O hábito de crescimento influencia o balanço entre o desenvolvimento vegetativo e o reprodutivo das plantas. Este, por sua vez, está diretamente vinculado a diversas variáveis de interesse agronômico, como produtividade e consumo de água. Em tomateiro, existem três hábitos de crescimento conhecidos: determinado, indeterminado e semi-determinado, sendo esse último na verdade determinado, porém com uma extensão do ciclo vegetativo. Cultivares de crescimento determinado são largamente utilizadas para produção de tomates destinados à indústria (molhos e ketchups), e as indeterminadas destinadas ao consumo in natura. Por outro lado, genótipos de crescimento semi-determinado, embora ainda sejam pouco explorados, apresentam-se como ótimas opções tanto para indústria quanto para o consumo in natura. Diante disto, o presente trabalho teve por objetivo avaliar a implicação do hábito de crescimento semi-determinado no desempenho produtivo e na eficiência no uso da água de plantas de tomateiro. Para tal, genótipos com diferentes hábitos de crescimento foram produzidos, por meio de introgressões de variações alélicas que afetam o hábito de crescimento das plantas, no background genético da cultivar miniatura de tomateiro Micro-Tom (MT). A caracterização desses genótipos demonstrou que os materiais de crescimento semideterminado apresentam um atraso no florescimento, emitindo em média uma folha a mais antes da formação da primeira inflorescência. Além disso, verificasse que essas plantas apresentam uma altura intermediária entre genótipos de crescimento determinado e indeterminado, aos 50 dias após a semeadura. Já para características agronômicas, constatou-se um aumento significativo na produtividade e no conteúdo de sólidos solúveis totais (brix) nos frutos dos genótipos de crescimento semi-determinado em comparação com o de crescimento determinado. Os dados sugerem que esse efeito seja resultante de um balanço mais equilibrado entre o desenvolvimento vegetativo e o reprodutivo, evidenciado pela ausência de diferença significativa na partição de massa seca oriunda do desenvolvimento vegetativo e do reprodutivo nesses genótipos, quando comparados aos genótipos de crescimento determinado e indeterminado. A eficiência no uso da água (EUA) foi avaliada tanto gravimetricamente (massa seca total produzida por quantidade de água transpirada), quanto através de discriminação isotópica. Os genótipos de crescimento semi-determinado apresentaram maior EUA do que os genótipos determinado e indeterminado aos 50 dias após a semeadura. Curiosamente, as plantas de crescimento semi-determinado mostraram-se mais resistentes, quando submetidas a um estresse de seca, que o genótipo de crescimento determinado utilizado como controle nas avaliações. Entretanto, são necessários estudos para elucidar o mecanismo envolvido nesta resistência. Em conclusão, os resultados aqui apresentados sugerem que os genótipos de crescimento semi-determinado atingiram o balanço ótimo entre desenvolvimento vegetativo e reprodutivo, de forma a aumentar concomitantemente, produtividade, conteúdo de brix nos frutos, e eficiência no uso da água. / Growth habit influences the balance between vegetative and reproductive development of plants. This, in turn, is directly linked to several variables of agronomic interest, such as yield and water-use efficiency (WUE). In tomato, there are three growth habits: determinate, indeterminate and semi-determinate, the latter being actually determinate, but with an extension of the vegetative cycle. Cultivars of determinate growth are widely used for processing-tomato industry (sauces and ketchups), and indeterminate for in natura consumption (production to salads). On the other hand, semi-determinate growth genotypes, although are still poorly explored, they present an excellent option for both the industry and in natura consumption. Thus, the aim of the present study was to evaluate the implication of the semi-determinate growth habit in productive performance and in WUE of tomato plants. For this reason, genotypes with different growth habits were produced through introgression of allelic variations that affect the plants growth habit, in the genetic background of the tomato cultivar Micro-Tom (MT). The characterization of these genotypes showed that the semi-determinate growth materials exhibit a delay in flowering, producing on average one extra leaf before the first inflorescence formation. In addition, this architecture presents an intermediate height between determinate and indeterminate growth genotypes, 50 days after sowing. As for agronomic traits, we found a significant increase in yield and total soluble solids content (brix) in the fruits of semi-determinate growth genotypes compared with determinate growth. Our data suggest this effect is resulting from a more balanced vegetative and reproductive development, evidenced by the absence of significant difference on the dry matter partition derived from the vegetative and reproductive development in these genotypes, when compared to determinate and indeterminate growth genotypes. WUE was evaluated both gravimetrically (dry mass produced per amount of water transpired), and through isotopic discrimination. The semideterminate growth genotypes showed higher WUE than determinate and indeterminate genotypes at 50 days after sowing. Interestingly, the plants of semideterminate growth were more resistant than determinate growth genotype used as control, when exposed to drought stress. However, studies are needed to elucidate the mechanism involved in this resistance. In conclusion, the results presented here suggest that the genotypes of semi-determinate growth reached the optimal balance between vegetative and reproductive development, in order to increase concomitantly, productivity, brix content in the fruits, and WUE.

Cette thèse visait à étudier la variabilité génétique et plasticité phénotypique de la vulnérabilité à la cavitation chez le hêtre (Fagus sylvatica L.). A cette fin, nous avons tout d’abord testé les variations dues à la méthodologie de mesure de la vulnérabilité à la cavitation. Notre étude a montré que les variations de vulnérabilité à la cavitation au cours du temps sont faibles. Néanmoins, il est préférable d’éviter de récolter les échantillons durant le début de la période de formation du bois. Par ailleurs il est possible de conserver au frais les échantillons sans dégrader les mesures durant au moins un mois. Nos résultats montrent également que la vulnérabilité à la cavitation peut être variable aussi bien au sein d’un même arbre qu’entre populations in situ. Ensuite, nous avons voulu déterminer la part de plasticité phénotypique de la part de variabilité génétique dans la variabilité de la vulnérabilité à la cavitation. Pour cela nous avons étudié 17 populations de hêtre venant de toute l’Europe et poussant dans une plantation comparative. Parmi les 17 populations 6 d’entre elles ont été étudiées dans trois plantations comparatives différentes (France, Espagne et Slovaquie). Nos résultats indiquent que chez le hêtre la vulnérabilité à la cavitation varie considérablement au sein de chaque population. Ils indiquent également que l’on observe peu de différenciation génétique entre populations. Les résultats montrent également que la plasticité phénotypique de la vulnérabilité à la cavitation est importante entre les plantations, et que le degré de cette plasticité peut varier d’une population à l’autre. Pour finir, nous avons regardé s’il existait des relations entre la vulnérabilité à la cavitation et des paramètres d’efficience hydraulique ainsi qu’avec l’efficience d’utilisation de l’eau. Nos résultats ne permettent pas de mettre en évidence des preuves d’un trade-off entre l’efficience et la sureté du xylème. / This work aimed at studying the genetic variability and the phenotypic plasticity of vulnerability to cavitation in beech (Fagus sylvatica L.). We tested the variations due to the methodology of measuring vulnerability to cavitation. Our study showed that the variations in vulnerability to cavitation over time are low. However, it’s better to avoid collecting samples during the period of initial wood formation. Furthermore it’s possible to store samples without degrading measures for during one month. Our results also show that vulnerability to cavitation can be variable both within the same tree and between populations in situ. We determined the proportion of phenotypic plasticity and the proportion of genetic variability in the variability of vulnerability to cavitation. For this we studied 17 beech populations from all Europe and growing in a common garden. Among the 17 populations 6 of them have been studied in three different common gardens (France, Spain and Slovakia). Our results indicate that for beech, vulnerability to cavitation varies considerably within populations. They also indicate that there are few genetic differentiations between populations. The results show that the phenotypic plasticity of vulnerability to cavitation is important among common garden, and the degree of this plasticity can vary between populations. To complete our study, we looked at the relationships between vulnerability to cavitation and hydraulic efficiency parameters and with the water use efficiency. Our results do not reveal evidence of relationships vulnerability to cavitation and other physiological traits.

Le potassium (K) est un élément majeur connu pour contribuer à la résistance des plantes à la sècheresse. L'étudede son influence sur la réponse physiologique du maïs (Zea mays L.) sous contrainte hydrique est essentiellepour prédire la future productivité dans un contexte de changements climatiques, en particulier de la diminutiondes précipitations. Des modalités d'apports en K et en eau ont été croisées et soumises à des plants de maïs,élevés en condition contrôlées ou cultivés au champ. La croissance (biomasses aériennes et racinaires,rendements en grain) ainsi que les mécanismes écophysiologiques du métabolisme carboné (photosynthèse,transport des sucres) et du statut hydrique (transpiration, conductance stomatique, potentiels hydriques) ont étéétudiés. L'apport de K a contribué à l'augmentation de la croissance, le développement et le rendement grain quelque soit le régime hydrique imposé au maïs et les conditions d'expérimentation. Les résultats attendus sur lameilleure régulation stomatique en cas de déficit hydrique sont moins évidents. L'effet du stress hydrique ou dela déficience en K tendent à diminuer la photosynthèse. Cependant, ces effets ressortent plus sur les feuillesâgées que sur les feuilles jeunes. Dans ces mêmes conditions, le transport des sucres ne semble pas être unélément limitant de la croissance. Plusieurs résultats convergent pour attribuer au K un rôle dans la maîtrise despertes en eau (par unité de surface foliaire) et sur la meilleure efficience d'utilisation de l'eau. Néanmoins, cetteefficience est imputée à des meilleurs rendements, liés à une surface foliaire plus importante, et non pas à unemoindre consommation de l'eau. / Potassium (K) is a major nutrient known to help plants resist drought. In the context of climate change,quantifying the role of K on maize physiological acclimation to reduced precipitations is essential to betterpredict future productivity. Maize (Zea mays L.) plants grown under controlled or field conditions weresubmitted to different K and water levels. Plant growth (shoot and root biomass, grain yield) as well as plantwater status (transpiration, stomatal conductance, water potential) and ecophysiological mechanisms of Carbonmetabolism (photosynthesis, sugar transport) were studied. Regardless of the water regime and experimentalconditions, K nutrition increased growth and whole-plant development and improved grain yield. The effect ofwater stress on stomatal regulation was not straightforward and depended on the level of K fertilization. Theeffects of water or K deficit tend to decrease photosynthesis. Drought or K nutrition affected more leafphotosynthesis in old than in young leaves, and sugar transport did not seem to be a growth limiting factor. Ourresults demonstrated a strong effect of K on biomass production and a higher water use efficiency with less of animpact on leaf-level physiology. This better water use was mainly the consequence of the positive effect of leafarea on yield, and not due to a reduce water use.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The irrigation of the rice crop is essential for good plant growth, assisting in achieving high grain yield levels. However, it results in large water volume used, thus the efficiency of water use is a major challenge to the sustainability of the crop. In this matter, early irrigation withholding can be considered an option for saving water. However, this practice can prejudice the quality of the crop, in yield and grain quality. In rice cultivars with large panicles, as in the case of hybrid rice, early withholding may be reflected in the quality of the grains from the bottom of the panicle, due to the difficulty of kernel filling in this region. Research was conducted during the growing seasons 2011/12 and 2012/13 , in order to verify the effect of anticipated moments of withholding irrigation on yield and water use efficiency ( Chapter II ) , and grain quality ( Chapter III ) of two rice cultivars . The experiments were conducted in the floodplains of the Departamento de Fitotecnia of the Federal University of Santa Maria (UFSM), using the experimental design of randomized blocks with four replications. Each experiment was composed of the factorial design appropriate to the factorsconsidered. Early withholding irrigation reduces the volume of water used in the rice crop, but depending on the moment and the cultivar, it can reduce productivity. For withholding irrigation performed before the recommended time it should be taken into account the cultivar, soil type and possible rainfall after the end of irrigation. Harvests with lower humidity than that recommended by research show a reduction in milling quality. Early withholding does not affect the milling quality, translucency, opaque and chalky grains; however, there was no difference in quality between the studied cultivars. / A irrigação da lavoura de arroz é fator imprescindível para o bom desenvolvimento da planta, auxiliando na obtenção de elevados níveis de rendimento de grãos. Entretanto resulta em grande volume de água utilizado, sendo a eficiência de uso de água um dos grandes desafios para a sustentabilidade da cultura. Neste sentido, a supressão antecipada da irrigação pode se constituir num aspecto de economia no uso de água. No entanto, essa prática pode comprometer a qualidade da lavoura no que se refere ao rendimento e à qualidade dos grãos. Em cultivares de arroz com características de panícula grande, como no caso do arroz híbrido, a supressão antecipada pode se refletir na qualidade dos grãos da parte inferior da panícula, em função da dificuldade do enchimento dos grãos nesta região. As ações de pesquisa foram conduzidas a campo durante as safras de cultivo de 2011/12 e 2012/13, com objetivo de verificar o efeito de momentos de supressão antecipada da irrigação no rendimento e na eficiência de uso da água (Capítulo II), e na qualidade dos grãos (Capítulo III) de dois cultivares de arroz irrigado. Os experimentos foram conduzidos a campo na área de várzea do Departamento de Fitotecnia da Universidade Federal de Santa Maria (UFSM), utilizando o delineamento experimental de blocos ao acaso com quatro repetições. Cada experimento foi constituído pelo delineamento fatorial adequado aos fatores em análise. A supressão antecipada da irrigação reduz o volume de água utilizado na lavoura, mas dependendo da época e do cultivar utilizado, pode reduzir a produtividade. Para a supressão da irrigação realizada antes da época recomendada deve-se levar em consideração o cultivar, tipo de solo e a possível precipitação pluvial após o término da irrigação. Colheitas realizadas com grau de umidade abaixo do preconizado pela pesquisa apresentam redução no rendimento de grãos inteiros. A supressão antecipada não interfere na qualidade de grãos inteiros, vítreos, opacos e gessados, no entanto, há diferença de qualidade entre os cultivares pesquisados.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis has the aim to evaluate growth of native grasses of natural grasslands Rio Grande do Sul state: Axonopus affinis, Paspalum notatum, Andropogon lateralis e Aristida laevis belonging to plant functional types A, B, C and D, respectively, in response to increasing N and P in soil. For this, the four grasses were grown in greenhouse with different N and P soil availability. The results were presented in two articles: the first evaluated species responses to increase N and P soil availability and relationships with functional traits and with tissue nitrogen concentration. The second article describes species response to increasing soil P availability besides P chemical fractions accumulated on plant tissue and acid phosphatase activity on leaves. All species respond to increase soil N and P availability but it was evidenced that resources capture species presented shorter time responses than conservation species. Independent of soil nutrients availability conditions where species were grown, the grass P. notatum showed the greater N and P use efficiency. The higher potential of relative response to increase N plus P and P availability was found for the grass A. affinis, which has leaf traits of resources capture species. For this, it was suggested that resources capture species have greater potential response to fertilization in relation to resources conservation species. / Esta tese tem o objetivo de avaliar o crescimento das gramíneas nativas das pastagens naturais do Rio Grande do Sul: Axonopus affinis, Paspalum notatum, Andropogon lateralis e Aristida laevis representantes dos tipos funcionais de plantas A e B de captura de recursos, e C e D de conservação de recursos, respectivamente, em reposta ao aumento na disponibilidade de nitrogênio e de fósforo no solo. Para isso, as quatro espécies foram cultivadas em casa de vegetação com diferentes condições de disponibilidade de P e N no solo. Os resultados foram apresentados em dois artigos: O primeiro avaliou a resposta das espécies à disponibilidade de N e P e as relações com atributos funcionais e com as concentrações de nitrogênio no tecido. O segundo artigo trata da capacidade das plantas em responder ao aumento da disponibilidade de P no solo além das frações químicas de acúmulo de P no tecido e da atividade da fosfatase ácida nas folhas. Nos dois artigos, as espécies responderam em massa tanto ao aumento da disponibilidade de N e de P quanto só de P. Porém no primeiro artigo, ficou evidenciado que a resposta foi identificada em um período mais curto para as espécies com características de captura de recursos em relação às de conservação de recursos. Independente das condições de disponibilidade de nutrientes onde as espécies foram cultivadas, a gramínea P. notatum demonstrou a maior eficiência de utilização tanto de N quando de P. O maior potencial de resposta relativo ao aumento da disponibilidade de N e P e de P foi encontrado para a gramínea A. affinis, a qual possui atributos foliares de captura de recursos. Assim, como esperado as espécies de captura de recursos têm maior potencial de resposta a adubação em relação às espécies de conservação de recursos.

Biogeochemical processes of reefs have been studied for over fifty years, however, information is still lacking on several fundamental reef processes. This lack of information has been limited essentially by techniques that cannot repeatedly sample large spatial areas. These limitations can be reduced with the use of an optical model to estimate biogeochemical processes. This project applied Monteith's light-use efficiency model to coral reef communities for determining photosynthetic and calcification efficiency of light. Gross primary production and net calcification were pooled from the peer-reviewed literature to calculate efficiency. Process efficiency was then compared across functional types of reef communities (i.e., coral, algae/seagrasses, mixed, and sand), and by year, location, season, and depth. Photosynthetic efficiency was calculated from 19 studies, showing an average of 0.039 mol O2 mol-1 photons. Photosynthetic efficiency differed significantly for mixed communities between studies, and for algae/seagrass communities among depths. Calcification efficiency averaged at 0.007 mol CaCO3 mol-1 photons. Significant differences were found in calcification efficiency of algae/seagrasses and mixed reef communities among studies and localities. Additionally, calcification efficiency of algae/seagrasses varied significantly in accordance with depth. Future use of the light-use efficiency model will require determining the efficiency of each functional type to estimate gross production and calcification. Additionally, further investigation of the light-use efficiency model will require long-term measurements of APAR, which is the fraction of incident light absorbed, and the incorporation of environmental parameters that reduce efficiency.

Introducing effective irrigation management in arid and semi-arid regions, like most areas of South Africa, is an indispensable way of maximising crop yield and enhancing productivity of scarce freshwater resources. Holistic improvements in agricultural water management could be realised through integrating the knowledge of crop-specific water requirements. In order to develop effective irrigation schedules for rose-scented geranium (Pelargonium capitatum x P. radens), greenhouse and field experiments were conducted at the Hatfield Experimental Farm of the University of Pretoria, Pretoria, South Africa, from 28 October 2004 to 2006. Results from 20, 40, 60 and 80% maximum allowable depletion (MAD) levels of the plant available soil water (ASW) indicated that plant roots extracted most of the soil water from the top 40 cm soil layer, independent of the treatment. Both essential oil yield and fresh herbage mass responded positively to high soil water content. Increasing the MAD level to 60% and higher resulted in a significant reduction in herbage mass and essential oil yields. An increase in the degree of water stress apparently increased the essential oil concentration (percentage oil on fresh herbage mass basis), but its contribution to total essential oil yield (kg/ha oil) was limited. There was no significant relationship between MAD level and essential oil composition. For water saving without a significant reduction in essential oil yield of rose-scented geranium, a MAD of 40% of ASW is proposed. Response of rose-scented geranium to a one-month irrigation withholding period in the second or third month of regrowth cycles showed that herbage mass and oil yield were positively related. Herbage yield was significantly reduced when the water stress period was imposed during the third or fourth month of regrowth. A remarkable essential oil yield loss was observed only when the plants were stressed during the fourth month of regrowth. Essential oil content (% oil on fresh herbage mass basis) was higher in stressed plants, especially when stressed late, but oil yield dropped due to lower herbage mass. The relationship between essential oil composition and irrigation treatments was not consistent. Water-use efficiency was not significantly affected by withholding irrigation in the second or in the third month of regrowth. With a marginal oil yield loss, about 330 to 460 m3 of water per hectare per regrowth cycle could be saved by withholding irrigation during the third month of regrowth. The overall results highlighted that in water-scarce regions withholding irrigation during either the second or the third month of regrowth in rose-scented geranium could save water that could be used by other sectors of society. In greenhouse pot experiments, rose-scented geranium was grown under different irrigation frequencies, in two growth media. Irrigation was withheld on 50% of the plants (in each plot) for the week prior to harvesting. Herbage and essential oil yields were better in the sandy clay soil than in silica sand. Essential oil content (% oil on fresh herbage mass basis) apparently increased with a decrease in irrigation frequency. Both herbage and total essential oil yields positively responded to frequent irrigation. A one-week stress period prior to harvesting significantly increased essential oil content and total essential oil yield. Hence, the highest essential oil yield was obtained from a combination of high irrigation frequency and a one-week irrigation-withholding period. In the irrigation frequency treatments, citronellol and citronellyl formate contents tended to increase with an increase in the stress level, but the reverse was true for geraniol and geranyl formate. Leaf physiological data were recorded during the terminal one-week water stress in the glasshouse pot trial. Upon rewatering, stomatal conductance (Gs) and transpiration rate (Rt) were significantly lower in the less often irrigated than in the more often irrigated treatments, while leaf water potential (yw) and relative water content (RWC) were the same for all plants, indicating that water stress had an after-effect on Gs and Rt. At the end of the stress period, Gs, Rt, yw and RWC were lower in the plants from the more often irrigated than from the less often irrigated treatments. Irrespective of irrigation treatment, one type of non-glandular and two types (different in shape and size) of glandular trichomes were observed. In water stressed-conditions, stomata and trichome densities increased, while the total number of stomata and trichomes per leaf appeared to remain more or less the same. Water stress conditions resulted in stomatal closure. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / unrestricted

La biodiversité favorise un grand nombre de fonctions et services écosystémiques des écosystèmes forestiers tels que la production de bois ou la résistance aux attaques d’insectes et aux maladies. Cependant l’impact de la diversité sur l’acquisition et l’utilisation de l’eau et du carbone reste largement méconnu dans ces écosystèmes. De plus, dans le contexte actuel de changement climatique, l’influence de la diversité sur la réponse des écosystèmes forestiers à des événements climatiques extrêmes tels que la sécheresse reste à étudier. L’objectif de ce travail est donc de déterminer l’impact de la diversité en espèces d’arbre sur d’importantes fonctions du cycle de l’eau et du carbone telles que la transpiration, la composition isotopique du carbone ou la profondeur d’extraction de l’eau à l’échelle de l’arbre et de l’écosystème sous des conditions contrastées dedisponibilité en eau du sol. Ce travail a été réalisé dans le cadre du projet FunDivEUROPE sur un réseau de parcelles forestières ainsi que dans des plantations expérimentales le long d’un gradient Nord-Sud en Europe afin de couvrir une importante gamme de conditions climatiques. Nos travaux ont montré une importante variabilité de la réponse à la diversité à l’échelle de l’arbre et de l’écosystème en termes de relations hydriques et carbonées à travers l’Europe. La diversité en espèces ne semble pas influencer les relations hydriques et carbonées des espèces et des écosystèmes forestiers dans des conditions non limitantes de disponibilité en eau. Cependant, un fort effet de la diversité a été observé en conditions de sécheresse pour certains types forestiers. A partir de ces résultats, je discute des mécanismes d’interaction entre espèces qui peuvent expliquer les effets observés. Nos données ont montré que l’influence de la diversité en espèces est fortement dépendante du contexte et peut êtremodifiée par les conditions environnementales locales et les conditions climatiques. En terme de gestion forestière, je suggère que pour certaines régions en Europe, promouvoir la diversité en espèces ainsi que contrôler la densité des parcelles doit être recommandé afin d’adapter les écosystèmes forestiers aux futures conditions climatiques / Biodiversity is known to support and boost a wide range of forest ecosystem functions and services like productivity and resistance against insect pests and diseases. However, whether tree species diversity also promotes water and carbon acquisition and use in forest ecosystems is still unclear. Furthermore, in the current context of global warming, information on how tree species diversity can influence the response of forest ecosystems to extreme climatic events such as drought are urgently needed. In this framework, the objective of my PhD thesis was to determine how tree species diversity influences important functions of the water and carbon cycle including transpiration, carbon isotope composition and water extraction depth at the tree- and ecosystem-Scale under contrasting soil water conditions. My work was conducted within the FunDivEUROPE project in a network of permanent forest stands and tree plantations across a North-South gradient in Europecovering a wide range of climatic conditions. I found considerable variability among species or forest types in the response of transpiration and carbon isotope composition at the tree- and ecosystem-Scale across Europe. Species diversity did not affect the water and carbon relations of tree species and forest ecosystems under non-Limiting soil water conditions. However, a strong effect of species diversity was observed under drought conditions in some forest types. Based on these data, I discuss the potential mechanisms of species interactions that may explain the observed patterns. I also point out that the influence of species diversity is highly context-Dependent, and changes with local environmental and climatic conditions. In terms of forest management applications, I suggest that, at least in some regions, controlling for tree species diversity along with stand density and total basal area could be recommended to help forests adapt to drier conditions

Plicatula is a taxonomic group within of the genus Paspalum that contains interesting species considering their phenotypic diversity for forage traits, and some of these species have been improved through artificial interspecific hybridization. Nitrogen (N) is an important limiting factor to produce biomass. Forage legumes contribute with symbiotic N2 fixation and can increase biomass yield and the nutritive value of the pastures. The objectives of this thesis were: (i) evaluate dry matter yield (DMY), N use efficiency (NUE), nutritive value, cold tolerance and plant persistence in hybrids of Paspalum plicatulum x P. guenoarum subjected to N application rates, (ii) compare biomass yield and nutritive value of the grass–legume system to a grass–N fertilizer system, and (iii) select the best hybrids for new steps within the breeding program. The study was conducted from September 2015 to May 2017. The experimental design was a randomized complete block in split-plot arrangement with three replicates. Treatments were five N rates (0, 60, 120, 240, and 480 kg N ha-1 N), and one grass-legumes mixture (Trifolium repens + Lotus corniculatus) as whole plots, and six genotypes (1020133, 102069, 103084, 103061, P. guenoarum ecotype Azulão and Megathyrsus maximus cv. Aruana used as a control) as subplots. Nitrogen rates of 240 and 480 kg N ha-1 increased Total-DMY, Leaf-DMY, cold tolerance and persistence but decreased NUE. Higher NUE was obtained with N rates between 60 and 120 kg N ha-1. Total-DMY for grass-legume mixture was similar to the N rates of 60 and 120 kg N ha-1. Hybrid 1020133 had Total-DMY similar to Azulão and Aruana, as well as Leaf-DMY greater than Aruana. Hybrid 1020133 showed greater cold tolerance and exhibited greater NUE at 60 kg N ha-1 than the other genotypes. At the N rate of 480 kg N ha-1 increased crude protein (27%) and digestibility (4%) and decreased neutral (6%) and acid (7%) detergent fiber compared to the 0 kg N ha-1. Grass-legume mixture showed greater nutritive value compared to N-fertilized grass. Hybrid 103061 had greater crude protein and digestibility and lower neutral and acid detergent fiber than Azulão and Aruana. Therefore, there is opportunity to increase DMY, NUE, cold tolerance and plant persistence, and improve the nutritive value through genotype selection and N management. In addition, grass-legume mixture showed greater nutritive value than N-fertilized grass and can be an alternative practice to replace to the application of N fertilizer up to the rate of 120 kg N ha-1. Hybrids 1020133 and 103061 should be indicated for new studies, such as seed production and animal performance.

As average global temperatures rise, cool-season C3 turfgrasses, such as the most commonly grown Kentucky bluegrass (Poa pratensis L.; KBG), struggle to tolerate extreme summer heat and increase their water consumption. Hybrid Bermudagrass (Cynodon dactylon [L.] Pers. × Cynodon transvaalensis Burtt Davy; HBG) is a warm-season C4 grass that may be increasingly suited for northern ecosystems traditionally classified as transition or cool-season climate zones. Glasshouse and field studies were conducted to compare HBG and KBG water use. The objective of the glasshouse study was to evaluate plant health and growth for two HBG cultivars (‘DT-1’ and ‘NorthBridge’) compared to a blend of KBG cultivars in all combinations of deficit, moderate, and high irrigation at optimum or short mowing height. The study was conducted in a glasshouse at Provo, UT, USA from 2020-2021. Grass was grown in pots arranged in a randomized complete block, full factorial design, with four replications of each treatment. The moderate KBG was also significantly different from both high and deficit for verdure and for the last half of NDVI. The objective of the field study was to evaluate two HBG cultivars (‘Tahoma 31’ and ‘Latitude 36’) compared to a blend of KBG cultivars for water loss and canopy health, temperature, and growth when subjected to deficit, moderate, and high irrigation. The study was arranged in a randomized complete block, full factorial design with three replications per treatment, and was conducted at Provo, UT, USA throughout the summer of 2021. In both the glasshouse and field trials, the deficit irrigated KBG consistently scored lower for NDVI and visual turf quality than all other treatments, including moderate and high KBG. This same trend was seen in the field study for percent cover. Although not observed in the glasshouse trial, it was observed in the field trial that the different irrigation levels of HBG resulted in no significant differences for any measurements but the HBG regularly scored better than KBG. The canopy temperatures of deficit irrigated KBG were also higher than all other treatments on most dates. The shoot mass, thatch mass, and total biomass of KBG were significantly less than either HBG cultivar. In the glasshouse trial it was observed that all deficit grasses were significantly lower than the other irrigation treatments and HBG had significantly deeper roots than KBG, although these results were not seen in the field trial. The data suggest that irrigation needs will be less for HBG than KBG and that HBG could provide a water-saving turfgrass alternative to KBG in semi-arid, cool-season regions with increasing water scarcity.