Thesis (MScConEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Heuweltjies are below ground termitaria found along the west coast and the south-western and -eastern Cape. They traversing different climates, soil and vegetation types within the Succulent Karoo and Fynbos biomes. From a birds eye view, heuweltjies appear as near-circular landscape features, demonstrating clear difference in vegetation structure to their surroundings. A study of aspects of the structure and function of heuweltjies, mima-like mounds of south-western South Africa was undertaken. The main aim of the study was to investigate topsoil properties and processes and vegetation structure and the ecophysiology of plants growing on these mounds, and compare it to areas off these patches. Four study sites across a rainfall gradient were chosen for soil and vegetation studies (two within the Succulent Karoo and two at the Fynbos biome). Ten sampling sites on heuweltjies and 10 off heuweltjie (interpatch) were chosen at each study site for these analyses. Soils samples from the top 10 cm were analysed for total nitrogen (N) and carbon (C) content, phosphorus (P) concentrations, particle-size distributions, pH and electrical conductivity (related to salinity). Soil biogeochemistry studies (i.e. potential N mineralization, potential soil respiration and phosphatase activity) were also done in the laboratory. In the field, the cover of soil cryptogams, selected plant growth forms and selected physical variables at each site, on and off heuweltjies, were estimated on 1m2 grids. Two of the study sites, one in the Succulent Karoo and one in Fynbos, were chosen for field measurements of stomatal conductance, predawn and midday xylem water potentials of two growth forms (deciduous and evergreen non-succulent shrubs) at selected times in the duration of the study. Leaf samples were taken to make once-off measurements of specific leaf area, C and N isotope compositions (δ13C, δ15N), and foliar N content. Furthermore, a fertilization experiment that has been running at the Tierberg Karoo Research Centre (Succulent Karoo) since 1997, where 10g m-2 of N have been added to interpatch vegetation twice annually, was included in the stomatal conductance and xylem water potential studies. The aim of including the fertilization experiment was to ascertain whether interpatch vegetation will eventually resemble heuweltjie vegetation in ecophysiology following N fertilization. Soil water probes were inserted, 10 cm deep, on one on heuweltjie and one off heuweltjie site for the long-term estimation of gravimetric water content and temperature at the Tierberg Karoo Research Centre. Heuweltjie soils were found to be hotspots for nutrients and biogeochemical activity. They had elevated levels of total % C, % N and available P (mg kg-1) compared to surrounding interpatch soils. pH and electrical conductivity (μS cm-1) of these soils were also high compared to interpatch areas. Heuweltjie soils have higher silt content and retain more water, and for a longer period following a rainstorm. Potential soil respiration, potential N mineralization and alkaline and acid phosphatase activity were generally higher on heuweltjies.Cover of the selected plant growth forms differed little between heuweltjies and the surrounding vegetation but site differences were observed. Heuweltjies differed from interpatches in the cover of soil cryptogams, with higher cover of mosses and lower cover of lichens on mounds. There was higher cover of plant litter and termite frass on the heuweltjies.There was a decrease in soil available P and increase in non-succulent shrub cover from low to high rainfall areas. On the other hand no significant differences were found in the xylem water potential of interpatch and heuweltjie plants at either of the study sites. At the Tierberg Karoo Research, stomatal conductance of interpatch plants was higher and water use efficiency (δ13C) lower compared to that of heuweltjie plants suggesting some level of water stress for heuweltjie plants at this site. Here, heuweltjie plants also had higher foliar N, lower C/N ratio values, signs of high photosynthetic potential and highly decomposable litter and higher δ15N. At Jonaskop, stomatal conductance and water use efficiency did not differ between heuweltjies and interpatch plants. There were also no differences in foliar N concentrations, C/N ratios and δ15N between heuweltjie and interpatch plants at this site. Plants growing in high N plots (the fertilizer plots) had higher xylem water potential and more variable stomatal conductance than those growing in control plots. The results of this study have shown heuweltjies to be hotspots for nutrients and biogeochemical cycling, and given enough water, will be ideal patches for plant growth. In the Succulent Karoo, high salinity (and finer textured soils) on the heuweltjies may contribute to water stress during dry periods, and together with disturbance, provide bottom-up controls on plant physiology, and ultimately, vegetation structure. In the Fynbos, plants may be limited by nutrients on heuweltjies, possibly because of increased interspecific competition, while increased rainfall may also lead to more nutrients leaching from the topsoils. The results presented are especially relevant to restoration programs, and may shed some light on restoration trajectories after overgrazing, cultivation and mining activities. / AFRIKAANSE OPSOMMING: Heuweltjies is ondergrondse termitaria wat langs die weskus, die suid-wes en oos Kaap van Suid Afrika voorkom. Hulle kom voor onder verskillende klimaatstreke, grondtipes en planttipes wat binne die Sukkulente Karoo en Fynbos biome voorkom. Vanuit die lug uitgesien, verskyn heuweltjies as sirkelvormige landskapseienskappe, wat duidelike verskille in plant struktuur en die omringende omgewing demonstreer. ʼn Studie van aspekte van struktuur enfunksie van ʼn heuweltjies, mima-agtige hope vansuidwestelike Suid-Afrikais onderneem. Die hoofdoel van die studie was om die eienskappe van oppervlakgrondeen -prosesse, plant struktuur, en die ekofisiologie van plante wat op heuweltjies groei te ondersoek, en dit te vergelyk met areas af van hierdie kolle. Vier studieareas wat oor „n reënvalgradient strek is gekies vir grond en plantegroei studies (twee binne die Sukkulente Karoo en twee binne die Fynbos biome). Tien monsterareas op heuweltjies en 10 af van heuweltjies (omringende areas) is gekies binne elke studiearea vir die bogenoemde analises. Grondmonsters van die boonste 10 cm van die grond is geneem en geanalieseer vir totale stikstof (N) en koolstof (C), fosfor (P) konsentrasies, gronddeeltjiegrootte, pH, en elektriese geleidingsvermoë, (hou verband met soutgehalte). Grond biogeochemie studies (d.i. potensiële stikstof mineralisasie, potensiële grond respirasie en fosfatase aktiwiteit) is ook in die laboratorium uitgevoer. In die veld was die dekking van grond kriptogame, geselekteerde plant groeivorms en fisiese veranderlikes by elke lokaliteit, beide op en van heuweltjies op 1m2vierkante bereken. Twee studie lokaliteite, een in die Sukkulent Karoo en een in die Fynbos, is gekies vir veld metings van huidmondjiegeleiding, voor dagbreek en middag xileem potensiale van twee groei vorms (bladwisselende en immergroen nie-sukkulente struike) op geselekteerde tye gedurende die studie. Blaarmonsters is geneem om eenmalige metings te maak van die spesifieke blaararea, C en N isotoop komposisies (δ13C, δ15N), en blaar N inhoud. Verder is „nbemestingseksperiment wat by die Tierberg Karoo Navorsing Sentrum (Sukkulente Karoo) loop sedert 1997, waar 10gm-2 van N jaarliks twee keer bygevoeg word by die plante wat tussen heuweltjies groei ingesluit in die stomata geleiding en xileem water potensiaal studies. Die doel van die bevrugting eksperiment was om vas te stel of die omliggende plante (af van heuweltjies) uiteindelik soos die van die heuweltjiessal lyk in terme van ekofisologie nadat dit met stikstof bemes is. Grondwater monitoreringsapparaat was ingesit (10cm diep) op een op heuweltjie en een lokaliteitaf van die heuweltjie vir die langtermyn bepaling van gravimetriese water inhoud (m3m-3) en temperatuur by die Tierberg Karoo Navorsing Sentrum. Daar is gevind dat grond op heuweltjies “skerpkolle” is vir voedingstowwe en biogeochemiese aktiwiteit. Hulle het ook verhoogte vlakke van totale %C, % N, en beskikbare P (mg kg-1) teenoor die omliggende areas om die heuweltjies. pH en elektriese geleidingsvermoë (μS cm-1) van hierdie gronde was ook hoër in vergelyking met die omliggende areas. Heuweltjie grond het „n hoër sout inhoud gehad en behou meer water vir ʼn langer periode na ʼn reënstorm. Potensiële grond respirasie, potensiële stikstof mineralisasie, en alkaliese en suur fosfatase aktiwiteit is oor die algemeen hoër op heuweltjies. Die voorkoms van die geselekteerde plant groeivorms verskil min tussen heuweltjies en die omliggende omgewing, maar verskille tussen studie areas is opgemerk. Heuweltjies het verskil van areas af van heuweltjies in die voorkoms van grond kriptogame, met ʼn hoër voorkoms van mosse en ʼn laer voorkoms van ligene op die heuweltjies. Daar was hoër voorkoms van plantafvalmateriaal en termiet uitwerpsel op die heuweltjies. Daar was ʼn afname in grond P (mg kg-1) en ʼn toename in nie-sukkulente struik bedekking van lae tot hoë reënval areas. Daar was geen verskil in die xileem water potensiaal van plante op die heuweltjies of af van die heuweltjies by enige van die studie lokaliteite nie. By die Tierberg Karoo Navorsing Sentrum was huidmondjie geleiding van plant in die areas tussen heuweltjies hoër en die water gebruik doeltreffendheid (δ13C) laer in vergelyking met die van die heuweltjie plante, wat op„n sekere vlak waterstres dui in heuweltjie plante by hierdie studiearea. Hier het heuweltjie plante ook hoër blaar N, laer C/N waardes, tekens van hoër fotosintetiese potensiaal en hoogs afbreekbare afvalmaterialgehad asook hoër δ15N. By Jonaskop het huidmondjie geleiding en water gebruik doeltreffendheid nie verskil tussen heuweltjie en omliggende plante nie. Daar was ook geen verskille in blaar N konsentrasies, C/N verhoudings en δ15N tussen heuweltjie en omliggende plante by hierdiestudiearea nie. Plante wat groei in hoë stikstof plotte, het hoër xileem water potensiaal (minder stres) en meer veranderlike stomatal geleiding as die plante wat in die kontrole plotte groei. Die resultate van die studie het getoon dat heuweltjies “skerpkolle” is van voedingstowwe en biogeochemiese siklusse, en gegewe genoeg grondwater, sal ideale areas wees vir die groei van plante. In die Sukkulente Karoodra hoë soutgehalte (en fyner grond teksture) op die heuweltjies by tot water stres gedurende droë tye, en saam met versteurings dra dit by tot grond tot plant kontrole op plantfisiologie, en uiteindelik plant gemeenskapsstruktuur. In die Fynbos word plante op die heuweltjies beperk deur te min voedingstowwe, moontlik omdat daar ʼn toename is in intraspesifieke kompetisie, terwyl hoër reenvalkan lei tot hoër loging van voedingstowwe vanuit die bogrond. Die resultate wat hier gerapporteer word is veral relevant vir restourasieprogramme, en mag lig werp op restourasie trajekte na oorbeweiding, aanplanting van gewasse en mynbou-aktiwiteite.

Les écosystèmes forestiers méditerranéens présentent des espèces d'arbres vivant en limite sud de leur aire de répartition sensibles aux stress climatiques et des espèces vivant au coeur de leur aire de répartition et a priori adaptées à ces mêmes stress. Ces contrastes interrogent sur la diversité potentielle des mécanismes régulant la dynamique des populations de leurs parasites, et en retour l'impact des parasites sur la dynamique de leurs hôtes. Les scolytes constituent un bon modèle pour l'étude de ces interactions hôte-parasite car ils alternent des phases endémiques et épidémiques. Nous avons développé une approche pluridisciplinaire couplant la caractérisation de traits écophysiologiques et dendrométriques impliqués dans la résistance des populations d'arbres aux attaques de scolytes avec la caractérisation de facteurs écologiques clés pour la démographie des scolytes. Chez le pin d'Alep, T. destruens est présent à un niveau endémique mais des attaques subsistent dans des patchs d'arbres formés par des arbres attaqués et morts suite aux attaques, des arbres attaqués qui ont résisté et des arbres non attaqués. Des stratégies de dispersion locale différentes selon les deux grandes phases du cycle de T . destruens semblent favoriser l'exploitation d'une ressource peu abondante. Chez le sapin pectiné, nous avons montré qu'une communauté abondante de scolytes s'attaque à des arbres déjà affaiblis par des sécheresses répétées et présentant un mauvais état sanitaire et une croissance en baisse. Ces deux écosystèmes forestiers permettent de mieux appréhender les mécanismes impliqués dans les interactions plantes-insectes dans un contexte de changement global. / Mediterranean forest ecosystems have both trees living in their southern range and being sensitive to climatic stress and tree species living in the core of their range and being non sensitive to the same stress. These contrasts in tree populations questioned about potential contrasts in their interrelationships with their parasites and on the impact of that parasites have on their host in turn. Bark beetles are a relevant model to study such host-parasite interactions because they alternate endemic and epidemic phases. We developed a multidisciplinary approach combining the characterization of ecophysiological and dendrometrical traits involved in resistance of tree populations to bark beetle attacks with this assessment of key ecological factors involved in bark beetles demography. We focused on the two following contrasted Mediterranean ecosystems in South-Eastern France: a healthy Aleppo pine interacting with a bark beetle population at an endemic state and a declining population of the Silver fir interacting with a bark beetle community at an epidemic state. Our results suggested that this Aleppo pine population, the pine shoot beetle T. destruens showed low abundance levels. All attacks remained in patches formed by dead trees following the attacks. T. destruens dispersal strategies seem to favor the exploitation of a scarce resource. On silver fir, we showed a bark beetle community attacking trees already weakened by repeated droughts and with poor health status and low growth. The study of these two contrasted forest ecosystems allowed us to shed some critical light on the mechanisms involved in plant-insect interactions in the context of global change.

Les lagunes côtières sont des écosystèmes semi-fermés à l'interface de la terre et des océans et sous l'influence de ces deux compartiments. De par ces caractéristiques, elles sont soumises à de fortes variations spatiales et saisonnières de leurs ressources trophiques. De par leur nature fermée et peu profonde, elles vont amplifier la force des processus qui conditionnent la disponibilité des ressources alimentaires et par conséquent l'écophysiologie des organismes benthiques qui composent les assemblages associés. Ce travail de thèse se propose de caractériser l'écophysiologie trophique de deux espèces de bivalves filtreurs (Nodipecten subnodosus et Spondylus crassisquama) au sein d'une lagune du Pacifique Nord-est (Basse Californie, Mexique). Une approche mufti-tissus et multi-traceurs (isotopes stables, acides gras, stérols et analyse isotopique sur acides gras) a été adoptée afin de pouvoir caractériser l'écologie trophique des espèces, mais aussi leurs régulations physiologiques face aux variations environnementales. Deux facteurs clés se sont révélés largement explicatifs de la variabilité spatio-temporelle observée dans le régime alimentaire : la période (hiver vs été) et la localisation dans la lagune par rapport à l'embouchure. L'importance des apports de phytoplancton océanique a été démontrée dans l'ensemble de la lagune, avec une contribution plus importante de diatomées océaniques notamment en période estivale pour les individus à proximité de l'embouchure. Par ailleurs, les bivalves en fond de lagune semblaient davantage dépendre de la matière organique locale, en particulier issue du recyclage bactérien, voire de la production des herbiers de phanérogames. Ces contrastes spatiaux se reflétaient également dans la composition des membranes cellulaires, mettant en évidence les interactions entre apports trophiques et régulations métaboliques des compositions en acides gras chez ces deux bivalves. Cette thèse présente une approche intégrée dédiée à la compréhension des variations spatiales et saisonnières des ressources trophiques d'un écosystème lagunaire, ainsi que leurs répercutions trophiques et physiologiques sur les assemblages benthiques. / Coastal lagoons are semi-enclosed ecosystems at the interface between land and ocean and under the influence of these two compartments. Owing to these characteristics these ecosystems are submitted to spatial and seasonal variations in their trophic resources. Because of their enclosed and shallow nature, lagoons amplify the intensity of processes conditioning the availability of food resources and consequently the ecophysiology of the benthic organisms which compose associated assemblages. This thesis aims to characterize the trophic ecophysiology of two species of suspension feeding bivalves (Nodipecten subnodosus and Spondylus crussisquomo) within a lagoon of Northeast Pacific (Baja California, Mexico). A mufti-tissue and multi-tracer approach (stable isotopes, fatty acids, sterols, and isotope analysis on fatty acids) was used in order to characterise the trophic ecology of both species, as well as their physiological regulations against environmental variations. Two key factors have been found to explain the observed spatio-temporal variability: the period (winter vs summer), and the location in the lagoon with respect to the distance from the mouth. The importance of oceanic phytoplankton inputs has been highlighted throughout the lagoon, with a greater contribution of oceanic diatoms particularly during the summer period for individuals near the mouth. Bivalves from the inner lagoon seemed more dependent of local organic matter, in particular resulting from bacterial recycling, or even from the production of eelgrass. These spatial contrasts were also reflected in the composition of cell membranes, highlighting the interactions between trophic contributions and metabolic regulation of fatty acid composition in both bivalves. This thesis presents an integrated approach to understand spatial and seasonal variations of the trophic resources of a lagoon ecosystem, as well as their trophic and physiological repercussions on benthic assemblages.

Dans le contexte actuel de changement global et particulièrement de réchauffement climatique et de pollution chimique chronique, se pose la question de la vulnérabilité des écosystèmes côtiers et notamment des populations d’invertébrés filtreurs jouant un rôle structurant dans la plupart de ces écosystèmes. Dans ces travaux de thèse, une approche couplée d’écophysiologie et de génomique fonctionnelle a été mise à profit afin de mieux comprendre les processus moléculaire, cellulaire et physiologique de réponse à une contamination chimique chronique modérée et d’évaluer la capacité à faire face à une augmentation de température chez des populations naturelles de moules bleues (Mytilus spp.) de la Rade de Brest. Les résultats obtenus révèlent qu’une contamination chronique modérée induit des réponses adaptatives au niveau subcellulaire chez les moules exposées, prévenant ainsi l’apparition de souffrances physiologiques et permettant aux populations de se maintenir dans un environnement variable. Ces réponses impliquent en particulier, une activation des mécanismes de défense cellulaire (métabolisme énergétique et défenses antioxydantes) et d’élimination des xénobiotiques. Par ailleurs, l’exposition à une augmentation de température en conditions expérimentales ne met pas en évidence de sensibilité particulière au stress thermique chez les moules provenant d’un site exposé à une contamination chronique modérée. En revanche, les résultats indiquent que ces dernières pourraient avoir une plus grande capacité à compenser grâce à des réponses adaptatives, les effets délétères générés par une augmentation de température. Cependant, le fort coût énergétique généré par la contamination chimique ainsi que les effets importants du stress thermique mis en évidence dans ces travaux indiquent que la combinaison de ces deux sources de stress pourrait provoquer des dysfonctionnements métaboliques et représenter à l’avenir, une menace pour les populations naturelles de moules bleues. Ces travaux de thèse ont également contribué au développement de nouvelles méthodologies permettant respectivement, de quantifier des contaminants environnementaux dans des tissus biologiques marins, d’étudier des réponses génomiques précoces de stress et de mesurer des paramètres physico-chimiques in situ. Ces méthodologies pourront contribuer à améliorer les performances du diagnostic de l’état de santé des populations naturelles de moules et au delà, d’espèces-sentinelles de mollusques bivalves dans un contexte de contamination chimique mais également de changements climatiques. / In the current context of chronic chemical pollution and on-going climate change, coastal ecosystems, and in particular keystone filter-feeding bivalve populations inhabiting them, appear vulnerable. In this thesis, an approach coupling ecophysiology and functional genomics was used to study the molecular, cellular and physiological responses of wild blue mussel populations of the Bay of Brest to a moderate chronic chemical contamination, and to assess the ability of these populations to face a heat stress. Results indicate a moderate chronic chemical contamination induces adaptive responses in wild mussel populations from the Brest harbour area, which prevents severe physiological disturbances and sustain long-term population survival. These responses include an activation of cellular stress response [energetic metabolism and antioxidant defences) and xenobiotic elimination mechanisms. Furthermore, experimental heat stress exposure does not highlight a higher sensitivity to a temperature increase in mussels sampled in a moderately contaminated area but suggests that these mussels could have a better ability to offset the adverse effects of heat stress thanks to adaptive responses. However, the high energetic cost of chemical contamination and the strong effects of heat stress presented in this work, suggest combined chemical and heat stress could be a future threat for wild blue mussel populations. This work also contributes to the development of new methodologies to, respectively, quantify environmental contaminants in marine biota, study early warning genomic stress responses and to survey physicochemical parameters in situ. These methodologies contribute to improving the health diagnostics of natural mussel populations and thus, appear as useful tools to assess health of bivalve sentinel species populations in biomonitoring studies, in a context of chemical contamination and climate change.

Prior to European settlement, native prairie dominated the landscape of the Willamette Valley. Today, due to urbanization, agriculture, and the cessation of burning, only isolated remnants of these grasslands still exist. In response to conservation concerns, there has been a move to restore the remaining prairies in the Willamette Valley, and prescribed burning and sowing native seed are often top candidates for grassland restoration. However, the effects of burning on native seedling establishment and the spread of weedy exotics are largely unknown. In this study, I investigated how prescribed burning affects native and exotic species seedling establishment on three upland prairie vegetation types in the Willamette Valley. The general approach was to sow a known number of seeds from several native and exotic grassland species into experimentally manipulated plots, designed to separate the effects of litter removal from the other effects of burning, and to monitor seedling densities. Germinability and dormancy characteristics of the sowed seeds were also addressed. An additional study focused on the fire temperatures at soil surface in three grassland vegetation types and two burn sizes. Burning increased the establishment of most or all of the sown native species in the two low quality, exotic grass sites. Exotic seedling establishment also tended to increase, but did not differ significantly from unburned plots for most species tested. On the higher quality, native bunchgrass site, burning did not significantly improve native species establishment, but did significantly increase the establishment of short-lived exotic species over those in unburned plots. The germination and dormancy characteristics of the native and exotic species tested indicate that grasses, both native and exotic, are more likely than forbs to be non-dormant in the autumn following dispersal. Forbs, especially native forbs tend to require cold-stratification for maximum germinability. During grassland fire, temperatures at soil surface were relatively cool. Fire temperature intensity was highest in the higher quality native bunchgrass vegetation. These burns reached higher temperatures significantly closer to the soil surface than the plot burns in lower quality sites dominated by annual or perennial exotic grasses. Average temperatures in a two hectare broadcast burn and in replicated 2m x 2.5m plot bums in an annual exotic grassland were very similar. Prescribed burning can be an excellent tool for the restoration of low-quality upland prairies when combined with sowing native seeds in the fall. However, on high-quality prairie, prescribed burning may be a poor restoration choice for promoting native seedlings, as burning promoted weedy species without enhancing native seedling establishment. / Graduation date: 1997

Resprouting is an important means of plant regeneration especially under conditions that do not favour regeneration through seeding such as frequent disturbances, low productivity, unfavourable soil conditions, extreme cold and limited understorey light availability. Sprouts may be advantageous over seedlings because they have higher survival and growth rates than seedlings, since they use resources from parent plants unlike seedlings that have to acquire their own resources. Resprouting is well documented for ecosystems that experience severe disturbances that damage aboveground biomass. For example, resprouting is important for plant persistence against fire in fire-prone savannas and Mediterranean shrub-lands, and hurricanes and cyclones in tropical forests. In these ecosystems, resprouting often results in multi-stemming, because this dilutes the risk of damage among many stems, improving the chances of individual survival. This study was conducted at coastal dune forest at Cape Vidal in north-eastern South Africa, where there is a high incidence of multi-stemmed trees due to resprouting in response to chronic disturbances of low severity. This study examines (1) the importance of resprouting to tree survival and dynamics in an environment where disturbance severity is low but pervasive, and (2) how this resprouting strategy differs from the more familiar sprouting response to severe disturbances such as fire and hurricanes. Analysis of the relationship between multi-stemming and a number of disturbances potentially causing multi-stemming revealed that stem leaning and substrate erosion were the most important disturbances associated with multi-stemming. There were fewer multistemmed trees on dune slacks that had a stable substrate and were protected from sea winds than on dune crests and slopes that had unstable substrate and were exposed to sea winds. Trees resprouted and became multi-stemmed from an early stage to increase their chances of survival against leaning caused by strong sea winds and erosion, and occasional slumping of the unstable dune sand substrate. These low severity disturbances are persistent and are referred to as chronic disturbances in this thesis. As a result of these chronic disturbances, both single and multi-stemmed trees had short stature because taller individuals that emerged above the tree canopy would be exposed to wind damage. Under chronic disturbances plants may manifest a phylogenetically determined sprouting response. However, in this study resprouting and multi-stemming were the results of the tree-disturbance interaction and not a property of a plant or species and were not phylogenetically constrained. Because the disturbances are predominantly of low severity, leaning trees were able to regain the vertical orientation of the growing section by turning upward (a process referred to as ‘turning up’ in this study) and hence survive without resprouting. Species that were prone to turning upward had a low incidence and degree of leaning of their individuals, low frequency of loss of primary stems and high abundance of individuals. Although turning up is less costly to the individual than resprouting, it could only be used by leaning trees that had small angles of inclination and were not eroded. High intensities of the latter require that individuals resprout to survive. The form and function of resprouting varied between seedlings and juvenile and mature trees. Resprouting in seedlings resulted in a single replacement shoot, unlike sprouting in juvenile and mature trees that resulted in multi-stemmed trees. Like sprouting in juvenile and mature trees, sprouting in seedlings was not phylogenetically constrained. Resprouting in seedlings increased seedling persistence; hence species with more sprout seedlings had larger individual seedlings and seedling banks. Resprouting in seedlings increased the chances of seedling recruitment, whereas resprouting in juvenile and mature trees increased the chances of an established plant maintaining its position in the habitat. After disturbances of high severity, which destroy the photosynthesizing parts, plants resprout using carbohydrates stored below- or above ground. In this study, good resprouters stored more carbohydrates both below- and above ground than poor resprouters. The carbohydrates were mobilized for resprouting after disturbance. More carbohydrates were stored in stems than in roots because the prevailing disturbances were mostly of low severity and hence above ground resources were readily available. Similar to storage by plants in severely disturbed habitats, carbohydrates were stored by reserve formation, which competes for carbohydrates with growth and maintenance and forms permanent storage, rather than accumulation, which temporarily stores carbohydrates in excess of demands for growth and maintenance. Stored carbohydrates are not necessary for resprouting of plants after disturbances of low severity because they can resprout using resources remobilized directly from the disturbed photosynthesizing parts. However, in this study, stored carbohydrates served as a bet-hedge against occasional severe disturbances that occurred in addition to chronic disturbances. Allocation of carbohydrates to permanent storage diverts them from growth and reproduction and hence good resprouters had lower growth rates, seed output, seed size and seedling recruitment than poor resprouters. However, the costs of these traits that resulted in low recruitment from seed by good resprouters, were compensated for by high persistence of established individuals of good resprouters through recruitment of sprout stems. This study demonstrates that resprouting is not only advantageous in severely disturbed environments, but also in environments where disturbances are of low severity but nevertheless confer an advantage on individuals that persist. Thus in forest environments where aboveground biomass is seldom destroyed and individuals are relatively long-lived, resprouting can confer significant fitness and selective advantage on individuals. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Made available in DSpace on 2016-08-12T19:18:34Z (GMT). No. of bitstreams: 1 RomuloMOF_TESE.pdf: 1235930 bytes, checksum: d0668b69077e4b615b5b9b7e4cd858f6 (MD5) Previous issue date: 2015-07-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The cowpea crop has great importance for the Brazilian Northeast, especially for the poorest population. One of the major problems encountered for this crop is drought stress caused by erratic rainfall, coupled with the high temperatures common in this region. The no-tillage system has features, such as reduction of soil water evaporation, higher water retention and lower soil temperature fluctuations, and can be a way to minimize the water stress in a cowpea crop. Two experiments were carried out at the experimental garden in the Departamento de Ciências Vegetais of the Universidade Federal Rural do Semi-Árido (UFERSA), in Mossoró city, RN, with the aim of evaluating the use and use efficiency of water, and the ecophysiological traits of cowpea plants under water shortage in tillage and no-till cropping systems. The first experiment was conducted in a randomized complete blocks design with subsampling and four replications. The treatments were the two cropping systems (tillage and no-till), and the subsamples were the six periods of irrigation suspension (2; 6; 10; 14; 18 e 22 days), applied at the beginning of the flowering stage. The plants parts dry mass and the leaf area 64 days after sowing (DAS), and the grain production, water use and water use efficiency at that 70 DAS were evaluated. For the second experiment, it was used a randomized complete blocks design with subsampling and sub-subsampling, with four replications. The treatments were the cropping systems (tillage and no-till), and the subsamples were three water availability conditions (no shortage, moderate shortage and severe shortage), and the sub-subsampling were the evaluation periods. Plants dry mass, leaf areas, photosynthesis, stomatal conductance, transpiration, lowest leaf CO2 internal concentration and leaf water potential were evaluated. In the first experiment, it was observed that the no-till system is promising for the cowpea crop, with better grain production and better water use efficiency. In this system, the cowpea cultivation was possible even under a moderate water shortage. Prolonged water shortage periods did affect the dry mass accumulation, grain yield and water use efficiency. In the second experiment, the water shortage affected all the studied variables, with the exception of the leaves water potential. The cowpea fully recovered all physiological traits after moderate and severe water shortage. Stomatal closure was the main mechanism of resistance to water shortage, and the cowpea may be considered as a water-saving species. The cropping system did not affect the photosynthesis rates. The plants had more dry weight and leaf areas at the no-till system / A cultura do feijão-caupi possui grande importância para a região Nordeste, principalmente para a população mais carente. Um dos grandes problemas encontrados para essa cultura é o estresse hídrico, provocado pela irregularidade das chuvas, aliado a altas temperaturas, comuns a esta região. O sistema de plantio direto possui características como redução da evaporação da água do solo, maior retenção do solo e menores oscilações da temperatura, e pode ser uma forma de minimizar o efeito do estresse hídrico para a cultura do feijão-caupi. Dois experimentos foram conduzidos na horta didática do Departamento de Ciências Vegetais da Universidade Federal Rural do Semi-Árido (UFERSA), no município de Mossoró-RN, com o objetivo de avaliar o consumo, e eficiência de uso da água, bem como as respostas ecofisiológicas de feijão-caupi sob estresse hídrico nos sistemas de plantio direto e convencional. O primeiro experimento foi realizado no delineamento experimental em blocos casualizados completos, no esquema de parcelas subdivididas, com quatro repetições. Nas parcelas, foram avaliados dois sistemas de plantio (convencional e direto) e nas subparcelas, seis períodos de suspensão da irrigação (2; 6; 10; 14; 18 e 22 dias) aplicados no início do período reprodutivo. Foram avaliadas a biomassa das partes das plantas e a área foliar, aos 64 dias após a semeadura (DAS) e o rendimento de grãos, consumo de água e eficiência de uso da água, aos 70 DAS. No segundo experimento, utilizou-se o delineamento experimental em blocos casualizados completos, no esquema de parcelas subsubdivididas, com quatro repetições. Nas parcelas, foram avaliados dois sistemas de plantio (direto e convencional), nas subparcelas, três condições hídricas (sem estresse, estresse moderado e estresse severo) e nas subsubparcelas, períodos de avaliação. Foram determinados: área foliar, matéria seca total, fotossíntese, condutância estomática, transpiração, concentração interna de CO2 e potencial hídrico foliar. No primeiro experimento, constatou-se que o sistema de plantio direto foi promissor para cultura do feijão-caupi, apresentando maior rendimento de grãos e maior eficiência de uso da água. Nesse sistema de plantio, foi possível o cultivo de feijão-caupi, sem perdas, mesmo com períodos de veranico moderados. Veranicos prolongados afetaram negativamente o acúmulo de biomassa, rendimento de grãos e eficiência de uso da água. No segundo experimento, o estresse hídrico afetou todas as variáveis avaliadas, com exceção do potencial hídrico foliar. O feijão-caupi apresentou recuperação de todas as características fisiológicas após estresse hídrico moderado e severo. O fechamento estomático foi o principal mecanismo de resistência à seca, sendo o feijão-caupi uma espécie conservadora. Os sistemas de plantio não afetaram as taxas de fotossíntese. O sistema de plantio direto promoveu maior acúmulo de biomassa e de área foliar

Orientador: Jose Teixeira Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-15T15:44:54Z (GMT). No. of bitstreams: 1 Tonello_KellyCristina_D.pdf: 3209931 bytes, checksum: ad807b85c48d80b43bb9c5e89fb27160 (MD5) Previous issue date: 2010 / Resumo: O crescimento e o desenvolvimento dos vegetais é conseqüência de vários processos fisiológicos controlados pelas condições ambientais e características genéticas de cada espécie vegetal. Este estudo teve por objetivo caracterizar o comportamento ecofisiológico da transpiração (E) e condutância estomática (Gs) de dois clones de Eucalyptus grandis x Eucalyptus urophylla (C041 e P4295) sob diferentes condições de disponibilidade hídrica no solo e em função de variáveis ambientais como radiação global (Rg), radiação fotossinteticamente ativa (Qleaf) e déficit de pressão de vapor da atmosfera (DPV). As aferições foram realizadas ao longo do período de fevereiro de 2007 a agosto de 2008 em três escalas de estudo designadas como vaso, parcela e bacia hidrográfica. Medidas de potencial hídrico antemanhã (?pd) foram realizadas para o acompanhamento das disponibilidades hídricas no solo. Após o conhecimento do comportamento ecofisiológico dos clones em função das variáveis ambientais e ?pd, buscou-se relacionar as respostas obtidas na escala vaso com as escalas parcela e bacia hidrográfica por meio de modelos ecofisiológicos desenvolvidos para a mudança de escala ao nível de folha. De acordo com os resultados, as variáveis ecofisiológicas estiveram diretamente associadas às variáveis ambientais e ao ?pd tanto para o clone C041 quanto para o clone P4295. Foram observados entre os clones comportamentos ecofisiológicos distintos quando associados à Qleaf, DPV e ?pd. Os clones apresentaram-se diferentes na amplitude de resposta de E e Gs em função de Qleaf e DPV entre as escalas, porém, observou-se a mesma tendência de comportamento, com exceção da relação Gs x DPV para o clone C041, entre escala vaso e parcela/bacia hidrográfica. Os modelos propostos para a mudança de escala de folha para folha mostraram-se satisfatórios, principalmente nas relações envolvendo a radiação fotossinteticamente ativa. Contudo, não apresentaram bons resultados para a extrapolação das respostas ecofisiológicas de Gs em função do DPV / Abstract: The growth and development of plants is a consequence of several physiological processes controlled by environmental conditions and genetic characteristics of each plant species. This study aimed to characterize the ecophysiological behavior of transpiration (E) and stomatal conductance (Gs) of two clones of Eucalyptus grandis x urophylla (C041 and P4295) under different soil water conditions and according to environmental variables such as global radiation (Rg), photosynthetic active radiation (Qleaf) and a vapor pressure deficit of the atmosphere (VPD). The measurements were performed during the period February 2007 to August 2008 on three scales of study designated as a pot, plot and watershed. Predawn leaf water potential (?pd) measurements were performed to monitor water availability in the soil. After the knowledge of the ecophysiological behavior of the clones on the basis of environmental variables and ?pd, sought to link the responses obtained in the pots scale with pot and watershed through ecophysiological models developed for scaling up leaf from leaf. According to the results, the ecophysiological behavior were directly associated with environmental variables and the ?pd both to the C041 as for P4295. Were observed among different clones ecophysiological behavior when associated with Qleaf, VPD and ?pd. The clones were different in amplitude of E and Gs as function of Qleaf and VPD between the scales, however, showed the same pattern of behavior, except for Gs x VPD for clone C041 between pot and plot / watershed scale. The proposed models for the scaling up from leaf to leaf were satisfactory, especially in relationships involving the Qleaf. However, they not provided good results for the extrapolation of ecophysiological responses of Gs as a function of VPD / Doutorado / Agua e Solo / Doutor em Engenharia Agrícola

Le compromis d’allocation de l’énergie entre les fonctions concurrentielles de la reproduction et de la maintenance (et à long terme la survie) est largement tributaire de la capacité de l’organisme à acquérir des ressources dans son milieu. Les mécanismes physiologiques sousjacents aux décisions d’acquisition et d’allocation de l’énergie sont actuellement peu connus. Le but de cette thèse est d’étudier le rôle de deux hormones, la corticostérone et la prolactine, dans ces prises de décisions chez un oiseau marin longévif, le manchot Adélie (Pygoscelis adeliae), et ce, pendant une phase couteuse en énergie : la période d’élevage des poussins. Pour ce faire, nous avons conduit des approches expérimentales couplant d’une part la manipulation hormonale (augmentation des niveaux de corticostérone ou diminution des niveaux de prolactine) et la mesure du comportement en mer grâce à l’utilisation d’enregistreurs miniaturisés de l’effort de plongée. Par ailleurs, le budget temps, la condition corporelle, le régime alimentaire (analyses des isotopes stables du carbone et de l’azote) ainsi que le succès de reproduction des individus ont été considérés. A l’échelle de la plongée, nous avons observé des rôles positifs et négatifs de la corticostérone et de la prolactine, respectivement, sur le comportement de recherche alimentaire. De façon contradictoire, il semble que la corticostérone ait eu un effet négatif à plus large échelle (e.g. diminution de la durée des voyages alimentaires). La complexité de l’implication de ces deux hormones dans le compromis entre survie et reproduction est finalement discutée à la lumière de ces résultats. / The trade-off in the allocation of energy between the competitive functions of reproduction and maintenance (and survival in the long term basis) is largely dependent on the capacity of organisms to acquire resources in its environment. However, physiological mechanisms underlying decisions of energy acquisition and allocation are currently poorly known. Theaim of this PhD is to examine the role of two hormones, corticosterone and prolactin, in these decision processes in a long-lived seabird, the Adélie penguin (Pygoseclis adeliae) during an energetically costly period: the chick-rearing stage. To achieve this, we conducted experimental approaches coupling hormonal manipulation (increasing corticosterone levels ordecreasing prolactin levels) and the monitoring of at-sea behaviour by using miniaturised time-depth recorders. Moreover, time budget, body condition, diet (via stable isotopes analyses) and reproductive success of individuals were considered. At the dive scale, we observed positive and negative roles of corticosterone and prolactin on the foraging behaviour, respectively. However on the contrary, it seems that corticosterone had a negative effect at a larger scale (e.g. a decrease in at-sea trip duration). The complexity of the involvement of these hormones in the trade-off between survival and reproduction is discussed in the light of these results.

En horticulture, les effets négatifs du déficit hydrique (WD) sur le rendement peuvent être en partie compensés par des effets positifs sur la qualité des fruits et la stimulation des défenses de la plante face à d’autres stress. L'objectif de la thèse était d'explorer un certain nombre de pistes permettant d'évaluer les effets positifs et négatifs du WD, et d'appréhender les facteurs de variations. Après avoir établi un état des connaissances actuelles des effets du WD sur la qualité des fruits, plusieurs questions ont été abordées: 1) quels sont les effets de WD appliqués à des stades précis du développement de la plante ou du fruit, 2) existe-t-il une mémoire du stress en cas d’alternance de période de WD et de récupération, 3) les défenses de la plante sont-elles stimulées par un WD lors d'une infection par un pathogène, et enfin 4) quelle est la variabilité génétique associée aux réponses au WD au travers des objectifs précédents. Pour cela, plusieurs expérimentations ont été réalisées en serres et en phytotrons. Les parents de la population MAGIC de la tomate (ayant une forte variabilité allélique) ont été étudiés, ainsi que deux tomates commerciales (pour l’étude de l’interaction WD – Botrytis cinerea). Les mécanismes de réponses induits lors du WD ont été caractérisés aux stades végétatif et reproductif à l’échelle de la plante, puis lors des phases de développement du fruit (division cellulaire, expansion cellulaire et maturation). Les stades végétatif et reproductif se distinguent par les mécanismes de gestion du stress oxydatif engendré par le WD. Les plantes végétatives seraient plus affectées au niveau des photosystèmes II alors que les plantes reproductives modulent plutôt leur besoin en eau et sont plus sensibles à l’approche des photosystèmes I. L’impact du WD sur la qualité des fruits diffère en fonction de leurs phases de développement. De forts effets génotypes ont été observés avec une amélioration de la qualité dite gustative (par rapport aux teneurs en sucres et acides) pour un génotype dont les caractéristiques initiales étaient plus faibles que le second génotype testé. L’alternance de périodes de WD et de récupérations constitue un bon compromis entre économie d’eau et adaptation des plantes (via une bonne gestion du stress oxydatif). Cette alternance de stress a des effets neutres à positifs sur les teneurs en sucres des fruits en fonction des génotypes et des réponses très variables pour les teneurs en acides organiques, caroténoïdes et acide ascorbique en fonction des génotypes. L’interaction entre un WD et B. cinerea génère une diminution du ratio C/N associé à une stimulation des défenses de la plante. Cependant l'interaction favorise le développement du pathogène dans les tiges. Cet effet délétère de l'interaction semble lié aux régulations hormonales mises en jeu avec la stimulation de l'ABA (par le WD) et de la voie SA (par B. cinerea et indirectement par le WD) qui sont antagonistes aux voies JA/ET de réponse aux pathogènes nécrotrophes. Toutefois, un effet positif a été observé pour les infections sur feuilles détachées qui constituent un instantané des défenses de la plante, et ce, uniquement pour les plantes déjà infectées sur tige. Ces résultats suscitent de nouvelles interrogations sur la stimulation des défenses de la plante. Ainsi, le WD permet une augmentation du pool de sucres solubles, sans impact notable sur le rendement, avec des effets variables sur les composés secondaires. Le WD permet également dans une certaine mesure de stimuler les défenses de la plante mais de nouvelles recherches sont nécessaires. Enfin, la variabilité génétique des réponses à l’échelle de la plante et du fruit est importante et interagit avec le WD. / In horticulture, yield losses associated to water deficit (WD) could be compensated by positive effects on fruit quality and stimulation of plant to others stresses. The aim of the thesis was to explore a number of questions to assess the positive and negative effects of the WD, and to understand factors variations after setting a current knowledge of the effects of WD quality fruit. The questions were: 1) to characterize the effects of WD applied at specific stages of development of plant or fruit, 2) to understand the stress memory effect by alternating period of WD and recovery, 3) to test the stimulation of plant defences by WD during an infection by a pathogen, and 4) to study the genetic variability associated with responses to WD through the previous objectives. For this, several experiments were conducted in greenhouses and growth chambers. The parents of the MAGIC population of tomato (with rich allelic variability) were studied, as well as two commercial tomatoes (for the study of the interaction between WD and Botrytis cinerea). Plant response mechanisms induced during a WD were characterized in both plant vegetative and reproductive stages, and then during the fruit development stages (cell division, cell expansion and maturation). The plant vegetative and reproductive stages are distinguished by different mechanisms of oxidative stress management generated by WD. Vegetative plants are more affected at the photosystem II while reproductive plants rather modulate their water needs and responses at the photosystem I. The impact of WD on fruit quality differs according to fruit developmental stages. Strong genotypes effects were observed with an important increase in fruit taste quality (according to the concentrations in sugars and acids) for one genotype, which had poorer initial fruit quality than the second. Alternating periods of WD and recovery is a good compromise between water saving and plant adaptation (through proper management of oxidative stress). This alternation of stress has neutral to positive effects on fruit sugar content according to the genotypes and highly variable responses for contents of organic acids, carotenoids and ascorbic acid according to the genotypes. The interaction between a WD and B. cinerea generates a decrease of C/N ratio that can be associated to a stimulation of the pool of plant defence. However, the interaction between B. Cinerea and this WD promote pathogen development in stems. This deleterious effect of interaction seems attributable to hormonal regulation with the stimulation of the ABA pathway (by WD) and the SA pathway (by B. cinerea), which are antagonistic to the JA / ET pathway involved in response to necrotroph pathogens. However, a positive effect was observed for infections in detached leaves of infected plants, detached leaves represent a snapshot of plant defences and these results raise new questions. Overall, these data provide that WD improve fruit taste (sugars and acids) without yield losses but had variables effects on health promoting compounds. WD could permit the stimulation of plant defence but more research is needed. To finish, the genetic variability induced important variability in plant and fruit responses and interact with WD.