Selected PCB congeners (PCB 52, 77, and 153) singly and in mixtures were spiked and aged in soil microcosms and subsequently planted with switchgrass (Panicum virgatum) or poplar (Populus deltoids x nigra DN34). The planted reactors showed significantly greater reductions in PCB parent compounds when compared to unplanted systems after 32 weeks, both in single congener exposures and when all three congeners were present in a mixture. There was evidence of reductive dechlorination in both planted and unplanted systems, but higher concentrations of transformation products were observed in the planted systems than the unplanted. Although planted systems resulted in greater biotransformation, this improvement in PCB-reduction was not the result of plant uptake but rather was due to transformations occurring in the root rhizosphere. Parent PCB congeners were transformed by reductive dechlorination resulting in successively less chlorinated PCB congeners. These dechlorination products accounted for approximately all of the molar mass of parent compound lost. Based on the transformation products, reductive dechlorination pathways are proposed for rhizospheric biotransformation of PCB 52, 77, and 153. Results suggest that PCB 52 transformation proceeds through PCBs 18 and 9 down to monochlorinated PCB 1. Biotransformation of PCB 77 occurs through the intermediaries PCB 35 and 37. The pathway for the rhizospheric transformation of PCB 153 is through PCB 101 and PCB 99. This study provides insight into rhizosphere biotransformation pathways for reductive dechlorination in marginally aerobic,intermittently flooded soil as evidenced by a mass balance on transformation products. Despite the marginally aerobic conditions it is likely that highly reduced microzones existed in the soil particles during flooding and provided the opportunity for reductive dechlorination. In these experiments, planted microcosms with fully developed roots and rhizospheres showed significant reductive dechlorination and greater biotransformation than unplanted reactors. In addition, planted systems that were intermittently flooded had greater transformation of the parent PCB compounds than systems that were not. A poplar planted system resulted in the complete removal of 26 of the 29 PCB congeners detected in a commercial garden soil, while the unplanted soil only had 2 congeners completely removed after 96 days. In addition, the most recalcitrant congener, PCB 52, only decreased by 0.1% in the unplanted reactors while declining by 22.3% in the planted system. There was also greater removal of a PCB 77 spike in the planted system when compared to the unplanted system, 17.2% in the planted system versus 2.8% in the unplanted system. The results suggest that phytoremediation may be an effective tool in cleaning commercially available garden soils that are lightly contaminated with PCBs.

Arsenic (As) is a problem with rice production systems throughout the world as high As concentrations are reported in rice grains originating from several parts of the world. This characteristic is mainly due to the flooded conditions utilized in rice culture. We hypothesized that the soluble As concentrations in the rice rhizosphere can be decreased by growing rice more aerobically through intermittent flooding. Intermittent water management practices might also change microbial populations in the rice rhizosphere that might potentially impact As chemistry and bioavailability. Two field-scale experiments were conducted over two years to study the impact of intermittent and continuous flooding on As speciation and microbial populations in the rice rhizosphere. As levels and speciation in the rhizosphere soil, root-plaque and pore-water were determined using a high performance liquid chromatography-inductively coupled plasmamass spectroscopy (HPLC-ICP-MS). The microbial populations were assessed from the rhizosphere soil and root-plaque samples using quantitative polymerase chain reaction (qPCR) and 16S rRNA sequencing. Pore-water and root-plaque total-As concentrations significantly decreased in the intermittent compared to the continuous flood plots. Inorganic arsenite (iAsIII) was predominant in pore-water and inorganic arsenate (iAsV) in root-plaque and soil. Rootplaque sequestered significantly higher levels of As (almost tenfold higher) than the adjacent rhizosphere soil. Grain As concentrations also decreased by 35 to 45 percent in the intermittent compared to the continuously flooded plots. Organic As species, monomethyl and dimethyl arsenate were detected in the rhizosphere with relative increases and decreases among the treatments. Bacteria were the predominant group (91 to 94 percent and 48 to 78 percent of total community in root-plaque and rhizosphere soils, respectively). Archaea were also a major component of rhizosphere soil with their populations being higher under continuous flooding. The relative abundance of iron-reducing bacteria was around 3 to 6 percent of the total community in root-plaque and around 6 to 6 percent in soil, with significantly lower abundance in the intermittent compared to the continuously flooded plots. Results of these studies demonstrated that intermittent flooding could be a potential management option to reduce grain As in rice cultivated on fields with moderate to high As concentrations.

The habitat diversity of the fungus Nectria haematococca MPVI has been shown to be due in part to conditionally dispensable (CD) chromosomes that carry habitat-defining genes. From a biological perspective, the CD chromosomes are analogous to plasmids that possess genes that determine the habitats of plant-associated bacteria. This study establishes that the N. haematococca CD chromosome that contains the genes for Pea Pathogenicity (PEP cluster) also carries genes for the utilization of homoserine, an amino acid found in pea root exudates. Competition studies presented here demonstrate that an isolate that lacks the PEP cluster, but carries a portion of the CD chromosome containing the homoserine utilization (HUT) genes, is more competitive in the pea rhizosphere than an isolate without the CD chromosome. Further competition studies show that both the PDA1 and PDA6 CD chromosomes confer a competitive advantage in the rhizosphere of soybean, whereas only the PDA6 CD chromosome confers a competitive advantage in the rhizospheres of tomato and alfalfa, and only the PDA1 CD chromosome confers a competitive advantage in the rhizosphere of pea. These studies suggest the presence of genes on the PDA6 and PDA1 CD chromosomes that enhance the ability of N. haematococca to expand its habitat and support the idea that fungal CD chromosomes are analogous to host-specifying plasmids in plant-associated bacteria. Transformation, insertional mutagenesis, and bioinformatics were used to identify a cluster of five genes on the PDA1 CD chromosome that was responsible for the HUT phenotype in N. haematococca. One of the genes was found only in N. haematococca, another was a fungal transcription factor, and the other three had homologs involved in the synthesis of the amino acids methionine, threonine, and isoleucine, in which homoserine is an intermediate. Competition experiments that compared isolates with or without the HUT cluster showed that the HUT cluster is responsible for increased competitive ability of HUT+ N. haematococca isolates in the rhizosphere of pea. This study establishes that homoserine utilization can be a rhizosphere competency trait for N. haematococca and, to our knowledge, is the first example of a rhizosphere competency trait identified in a fungus.

Shade tree incorporation is beneficial in coffee cropping systems under sub-optimal conditions. This study was performed in lowland Costa Rica, at a 12-year-old experimental coffee farm. The main objective was to compare the effect of a nitrogen fixing shade tree, Erythrina poeppigiana, on nutrient availability in the rhizosphere of coffee under conventional fertilization. Accumulation of nutrients (mineral N, available P, and exchangeable base cations) in rhizosphere relative to bulk soil was greater under shade than full sun. Low nitrate availability in rhizosphere soil of full sun coffee was explained by root-induced acidification relative to bulk soil, as abundance of ammonia-oxidizing bacteria (AOB), which mediate nitrification, were positively correlated with pH. Organic fertilization enhanced AOB abundance and altered soil bacterial community structure relative to conventional fertilization. This study indicates clear effects of shade-tree presence on nutrient availability at the micro-scale, management of which is critical for stability of coffee agroforestry systems.

Shade tree incorporation is beneficial in coffee cropping systems under sub-optimal conditions. This study was performed in lowland Costa Rica, at a 12-year-old experimental coffee farm. The main objective was to compare the effect of a nitrogen fixing shade tree, Erythrina poeppigiana, on nutrient availability in the rhizosphere of coffee under conventional fertilization. Accumulation of nutrients (mineral N, available P, and exchangeable base cations) in rhizosphere relative to bulk soil was greater under shade than full sun. Low nitrate availability in rhizosphere soil of full sun coffee was explained by root-induced acidification relative to bulk soil, as abundance of ammonia-oxidizing bacteria (AOB), which mediate nitrification, were positively correlated with pH. Organic fertilization enhanced AOB abundance and altered soil bacterial community structure relative to conventional fertilization. This study indicates clear effects of shade-tree presence on nutrient availability at the micro-scale, management of which is critical for stability of coffee agroforestry systems.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Thesis (doctoral)--Martin-Luther-Universität Halle-Wittenberg, 2006. / Includes bibliographical references (p. 99-111).

Forests play an important role in mitigating climate change by removing carbon dioxide (CO2) from the atmosphere via photosynthesis and storing it in plant tissues and soil organic matter (SOM). Plant roots are a major conduit for transporting recently fixed CO2 belowground, where carbon (C) remains in SOM or returns to the atmosphere via respiration of soil microbes. Compared to aboveground plant processes related to the C cycle, there is little understanding of how belowground plant-C allocation to roots, symbiotic root fungi and secretions into the soil influence the gain or loss of C from the soil. Further, the uncertainty in the timing and amount of root growth that occurs in forests is a barrier to understanding how root activity responds to global change and feeds back to the C cycle. Therefore, the objective of my research is to quantify the timing and magnitude of C allocation to roots and soil via data compilation, field studies and modeling across broad spatial scales. Using data compilation at the global scale, I show that root and shoot phenology are often asynchronous and that evergreen trees commonly have later root growth compared to deciduous trees using meta-analysis across four biomes. At the plot scale, field studies in a mid-latitude forest demonstrate that deciduous stands allocate more C belowground earlier in the growing season compared to a conifer stand. The difference in phenology between stands can be attributed to the timing of root growth. At the root scale, zymographic analysis demonstrates that microbial extracellular enzyme activity is concentrated near the surface of roots and that the rhizosphere can extend well beyond 2 mm from the root surface. Finally, I developed a new model of microbial physiology and extracellular enzyme activity to assess how climate change may affect plant - microbe interactions and soil organic matter decomposition. I show that increases in temperature and the quantity of C inputs substantially alter decomposition. Collectively, these results demonstrate the importance of belowground allocation to the C cycle of terrestrial ecosystems.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Objetivando avaliar o comportamento das emissões de CO2 do solo em áreas mineradas do município de Santo Antônio de Pádua-RJ e sua correlação com a rizosfera, este presente estudo utilizou uma câmara fechada com sensor de infravermelho em três diferentes paisagens, a saber: A-1 (área reflorestada há 10 anos), A-2 (área desmatada) e A-3 (área em processo de recuperação). Em cada área foi instalada três cilindros para efeitos de repetição. O monitoramento foi realizado durante os meses representativos de cada estação do ano de 2013, sendo a análise realizada durante dois dias consecutivos. Concomitantemente as coletas de CO2 foram realizadas coletas de dados de temperatura e umidade do solo, sendo também avaliadas informações pedológicas através das análises de granulometria, porosidade, pH, carbono orgânico e matéria orgânica. Informações meteorológicas e microclimatológicas também foram extraídas através de uma estação meteorológica automática e através de sensores portáteis. Os resultados permitem concluir que existe uma variação sazonal dos fluxos de CO2, havendo uma tendência de máximos de emissão durante o verão e de mínimas durante o inverno, sendo o outono e a primavera marcados por valores medianos. A correlação das áreas entre os dois dias monitoramento indicam que as emissões foram semelhantes ao da análise em dia anterior, apresentando uma correlação significativa a 5% para A-1 e A-2 e de 1% para A-3. A-1 e A-2 apresentaram emissões de CO2 mais homogêneas que A-3, havendo, entretanto, um maior fluxo de CO2 durante o verão para todas as áreas. Os dados de MOS, COS e pH demonstraram não haver uma correlação direta com as emissões de CO2. Os dados de porosidade e densidade, porém, apontam para uma possível correlação com as menores emissões de CO2 em A-3 devido a menor porosidade e maior densidade de seus solos. A temperatura do solo foi a variável que mais se correlacionou com as emissões de CO2, havendo um índice igual a r =0,68 para A-1 e de r =0,74 para A-2, sendo que em A-3 esta correlação não foi significativa. A temperatura do ar demonstrou uma correlação somente na área descampada de A-2. No que se refere à correlação da umidade do solo não houve correlações diretas significativas, sendo que somente houve uma correlação negativa (r=-0,50) significativa a 5% em A-3 com a umidade do ar. O diagnóstico ambiental das áreas de monitoramento revela que estas possuem baixos indicadores de qualidade, sendo afetados também pela escassez hídrica da região durante oito meses do ano. A-1 apresenta os melhores indicadores biológicos, químicos e microclimáticos, seguidos por A-2 e A-3 que apresentam diversas deficiências e problemas em termos de estrutura e atividade biológica dos solos. Neste estudo permite-se concluir que áreas próximas, porém com características distintas podem produzir diferentes padrões de emissão de CO2, dificultando, portanto, estimativas globais de emissão de CO2. Os elementos mais associados às emissões de CO2 parecem estar relacionados à temperatura do solo e do ar, umidade do ar e estrutura do solo, havendo, entretanto, outros fatores que podem estar indiretamente relacionados e que exercem diferentes influências de acordo com o ambiente analisado. / Seeking evaluate the performance of CO2 emissions from soil in mined areas in the municipality of Saint Anthony of Padua - RJ and its correlation with the rhizosphere , the present study used a closed chamber with infrared sensor in three different landscapes , namely: A- 1 ( reforested area 10 years ago ) , a- 2 ( pasture) and A- 3 (area under recovery ) . In each area was installed three cylinders for the purpose of repetition. Monitoring was conducted during the months representing each season of the year 2013, with an analysis performed for two consecutive days. Simultaneously the analyses of temperature and soil moisture were performed, and also evaluated soil information by analyzing particle size , porosity, pH , organic carbon and organic matter information microclimatológicas and of weather were also extracted through sensors automatic and portable.The results indicate that there is a seasonal variation in CO2 fluxes , there is a trend of maximum emission during summer and minimum during winter , with autumn and spring marked by median values . The correlation among the areas two days indicate that monitoring emissions analysis were similar to the previous days, presenting a significant correlation to 5 % for A -1 and A -2 and A- 1 to 3 %. A- 1 and A- 2 had CO2 emissions more homogeneous than A- 3, there are, however, a greater flow of CO2 during the summer for all areas. MOS data, COS and pH showed no direct correlation with CO2 emissions. The porosity and density data, however, point to a possible correlation with the lowest CO2 emissions in A- 3 due to lower porosity and higher density of your soil. Soil temperature was the variable that was most associated with CO2 emissions, with an equal index for air = 0.68 A- 1 and r = 0.74 for A- 2, and A- 3 in this correlation was not significant. The air temperature showed a correlation only in the open area A- 2. With regard to the correlation of soil moisture no significant direct correlations, and only there was a significant negative correlation (r = -0.50) to 5 % in A- 3 with the humidity. The environmental assessment of the areas of monitoring shows that these have low quality indicators is also affected by water shortages in the region for eight months of the year. A- 1 shows the best biological, chemical and microclimatic indicators, followed by A-2 and A- 3 which have several deficiencies and problems in terms of structure and biological activity of soil. In this study, we conclude that nearby areas , but with distinct characteristics can produce different patterns of CO2 emission , thus hindering global estimates of CO2 emissions . Most elements associated CO2 emissions appear to be related to soil temperature and air temperature , humidity and soil , however , other factors that may be indirectly related and exert different influences according to the analyzed environment .