Silicon is a major component of most soils, and is found in significant concentration in plant tissue. Plants vary widely in the amount of silicon they take up, with some plants excluding it, and others using transporters to move the silicon from the soil into their roots. Early plant physiology studies were unable to determine conclusively whether silicon was essential to plant growth, but for some plants, most notably rice, it has proved to be important enough to justify fertilizing silicon deficient fields. Researchers at the USU Crop Physiology Lab tested the effect of silicon on wheat growth and seed yield components. One study was grown in buckets of peat moss, with half the buckets being stressed with low water. The other study was grown in hydroponic tubs, with half the tubs being stressed with high levels of salt. The results from these studies showed that silicon does increase wheat seed yield and vegetative mass. Wheat with low levels of silicon exhibited twisting of the awns and decreased roughness of leaf surfaces. Silicon also improved water efficiency of drought stressed plants, and affected the concentration of many micro- and macro-nutrients in leaf tissue.

Silicon is not considered an essential nutrient, but it is typically abundant in soils and can be taken up in large amounts by plants. Silicon is known to have beneficial effects when added to rice and several other plants. These effects include disease and insect resistance, structural fortification, and regulation of the uptake of other ions. In this study, the effect of silicic acid fertilization on the growth and drought tolerance of four crop plants (corn, wheat, soybean, and rice) was analyzed. Plants were studied using three cultivation techniques: 1) hydroponic solution and subjected to salt stress, 2) low-silicon soil-less medium (peat) and subjected to gradual drought stress, and 3) low-silicon soil-less medium (peat) and subjected to acute drought stress. Silicon was added both as reagent-grade Na2SiO3 and as a siliceous liming agent (PlantTuff). Both forms of Si generally improved drought and salt stress tolerance, but the effects were inconsistent. Silicon increased corn dry mass by up to 18% and the effect was statistically significant (p<0.05) in two out of three techniques. Silicon increased water use efficiency in corn by up to 36% and the effect was statistically significant (p<0.05) in one out of two techniques. In the acute drought stress technique, silicon increased wheat dry mass by 17% and the effect was statistically significant (p<0.05). Silicon increased soybean and rice dry mass by 20 to 30%, but the effect was not statistically significant. Silicon in oldest corn leaves increased from 0.4% to 3% as Si increased from less than 0.01 to 0.8 mM in the hydroponic solution. There was a statistically significant effect of silicon supply on the concentration of some other nutrients, but the effect was often not great enough to be considered biologically important. Rice accumulated the greatest concentration of foliar silicon, corn and wheat were intermediate, and soybean accumulated the least. Collectively, these results indicate an effect of silicon in drought and salinity stress tolerance, but additional studies on the rate and onset of drought are needed to determine interacting factors and better understand the inconsistent results.

No description available.

Bibliography: leaves 187-203. Evaluates critically a number of physiological traits which may be related to drought resistance in cereals and examines the feasibility of using these screening techniques in selecting more drought resistant genotypes of barley for South Australia.

<p>A tree-ring width chronology from Scots pine (<em>Pinus sylvestris</em> L.) was constructed from a xeric site in Stockholm to investigate the relationships between climate and tree growth and to reconstruct past moisture variability. The measure of moisture conditions employed here is a self-calibrating Palmer Drought Severity Index (PDSI). The index is derived from temperature, precipitation, and available water capacity of the soil, and assesses the intensity and duration of drought. It is widely used in tree-ring based climate reconstructions, a method which has never before been tested in the Nordic countries.</p><p>The comparison of the Stockholm tree-ring chronology with monthly temperature and precipitation data from a nearby meteorological station shows that tree growth is reduced by high summer temperatures, whereas high precipitation at the beginning of the growing season favours growth. The comparison with a PDSI calculated from this meteorological data shows that negative PDSI values are associated with narrow rings. Although tree growth in the humid climate of central Sweden is generally not limited by precipitation, the trees sampled for this study prove to be sensitive to changes in water supply. Their rings thus provide a record of past moisture variability and enable the reconstruction of precipitation and drought. The transfer function models for the reconstructions are calibrated using linear regression. A detailed verification of the results using the more than 200-year long meteorological record from Stockholm affirms the good model performance. May–June precipitation sums and the July PDSI could be reconstructed back to 1625.</p><p>The Palmer Drought Severity Index is found to be a useful tool in a tree-ring based reconstruction of past moisture variability, approximating the fraction of rainfall which is actually available to the tree, by including soil moisture storage, runoff, and the influence of temperature on evapotranspiration. It cannot completely account for the combined temperature and precipitation forcing of tree growth, and the use of the index does not improve the reconstruction compared to using precipitation alone. However, a reconstruction of both precipitation and the PDSI is possible when selecting an adequate sample site.</p>

Summer drought is a major factor limiting the regrowth of perennial ryegrass seed crops. This phase of crop development has a strong influence on seed yield because most of the tillers that contribute towards next season's seed crop are produced or regrown during this period. In recent years many seed fields have exhibited premature decline probably because of extensive drought after harvesting. Therefore, this study was undertaken to (i) assess how post-harvest leaf and tiller development is impacted by the timing and severity of water stress and (ii) identify potential relationships of water stress to flowering and seed yield. Rain-out shelters were used to exclude rainfall from two cultivars which received either no irrigation or 2.5 cm of simulated rainfall in mid-August or mid-September or both. These were compared to an ambient treatment. No rainfall decreased total tiller production by approximately 30% in 1995 and 50% in 1996. There were also moderate reductions in tiller dry weight, tiller height, and slight decreases in number of leaves and the basal diameters. The trend showed that the cultivar Affinity responded quicker to an early irrigation whereas the cultivar Buccaneer had a longer period of summer dormancy. Total soluble sugars concentrations increased as tiller number decreased suggesting the potential for rapid compensatory growth upon alleviation of drought. Limited irrigation during the post-harvest period of regrowth did not generally affect fertile tiller number nor seed yields. Fewer vegetative tillers as the stands aged, together with other changes in plant parameters, may mark the beginning of the dieback problem. In greenhouse studies, four cultivars were rapidly stressed using vermiculite as a growth medium. Though little differences were observed among cultivars when physiological responses were evaluated, stomata' diffusive resistance and leaf temperatures increased, whereas plant water potential and leaf transpiration decreased as stress was prolonged. Plant survival following water stress was largely dependent on cultivar and gravimetric water content of vermiculite. This technique did not reasonably simulate natural drought conditions in terms of plant physiological performances nor soil characteristics, but it was useful to differentiate the ability of different genotypes to survive a drought-induced dieback. / Graduation date: 1998

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.

S'ha muntat un sistema experimental a l'alzinar de Prades per simular la sequera prevista per a les properes dècades al bosc mediterrani. S'ha realitzat el seguiment de la fotosíntesi, la morfologia i demografia foliar, la fenologia i el creixement de les espècies llenyoses dominants. Els resultats mostren una lleugera disminució en les taxes fotosintètiques i l'eficiència fotoquímica, així com una reducció en la quantitat total de fulles quan la disponibilitat hídrica disminueix. Aquestes variacions han comportat un menor creixement diametral dels troncs i una major mortalitat d'individus. Les diferents espècies dominants d'aquest bosc mostren diferents sensibilitats a l'estrès hídric experimental: Quercus ilex i Arbutus unedo han resultat molt més afectades per la sequera que Phillyrea latifolia.La disponibilitat hídrica constitueix un dels factors més determinants del creixement i la distribució de les espècies vegetals mediterrànies. Els models de canvi climàtic preveuen un augment de la temperatura a zones de clima mediterrani, cosa que implicaria un augment en l'evapotranspiració que, segons els mateixos models, no aniria acompanyada d'un augment en les precipitacions. Per tant, la disponibilitat hídrica dels boscos mediterranis podria disminuir en les properes dècades, encara més del que ho ha fet les darreres.Per estudiar els efectes d'una disminució en la disponibilitat hídrica en ecosistemes forestals mediterranis, s'està fent un experiment a l'alzinar de la Solana dels Torners (serra de Prades). Es tracta d'un bosc de rebrot d'uns 6 m d'alçada i una densitat mitjana de 16.600 peus ha-1, dominat per Quercus ilex, Phillyrea latifolia i Arbutus unedo. L'experiment consisteix en excloure parcialment l'aigua de la pluja i l'escorriment superficial, i assolir un 15% menys d'humitat del sòl a les zones amb exclusió d'aigua respecte de les no tractades experimentalment. S'ha realitzat el seguiment de la fotosíntesi, la morfologia i demografia foliar, la fenologia i el creixement de les espècies llenyoses dominants a cadascuna de les quatre parcel·les control i quatre parcel·les tractament.Una disminució en el 15% de la disponibilitat hídrica superficial ha reduït subtilment les taxes fotosintètiques durant les hores centrals del dia (com a màxim 20% només en determinades estacions de l'any en Quercus ilex), i de l'eficiència fotoquímica durant els períodes més freds de l'any. També ha comportat una reducció de la quantitat total de fulles en Quercus ilex (30%), i la formació de noves fulles amb un menor gruix i una menor àrea. La producció de flors i fruits ha disminuït lleugerament en Quercus ilex i més clarament en Arbutus unedo en resposta a la sequera. L'aparició de diversos estadis fenològics ha estat alterada, especialment en Arbutus unedo. Tots aquests efectes han comportat una reducció del creixement diametral dels troncs en un 37%, però no totes les espècies són afectades per igual. Algunes resulten bastant sensibles, com Arbutus unedo i Quercus ilex, que mostren respectivament, un creixement diametral 77% i 55% més baix en condicions de sequera, mentre que Phillyrea latifolia no experimenta cap disminució apreciable en el creixement diametral. La mortalitat dels individus mostra un patró semblant, ja que en condicions de sequera la mortalitat augmenta, i Arbutus unedo i Quercus ilex mostren una mortalitat més elevada que Phillyrea latifolia. Sota condicions de sequera, l'increment de biomassa aèria (calculada mitjançant al·lometries a partir del diàmetre dels troncs) ha disminuït un 42%.L'experiment ha posat de manifest que, sota condicions més àrides que les actuals, els boscos mediterranis poden minvar bastant les seves taxes de creixement, i per tant, la seva capacitat per segrestar carboni atmosfèric. No totes les espècies vegetals en resultarien igualment afectades, a llarg terme podria haver-hi un canvi en la composició específica, de manera que en resultessin més afavorides les més resistents a la sequera. / An experimental system was installed in Prades holm oak forest to simulate the drought conditions predicted for the next decades in Mediterranean forests. Photosynthetic activity, leaf morphology and demography, phenology and growth of the dominant woody species are monitored. The results show an slight decrease in photosynthetic rates and photochemical efficiency, and also a reduction in the total amount of leaves when water availability decreases. This changes are followed by a reduction in stem radial growth and an increment in stem mortality rates. Different dominant species of this forest show different sensitivity to the experimental drought: Quercus ilex and are Arbutus unedo more affected by drought treatment than Phillyrea latifolia.Water availability is one of the most important factors determining growth and distribution of Mediterranean plant species. Climate change models predict an increase of temperature in Mediterranean areas, with a consequent increase in evapotranspiration. Since no increase in precipitation is expected by these models, water availability in Mediterranean forests would decrease during the next decades, even more than during the last decades.To study the effects of a decrease in water availability in Mediterranean forest ecosystems, an experimental drought is currently being conducted in "Solana dels Torners" holm oak forest (Prades mountains). This forest is constituted by resprouts about 6 m high and a mean density of about 16.000 stems ha-1. The dominant species are Quercus ilex, Phillyrea latifolia and Arbutus unedo. Experimental drought consists of partial rain and water runoff exclusion to reach 15% lower soil moisture in water exclusion areas than in control areas. Photosynthetic activity, leaf morphology and demography, phenology and growth of the dominant woody species are monitored in each one of four control plots and four drought plots.A 15% decrease in water availability slightly reduced photosynthetic rates during central hours of the day (maximum 20% only during few seasons in Quercus ilex), and photochemical efficiency during the coldest periods. The total amount of leaves is also reduced under drought in Quercus ilex (30%), and new leaves are smaller and thinner. Flower and fruit production is slightly reduced in Quercus ilex under drought conditions, but Arbutus unedo show a strong reduction. Some phenological events are delayed by drought, specially in Arbutus unedo. These changes are followed by a 37% reduction in stem radial growth, but not all species have presented the same response. Some species show a great sensitivity. Arbutus unedo and Quercus ilex decrease 77% and 55% their radial growth under drought conditions. On the other hand, the other co-dominant species, Phillyrea latifolia, show similar radial growth in control and drought conditions. Stem mortality shows a similar pattern because Arbutus unedo and Quercus ilex show higher mortality rates than Phillyrea latifolia under drought treatment. Under drought conditions, aerial biomass increment (calculated from allometric relationships with stem diameter) decreases about 42%.This experiment is suggesting that under drier conditions, Mediterranean forests could decrease their growth rates in the future and, in consequence, their atmospheric carbon sequestration capacity. Not all the species will be equally affected and, in the long term, drought-resistant species can be favoured in detriment of less resistant ones, with possible changes in species composition of Mediterranean forests.

Esta tesis se ha desarrollado como parte del proyecto VULCAN (Vulnerabibilty assessment of shrubland ecosystems under climatic changes), un proyecto de investigación llevado a cabo en seis ecosistemas de matorrales europeos (Gales-Reino Unido, Dinamarca, Holanda, Hungría, Cerdaña-Italia y Catalunya-España), distribuidos en un gradiente de temperatura (8.2 - 15.6 ºC) y precipitación (511 - 1427 mm). En ella se han incluido datos recogidos durante el periodo 1999-2005.El objetivo global de la investigación fue el de aportar conocimientos y reducir incertidumbres acerca del funcionamiento de los matorrales europeos y del rol que pueden desempeñar éstos como fuente o sumidero de carbono bajo la perspectiva del cambio climático.En las parcelas de los diferentes países se instalaron novedosas manipulaciones experimentales para aumentar la temperatura y para reducir el agua disponible en campo, simulando los efectos del cambio climático previstos para las décadas futuras. En este trabajo se han estudiado los efectos de los tratamientos en la diversidad vegetal, en la productividad primaria aérea, así como en la fenología del crecimiento y en la elongación de ramas de las especies vegetales dominantes de los ecosistemas arbustivos europeos. Además en las parcelas experimentales de Garraf se investigó la sensibilidad de los procesos relacionados con la captación de carbono por la vegetación a nivel de hoja (fluorescencia, fotosíntesis, conductancia estomática) y se estudió la respuesta de la floración no primaveral de las dos especies arbustivas dominantes, Erica multiflora y Globularia alypum.Los efectos del cambio climático a nivel de ecosistema fueron complejos debido a la gran variabilidad de respuestas de las plantas a los tratamientos según las variables medidas, las especies, estaciones u años, sitios y periodos de experimentación.En Garraf, una zona que sufrió un incendio en 1994, encontramos una clara reducción en el número de especies por transecto en las parcelas de sequía respecto a las control, sin embargo no encontramos efectos similares en el resto de Europa lo que sugiere que la riqueza de especies en comunidades en proceso de recuperación después de una perturbación puede ser especialmente sensible al cambio climático respecto a otras comunidades en estadios más maduros. Concretamente, encontramos que los tratamientos de calentamiento y sequía redujeron la habilidad competitiva de Pinus halepensis (germinador obligado) frente a los arbustos rebrotadores y que la estrategia en el uso del agua pudo ayudar a G. alypum a mantener una posición dominante en las parcelas de sequía de Garraf. En los países con menor aridez las respuestas de la biomasa anual acumulada al calentamiento fueron más positivas sin embargo, el hecho de que también encontremos especies mediterráneas como E. multiflora que respondieron positivamente al calentamiento, junto con el hecho de que fenómenos extremos como la ola de calor Europea en 2003 redujeran la productividad primaria, matizan la hipótesis de que sea en los ecosistemas más fríos en los que el calentamiento global de lugar a una mayor absorción de carbono. Concretamente, la respuesta a los tratamientos de la biomasa a nivel de cubierta en Garraf pudo anularse debido a respuestas opuestas de las especies dominantes. En este estudio, el gradiente geográfico que dibuja los matorrales estudiados no determinó la sensibilidad de las especies al calentamiento ni la intensidad de la respuesta en lo que a fenología del crecimiento y elongación de ramas se refiere. La fenología del crecimiento de algunas especies mediterráneas fue tan sensible al calentamiento experimental (se avanzó) como algunas especies de distribución más septentrional.Aunque nuestro estudió mostró que la floración de E. multiflora y G. alypum, que tiene lugar en otoño-invierno, dependió en gran medida de la lluvia acumulada y su distribución durante el periodo primavera-verano, los tratamientos experimentales no afectaron esta variable. Estos resultados se explican en parte por la mayor variación de humedad que hubo entre años respecto a la diferencia de humedad que hubo entre las parcelas de sequía y controles. / This PhD thesis has been developed as part of the VULCAN project (Vulnerabibilty assessment of shrubland ecosystems during climatic changes), a research project conducted in six European shrublands (Wales, United Kingdom, Denmark, Holland, Hungary, Italy-Cerdagne and Catalonia-Spain), distributed in a gradient of temperature (8.2 - 15.6 ° C) and precipitation (511 - 1427 mm). It includes data collected during the 1999-2005 period. The overall objective of the research was to provide knowledge and reduce uncertainties about the functioning of the shrublands and the role that they can play as a source or sink of carbon under the prospect of climate change. At each site, novel experimental manipulations were installed to increase the temperature and to reduce the water available in field, simulating the effects of climate change projected for the future decades.In this work we have studied the effects of treatments on plant diversity, aboveground primary productivity, as well as on the phenology of growth and on the shoot elongation of dominant species. In addition, in Garraf we investigated other processes at leaf level such fluorescence, photosynthesis, stomatal conductance and other at plant level such the response of the non-spring flowering species, Erica multiflora and Globularia alypum. The effects of climate change at the ecosystem level were complex because of the great variability of plant responses to treatment according to the variables, species, seasons or years, sites and periods of experimentation. In Garraf, an area which suffered a fire in 1994, we found a clear reduction in the number of species per transect on drought plots, but no similar effects were found in the rest of Europe, suggesting that communities in process of recovery after disturbance can be particularly sensitive to climate change compared to other communities in more mature stages. Specifically, we found that the experimental treatments reduced the competitive ability of the obligate seeder Pinus halepensis against native resprouter shrubs and that the water spender strategy of G. alypum may allow this species to maintain a dominant position in drought plots in Garraf. In sites with lower aridity, the responses of the annual accumulated biomass to warming were more positive. However, the fact that we found Mediterranean species such as E. multiflora responding positively to global warming, coupled with the fact that extreme events such as the European heat wave in 2003 reduced primary productivity, challenge the assumption that it is in colder ecosystems where global warming will result in a greater carbon sequestration. Specifically, opposite responses of the dominant species could cancel out a clear response of biomass accumulation at canopy level in Garraf.In this study, the geographical gradient did not determine the susceptibility of the species or the intensity of the response of the phenology of growth and shoot elongation to the warming treatment. The phenology of growth of some Mediterranean species was very responsive to warming treatment (mainly advances) as some species of northernmost distribution. The study also shows that although flowering of E. multiflora and G. alypum, which takes place in the autumn-winter, depended largely on the accumulated rainfall and its distribution during the spring-summer period, the experimental treatments did not affect this variable. These results are explained in part by the greater range of soil moisture between years than between drought and controls plots.

Water resources in Canada are of major environmental, social and economic value. It is expected that climate change will be accompanied by more intense competition for water supply in water-stressed agricultural areas such as the southern Prairies. Beyond physical impacts, drought can be seen as a socio-economic and political problem which ultimately has implications for community-level vulnerability to climate change. This thesis presents empirical vulnerability case studies focused on the exposure-sensitivity and adaptive capacity of Coronach and Gravelbourg in southern Saskatchewan. The results illustrate the fact that farmers or ranchers are not merely passive victims of drought. They also take an active role in shaping the environment around them, thus affecting their own vulnerability to drought. Therefore, by understanding the causal linkages of the coupled social-environment system, a more comprehensive understanding of community vulnerability is achievable and informed decisions can be made based on this thorough understanding of local conditions. In the second part of this thesis, the potential of soft water path is evaluated as a possible adaptation strategy. Based on the results gathered in the first part of this thesis, adaptation measures are tailored to address specific needs of different sectors in the Town of Coronach and the Town of Gravelbourg while ensuring ecological sustainability. Examples of possible paths (adaptation measures) are suggested in order to increase community adaptive capacity to water shortages in light of future climate changes.