Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The performance of beef heifers grazing Italian ryegrass (Lolium multiflorum Lam) from eight until twelve months receiving or not energetic supplement (whole corn grain or steam-rolled) at level of 1% body weight were studied. The grazing method was continuous with variable number of animals. The suplement was given daily at 2 pm and presented 9,5% crude protein, 8,4% neutral detergent fiber and 83% total digestible nutrients. The experimental design was completely randomized with repeated measures on time and the sward and animals variable were studied. The beef heifers were submitted to average values of forage mass (1525,2 kg/ha of dry matter) and sward height (9,6 cm). There was no difference between the performance of beef heifers that receiving different physical forms of corn grain (P>0,05) and the average values of whole corn grain and steam-rolled corn was used. The beef heifers receiving corn grain had higher average daily gain, body condition score and body weight:height ratio than heifers exclusively on pasture. The use of corn grain as a supplement expressed no change in pelvic area and reproductive tract score of beef heifers. The supplementation with corn grain allows higher number of beef heifers grazing on ryegrass pasture and gain per area. / Foi estudado o desempenho de bezerras de corte, dos oito aos doze meses de idade, em pastagem de azevém (Lolium multiflorum Lam.) recebendo ou não suplemento energético na proporção de 1% do peso corporal, na forma de grão de milho inteiro ou laminado (Zea mays). Foi utilizado o método de pastejo contínuo com número variável de animais. O suplemento foi ministrado diariamente às 14 horas e apresentou teores de 9,5% de proteína bruta (PB), 8,4% de fibra em detergente neutro (FDN) e 83% de nutrientes digestíveis totais (NDT). O delineamento experimental foi o inteiramente casualizado, com medidas repetidas no tempo e foram estudadas variáveis do pasto e dos animais. As bezerras de corte foram submetidas a valores médios de massa de forragem (1525,2 kg/ha de matéria seca) e altura do dossel (9,6cm). Não houve diferença no desempenho de bezerras de corte que receberam diferentes formas físicas de grão de milho (P>0,05), sendo utilizada a média entre grão de milho inteiro e laminado. As bezerras que recebem grão de milho apresentam maior ganho médio diário, escore de condição corporal e relação peso corporal:altura do que bezerras exclusivamente em pastejo. O uso do grão de milho como suplemento não expressa alteração na área pélvica e no escore de trato reprodutivo de bezerras de corte. A suplementação com grão de milho permite maior número de bezerras em pastejo em azevém e ganho de peso corporal por área. Foi estudado o desempenho de bezerras de corte, dos oito aos doze meses de idade, em pastagem de azevém (Lolium multiflorum Lam.) recebendo ou não suplemento energético na proporção de 1% do peso corporal, na forma de grão de milho inteiro ou laminado (Zea mays). Foi utilizado o método de pastejo contínuo com número variável de animais. O suplemento foi ministrado diariamente às 14 horas e apresentou teores de 9,5% de proteína bruta (PB), 8,4% de fibra em detergente neutro (FDN) e 83% de nutrientes digestíveis totais (NDT). O delineamento experimental foi o inteiramente casualizado, com medidas repetidas no tempo e foram estudadas variáveis do pasto e dos animais. As bezerras de corte foram submetidas a valores médios de massa de forragem (1525,2 kg/ha de matéria seca) e altura do dossel (9,6cm). Não houve diferença no desempenho de bezerras de corte que receberam diferentes formas físicas de grão de milho (P>0,05), sendo utilizada a média entre grão de milho inteiro e laminado. As bezerras que recebem grão de milho apresentam maior ganho médio diário, escore de condição corporal e relação peso corporal:altura do que bezerras exclusivamente em pastejo. O uso do grão de milho como suplemento não expressa alteração na área pélvica e no escore de trato reprodutivo de bezerras de corte. A suplementação com grão de milho permite maior número de bezerras em pastejo em azevém e ganho de peso corporal por área.

The objective of the work was to evaluate the chemical composition and production of dry matter and seed in five genotypes of ryegrass subjected to different number of cuts, with emphasis on growing dual purpose. The experimental delineation was adopted in blocks at random, with four repetitions and the treatments were distributed in factorial scheme 5x5 (genotypes x number of cuts). Was used five genotypes: Comum , São Gabriel , Estanzuela 284 , Avance and Titán and five cut number (one, two, up to five cuts). It was observed (P <0.05) significance interaction with genotype x number of cut for all the variables studied. The increase in the number of cuts ordered greater accumulation of total dry matter (leaves and stems), but lower seed production for all genotypes studied. The response of the chemical composition of dry matter varied depending on the genotype and the number of cuts. The increase in the number of cuts promoted lower crude protein content of leaf and stem for all genotypes studied. The highest level of neutral detergent fiber of stem genotype was found in São Gabriel and Comum . The genotypes showed quadratic answer to the contents of neutral detergent fiber of leaves, and the lowest level was observed when there were up to three cuts. Aiming the dual-purpose, you must choose from two to three cuts, given a good production of dry matter to animals but also promoting a seed production satisfactory. / O objetivo do trabalho foi avaliar a composição bromatológica e produção de matéria seca e de sementes em cinco genótipos de azevém submetidos em diferentes número de cortes, com ênfase no cultivo duplo propósito. Adotou-se o delineamento experimental em blocos ao acaso, com quatro repetições e os tratamentos distribuídos em esquema fatorial 5x5 (genótipos x número de cortes). Foram utilizados cinco genótipos (Comum, Estanzuela 284, Avance, Titán e São Gabriel) e o número de cortes variou de um até cinco. Foi observada significância (P<0,05) à interação genótipos x número de corte para todas as variáveis analisadas. O aumento do número de cortes determinou maior acúmulo de matéria seca total (folha e colmo), porém menor produção de sementes para todos genótipos estudados. A resposta da composição bromatológica da matéria seca variou conforme o genótipo e o número de cortes. O aumento do número de cortes promoveu menor teor de proteína bruta de folha e colmo para todos os genótipos. O maior teor de fibra detergente neutro de colmo foi verificada nos genótipos São Gabriel e Comum. Os genótipos apresentaram resposta quadrática quanto ao teor de fibra em detergente neutro de folhas, sendo que o menor teor foi observado quando se realizaram até três cortes. Visando o duplo-propósito, deve-se escolher de dois até três cortes, atendendo uma boa produção de matéria seca para os animais, mas também promovendo uma produção de sementes satisfatória.

Aiming to evaluate non apparent relations among individual studies and provide a set of more accurate information about supplement utilization on cool-season cultivated pastures, variables from nine experiments wich tested levels and kinds of supplements offered to beef heifers were analyzed. At first, data were stratified in two groups: with and without supplement utilization. Afterwards, supplements offered in different levels were collected in three groups, to estimate the effect of sources ( by-product , grain , ration ). Pasture was evaluated in relation to the availability, structure, chemical composition and digestibility. For animals and per unit of area, the variables analyzed were average daily gain (ADG), body condition score (BCS), back height, stocking rate and live weight gain per hectare. The addition and substitution rates and the efficiency of transformation of grass and supplement were calculated. The availability and the structure of the grass were similar for both groups. Heifers that received supplement presented greater ADG and ingested grass with lesser neutral detergent fiber detergent. At the end of the pasture utilization, the heifers that received supplement were heavier, higher and presented greater BCS. Females that received ration presented higher average daily gain than heifers that received grain or by-product (P<0,05), while the higher stocking rate were verified when the beef heifers received byproduct (P<0,05), with an increment of 45,1% in relation to the others. The live weight gain per hectare was similar between the different kinds of supplement. The utilization of grains provided better results on individual and per area performance when were given at a rate of 0,8% of live weight (LW). For by-product , grain and ration , the substitution rate were 0,8, 0,1 e 0,0 kg of dry matter (DM) of grass/kg of supplement, respectively. The efficiency of transformation of the supplement into kg of LW was similar (P>0,05) among kinds of supplement. However, when the females received ration, the efficiency of transformation of the grass was higher. The choice of the kind of supplement to use in high quality pastures should be based on the purpose of the production system. Rations provide greater increments on the individual performance while by-products provide greater stocking rate and individual performance. / Com o objetivo de avaliar relações não aparentes nos estudos individuais e providenciar um conjunto de informações mais acuradas sobre o uso de suplementos em pastagens cultivadas de clima temperado, foram analisadas em conjunto as variáveis medidas em nove experimentos, que testaram níveis e tipos de suplementos para novilhas de corte. Os dados foram inicialmente estratificados em dois grupos: com e sem o uso de suplemento. Posteriormente, os suplementos fornecidos em diferentes níveis, foram reunidos em três grupos, para estimar o efeito de fontes ( subproduto , grão , ração comercial ). O pasto foi avaliado quanto à disponibilidade, estrutura, composição química e digestibilidade. As variáveis analisadas nos animais e por unidade de área foram o ganho médio diário (GMD), escore de condição corporal (ECC), altura da cernelha, taxa de lotação e ganho de peso por área. Foram calculadas as taxas de adição e substituição, eficiência de transformação do pasto e do suplemento. A disponibilidade e a estrutura do pasto foram semelhantes para os grupos com e sem suplemento. Bezerras que receberam suplemento apresentaram maior GMD e consumiram pasto com menor teor de fibra em detergente neutro. Ao final do período de utilização da pastagem as bezerras que receberam suplemento foram mais pesadas, mais altas e apresentaram maior ECC. Fêmeas que receberam ração apresentaram maior ganho médio diário GMD que bezerras que receberam grão ou subproduto (P<0,05), enquanto as maiores taxas de lotação foram verificadas quando as bezerras receberam sub-produto (P<0,05), com acréscimo de 45,1% em relação à ração e aos grãos. O ganho de peso por área foi semelhante nos diferentes tipos de suplemento. O uso de grãos proporcionou melhores resultados no desempenho individual e por área quando fornecido na proporção de 0,8% do peso vivo (PV). As taxas de substituição foram de 0,8; 0,1 e 0,0 kg de MS do pasto/kg de suplemento, para sub-produto , grão e ração , respectivamente. A eficiência de transformação do suplemento em kg de PV foi semelhante (P>0,05) entre os tipos de suplemento. A eficiência de transformação do pasto, no entanto, foi maior quando as fêmeas receberam ração. Em pastagens de alta qualidade a escolha do tipo de suplemento depende do objetivo do sistema de produção. Rações proporcionam maiores incrementos no desempenho individual enquanto subprodutos proporcionam maiores taxas de lotação e desempenho individual.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The productive and reproductive performance of beef heifers grazing Italian ryegrass (Lolium multiflorum Lam) were studied with animals exclusively on pasture or receiving 0.8% of body weight of rice bran plus monensin or not. The rice bran was given daily at 2 pm and the monensin was provided in the amount of 200mg per animal. The grazing method was continuous with variable number of animals. The experimental design was completely randomized with repeated measures on time, three treatments and three area replicates. The beef heifers were submitted to average values of forage mass (1490.0±134.9kg ha-1 MS) and sward height (10±0.68cm). Beef heifers supplemented with rice bran plus monensin or not had higher daily gain, weight body, body condition score and body weight:height ratio. Beef heifers receiving rice bran with or without ionophore in 112 days of grazing gain 28% of body weight in relation to adult weight. The supplementation with rice bran to grazing animals no change in pelvic area, stocking rate and area weight gain. / Foi estudado o desempenho de bezerras de corte em pastagem de azevém (Lolium multiflorum Lam.), com animais exclusivamente em pastejo ou recebendo farelo de arroz integral (FAI) em nível de 0,8% do peso corporal associado ou não à monensina. O FAI foi ministrado diariamente às 14 horas, e a monensina foi fornecida na quantidade de 200mg por animal. O método de pastejo foi contínuo com número variável de animais. O delineamento experimental foi o inteiramente casualizado, com medidas repetidas no tempo, com três tratamentos e três repetições de área. As bezerras de corte foram submetidas a valores médios de massa de forragem (1490,0±134,9kg ha-1 MS) e altura do dossel (10±0,68cm). As bezerras que receberam FAI independente do uso da monensina, apresentaram maior ganho diário, peso corporal, escore de condição corporal e relação peso corporal:altura. Em 112 dias de pastejo, as bezerras que receberam FAI com ou sem ionóforo, ganharam 28% do peso corporal em relação ao peso adulto projetado. O uso de FAI associado ou não a monensina não expressou alteração na área pélvica das bezerras, na taxa de lotação e no ganho de peso por área.

O crescimento das atividades urbano-industriais tem provocado um significativo aumento nas emissões de poluentes aéreos para a atmosfera. A poluição do ar, um dos principais fatores determinantes da destruição do meio ambiente, causa estresse às plantas, já que apresenta compostos altamente reativos e danosos, como os metais pesados. O uso de plantas bioindicadoras de poluição aérea é uma prática comum para o monitoramento da qualidade do ar e para o diagnóstico dos efeitos da poluição aérea na vegetação. Entre as plantas bioindicadoras mais utilizadas, destaca-se a gramínea C3 de clima temperado Lolium multiflorum ssp. italicum Beck var. Lema, que acumula metais pesados, fluoretos e enxofre quando se desenvolve na presença desses elementos químicos no ar. Além disso, esta espécie acumula frutano, um carboidrato solúvel cuja produção pode ser alterada por um número variado de perturbações ambientais. O presente trabalho foi dividido em três experimentos com os objetivos de (1) verificar a partição de carboidratos solúveis em cinco partes distintas (lâmina em alongamento, lâmina expandida, porção superior do estolho, porção inferior do estolho e raízes) de plantas de L. multiflorum; (2) analisar as relações sazonais e diurnas entre concentrações de poluentes aéreos urbanos, principalmente de dióxidos de enxofre e de nitrogênio e de material particulado, entre outros fatores ambientais, concentrações foliares de metais e mudanças no acúmulo de frutanos em plantas de Lolium multiflorum Lam ssp. italicum expostas a diferentes condições de poluição do ar na cidade de São Paulo; (3) verificar se as variações sazonais e diurnas no conteúdo de frutanos são determinadas por acúmulos foliares de enxofre e metais pesados ou por variações nas concentrações de poluentes gasosos; e (4) verificar a eficiência bioacumuladora da variedade “Lema” de Lolium multiflorum para a região tropical. Para isso, as plantas foram expostas durante períodos consecutivos de 28 dias ou 2 meses, em cada estação do ano, em Congonhas (local com altos níveis de poluentes aéreos) e em casa de vegetação com ar filtrado (local controle). Após cada exposição, a frutose total foi quantificada pelo método de antrona e os frutanos analisados qualitativamente por HPAEC-PAD. As concentrações de enxofre foram determinadas por turbidimetria, enquanto que as concentrações de metais pesados (Al, Fe, Cu, Zn, Pb, Cd e Ba) foram medidas utilizando um espectrofotômetro de absorção atômica, após digestão ácida. Os resultados mostraram que o estolho contendo as bainhas foliares de L. multiflorum acumulou mais frutanos, enquanto que as raízes acumularam os menores níveis desse carboidrato. As variações sazonais no conteúdo dos carboidratos solúveis foram marcantes no presente trabalho e pareceram estar relacionadas com as condições climáticas, mas intensificadas pelas concentrações de poluentes aéreos, especialmente de metais pesados contidos no material particulado, e acumulados nas folhas de L. multiflorum expostas em Congonhas. Já as variações diurnas foram sutis, mas suficientes para refletir as variações de irradiância, temperatura e de alguns poluentes gasosos ao longo do dia. Tanto no experimento sazonal como no diurno, os frutanos de alto peso molecular pareceram ter sido hidrolisados sendo o acúmulo de frutanos de peso molecular intermediário preferencial nas plantas dos dois locais de estudo. As interferências no conteúdo e na composição de frutanos influenciaram a produção de biomassa e a partição desta entre as partes da plantas, o que ode ter alterado a capacidade acumuladora da espécie de elementos provenientes da poluição atmosférica. Assim, o uso da variedade Lema de L. multiflorum para fins de biomonitoramento da qualidade do ar em regiões tropicais deve ser cuidadoso. / The development of urban and industrial activities has caused a significant increase in the emissions of pollutants to the atmosphere. Air pollution, one of the most destructive factors of the environment, causes stress to plants, since certain compounds such as heavy metals are very reactive and dangerous to plant cells. The utilization of bioindicator plants is an usual practice to monitor the air quality and to diagnose the effects of air pollution on vegetation. The C3 temperate grass Lolium multiflorum ssp. italicum Beck var. Lema is usually employed as bioindicator of air pollution, due to its high capacity of accumulating heavy metals, fluorine and sulfur when growing in the presence of these chemical elements in the air. This species also accumulates fructan, a soluble carbohydrate, whose production can be altered by to many environmental perturbations. In the present work three experiments were performed aiming (1) to verify the partitioning of water total carbohydrates in five different parts of plants of L. multiflorum (upper stubble; under stubble; elongating leaf, expanded leaf and roots); (2) to analyze the seasonal and the diurnal relationships between the concentrations of urban air pollutants, mainly nitrogen and sulfur dioxides and particulate material, among other environmental factors, leaf concentrations of heavy metals and changes in fructan accumulation in plants of L. multiflorum exposed to different conditions of air pollution in São Paulo city; (3) to verify if the seasonal and diurnal variations in the content of fructans are determined by leaf accumulation of sulfur and heavy metals or by variations in the concentrations of gaseous pollutants or other environmental factors; and (4) to verify the bioindicator efficiency of the variety “Lema” of Lolium multiflorum in tropical areas. Plants were consecutively exposed during 28 days or two months in each season at Congonhas (site reached by high levels of air pollutants) and at a glasshouse with filtered air (reference situation). After each exposure, fructan composition as well as leaf concentrations of total fructose and of sulfur and metals (Al, Fe, Cu, Zn, Pb, Cd and Ba) were measured. Total fructose was quantified by the anthrone method and fructan composition was analyzed by HPAEC-PAD. Sulfur concentrations were determined by the turbidimetric method, whereas metal concentrations were measured using an atomic absorption spectrophotometer, after acidic digestion. Results showed that the stubble containing the leaf sheaths of L. multiflorum accumulated the highest levels of fructans, while the roots accumulated the lowest levels. Seasonal variations in the contents of soluble carbohydrates were evident in the present work and seemed to be related with the climatic conditions but intensified by the air pollutants, especially heavy metals contained in the particulate matter, and accumulated in the leaves of L. multiflorum exposed in Congonhas. However the diurnal variations were tenuous, but reflected the variations of irradiance, temperature and of some gaseous pollutants during daytime. In the both seasonal and diurnal experiments, the fructans of high molecular weight seemed to be hydrolyzed and the accumulation of fructans of intermediary molecular weigh was significant in the plants from both sites. The changes in the content and in the composition of fructans altered the biomass production and partition among roots and shoots, which might have been disturbed their characteristic of accumulating chemical elements from air pollution in the leaves. So, the use of the variety Lema of L. multiflorum for biomonitoring purposes in tropical areas should be carefully evaluated.

Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Bibliography: leaves 213-229. / xxiii, 229, 26 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2000

With the loss of field burning the amount of crop residue that remains in perennial ryegrass fields has increased. As the amount of crop residue remaining in the field increases so does annual bluegrass. This has resulted in the increased use of herbicides to control annual bluegrass. However, this increased use has also resulted in herbicide-resistant annual bluegrass. Field experiments were initiated in 1997 to investigate residue management options available to growers and their impacts on annual bluegrass emergence. Two sites, Glaser and Wirth, were established with three residue management treatments replicated four times. The treatments included full-straw, bale/flail, and vacuum sweep. Perennial ryegrass seed yield and annual bluegrass seed contamination were evaluated. The vacuum sweep treatment had lower annual bluegrass emergence than the full-straw or the bale/flail treatments during the 1997-98 growing season, for both sites. The fall of 1998 was much drier than the fall of 1997. Annual bluegrass emergence in all plots was lower in 1998 than in 1997 because of the dry conditions. Fall emergence in 1998 was higher in the vacuum sweep treatment than in the other two treatments, which may have been the result of better soil-seed contact in the vacuum sweep treatment. Lower emergence in the spring at the Wirth site compared to the Glaser site may have been due to narrow crop row spacing and cultivar selection, which shaded the annual bluegrass. When growing seasons were combined, there were no treatment differences. However, more emergence was observed in the spring at the Glaser site compared to the Wirth site. Yield was highest for the vacuum sweep treatment at the Glaser site in the 1998-99 growing season. However, competition from volunteer perennial ryegrass in the full-straw and bale/flail treatments could have accounted for this increase. No other differences in yield and no difference in contamination among treatments were observed. However, contamination at the Glaser site was higher in the 1998-99 growing season than in the 1997-98 growing season. Experiments were conducted in growth chambers to determine how differing environmental conditions affect seed germination of diuron-susceptible and diuron-resistant annual bluegrass. Cumulative germination for the susceptible-biotype decreased from 96% to 88% while the resistant-biotype remained above 95% as temperature decreased from 3 0/20 C to 10/2 C. The susceptible-biotype germinated sooner than the resistant-biotype regardless of temperature. The susceptible-biotype had a higher rate of germination than the resistant-biotype at 30/20 C, but not when the temperature decreased to 10/2 C. Germination response to differing matric potentials did not vary much within a biotype for a given soil type and temperature. Therefore, parameters estimated at -1.03 MPa were chosen to contrast susceptible- and resistant biotypes, and soil types, for each temperature. Maximum cumulative germination was greater than 96% for all treatments. When germination on a given soil type was contrasted, differences were only seen for the susceptible biotype vs. resistant biotype on Dayton soil; and the resistant biotype on Dayton soil vs. resistant biotype on Woodburn soil at both temperatures. The lag in onset of germination was shorter for the susceptible biotype on Dayton soil and resistant biotype on Woodburn soil than the resistant biotype on Dayton soil at 30/20 C. At 18/5 C, the lag in onset of germination was shorter for the susceptible biotype on Dayton soil and resistant biotype on Woodburn soil than the resistant biotype on Dayton soil (P = 0.000 1 and 0.0001, respectively). But the rate of germination was faster for the resistant biotype on Dayton soil than both the susceptible biotype on Dayton soil and resistant biotype on Woodburn soil at 18/5 C (P = 0.02 and 0.0004, respectively). The rate of germination did not differ at 3 0/20 C. When just the soils were contrasted, at 18/5 C all annual bluegrass seeds on the Woodburn soil germinated sooner and the rate of germination was higher than on the Dayton soil. These results indicate that the hydraulic properties of the soils may influence germination. However, this was not observed at 30/20 C. The results suggest that the susceptible-biotype was more sensitive to temperature while the resistant-biotype was more sensitive to moisture. Changing crop management in ways that will reduce annual bluegrass emergence and establishment is needed. By altering management strategies, growers may obtain more efficient and effective use of herbicides, while reducing the selection of herbicide-resistant annual bluegrass. / Graduation date: 2000

Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Thèse de doctorat : Sciences agronomiques : INPL : 2007. / Titre provenant de l'écran-titre. Bibliogr.