Herbicide treatments were tested on mature stands of Miscanthus in 2013 and 2014 in Winston and Oktibbeha counties Mississippi. Twenty-one different herbicide treatments and two application timings, summer and fall, were evaluated. Glyphosate at 4,500 g ae ha-1 applied in the summer provided the best Miscanthus control at each location. Control with fall applications of glyphosate varied between locations. Two greenhouse studies were conducted in 2014 and 2015 at Mississippi State, MS to evaluate the effects of mowing on seedling Miscanthus, as well as the time period between seed germination and rhizome initiation. Rhizomes were visible on seedling plants 15 or 13 weeks after germination in 2014 and 2015, respectively. Removal of the Miscanthus terminal reduced the number of rhizomes produced compared to plants with intact terminals. However, terminal removal increased the number of shoots produced compared to plants with intact terminal.

No description available.

A more thorough knowledge of rooting behavior of transplanted trees is needed to better understand plant establishment. The objectives of this research were to: 1) determine if transplant timing affected root system regeneration of northern red oak (Quercus rubra L.) and willow oak (Q. phellos L.), 2) determine the effect of transplant timing and nursery production system on root, shoot, and trunk growth periodicity of balled-and-burlapped (B&B) and pot-in-pot (PIP) sugar maple (Acer saccharum Marsh.), and 3) characterize seasonal patterns of root production and mortality of transplanted sugar maple. No new root growth occurred outside or within the root balls of red or willow oak between November transplanting and January excavation. However, new root growth was observed when November- and March-transplanted oaks were excavated in April, indicating that new root growth occurs primarily in late winter and/or early. Transplanted and non-transplanted sugar maples exhibited a pattern of maximum rates of shoot extension in early May, root length accumulation in late May, and trunk expansion in mid June. Rate of root length accumulation was less in summer and fall. Transplanting did not appear to disrupt the normal growth periodicity of sugar maple, except when transplanted in July. Abundant root length accumulation occurred in the July transplants at a time when root length accumulation had slowed in all other treatments, resulting in the July transplants having similar standing root lengths as the other transplants by fall. Standing root length of non-transplanted PIP sugar maple declined dramatically in spring. While root production in sugar maple was limited to the growing season, root mortality occurred at a steadier rate throughout the year. Most root mortality occurred in winter in transplanted trees and spring and summer in non-transplanted trees. Non-transplanted PIP trees had greater standing root length, production, and mortality than the other treatments. Indices of root activity (analogous to turnover rates) and production:mortality ratios illustrated the dominant role that root production plays relative to mortality in recently transplanted trees. These data indicate that transplanting and the PIP production system disrupt typical patterns of root production and mortality in sugar maple. / Ph. D.

Mountain laurel (Kalmia latifolia L.) is relatively difficult to establish in landscapes. One experiment tested the effect of container size on the water relations of pinebark substrate embedded in field soil. Two other experiments tested the effects of transplant season and container size on landscape establishment of nursery-produced mountain laurel. Experiment one compared volumetric water content of embedded substrate of five sizes (4-L to 100-L) to adjacent field soil at two depths with time domain reflectometry (TDR) during a dry down cycle. Available water was calculated by subtracting unavailable water (estimated with pressure plates) from volumetric water content (TDR measurements). Adjacent soil contained more available water than embedded substrate. The middle depth held more water than the top. Larger pinebark substrate volumes retained higher volumetric water content than smaller volumes. The second experiment consisted of 7.6- and 19-L containers of Kalmia latifolia L. ‘Olympic Wedding’, transplanted into field soil in October or May. Larger container plants generally had lower xylem potential than smaller plants, but better visual ratings. Root growth into surrounding soil was negligible for all treatments. Leaf area was higher for spring transplants than fall transplants. Experiment three was a rhizotron study with 19-L plants, transplanted in October or May. Canopy growth of spring transplants was greater than fall transplants, but fall transplants had longer roots into the backfill. Overall, our data suggest that fall transplanting will potentially allow faster plant establishment than spring transplanting. The effect of container size on plant establishment could not be determined. / Master of Science

As the atmosphere warms, precipitation events are likely to become less frequent but more intense. While extensive efforts have been made to understand how changes in mean annual precipitation will affect plant growth, particularly in semi-arid systems, relatively little is known about how increasing precipitation intensity will affect plant growth and hydrologic cycles. A recent study by Kulmatiski and Beard (2013) found that small increases in precipitation intensity increased woody plant growth and decreased grass growth in a three-year experiment in a savanna system, Kruger National Park. Here we report results from the following two years of that experiment. Due to naturally large precipitation events, plant available water was similar between treatment and control plots in the last two years of the study allowing us to test woody plant and grass responses to treatment removal (i.e., legacy effects). Treatment effects on grass and tree growth disappeared within months of treatment removal. However, due to a legacy effect of treatments, tree mass was greater in treatment that control plots at the end of the experiment. Measurements of root recruitment and hydrological tracer uptake, but not root volume helped explain plant growth responses to treatments. Results suggest that savanna plants respond rapidly to changes in precipitation intensity, but because of legacy effects, occasional increases in precipitation intensity can result in long-term shrub encroachment.

Cereais como a cevada e o arroz e leguminosas como o feijão, são importantes fontes de alimento no mundo. Alcançar maiores índices de produtividade não é apenas um fator econômico, mas social. Os reguladores vegetais têm o papel de estimular os diversos processos do desenvolvimento vegetal. Defensivos agrícolas passaram a serem estudados também como estimulantes vegetais, ao ser verificado que certas substâncias promoviam efeitos positivos na produtividade de cultivos. A fim de estudar esses efeitos em parâmetros de produtividade, quanto ao uso de substância específica e se ocorre diferença quando se modifica a fonte de reguladores vegetais numa formulação, foi realizada pulverização foliar com doses fixas dos produtos: (GA+NAA+BA), (GA+IBA+CN), nano TiO2 (nano dióxido de titânio) e tiametoxam em plantas de feijoeiro, cevada, arroz e em tomateiro cultivar Micro-Tom. Além disso, foi instalado um experimento com feijão via tratamento de sementes, com doses fixas dos produtos já citados, em rizotron e em vasos para avaliar o crescimento radicular. Os experimentos foram conduzidos em casa de vegetação no Departamento de Ciências Biológicas da ESALQ/USP. Os resultados obtidos foram submetidos à análise de variância e ao teste de Duncan através do software estatístico SAS. Em feijoeiro (aplicação via foliar) e tomateiro não foram encontrados efeitos significativos dos produtos na produtividade das plantas, contudo, alguns parâmetros foram influenciados por determinados tratamentos. Foi observada possível fitotoxidez no cultivo de tomate com o uso de tiametoxam ao se avaliar sua produtividade em relação ao controle. Em cevada, a aplicação de nano TiO2 aumentou a altura das plantas, o índice SPAD e o índice de colheita. Em arroz o tratamento GA+NAA+BA aumentou a altura das plantas e o tratamento tiametoxam promoveu maior número de perfilhos. Na análise do tratamento de sementes em vasos os resultados não foram significativos. Entretanto, o uso de nano TiO2 influenciou na área radicular. Em rizotron foi observado o maior CRV (crescimento radicular vertical) no tratamento com GA+NAA+BA. Ao final dos experimentos pode-se constatar também que o tratamento com GA+NAA+BA teve desempenho semelhante ao tratamento GA+IBA+CN. / Cereals like barley, rice and legumes like beans are important sources of food in the world. To achieve higher rates of productivity is not just an economic but a social factor. Plant regulators have the role of stimulating the various processes of plant development. Agricultural defensives were also studied as plant stimulants, as it was verified that certain substances promoted positive effects on crop productivity. In order to study these effects in productivity parameters, regarding the use of specific substance and if difference occurs when the source of plant regulators in a formulation is modified, a fixed dose of foliar spray was carried out: (GA+NAA+BA), (GA+IBA+CK), nano TiO2 (nano titanium dioxide) and thiamethoxam in common bean, barley, rice and tomato (Micro-Tom cultivar) plants. In addition, a bean experiment was installed through seed treatment with fixed doses of the mentioned products, in rhizotron and in pots to evaluate root growth. The experiments were conducted in a greenhouse at the Biological Sciences Department of ESALQ/USP. The results were submitted to analysis of variance and the Duncan test through SAS statistical software. In bean (foliar application) and tomato, no significant effects of the products were found on plant productivity; however, some parameters were influenced by certain treatments. Possible phytotoxicity was observed in tomato leaves with the use of thiamethoxam when evaluating its productivity in relation to the control. In barley the application of nano TiO2 increased the plant height, SPAD chlorophyll and the harvest indexes. In rice, the treatment GA+NAA+BA increased the plant height and the treatment with thiamethoxam increased the number of tillers. In the seed treatment in pots, analyses of the results were not significant. However, the use of nano TiO2 influenced the root area. In rhizotron, the highest CRV (vertical root growth) was observed in the GA+NAA+BA treatment. At the end of the experiments, it could be seen that the GA+NAA+BA treatment performed similarly to GA+IBA+CK treatment.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-05-07T12:36:43Z No. of bitstreams: 2 Dissetação - Victor Alves Ribeiro - 2014.pdf: 1778484 bytes, checksum: 0d2bf14dfc71e24ba8738b45c3f4a508 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-05-07T12:40:57Z (GMT) No. of bitstreams: 2 Dissetação - Victor Alves Ribeiro - 2014.pdf: 1778484 bytes, checksum: 0d2bf14dfc71e24ba8738b45c3f4a508 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-05-07T12:40:57Z (GMT). No. of bitstreams: 2 Dissetação - Victor Alves Ribeiro - 2014.pdf: 1778484 bytes, checksum: 0d2bf14dfc71e24ba8738b45c3f4a508 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The objective of this study was to evaluate and characterize root growth in cotton genotypes, and identify the most appropriate time to evaluate the related traits in rhizotrons systems. It was also tried to estimate the genetic parameters inherent in these traits, among which were included the total length, surface area, total volume and average diameter of roots. Thus, two different studies were developed. The first consisted in an experiment to characterize ten cotton genotypes, in rhizotrons. This experiment was conducted in randomized block design with split plot in time, and four replications. Six evaluations were made per plots, at 7, 14, 21, 28, 35 and 42 days after seedling emergence. Each measure was resulted of the image captured from a rhizotron (experimental unit). The variance analysis was made, and Scott & Knott test was used to cluster the genotype means. Linear regression analysis was performed to evaluate the time effect within genotypes. The phenotypic, genotypic and environmental correlations between each pair of traits were also estimated. The daily root growth per genotype was also observed, applying the same method of mean grouping for the genotypic discrimination. The second study was also conducted in rhizotrons system, in order to estimate the genetic parameters related to the same traits. Two crosses were performed involving contrasting parents: CD 408 x CNPA GO 2008-1265 and CD 408 x CNPA GO 2007-423. Each cross was assessed in a different experiment conducted as completely randomized design with six treatments (parents, and F1, F2, RC1 and RC2 generations). The data analysis allowed identifying outstanding genotypes for each trait, as well as the most appropriate time for the respective assessment. It was found high correlations among the evaluated traits. The estimation of genetic parameters allowed approximate inferences about the minimal number of genes involved in the genetic control of these traits. The main conclusions were: i) there is genetic variability in the evaluated characters related to development and growth of root in cotton upland; ii) the evaluation of these traits at 35 days after seedling emergence enables better genetic discrimination for selection purposes; iii) the lines CNPA GO 2008-1265 and CNPA GO 2002-2043 are predominantly superior than other genotypes, especially in the total length root; iv) CNPA GO 2007-423 genotype is outstanding in relation to others by its higher total volume of roots; v) there are high genetic associations among the traits total length, total area, total volume, and total diameter of roots; and vi) the estimated number of genes involved in the genetic control of these traits indicate oligogenic inheritance, although there is also evidence of strong environmental influence, suggesting also the possibility of polygenic or mixed inheritance (major genes and polygenes). / O objetivo deste trabalho foi avaliar e caracterizar o crescimento radicular em genótipos de algodoeiro, bem como identificar o tempo mais adequado para avaliação de caracteres relacionados, em sistema de rizotrons. Também buscou-se estimar parâmetros genéticos inerentes a esses caracteres, dentre os quais se incluíram comprimento total, área superficial, volume total e diâmetro médio de raízes. Para isso, foram conduzidos dois estudos independentes. O primeiro deles constituiu-se num experimento para a caracterização de dez genótipos de algodoeiro, em rizotrons, sob o delineamento de blocos ao acaso com parcelas subdivididas no tempo, e quatro repetições. Foram realizadas seis avaliações (medidas repetidas) por parcela, aos 7, 14, 21, 28, 35 e 42 dias da emergência das plântulas. Cada medida resultou da captura de uma imagem do sistema por rizotron (unidade experimental). Foi, então, realizada a análise da variância e aplicou-se o teste Scott & Knott para agrupamento das médias de genótipos. Também foi empregada análise de regressão para avaliar o efeito da fonte de variação “tempo” dentro de genótipos. Estimaram-se ainda as correlações fenotípica, genotípica e de ambiente entre os caracteres avaliados. Também avaliou-se a taxa de crescimento radicular diária por genótipo, aplicando-se o mesmo teste de agrupamento de médias para a discriminação genotípica. O outro estudo foi conduzido, também em rizotrons, visando estimar parâmetros genéticos associados aos mesmos caracteres. Realizaram-se dois cruzamentos envolvendo genitores contrastantes: CD 408 x CNPA GO 2008-1265 e CD 408 x CNPA GO 2007-423. Cada cruzamento correspondeu a um ensaio em delineamento inteiramente casualizado, com seis tratamentos (os genitores e as gerações F1, F2, RC1 e RC2). A análise dos dados permitiu identificar genótipos superiores em relação aos caracteres avaliados, bem como um momento mais adequado para a sua avaliação. Houve correlações significativas e de elevada magnitude entre os caracteres avaliados. E a estimação de parâmetros genéticos permitiu inferir aproximadamente sobre o número mínimo de genes envolvidos no controle genético dos caracteres. As principais conclusões foram: i) há variabilidade genética nos caracteres avaliados inerentes ao crescimento e desenvolvimento radicular do algodoeiro; ii) a avaliação desses caracteres aos 35 dias após a emergência possibilita melhor discriminação genotípica para fins de seleção; iii) as linhagens CNPA GO 2008-1265 e CNPA GO 2002-2043 são predominantemente superiores aos demais genótipos avaliados, sobretudo no caráter comprimento total de raízes; iv) na época de avaliação indicada (35 dias) o genótipo CNPA GO 2007-423 destaca-se pelo seu maior volume total de raízes; v) há alto grau de associação genética entre os caracteres comprimento total de raízes, área total de raízes, volume total de raízes e diâmetro médio de raízes; e vi) o número estimado de gene envolvidos no controle genético dos caracteres sugere herança oligogênica, embora haja também indícios de forte influência ambiental, o que abre a possibilidade de herança poligênica ou, até mesmo, herança mista (genes de efeitos maiores e poligenes).

Cereais como a cevada e o arroz e leguminosas como o feijão, são importantes fontes de alimento no mundo. Alcançar maiores índices de produtividade não é apenas um fator econômico, mas social. Os reguladores vegetais têm o papel de estimular os diversos processos do desenvolvimento vegetal. Defensivos agrícolas passaram a serem estudados também como estimulantes vegetais, ao ser verificado que certas substâncias promoviam efeitos positivos na produtividade de cultivos. A fim de estudar esses efeitos em parâmetros de produtividade, quanto ao uso de substância específica e se ocorre diferença quando se modifica a fonte de reguladores vegetais numa formulação, foi realizada pulverização foliar com doses fixas dos produtos: (GA+NAA+BA), (GA+IBA+CN), nano TiO2 (nano dióxido de titânio) e tiametoxam em plantas de feijoeiro, cevada, arroz e em tomateiro cultivar Micro-Tom. Além disso, foi instalado um experimento com feijão via tratamento de sementes, com doses fixas dos produtos já citados, em rizotron e em vasos para avaliar o crescimento radicular. Os experimentos foram conduzidos em casa de vegetação no Departamento de Ciências Biológicas da ESALQ/USP. Os resultados obtidos foram submetidos à análise de variância e ao teste de Duncan através do software estatístico SAS. Em feijoeiro (aplicação via foliar) e tomateiro não foram encontrados efeitos significativos dos produtos na produtividade das plantas, contudo, alguns parâmetros foram influenciados por determinados tratamentos. Foi observada possível fitotoxidez no cultivo de tomate com o uso de tiametoxam ao se avaliar sua produtividade em relação ao controle. Em cevada, a aplicação de nano TiO2 aumentou a altura das plantas, o índice SPAD e o índice de colheita. Em arroz o tratamento GA+NAA+BA aumentou a altura das plantas e o tratamento tiametoxam promoveu maior número de perfilhos. Na análise do tratamento de sementes em vasos os resultados não foram significativos. Entretanto, o uso de nano TiO2 influenciou na área radicular. Em rizotron foi observado o maior CRV (crescimento radicular vertical) no tratamento com GA+NAA+BA. Ao final dos experimentos pode-se constatar também que o tratamento com GA+NAA+BA teve desempenho semelhante ao tratamento GA+IBA+CN. / Cereals like barley, rice and legumes like beans are important sources of food in the world. To achieve higher rates of productivity is not just an economic but a social factor. Plant regulators have the role of stimulating the various processes of plant development. Agricultural defensives were also studied as plant stimulants, as it was verified that certain substances promoted positive effects on crop productivity. In order to study these effects in productivity parameters, regarding the use of specific substance and if difference occurs when the source of plant regulators in a formulation is modified, a fixed dose of foliar spray was carried out: (GA+NAA+BA), (GA+IBA+CK), nano TiO2 (nano titanium dioxide) and thiamethoxam in common bean, barley, rice and tomato (Micro-Tom cultivar) plants. In addition, a bean experiment was installed through seed treatment with fixed doses of the mentioned products, in rhizotron and in pots to evaluate root growth. The experiments were conducted in a greenhouse at the Biological Sciences Department of ESALQ/USP. The results were submitted to analysis of variance and the Duncan test through SAS statistical software. In bean (foliar application) and tomato, no significant effects of the products were found on plant productivity; however, some parameters were influenced by certain treatments. Possible phytotoxicity was observed in tomato leaves with the use of thiamethoxam when evaluating its productivity in relation to the control. In barley the application of nano TiO2 increased the plant height, SPAD chlorophyll and the harvest indexes. In rice, the treatment GA+NAA+BA increased the plant height and the treatment with thiamethoxam increased the number of tillers. In the seed treatment in pots, analyses of the results were not significant. However, the use of nano TiO2 influenced the root area. In rhizotron, the highest CRV (vertical root growth) was observed in the GA+NAA+BA treatment. At the end of the experiments, it could be seen that the GA+NAA+BA treatment performed similarly to GA+IBA+CK treatment.

Pour d'évidentes raisons agronomiques et environnementales, être en mesure de concevoir et mettre en place des systèmes de culture dans lesquels les plantes accèdent aux ressources de manière optimale revêt une importance cruciale pour tous les intervenants impliqués dans la production agricole. Les techniques d'intensification telles que la mise en place de cultures d'inter-rang et l'agro-foresterie visent à accroître la productivité globale des terres tout en assurant la durabilité des agro-écosystèmes, via une optimisation de l'utilisation des ressources environnementales (lumière, eau et nutriments) par les plantes et une préservation des cycles géochimiques. En théorie, les moyens d'atteindre ces objectifs sont nombreux mais en pratique, les interactions souterraines sont complexes et difficiles à mesurer, de sorte que les progrès réalisés dans la conception d'agro-écosystèmes améliorés et durables demeurent modestes. Dans ce contexte, l'objectif de ce travail a été d'évaluer, au travers de mesures racinaires detaillées en rhizotron et au champ, les effets des cultures d'inter-rang sur la croissance des jeunes hévéas. La dynamique des interactions souterraines a été étudiée, tant au niveau de la racine individuelle qu'à celui du système racinaire entier, sur la base, notamment, de descriptions numériques détaillées. Une telle approche a permis de proposer, en outre, une voie novatrice pour l'analyse de la dynamique racinaire à l'echelle du systeme racinaire entier, à savoir l'analyse des trajectoires de croissance. Dans le cas de l'association maïs-hévéa, les expérimentations en rhizotron ont permis de mettre en evidence que les interactions souterraines entre ces deux plantes peuvent induire des modifications de la croissance de leurs racines, à la fois à l'échelle de la racine individuelle et à celle du système racinaire entier. Toutefois, une telle coordination des dynamiques racinaires des plantes associées n'a pas pu être confirmée dans le cas des traitements manioc-hévéa et arachide- hévéa. Les expérimentations au terrain ont fourni, de manière assez prévisible, une image complexe des interactions souterraines entre hévéa et cultures d'inter-rang. Toutefois, un premier résultat obtenu par le biais de la mise en place de 'pièges à racines' dans un traitement niébé-hévéa, a été de montrer que ces deux plantes n'avaient pas un comportement compétitif marqué l'une vis-à-vis de l'autre. Il est également apparu que les hévéas paraissent 'investir' dans des racines 'coûteuses', car de faible longueur spécifique, probablement pour assurer une certaine durabilité de ces organes, tandis que les cultures d'inter-rang favorisent l'allocation des assimilâts vers des racines de longueur spécifique élevée, de construction moins 'coûteuses', probablement en réponse a un impératif de croissance plus rapide (suggéré par les taux d'élongation racinaire mesurés au cours des expérimentations en rhizotron). Enfin, excepté le cas du manioc, l'introduction de cultures d'inter-rang telles que le maïs et l'arachide n'a pas eu d'impact significatif sur le développement des jeunes hévéas, comme en attestent l'évolution de leur circonférence, hauteur et développement foliaire. Ce résultat de terrain est compatible avec les résultats des expérimentations en rhizotron qui n'ont démontré aucun effet inhibiteur des cultures d'inter-rang sur le développement de la partie aérienne des hévéas. Bien que les travaux présentés dans ce rapport, ne permettent pas, à eux seuls de conclure de manière définitive sur la façon dont les espèces cultivées en association peuvent se compléter mutuellement sur le plan fonctionnel, ils apportent des éléments de réponse préliminaires à cette question complexe ainsi que des méthodes permettant de les obtenir. Au total, ce travail représente donc une contribution à la conception des agro-écosystèmes durables qui deviennent de plus en plus indispensables dans le contexte d'une demande mondiale croissante en produits alimentaires et matières premières. En outre, certains des résultats obtenus dans le cadre de cette thèse ouvrent des perspectives pour des recherches plus approfondies, avec une finalité agronomique appliquée

Interactions between plant roots and soil microorganisms in the rhizosphere are critical for plant growth. However, understanding of precisely how root exudates influence the diversity and activity of rhizosphere microorganisms is limited. The main objective of this study was to investigate the effect of radiata pine (Pinus radiata) root exudates on rhizosphere soil microbial communities, with an emphasis on the role of low molecular weight organic anions. The study involved the development and validation of new methods for investigating rhizosphere processes in a purpose-built facility. This included development of an in situ sampling technique using an anion exchange membrane strip to collect a range of organic anions exuded from radiata pine roots grown in large-scale rhizotrons. These included tartarate, quinate, formate, malate, malonate, shikimate, lactate, acetate, maleate, citrate, succinate and fumarate. Soil microbial activity and diversity were determined using dehydrogenase activity and denaturing gradient gel electrophoresis. Links between organic anions in root exudates and rhizosphere soil microbial community structures were investigated by comparing wild type and genetically modified radiata pine trees which were grown in rhizotrons for 10 months. As expected, there was considerable temporal and spatial variability in the amounts and composition of organic anions collected, and there were no consistent or significant differences determined between the two tree lines. Significant differences in rhizosphere microbial communities were detected between wild type and genetically modified pine trees; however, they were inconsistent throughout the experiment. The shifts in microbial communities could have been related to changes in exudate production and composition. Based on results from the main rhizotron experiment, a microcosm study was carried out to investigate the influence of selected pine root exudate sugars (glucose, sucrose and fructose) and organic anions (quinate, lactate and maleate) on soil microbial activity and diversity. Soil microbial activity increased up to 3-fold in all of the sugar and organic anion treatments compared to the control, except for a mixture of sugars and maleate where it decreased. The corresponding impacts on soil microbial diversity were assessed using denaturing gradient gel electrophoresis and 16S rRNA phylochips. Addition of the exudate compounds had a dramatic impact on the composition and diversity of the soil microbial community. A large number of bacterial taxa (88 to 1043) responded positively to the presence of exudate compounds, although some taxa (12 to 24) responded negatively. Organic anions had a greater impact on microbial communities than sugars, which indicated that they may have important roles in rhizosphere ecology of radiata pine. In addition, a diverse range of potentially beneficial bacterial taxa were detected in soil amended with organic anions, indicating specific regulation of rhizosphere microbial communities by root exudates. This project highlighted the considerable challenges and difficulties involved in detailed investigation of in situ rhizosphere processes. Nonetheless, the findings of this study represent a significant contribution to advancing understanding of relationships between root exudates and soil microbial diversity, which will be further enhanced by refinement and application of the specific methodologies and techniques developed.