TERPENE AND TERPENOID EMISSIONS AND SECONDARY ORGANIC AEROSOL PRODUCTION

Approximately 90% of fine aerosol in the Midwestern United States has a regional component with a sizable fraction attributed to secondary production of organic aerosol (SOA). The Ozark Forest is an important source of biogenic SOA precursors like isoprene (> 150 mg m-2 d-1), monoterpenes (10-40 mg m-2 d-1), and sesquiterpenes (10-40 mg m-2d-1). Anthropogenic sources include secondary sulfate and nitrate and biomass burning (51-60%), vehicle emissions (17-26%), and industrial emissions (16-18%). Vehicle emissions are an important source of volatile and vapor-phase, semivolatile aliphatic and aromatic hydrocarbons that are important anthropogenic sources of SOA precursors. The short lifetime of SOA precursors and the complex mixture of functionalized oxidation products make rapid sampling, quantitative processing methods, and comprehensive organic molecular analysis essential elements of a comprehensive strategy to advance understanding of SOA formation pathways. Uncertainties in forecasting SOA production on regional scales are large and related to uncertainties in biogenic emission inventories and measurement of SOA yields under ambient conditions. This work presents a bottom-up approach to develop a conifer emission inventory based on foliar and cortical oleoresin composition, development of a model to estimate terpene and terpenoid signatures of foliar and bole emissions from conifers, development of processing and analytic techniques for comprehensive organic molecular characterization of SOA precursors and oxidation products, implementation of the high-volume sampling technique to measure OA and vapor-phase organic matter, and results from a 5 day field experiment conducted to evaluate temporal and diurnal trends in SOA precursors and oxidation products. A total of 98, 115, and 87 terpene and terpenoid species were identified and quantified in commercially available essential oils of Pinus sylvestris, Picea mariana, and Thuja occidentalis, respectively, by comprehensive, two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GC × GC-ToF-MS). Analysis of the literature showed that cortical oleoresin composition was similar to foliar composition of the oldest branches. Our proposed conceptual model for estimation of signatures of terpene and terpenoid emissions from foliar and cortical oleoresin showed that emission potentials of the foliar and bole release pathways are dissimilar and should be considered for conifer species that develop resin blisters or are infested with herbivores or pathogens. Average derivatization efficiencies for Methods 1 and 2 were 87.9 and 114%, respectively. Despite the lower average derivatization efficiency of Method 1, distinct advantages included a greater certainty of derivatization yield for the entire suite of multi- and poly-functional species and fewer processing steps for sequential derivatization. Detection limits for Method 1 using GC × GC- ToF-MS were 0.09-1.89 ng μL-1. A theoretical retention index diagram was developed for a hypothetical GC × 2GC analysis of the complex mixture of SOA precursors and derivatized oxidation products. In general, species eluted (relative to the alkyl diester reference compounds) from the primary column (DB-210) in bands according to n and from the secondary columns (BPX90, SolGel-WAX) according to functionality, essentially making the GC × 2GC retention diagram a Carbon number-functionality grid. The species clustered into 35 groups by functionality and species within each group exhibited good separation by n. Average recoveries of n-alkanes and polyaromatic hydrocarbons (PAHs) by Soxhlet extraction of XAD-2 resin with dichloromethane were 80.1 ± 16.1 and 76.1 ± 17.5%, respectively. Vehicle emissions were the common source for HSVOCs [i.e., resolved alkanes, the unresolved complex mixture (UCM), alkylbenzenes, and 2- and 3-ring PAHs]. An absence of monoterpenes at 0600-1000 and high concentrations of monoterpenoids during the same period was indicative of substantial losses of monoterpenes overnight and the early morning hours. Post-collection, comprehensive organic molecular characterization of SOA precursors and products by GC × GC-ToFMS in ambient air collected with ~2 hr resolution is a promising method for determining biogenic and anthropogenic SOA yields that can be used to evaluate SOA formation models.

1200 years of decadal-scale variability of Mediterranean vegetation and climate at Pantelleria Island, Italy

A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from ad 800 to 1000 that corresponds to the ‘Medieval Warm Period’ (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at ad 1000, when carbonate content became very low suggesting wetter conditions until ad 1850–1900. Broadly, this period coincides with the ‘Little Ice Age’ (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around ad1750.

Modeling tree water deficit from microclimate: an approach to quantifying drought stress

Tree water deficit estimated by measuring water-related changes in stem radius (DeltaW) was compared with tree water deficit estimated from the output of a simple, physiologically reasonable model (DeltaW(E)), with soil water potential (Psi(soil)) and atmospheric vapor pressure deficit (VPD) as inputs. Values of DeltaW were determined by monitoring stem radius changes with dendrometers and detrending the results for growth, We followed changes in DeltaW and DeltaW(E) in Pinus sylvestris L. and Quercus pubescens Willd. over 2 years at a dry site (2001-2002; Salgesch, Wallis) and in Picea abies (L.) Karst. for 1 year at a wet site (1998; Davos, Graubuenden) in the Swiss Alps. The seasonal courses of DeltaW in deciduous species and in conifers at the same site were similar and could be largely explained by variation in DeltaW(E). This finding strongly suggests that DeltaW, despite the known species-specific differences in stomatal response to microclimate, is mainly explained by a combination of atmospheric and soil conditions. Consequently, we concluded that trees are unable to maintain any particular DeltaW. Either Psi(soil) or VPD alone provided poorer estimates of AWthan a model incorporating both factors. As a first approximation of DeltaW(E), Psi(soil) can be weighted so that the negative mean Psi(soil) reaches 65 to 75% of the positive mean daytime VPD over a season (Q. pubescens: similar to65%, P abies: similar to70%, P sylvestris: similar to75%). The differences in DeltaW among species can be partially explained by a different weighting of Psi(soil) against VPD. The DeltaW of P. sylvestris was more dependent on Psi(soil) than that of Q. pubescens, but less than that of P. abies, and was less dependent on VPD than that of P. abies and Q. pubescens. The model worked well for P. abies at the wet site and for Q. pubescens and P. sylvestris at the dry site, and may be useful for estimating water deficit in other tree species.

Microstructural, chemical and isotopic evidence for the origin of late neolithic leather recovered from an ice field in the Swiss Alps

Archaeological leather samples recovered from the ice field at the Schnidejoch Pass (altitude 2756 m amsl) in the western Swiss Alps were studied using optical, chemical molecular and isotopic (δ13C and δ15N of the bulk leather, and compound-specific δ13C analyses of the organic-solvent extracted fatty acids) methods to obtain insight into the origin of the leather and ancient tanning procedures. For comparison, leathers from modern native animals in alpine environment (red deer, goat, sheep, chamois, and calf/cow) were analyzed using the same approach. Optical and electron microscopically comparisons of Schnidejoch and modern leathers showed that the gross structure (pattern of collagen fibrils and intra-fibrils material) of archaeological leather had survived essentially intact for five millennia. The SEM studies of the hairs from the most important archaeological find, a Neolithic leather legging, show a wave structure of the hair cuticle, which is a diagnostic feature for goatskins. The variations of the bulk δ13C and δ15N values, and δ13C values of the main fatty acids are within the range expected for pre-industrial temperate C3 environment. The archaeological leather samples contain a mixture of indigenous (from the animal) and exogenous plant/animal lipids. An important amount of waxy n-alkanes, n-alkan-1-ols and phytosterols (β-sitosterol, sitostanol) in all samples, and abundant biomarker of conifers (nonacosan-10-ol) in the legging leathers clearly indicate that the Neolithic people were active in a subalpine coniferous forest, and that they used an aqueous extract of diverse plant material for tanning leather.

Lateglacial and Holocene vegetation belts in the Pirin Mountains (southwestern Bulgaria)

Pollen stratigraphy of a core 270 cm long from Lake Dalgoto at 2310 m in the Northern Pirin Mountains, southern Bulgaria, was treated by optimal partitioning and compared to a broken-stick model to reveal statistically significant pollen zones. The vegetational reconstructions presented here are based on pollen percentages and pollen influx, on comparisons of modern and fossil pollen spectra, and on macrofossil dates from other sites in the mountains. During the Younger Dryas (11000–10200 14C yr BP), an open xerophytic herb vegetation with Artemisia and Chenopodiaceae was widely developed around the lake. Deciduous trees growing at lower elevations contributed to the pollen rain deposited at the higher-elevation sampling sites. Specifically, from 10200 to 8500 yr BP, Quercus, Ulmus, Tilia and Betula expanded rapidly at low and intermediate elevations, and between 8500 and 6500 yr BP they extended to higher elevations close to the upper forest limit, which was formed by Betula pendula at about 1900 m. Coniferous species were limited in the region at this time. After 6500 yr BP, the expansion of conifers (Pinus peuce, P. sylvestris, P. mugo, Abies alba) at high elevations forced the deciduous trees downward. Between 6500 and 3000 yr BP, the forest limit at 2200 m was formed by P. peuce, and A. alba had its maximum vertical range up to 1900 m. Later the abundance and vertical range of P. peuce and A. alba were reduced. After 3000 yr BP, Picea expanded.

Treeline Fluctuations Recorded for 12,500 Years by Soil Profiles, Pollen, and Plant Macrofossils in the Central Swiss Alps

Past treelines can rarely be recorded by pollen percentages alone, but pollen concentration, pollen influx, and plant macrofossils (including stomata of conifers) are more reliable indicators. In addition, ancient forest soils above today's treeline may trace the maximum upper expansion of the forest since the last glaciation. Charcoal in such soil profiles may be radiocarbon dated. Our example from the Central Swiss Alps at the Alpe d'Essertse consists of a plant-macrofossil diagram and pollen diagrams of the pond Gouille Rion at 2343 m a.s.l. and a sequence of soil profiles from 1780 m to 2600 m a.s.l. The area around the pond was forested with LariJc decidua and Pinus cembra between 9500 and 3600 BP. After 4700 BP the forest became more open and Juniperus nana and Alnus viridis expanded (together with Picea abies in the subalpine forest). Between 1700 and 900 BP the Juniperus nana and Alnus viridis scrubs declined while meadows and pastures took over, so that the pond Gouille Rion was definitively above timber­ line. The highest Holocene treeline was at 2400 to 2450 m a.s.l. (i.e. 50 to 100 m higher than the uppermost single specimen of Pinus cembra today) between 9000 and 4700 BP, but it is not yet dated in more detail. The highest charcoal of Pinus cembra at 2380 m a.s.l. has a radiocarbon date of 6010 ± 70 BP. Around 6900 BP a strong climatic deterioration caused an opening of timberline forest. First indicators of anthropogenic influence occurred at 4700 BP, when the forest limit started to move down. The lowering of timberline after 4700 BP was probably due to combined effects of human and climatic impact.

Comportamiento de coníferas bajo riego en Dique Yaucha : Mendoza, Argentina

La provincia de Mendoza, que se ubica en el Centro-Oeste de la República Argentina, posee una extensión de 150.830 km2. Prácticamente todas las actividades agropecuarias y forestales están concentradas en el 3% de su territorio que es posible irrigar. Al oeste, en el límite con la República de Chile, está la cadena montañosa que forma parte de la región fitogeográfica del Desierto Andino que se extiende por más de 500 km, con un ancho promedio de 100 km. El objetivo de este trabajo fue evaluar la supervivencia y el comportamiento de distintas especies de coníferas en zonas del piedemonte mendocino. Para ello se instaló una parcela experimental en el Dique Yaucha, ubicado en el Departamento de San Carlos a 34°00' S y 69°07' O, a una altura de 1213 msnm. Las especies del ensayo fueron: Pinus pinea L., Pinus halepensis Mill. y Cupressus arizonica Greene. Se llevaron plantas de aproximadamente 0,70 m de altura, que se instalaron a una distancia de plantación definitiva de 3 x 3 m y se regaron superficialmente por surcos. Se tomaron periódicamente datos dasométricos de diámetro altura de pecho (DAP) de todas las plantas, altura total de los árboles promedio de cada especie, registrándose además las fallas producidas y el estado sanitario. Los resultados obtenidos a la edad de 17 años son: Pinus pinea: diámetro promedio 17 cm, altura 6,60 m y 22,5% de fallas; Pinus halepensis: diámetro promedio 16 cm, altura 8,60 m y 12,2% de fallas; Cupressus arizonica: diámetro promedio 20 cm, altura 7,75 m y 18,1% de fallas. Es de destacar que P. pinea presenta el 6% de fustes bifurcados a baja altura. Todas las especies tienen un buen estado sanitario, no registrándose hasta la fecha plagas o enfermedades que hayan afectado el desarrollo del ensayo.

Palynology on a profile from the Krusné Hory Mountains

Site details: The raised bog Fláje-Kiefern (50°429N, 13°329 E; 760 m a.s.l.; size ca. 500x500 m) lies in the Krusné Hory Mountains (Erzgebirge), Czech Republic, about 10 km from Georgenfelder Moor in Germany. Hejny and Slavík (1988) described the phytogeographic region of the Krusne Hory Mountains as 'a region of mountain flora and vegetation, with thermophilous species largely missing. In the natural forests, conifers, especially spruce (Picea excelsa) prevail. The deforested areas have been converted into meadows and pastures'. The climate is cool with annual average temperatures of about 5°C and annual precipitation of about 900 mm. The bedrock is Precambrian crystallinicum.

Organic-geochemical and petrographical composition of sediments from ODP Leg 164 sites

Sediments from Holes 994C, 995A, 997A, and 997B have been investigated for "combined" gases (adsorbed gas and that portion of free gas that has not escaped from the pore volume during core recovery and sample collection and storage), solvent-extractable organic compounds, and microscopically identifiable organic matter. The soluble materials mainly consist of polar compounds. The saturated hydrocarbons are dominated by n-alkanes with a pronounced odd-even predominance pattern that is derived from higher plant remains. Unsaturated triterpenoids and 17ß, 21ß-pentacyclic triterpenoids are characteristic for a low maturity stage of the organic matter. The low maturity is confirmed by vitrinite reflectance values of 0.3%. The proportion of terrestrial remains (vitrinite) increases with sub-bottom depth. Within the liptinite fraction, marine algae plays a major role in the sections below 180 mbsf, whereas above this depth sporinites and pollen from conifers are dominant. These facies changes are confirmed by the downhole variations of isoprenoid and triterpenoid ratios in the soluble organic matter. The combined gases contain methane, ethane, and propane, which is a mixture of microbial methane and thermal hydrocarbon gases. The variations in the gas ratios C1/(C2+C3) reflect the depth range of the hydrate stability zone. The carbon isotopic contents of ethane and propane indicate an origin from marine organic matter that is in the maturity stage of the oil window.

Survey of pollen and spores in DSDP Holes 96-618 and 619

A preliminary palynological survey of 118 samples from the Mississippi Fan (Sites 615, 616, and 620) and from 2 intraslope basins (Sites 619 and 618) shows pollen in all samples. Reworked pollen is generally abundant, forming over 50% of the sum of pollen and reworked pollen. Concentration of nonreworked pollen is usually low (on the order of tens to hundreds of pollen grains per cubic centimeter wet sediment). Conifers, primarily Pinus, Picea, and Tsuga, dominate Pleistocene marine pollen spectra; significant percentages of Quercus are present in Holocene sediments and in sediments deposited during oxygen-isotope Stage 5.

Cenozoic terrestrial palynomorphs from the late Oligocene to early Miocene section of sediment core CRP-2/2A (Table 1)

Sparse terrestrial palynomorphs (spores and pollen) were recovered from glacigene Lower Miocene and Oligocene core samples from the Cape Roberts Project (CRP) drillhole CRP-2/2A, Victoria Land Basin, Antarctica. Rarity of palynomorphs probably results from the spares periglacial vegetation in the surrounding landscape at the time of deposition, as well as dilution from rapid sediment accumulation. The Miocene and Late Oligocene vegetation is interpreted as including herb-moss tundra with low-growing woody plants (including Nothofagus and podocarp conifers) in more protected areas, similar to that encountered in the Miocene of CRP-1. Species richness and numbers of specimens increase downhole, a trend that begins very gradually below ~307 mbsf, and increases below ~443 mbsf through the Early Oligocene. These lower assemblages reflect low diversity woody vegetation dominated by several species of Nofhofagus and podocarps, growing in somewhat milder conditions, though still cold temperate to periglacial in the Early Oligocene. The CRP-2/2A core provides new biostratigraphical information, such as the First Appearance Datums (FADS) of Tricolpites sp. a near the Oligocene/Miocene boundary, and Marchantiaceae in the Early/Late Oligocene transition: these are taxa that along with N. lachlaniae, Coptospora spp. and Podocarpidites sp.b characterize assemblages recovered from outcrops of the Pliocene Sirius Group in the Transantarctic Mountains. Some elements of the extremely hardy periglacial tundra vegetation that survived in Antarctica into the Pliocene had their origin in the Oligocene during a time of deteriorating (colder, drier) climatic conditions. The CRP results highlight the long persistence of this tundra vegetation, through approximately 30 million years of dynamically changing climatic conditions. Rare Jurassic and more common Permian-Triassic spores and pollen occur sporadically throughout the core. These are derived from Jurassic Ferrar Group sediments, and from the Permian-Triassic Victoria Group, upper Beacon Supergroup. Higher frequencies of reworked Beacon palynomorphs and coaly organic matter below ~307 mbsf indicate greater erosion of the Beacon Supergroup for this lower part of the core. A color range from black, severely metamorphosed specimens, to light-colored, yellow (indicating low thermal alteration), reworked Permian palynomorphs, indicates local provenance in the dolerite-intruded Beacon strata of the Transantarctic Mountains, as well as areas (now sub-ice) of Beacon strata with little or no associated dolerite well inland (cratonwards) of the present Transantarctic Mountains.

(Table 1) Comparison of localities where Switzianthus (Anderson & Anderson) has been found with Dejerseya and Heidiphyllum occurrence

Fossil leaves of the Voltziales, an ancestral group of conifers, rank among the most common plant fossils in the Triassic of Gondwana. Even though the foliage taxon Heidiphyllum has been known for more than 150 years, our knowledge of the reproductive organs of these conifers still remains very incomplete. Seed cones assigned to Telemachus have become increasingly well understood in recent decades, but the pollen cones belonging to these Mesozoic conifers are rare. In this contribution we describe the first compression material of a voltzialean pollen cone from Upper Triassic strata of the Transantarctic Mountains. The cone can be assigned to Switzianthus Anderson & Anderson, a genus that was previously assumed to belong to an enigmatic group of pteridosperms from the Triassic Molteno Formation of South Africa. The similarities of cuticle and pollen morphology, together with co-occurrence at all known localities, indicate that Switzianthus most probably represents the pollen organ of the ubiquitous Heidiphyllum/Telemachus plant.

Pollen profile from sediment core Höllerer See

(expanded by Eberhard Grüger, Göttingen) The site "Höllerer See" is a lake in the northern foreland of the Alps, about 30 km north of the city of Salzburg/Austria, situated in the south-western part of Oberösterreich/Austria. A 2 m long piston core from this locality, consisting entirely of calcareous gyttja, was studied by pollen analysis. The three lowermost samples (1.98, 1.95 and 1.92 m) were deposited during the Preboreal when Pinus and Betula were still the dominating forest trees. High pollen values of thermophilous woody species (mainly Corylus and Quercus, but also Ulmus, Tilia, Fraxinus) prove the Boreal age of the next younger sample (1.91 m). The following two pollen spectra attest that Alnus (1.89 m) and - later (1.88 m) - Fagus had become important members of the local (Alnus) and the regional (Fagus) vegetation. From this level up to the top of the profile these two tree taxa contribute - together with Betula - always 50 to 80 % to the arboreal pollen sum. The upper 1.89 m of sediment of the Höllerer See core evidently date from the Subboreal and the Subatlantic. As Preboreal sediment was stated at the base of the profile it must be concluded that most of the Boreal and the Atlantic is - for whatever reason - not represented by sediment in this core. As no radiocarbon dates are available age estimates of the distinguished pollen zones can be achieved only by correlating major changes of the former vegetation with historical events which probably influenced the then contemporary vegetation. The pollen grains of the Triticum and Hordeum type found in samples of zone 2.1 might indicate the growing of cereals in the region during the Late Bronze Age. The first pollen grains of Secale date from the boundary Hallstatt/Latène Age (zone 2.2). The cereal curves become continuous in Bavarian times (Bajuwarenzeit, Middle Ages, zone 3.3). The Plantago laceolata curve, continuous since 1.7 m depth (zone 2.1), points to animal breeding since the Early Subatlantic (Hallstattzeit). This curve reaches its absolute maximum in Roman time (zone 3.1). Roman time forest clearance caused a drastic decrease of tree pollen curves (start of zone 3.1). Values of anthropogenic indicators as high as in zone 3.1 are found again - after a distinct decrease in zone 3.2 - not till the Bavarians settled in the region (6th century). Maximal Fagus values and the simultaneous total lack of anthropogenic indicators mark the Migration Period (zone 3.2). The Younger Subatlantic (zone 4) is characterized by a decrease of deciduous forests due to medieval forest clearance. At the same time the conifers Pinus and Picea gained in importance. The lake was probably used for retting hemp in Medieval times. The distinction of the pollen grains of Cannabis and Humulus might not be certain in all cases. It is known that hemp as well as hop was cultivated in the study area. Markers were added to the samples at the beginning of pollen preparation (13500 Lycopodium spores, sample volume 0.5 cm**3) and counted together with the pollen grains. Therefore pollen concentrations can be calculated: Concentration = C * F / V (with C = number of grains of a particular pollen type, V = volume of the untreated pollen sample, F = marker added/marker counted). F ranges from 39 to 1688. Factors that large are not suited to produce reliably interpretable pollen concentrations. Consequently no use was made of the pollen concentrations in this thesis, although a concentration diagram is added.

Analysis of adaptive responses of Pinus pinaster to changing environmental conditions in the Mediterranean region

Recent climate evolution studies highlight the progressive temperature increase and prevalence of seasonal drought, with specially incidence in the Mediterranean region. Although conifers are very important species regarding forest conservation, sustainability and productivity, given the large forest surface they cover in Spain and their active role in preventing soil erosion and desertification, we know little about the molecular mechanisms which control adaptation in this ancient taxonomic group

Genes implicados en la respuesta molecular al estrés hídrico en Pinus pinaster Ait

La presente tesis doctoral se centra en el estudio de la respuesta molecular de las coníferas mediterráneas al estrés hídrico. Para ello se ha escogido como especie modelo Pinus pinaster Ait., la conífera más abundante en España, y que habita un amplio rango de situaciones ecológicas, especialmente en lo relativo a la disponibilidad de agua. En primer lugar, se ha aplicado un estrés hídrico controlado en cultivo hidropónico y se ha generando una genoteca sustractiva con objeto de identificar los genes inducidos por el estrés, analizando su expresión en raíces, tallos y acículas. A continuación, se ha analizado, la expresión de los genes anteriormente obtenidos así como de otros seleccionados de las bases de datos disponibles, durante una sequía prolongada en tierra, similar a las que las plantas deben afrontar en la naturaleza. Se ha utilizado en este caso, además de P. pinaster, P. pinea, otra conífera mediterránea adaptada a las sequías recurrentes. Este trabajo ha permitido identificar genes candidato expresionales, presumiblemente comunes en la respuesta molecular de las coníferas al déficit hídrico. Se han detectado diferencias notables en la expresión de determinados genes, que podrían ser los responsables de las diferencias exhibidas por ambas especies en el comportamiento frente a la sequía. Entre los genes identificados como inducidos por el estrés hídrico se encuentran varios miembros de la familia de las deshidrinas. Trabajos previos han utilizado deshidrinas como genes candidato; no obstante, la falta de especificidad de ciertos fragmentos y marcadores utilizados, debido a la complejidad estructural de esta familia, resta fiabilidad a algunos de los resultados publicados. Por este motivo, se ha estudiado en detalle esta familia en P. pinaster, se han identificado y caracterizado 8 miembros y se ha analizado su patrón de expresión frente a sequía. Este estudio ha permitido describir por primera vez unos segmentos conservados en la secuencia de aminoácidos de las deshidrinas de pináceas, cuya presencia y número de repeticiones parece estar relacionado con su especificidad. Por último, se han escogido tres genes implicados en distintas fases de la respuesta al estrés hídrico para su análisis exhaustivo: una deshidrina, una nodulina y un factor de transcripción tipo AP2. Se ha caracterizado su estructura exón/intrón y secuenciado su región promotora. Además, se han obtenido líneas transformadas que sobreexpresan estos genes tanto de forma heteróloga, en la especie modelo Arabidopsis thaliana, como en el propio P. pinaster. Este material facilitará la realización de futuros estudios sobre la función y el mecanismo de actuación de estos genes en la respuesta al estrés hídrico. ABSTRACT This thesis focuses in the study of the molecular response to water stress in Mediterranean conifers. For this purpose, P. pinaster was selected as model species. It’s the most abundant conifer in Spain, living in a wide range of ecological conditions, especially regarding water availability. First, we have applied a controlled polyethylene glycol-induced water stress in hydroponic culture and obtained a suppression subtractive hybridization (SSH) library, with the aim of identifying genes induced by water stress, analysing their expression in roots, stems and needles. We have then analysed the expression patterns of the identified genes, together with other genes selected from public databases. This study was conducted throughout a prolonged drought stress in soil, similar to the ones plants have to face in nature. In this case not only P. pinaster was analysed but also P. pinea, another Mediterranean conifer well adapted to recurrent droughts. This work has enabled us to identify of reliable candidate genes, presumably shared with other conifers in the response to water stress. We observed remarkable differences in the expression of some genes, which could be involved in the differential behaviour that these species show in the water stress response. Within the genes induced by water stress, several members of the dehydrin gene family were identified. Due to the structural complexity of the family, certain ambiguities and inconsistencies have been detected in previous works that have used dehydrins as candidate genes. For this reason, we have analysed thoroughly this gene family in P. pinaster, and have identified and characterized eight different members, whose expression patterns during drought have also been assessed. This study has allowed us to identify for the first time novel conserved segments in the amino acids sequences of Pinaceae. The presence and number of repetitions of these segments could be associated with the functional specificity of these proteins. Finally, three genes involved in different steps of the water stress response were selected for an exhaustive analysis: a dehydrin, a nodulin and an AP2 transcription factor. For all of them, the exon/intron structure was established and their promoter region was sequenced. Also, transformed lines were obtained both in Arabidopsis thaliana and in P. pinaster for the constitutive overexpression of these genes. This material will facilitate the development of further studies to investigate the function of these genes during the water stress response