the Netherlands.This work was supported by the Spanish Ministry of Science and Innovation (AGL 2011-30022-C02-01-02) and Fundación Séneca (15356/PI/10).Peer Reviewe

The orchestration of processes in relation to the product, and the role of psychological variables in written composition

p. 96-108Se investiga la distribución temporal de los procesos de escritura, mediante una técnica on-line de retrospección directa, y diferencias en el producto textual, desde los cursos más inferiores donde es posible atender a su estudio hasta últimos cursos de la enseñanza obligatoria. Además, se atiende al análisis de diversas variables psicológicas para analizar su inciden-cia moduladora en la escritura. Se utilizó una muestra muy depurada de 348 alumnos, con edades comprendidas entre los 9 y 16 años, con un desarrollo normalizado y unos niveles de competencia curricular y escritora dentro de la media. Los resultados indican patrones complejos de evolución del proceso de escritura y su orquestación, en comparación con el producto escrito, constatando que no existe una traducción directa entre la evolución del proceso de escritura y su distribución temporal, y la mejoría del producto escrito; todo ello mediado por variables psicológicas relacionadas con la presencia de creencias de auto-eficacia hacia el despliegue y uso de procesos escritores no calibradas de forma adecuada y la realización de atribuciones causales a factores externos, en los niveles educativos más inferiores. Se discuten las implicaciones, limitaciones y perspectivas futurasS

Regulated deficit irrigation in different phenological stages of potted geranium plants: Water consumption, water relations and ornamental quality

The irrigation water requirements and sensitivity to water deficits of ornamental plants is of great interest to horticultural producers for planning irrigation strategies. The effect of different deficit irrigation strategies on physiological and morphological parameters in geranium plants was studied in different growth phases to evaluate how such strategies can be safely used and to ascertain whether the flowering phase is sensitive to deficit irrigation. Pelargonium × hortorum L. H. Bailey plants, grown in a controlled growth chamber, were subjected to four irrigation treatments: control (100 % water field capacity throughout the experiment), sustainable deficit irrigation (75 % water field capacity throughout the experiment), and two regulated deficit irrigation treatments that included water stress during the vegetative growth phase or during the flowering development phase. Although the total amount of irrigation water was similar in the three deficit irrigation treatments (around 80 % of the control value), the lowest values for both height and flowering were found when deficit irrigation was applied during flowering. This indicates that plant quality does not only depend on the amount of water applied but also on the time when the reduction is applied, and that flowering is the most sensitive phase to water stress. Evapotranspiration was related to the formation of inflorescences and to increased plant height. When the irrigation strategy was changed, plants increased or decreased their water consumption and stomatal conductance to adjust to the new conditions by regulating stomatal opening, although, in general, the values of both parameters remained below those observed in the control plants. © 2012 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.This work was supported by the Spanish Ministry of Science and Innovation (AGL 2008-05258-C02-1-2, AGL 2011-30022-C02-01) and Fundación Séneca (15356/PI/10).Peer Reviewe

Efficient computation of current collection in bare electrodynamic tethers in and beyond OML regime

One key issue in the simulation of bare electrodynamic tethers (EDTs) is the accurate and fast computation of the collected current, an ambient dependent operation necessary to determine the Lorentz force for each time step. This paper introduces a novel semianalytical solution that allows researchers to compute the current distribution along the tether efficient and effectively under orbital-motion-limited (OML) and beyond OML conditions, i.e., if tether radius is greater than a certain ambient dependent threshold. The method reduces the original boundary value problem to a couple of nonlinear equations. If certain dimensionless variables are used, the beyond OML effect just makes the tether characteristic length L* larger and it is decoupled from the current determination problem. Avalidation of the results and a comparison of the performance in terms of the time consumed is provided, with respect to a previous ad hoc solution and a conventional shooting method

Modified Clebsch-Gordan-type expansions for products of discrete hypergeometric polynomials

Starting from the second-order difference hypergeometric equation satisfied by the set of discrete orthogonal polynomials ∗pn∗, we find the analytical expressions of the expansion coefficients of any polynomial rm(x) and of the product rm(x)qj(x) in series of the set ∗pn∗. These coefficients are given in terms of the polynomial coefficients of the second-order difference equations satisfied by the involved discrete hypergeometric polynomials. Here qj(x) denotes an arbitrary discrete hypergeometric polynomial of degree j. The particular cases in which ∗rm∗ corresponds to the non-orthogonal families ∗xm∗, the rising factorials or Pochhammer polynomials ∗(x)m∗ and the falling factorial or Stirling polynomials ∗x[m]∗ are considered in detail. The connection problem between discrete hypergeometric polynomials, which here corresponds to the product case with m = 0, is also studied and its complete solution for all the classical discrete orthogonal hypergeometric (CDOH) polynomials is given. Also, the inversion problems of CDOH polynomials associated to the three aforementioned nonorthogonal families are solved.Dirección General de Enseñanza SuperiorJunta de Andalucí

Chlorella stigmatophora for urban wastewater nutrient removal and CO2 abatement.

Batch experiments were performed to study biomass growth rate, nutrient removal and carbon dioxide bio-fixation of the marine microalgae Chlorella stigmatophora. Four different cultures at different salinities were tested: wastewater (WW), synthetic wastewater (SWW), seawater (SW) and diluted seawater (DSW). Experimental results showed that Chlorella stigmatophora grew satisfactorily in all culture media, except in SWW where inhibition occurred. In all cases, biomass experimental data were fitted to the Verlhust Logistic model (R2 > 0.982, p ≤ 0.05). Maximum biomass productivity (Pbmax ) and CO2 biofixation (PvCO2) were reached in the WW medium, 1.146 g SS·L−1·day−1 and 2.324 g CO2·L−1·day−1 respectively. The order of maximum specific growth rates (μmax) was WW >DSW>SW. In order to compare nitrogen and phosphorous removal kinetics, an estimation of the time required to reach the most restrictive concentration of total N and P in effluents as defined in the Directive 98/1565/CE (10 mg ΣN·L−1 (T10( N)) and 1 mg ΣP·L−1 (T1(P) ) was performed. In the WW test T10( N) and T1(P) needed were of 45.15 and 32.27 hours respectively and at the end of the experimental the removal was in both 100