<p>The hydrologic cycle may be described in essence as the process of water rising and falling in its various phases between land and atmosphere. In this minimal description of the hydrologic cycle two features come into focus: intermittency and irreversibility. In this dissertation intermittency and irreversibility are investigated broadly in the soil-plant-atmosphere system. The theory of intermittency and irreversibility is addressed here in three ways: (1) through its effect on components of the soil-plant-atmosphere system, (2) through development of a measure of the degree of irreversibility in time-series, and (3) by the investigation of the dynamical sources of this intermittency. First, soil infiltration and spring frost risk are treated as two examples of hydrologic intermittency with very different characters and implications for the soil plant system. An investigation of the water budget in simplified soil moisture models reveals that simple bucket models of infiltration perform well against more accurate representation of intra-storm infiltration dynamics in determining the surface water partitioning. Damaging spring frost is presented as a ``biologically-defined extreme event'' and thus as a more subtle form of hydrologic intermittency. This work represents the first theoretical development of a biologically-defined extreme and highlights the importance of the interplay between daily temperature mean and variance in determining the changes in damaging frost risk in a warming climate. Second, a statistical measure of directionality/asymmetry is developed for stationary time-series based on analogies with the theory of nonequilibrium thermodynamics. This measure is then applied to a set of DNA sequences as an example of a discrete sequence with limited state-space. The DNA sequences are found to be statistically asymmetric and further that the local degree of asymmetry is a reliable indicator of the coding/noncoding status of the DNA segment. Third, the phenomenology of rainfall occurrence is compared with canonical examples of dynamical intermittency to determine whether these simple dynamical features may display a dominant signature in rainfall processes. Summer convective rainfall is found to be broadly consistent with Type-III intermittency. Following on this result we studied daytime atmospheric boundary layer dynamics with a view toward developing simplified models that may further elucidate the interaction the interaction between land surface conditions and convective rainfall triggering.</p> / Dissertation

Bud dormancy is an essential characteristic of deciduous woody perennials, including apple, to cope with the low temperatures during winter. The release from dormancy and subsequent budburst in apple can only occur after fulfillment of chilling and heat requirements. In the Mid-Atlantic region, dormancy release and bud break of apple often coincide with late-spring freezes that cause severe damages to flowers, and small fruitlets. Therefore, the present study aimed to better understand mechanisms underlying bud dormancy in apple, with an ultimate goal of exploring chemical and/or genetic approaches for bloom-time modulation to avoid spring frost. Using two apple cultivars, 'Cripps Pink' and 'Honeycrisp,' representing early- and late-blooming cultivars, respectively, the present study specifically investigated the accumulation kinetics of plant hormones, carbohydrates, and reactive oxygen species (ROS) throughout the dormancy-regrowth cycle. Our results indicated that both cultivars required 1000 chilling hours for endodormancy release, but 'Honeycrisp' required 1000 growing degree hours (GDHs) more than 'Cripps Pink' for ecodormancy release and budburst. Among plant hormones, abscisic acid (ABA) showed remarkably elevated levels in the dormant buds of both cultivars during endodormancy, but its levels were significantly higher in 'Honeycrisp'. The decline of the ABA level at bud burst was combined with increased levels of cytokinin (CK). The ABA accumulation pattern during dormancy paralleled with an upregulation and downregulation of ABA biosynthetic and catabolic genes, respectively. On the other hand, the levels of hydrogen peroxide (H2O2) and superoxide (O2.-) were significantly higher in 'Cripps Pink' than 'Honeycrisp', particularly by the time of endodormancy and ecodormancy release, respectively. Our findings also showed a gradual decline in starch levels with the dormancy progression and increased levels of total soluble sugars (TSS) that were generally higher in the early-blooming cultivars. Transcriptomic profiling and module-trait relationship identified two modules that contrast between two cultivars mainly during eco-dormancy. Gene ontology (GO) analysis indicated that these DEGs were mostly involved in pathways related to hormones and signaling and co-expressed with H2O2 whereas, during ecodormancy pathways related to glutathione metabolism, auxin biosynthesis, carbohydrate metabolism and reproductive development were co-expressed with O2.-. Together, our results suggest that the contrasting bloom dates between 'Cripps Pink' and 'Honeycrisp' can be explained, at least partially, by the differential accumulation levels of ABA, ROS, antioxidants, and their associated genes in the buds of these cultivars throughout the dormancy cycle. / Doctor of Philosophy / Spring frosts represent a significant threat to apple production in many fruit-producing states of the United States including Virginia. The risk of frost damage is rising due to global climate change, and there is a high demand for effective measures to reduce frost damage. Exogenous applications of plant growth regulators (PGRs) to delay bloom has been suggested as an effective frost avoidance strategy, but with limited success. Therefore, the present study aimed to investigate molecular and biochemical pathways regulating bud dormancy and bloom time in apple, which can ultimate lead to novel approaches for bloom delay and frost mitigation. To this end, the accumulation patterns of major plant hormones (e.g. abscisic acid, ABA, cytokinin, CK and jasmonic acid, JA), reactive oxygen species (ROS) and carbohydrates (e.g. starch, sucrose, glucose and fructose) were thoroughly monitored throughout the dormancy-regrowth cycle in two apple cultivars, 'Cripps Pink' and 'Honeycrisp,' representing early- and late-blooming cultivars, respectively. Both these cultivars had similar chilling requirements (1000 chilling hours) but differed in their heat requirements; with 'Honeycrisp' requiring 1000 growing degree hours more than 'Cripps Pink'. Among plant hormones, ABA increased with the progression of dormancy and decreased with dormancy release in both cultivars. However, ABA levels were significantly higher in 'Honeycrisp' compared to 'Cripps Pink'. On the contrary, during dormancy release, the growth-promoting hormone, CK, increased earlier in 'Cripps Pink'. The levels of ROS, e.g., hydrogen peroxide (H2O2), and superoxide (O2.-), were also higher in 'Cripps Pink' than 'Honeycrisp', particularly by the time of endodormancy and ecodormancy release, respectively. Our data showed that starch levels generally declined during dormancy, whereas soluble sugars increased. However, there was no significant alternations in the carbohydrate accumulation profiles between the two cultivars that could account for the differences in their bloom dates. These results were verified further at the transcriptomic level. Using the RNA-sequencing technology, identified two modules that contrast between two cultivars mainly during eco-dormancy. Gene ontology (GO) analysis indicated that these genes were mostly involved in pathways related to hormones and signaling and co-expressed with H2O2 whereas during ecodormancy pathways related to glutathione metabolism, auxin biosynthesis, carbohydrate metabolism and reproductive development were co-expressed with O2.-. Overall, our results suggest that ABA, cytokinin, H2O2, and O2.- may, at least partially, explain the differences in the bloom time between the two apple cultivars. Further analysis of these molecules and their associated genes in other apple cultivars with contrasting bloom dates is necessary for better understanding of bloom time regulation in apple and developing strategies against frost damage.

Sour cherry (Prunus cerasus L. (sin. Cerasus vulgaris Mill., Prunus vulgaris Schur)) is widely grown stonefruit tree in Lithuania. Productivity of sour cherry orchard depends on many tightly related factors. It's know that negative temperature and spring frosts are important factors determinating plant productivity. These factors must be considered in plant breeding. Risks of extreme temperatures, humidity deficiency and spring frosts increases due to climate change. Plant reaction to climate change depends on plant species, cultivar and on biotic or abiotic factors. Spring starts earlier and suddenly during past years, thus vegetation of cherries starts earlier. However, probability of plant damage to spring frosts increases due to earlier vegetation, because plants are susceptible to negative temperatures due to loss of the predictive and consequential (secondary) dormancy. The aim of the research was to evaluate DNA polymorphism of sour cherry cultivars with different resistance to spring frosts, to characterize nature of phenological phase changes, to evaluate biochemical characteristics of sour cherry resistance to spring frosts formation by analysis of changes in carbohydrate amount and composition in generative organs and fruit ovaries at different phenological phases, and to evaluate changes in gene expression levels of galactinol synthase and raffinose synthase during flower development. It was established, that specific rhythm of phenological development is... [to full text] / Paprastoji vyšnia (Prunus cerasus L. (sin. Cerasus vulgaris Mill., Prunus vulgaris Schur)) yra plačiai auginamas kaulavaisinis augalas Lietuvoje. Vyšnių sodo produktyvumas priklauso nuo daugelio tarpusavyje susijusių veiksnių. Oro temperatūra yra vienas svarbiausių vyšnių paplitimą ir jų derlių lemiantis veiksnys. Žinoma, kad neigiamos temperatūros ir pavasario šalnos yra svarbus veiksnys, į kurį reikia atsižvelgti vykdant augalų selekciją. Keičiantis klimatui, didėja ekstremalių temperatūrų ir drėgmės deficito pavojus bei pavasario šalnų rizika (Augspurger, 2013). Augalų reakcija į klimato kaitos pokyčius priklauso nuo augalo rūšies ir veislės bei abiotinių ir biotinių veiksnių. Pastaraisiais metais pavasaris ateina greičiau ir staigiai. Tai paveikia vyšnias – jų vegetacija prasideda anksčiau. Anksti pradėjus vegetuoti išauga tikimybė, kad augalus pažeis pavasario šalnos. Lietuvoje nuostolių padaro vėlyvos pavasario šalnos, kurių metu pažeidžiami žiedai ir vaisių užuomazgos. Tuo metu augalai jau būna išėję iš būtinosios ir priverstinės ramybės ir jautrūs neigiamoms temperatūroms. Tyrimų tikslas buvo įvertinti skirtingo atsparumo šalnoms vyšnios veislių DNR polimorfizmą, fenologinių tarpsnių kaitos pobūdį, atskleisti paprastosios vyšnios atsparumo pavasario šalnoms formavimosi biochemines ypatybes ištiriant bendro angliavandenių kiekio ir jų sudėties kitimą skirtinguose fenologiniuose tarpsniuose esančių augalų generatyviniuose organuose ir vaisių užuomazgose, nustatyti... [toliau žr. visą tekstą]

La phénologie du débourrement est un caractère majeur d’adaptation des arbres à leurenvironnement en milieu tempéré. Notre objectif a été de caractériser les contraintes biotiques (oïdium) etabiotiques (températures hivernales et printanières / gels tardifs) s’exerçant sur le débourrement afind’expliquer les patrons de variation phénologique intra et inter populationnelle observés chez le chêne(Quercus petraea) le long d’un gradient altitudinal. Nous avons utilisé une approche combinantobservations in situ, expérimentation, et modélisation. Nous avons mis en évidence que l’évitement desgels tardifs printaniers est un caractère adaptatif majeur le long du gradient altitudinal. La tardiveté dudébourrement pourrait être due à des besoins plus importants en température de forcing. Par ailleurs, lechampignon n’est pas adapté localement à la phénologie de son hôte et les individus et les populationssont alors inégalement exposés à la maladie. En montant en altitude, les chênes sont de plus en plusexposés au champignon, mais les facteurs environnementaux sont défavorables à une plus forte infection.A basse altitude, l’oïdium et les gels tardifs favorisent des phénotypes phénologiques opposés(respectivement précoces vs. tardifs) ; la combinaison des deux contraintes pourrait donc contribuer aumaintien de la forte diversité phénologique observée. D’autre part, nous avons observé que l’infection parl’oïdium engendre une augmentation du polycyclisme chez les semis de chêne au cours de la saison decroissance, ce qui les rend moins résistants aux gels hivernaux. Nous montrons qu’il est important que lesmodèles phénologiques à visée prédictive intègrent la phase de chilling aboutissant à la levée dedormance. Le manque de chilling ne semble pas encore un facteur limitant, mais la tendance actuelle à undébourrement de plus en plus précoce sera probablement freinée voire inversée au milieu du siècle enbasse altitude, dans la marge sud de distribution de Q. petraea. / Budburst phenology is a major adaptive trait of trees to the environment in temperateclimate. Our aim was to characterize the biotic (powdery mildew) and abiotic (winter and springtemperatures / spring frost) constraints acting on budburst in view to explain the patterns of intra and interpopulations’ phenological variation observed in sessile oak (Quercus petraea) along an elevation gradient.We based our approach on in situ monitoring, experimentation and modeling. Our results highlight that theavoidance of late spring frosts is a major adaptive trait along the elevation gradient. The lateness inbudburst might be due to higher requirements in forcing temperatures. Otherwise, the fungus is not locallyadapted to its host phenology so oak individuals and populations are unequally exposed to the disease.With increasing elevation, oaks are more and more exposed to the fungus, but the environmental factorsare unfavorable to higher infection. At low elevation, powdery mildew and late spring frosts favor oppositephonological phenotypes (early-flushing vs. late-flushing trees, respectively); the combination of the twopressures may thus contribute to the maintenance of the observed high phenological diversity. We alsoshowed that powdery mildew infection induced an increased polycyclism during the growing season in oakseedlings, which made them less resistant to winter frosts. Predictive phenological models will have toinclude the chilling phase which conditions dormancy breaking. Although the lack of chilling is not yet alimiting factor, the current trend in increasingly advanced budburst will certainly be slowed or even reversedin the middle of the century at low elevation, in the southern margin of the distribution area of Q. petraea.

In dieser Arbeit wurden die Veränderungen der agrarklimatologischen Bedingungen im Zuge des Klimawandels für ausgesuchte Sauerkirschanbauregionen in Europa und Nordamerika untersucht. Es wird auf veränderte Risiken (Spätfrost, Hitzewellen, Wassermangel) hingewiesen, die durch nachhaltige, praxisorientierte und ökonomisch vertretbare Anpassungsmaßnahmen (Überdachung, Frostschutz, Bewässerung, Anbausystem, Wahl der Sorte und Unterlage, etc.) begrenzt werden können. Der Klimawandel kann neben Risiken aber auch Chancen für den Sauerkirschanbau eröffnen. Höhere Temperaturen und eine längere Vegetationsperiode können regional differenziert zu günstigeren Anbaubedingungen führen. Ein besonderer Schwerpunkt wurde auf die Entwicklung phänologischer Modelle gelegt, mit denen Veränderungen im Entwicklungsrhythmus der Sauerkirschgehölze analysiert werden konnten. Dafür wurden acht Modelle zur Vorhersage des Blühbeginns und Blühendes entwickelt. Weitere phänologische Stadien konnten mit dem Modell von Zavalloni et al. (2006) berechnet werden. Die Untersuchungen haben ergeben, dass sich der Blühbeginn unter geänderten Klimabedingungen verfrüht, aber nur geringe Verkürzungen der Zeiträume zwischen den phänologischen Stadien zu erwarten sind. Zu den gefürchteten Witterungsschäden im Obstbau gehört Spätfrost, der zu hohen Ertragsverlusten führen kann. Im Zuge des Klimawandels können sich die Häufigkeit und Stärke der Fröste ändern. Die Frostwahrscheinlichkeit während der untersuchten Entwicklungsphasen von Sauerkischgehölzen könnte in diesem Jahrhundert in Rheinland-Pfalz und Eau Claire abnehmen, während sich die Verhältnisse in den anderen Anbaugebieten nur geringfügig ändern. In einem zweiten Schritt wurden die Ertragsverluste durch Frost bestimmt. Hierbei hat sich ergeben, dass die Frostschäden in den untersuchten Anbauregionen wahrscheinlich geringer werden. Allerdings differieren die Ergebnisse zwischen den Berechnungen mit beobachteten und modellierten Temperaturen oft stark. / This thesis investigates the changes in agro-climatic conditions for selected growing region in Europe and North America under current and future climate conditions. The overall aim of the study was to identify possible risks (spring frosts, heat waves, water shortages), which can be limited by sustainable, practically oriented and economically viable adaptation measures (hail- and frost-protection, irrigation, cultivation system, choice of variety and rootstock). Besides risks, climate change can provide new opportunities. Higher temperature levels and extended growing season lengths could regionally differentiated improve the growing conditions. Particular focus was given to developing phenological models, used to investigate shifts in spring phenology of sour cherry trees due to climate change. Therefore, eight models to predict the beginning and end of blossom were optimized and validated. Further phenological stages were calculated with the model by Zavalloni et al. (2006). The results show an earlier onset in the beginning of sour cherry blossom under future climate conditions, while the length of the period between the phenological stages only shortens slightly. Spring frosts are feared weather hazards in orchards which can cause substantial yield losses. The changing climate conditions could influence the frequency and strength of spring frosts. In the course of this century the spring frost probability is likely to decrease in Rhineland-Palatinate and Eau Claire, while only slight changes are expected in the other growing regions. In the second step, yield losses caused by spring frost were calculated. The frost damages on sour cherries in the investigated growing regions will probably decrease. However, the yield losses calculated with observed and modeled temperatures often differ strongly.